lssa i project - nasa jet propulsion laboratory (jpl)...is themost important consideration in...

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~ 0 4 ~ ~ ~ / 1 0 1 2 - 3 Distribution Category UC-63b

LSSA . .

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. . . .: . . . . . . . . . . . . LOW-COST SILICON SOLAR ARRAY . . . . ; ..:) ' :.. . . . . . . . .< . . . .. - . .. . . , : 9 ...,; ..: . , : . . . . )+;.. ':,. .

.. . . . . . . . . . . i .'. ..'. . . . _ .,.... .'I. . . . .. . . . . . PROJECT : ; ,:,. . . . . v . . . . . . . :. ... A 5 . . . ,:..,.. .,.. .. ::. ;: 2;;:;; : . . I., . . . . . . . . . . . . . . . . . . . . . . . . . . . . :. . . >.

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ENERGY RESEARCH .AND O E V E ~ nPMENT ADMINISTRATION

NOTICE

Prepa~d as an account work 'POnrorcd by the United Stater C O V L ~ ~ ~ ~ ~ .

~ ~ i ~ , , ~ ~ U1e United States no: the United states D~~~~~~~~~ or

Encrw. "0' any of their employees, nor of their contmctor:, subcontracton, or their cmployn, maker

warranv, cxPxu or implied, or anumcs any legal

!

NATIONAL AERONAUTICS AND SPACE ADPAINISTRATION

JET PROPULSION LABORATORY

CALIFORNIA INSTITUTE OF TECHNOLOGY

PASADENA, CALIFORNIA t9 DIITRIBUTICN GI. TBIS DOCUMENT IS UNLIMITED

CONTENTS

I. INTRODUCTION AND PROJECT OVERVIEW --------.------------------- 1 - 1

11. SUMMARY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-1

A. PROJECT ANALYSIS AND INTEGRATION AREA -----------------' 2- 1

2. Large-Area Silicon Sheet Task ......................... 2-1

C. PRODUCTION PROCESS AND EQUIPMENT AREA ----------------- 2-3

111. PROJECT ANALYSIS AND,INTEGRATION AREA ....................... . .

3- 1

A . PL'ANNTNG AND INTEGRATION TASK ------------------a=----- 3- 1

, . TECHNOLOGY DEVET.I)PMENT AREA --------=------------------5-----, 42 1

A. SILICON MATERIAL TASK ------------lcs.r;-o---------w x . !I- 1

2. Organization and Coordination of the Silicon Material Task Effort .................................. 4- 1

3 . Silicon Material Task Contracts ....................... 4-3.

4. Silicon Material Task Technical Activity -------------- 4-3

B. LARGE-AREA SILICON SHEET TASK ......................... 4-16

1. Technical Background .................................. 4-17 e

2. Organization and Coordination of the Large-Area Silicon Sheet Task Effort ............................. 4- 17

3. Large-Area Silicon Sheet Task Contracts --------------- 4- 18 4. Large-Area Silicon Sheet Task Technical Activity ------ 4-18

2. Organization and Coordination of the Encapsulation Task Effort ........................................ 4-28

3. Encapsulation Task Contracts .......................... 4-29

4. Encapsulation Task Technical Activities --------------- 4-31

V. . PRODUCTION-PROCELS AND EQUIPMENT AREA ....................... 5- 1

B. ORGANIZATION AND COORDINATION OF THE PRODUCTION PROCESS AND EQUIPMENT AREA EFFORT ..................... 5- 1

C. PRODUCTION PROCESS AND EQUIPMENT AREA CONTRACTS ------- 5- 3

D. PRODUCTION PZOCESS AND EQUIPMENT AREA TECHNICAL ACTIVITIES .................................. 5-4

1. Manufacturing Processes Assessment - Motorola, RCA, and Texas Instruments ............................ 5-11

2. Large-Area Czochralski Silicon Ingot Growth and Wafering Improvements - Texas Instruments ------------- 5-5

3. Processing Energy Study - Solarex ..................... 5-5

2. ' Module ~nte rconnec t ions /~e r%nina t ions --i-------------- 6- 1 . .

3 . , ' Mechanical ~onfl~&ation ~r~iir~ments ----------------- 6-2

4. Module E f f i c i e n c y Requirements ........................ 6-2

C. IMPACT LOADING (HAIL) TEST DEVELOPMENT ---------------- 6-7

1 . H a i l s t o n e P r o b a b i l i t y Model and Data A c q u i s i t i o n ------ 6-8

2. H a i l T e s t i n g .......................................... 6-10

D . CYCLIC LOADING ANALYSIS ............................... 6-1 1

1. Block 1 ( 4 6 kW) -I---,-----------i-----------II----- 7- 1

D. PERFO.RMANCE,MEASUREMENTS AND STANDARDS ---------------- . . . . . ,

7-8

6. FAILURE A M B L Y ~ I ~ ..-------------------------------------- 7-8 . .

, .

' 4-1. . Dependence o f Open C i r c u i t Vol tage , Voc,. 0" - .

S u b s t r a t e R e s i s t i v i t y o f n+p Cells .................... 4-10

4-2. ~ e ~ e n d e n c e o f S h o r t C i r c u i t c u r r e n t , 1; ; on S u b t r a t e R . e s i s t i v i t y of q+p S o l a r ~ e f l s ------------ 4-10

4 3 . V a r i a t i o n o f t h e Cell E f f i c i e n c y , q, With S u b s t r a t e .

Doping of n+p Cells ................................... 4-10

4-4. C a p i l l a r y Die Growth (EFG a n d CAST) - Mobil-Tyco and IBM .................................... 4-20

. . . . - 5 I n v e r t e d ~ t e p a n o v , T e c h n i q u e - RC$ .---------A ----, ------ 4-22 . .

4-6. Web-Dendr i t i c Growth - U n i v e r s i t . ~ o f . .

S o u t h C a r o l i n a ........................................ 4 -2 3

4-7. L a s e r Zone C r y s t a l l i z a t i o n - M o t o r o l a ----------------- 4-24

4-8. Chemical ' Vapor D e p o s i t i o n on Low-Cost S u b s t r a t c s - Rockwel l I n t e r n a t i o n a l ------------------- 4-25

4-9. C r y s t a l . J r .owth U s i n 5 t h e Heat ~ x c h a n g e r Method - C r y s t a l S y s t e m s .............................. 4-26

5-1. P r o d u c t i o n P r o c e s s and Equipment Area S c h e d u l e .............................................. 5-2

6-2. Use o f G r i d S y s t e m . t o D e t e r m i n e T e m p e r a t u r e . C y c l e s -----.------------------------------------------- 6-1 3

6-3. S c h e m a t i c o f Wind-Load S p e c t r o m e t e r ------------------- 6-1 4 . .

. . 6-4. Wind-Load S p e c t r o m e t e r ( I l l u s t r a t i o n o f F u n c t i o n ) ----- 5-15

'6-5. I n s o l a t i o n Def ic i t V e r s u s p e r i o d L e n g t h f o r . .

S e a t t l e i n A p r i l ...................................... 6-1 6

,6-6. Ten-Year Mean o f Maximum Defici ts D u r i n g Each 0 B i m o n t h l y P e r i o d ( 6 0 T i l t , S e a t t l e ) ------------------ 6-1 7

6-7. S y s t e m S i z e V e r s u s Deficit C o v e r i n g C a p a b i l i t y f o r a F i x e d B a t t e r y / A r r a y R a t i o =.SO kW-h/kW ---------- 6-1 8

7-1. R e p r e s e n t a t i v e Computer T a b u l a t i o n o f LAPSS I - V Data f o r a Module i n t h e F i e l d a t P a s a d e n a ------------ 7-7

T a b l e s .

4-1. O r g a n i z a t i o n o f t h e S i l i c o n Material Task E f f o r t ------ 4-2

4-2. S i l i c o n Material Task C o n t r a c t o r ...................... 4 -4

4-3. Large-Area S i l i c o n S h e e t T a s k C o n t r a c t o r s ------------- 4-19

4-4. E n c a p s u l a t i o n Task C o n t r a c t o r s ----.-------------------- 4-30

5-1. P r o d u c t i o n P r o c e s s and Equipment Area C o n t r a c t o r s ----- 5-4

6-1. C e l l C h a r a c t e r i s t i c s f o r Block 1 and Block 2 -Modules ........................................ 6-4 . . .

6-2. C h a r a c t e r i s t i c s o f Candidate Modules with E f f i c i e n c i e s Grea t e r Than 79 .......................... 6-6

6 -2 . NOCT and yNOCT ~ u m a r y ............................... 6-7

6 - The P r o b a b i l i t y o f a 10 ~t~ Area Being Hit by a Ha i l s tone of Diameter 1 Inch o r Grea t e r i n 20 Years ........................................... 6-10

6-5. Ha i l s tone C h a r a c t e r i s t i c s a s a Function of nj.ameter ........................................... 6-1 1

7-'I. Br ie f Desc r ip t i on of Exploratory Tes t Procedures ------ 7-2

7-2. 46 kW, Phase 2 - Explora tory Tes t R e s u l t s ------------- 7-3

7-3. Add-on Procurement - Q u a l i f i c a t i o n Tes t Resu l t s ------- 7-4

7-4. Block 2 (130 kW).Modules - Q u a l i f i c a t i o n , T e s t Resu l t s ............................................... 7-5

SECTION I

INTRODUCTION AND PROJECT OVERVIEW

A . INTRGDUCTION

T h i s r e p o r t d e s c r i b e s t h e a c t i v i t i e s o f t h e Low-Cost S i l i c o n S o l a r Array P r o j e c t d u r i n g t h e p e r i o d January t h r o u g h March 1977. The. LSSA P r o j e c t i s ags igned r e s p o n s i b i l i t y f o r advancing s i l i c o n s o l a r a r r a y t e c h n o l o g y w h i l e encourag ing i n d u s t r y t o r e d u c e t h e p r i c e of a r r a y s ' t o . a l e v e l a t '.which p h o t o v o l t a i c e l e c t r i c pokier . .system.i w i l l . .

be c o m p e t i t i v e w i t h more c o n v e n t i o n a l power s o u r c e s e a r l y i n , t h e n e x t .decade. S e t f o r t h h e r e a r e t h e g o a l s and p l a n s w i t h which. . t h e . P r o j e c , ~ , . . ~ . . . ,;, .. .. ' . * . .

i n t e n d s t o accompl i sh t h i s , and t h e p r o g r e s s t h a t was made' J u ~ . i ~ i g " t h e " : ' - ' : . . . '..

'. . . . . . . . q u a r t e r . . . .

. . . . . . , . , . , , . . . .

The P r o j e c t o b j e c t i v e is t o d e v e l o p t h e n a t i o n a l :ii;pabii.i$.y:.t'o : . ' . ' .

produce low-cos t , l o n g - l i f e p h o t o v o l t a i c . a r r a y s a t a r a t e : g r e , a t e r t h a n 500 megawatts p e r y e a r and a p r i c e o f l e s s t h a n $500, Ser ' Ril .ow.a. t t ' . peak by 1986. The a r r a y performance q o a l s i n c l u d e a n e f f i c i e n c y . . . g r e a t e r .

t h a n 10% and a n o p e r a t i n g l i f e t i m e i n e x c e s s o f 20 ye+,&. "' ... ;: ..': . . . . . . , . . . . . . . .

. . . . . . . . . . . . . ... ..... . .. . . ..

. . . . . . . . . ..

PROJECT OVERVIEW B. .. ,

By t h e end o f 1976, t h e P r o j e c t had e s s e n t i a l l y a t t a i n e d i ts Phase I g o a l s i n a s s e s s i n g t h e s t a t e o f t h e a r t o f s i l i c o n s o l a r c e l l t e c h n o l o g y , c o n t r a c t i n g f o r l a r g e - s c a l e p r o d u c t i o n o f modules , and . .

beg inn ing advanced r e s e a r c h . During J a n u a r y , F e b r u a r y , and March 1977, P r o j e c t e f f o r t s were expanded from t h i s f o u n d a t i o n .

The Block 1 s o l a r a r r a y purchase o f 43 kW and a 15 kW add-on had been completed i n l a t e 1976, and t e s t i n g c o n t i n u e d i n t o t h e first q u a r t e r o f 1977. Q u a l i f i c a t i o n and env i ronmenta l t e s t i n g d e t e c t e d t e c h n i c a l shor tcomings i n Block 2 module p r o t o t y p e s ; t h e s e were s u b s e q u e n t l y c o r r e o t e d by t h e m a n u f a c t u r e r s . About 3 kW o f . p r o d u c t i o n modules i n t h e Block 2 purchase had been r e c e i v e d by t h e end o f t h e q u a r t e r . A Request f o r P r o p o s a l and s p e c i f i c a t i o n were completed f o r a p r o j e c t e d 150 kW procurement , and r e q u i r e m e n t s f o r a p r o j e c t e d 160 kW buy were s t u d i e d .

.. . . . , Forty-seven c o n t r a c t s were i n e f f e c t a t t h e end o f t h e q u a r t &

f o r t echno logy development and cost. a n a l y s i s . ~ c c e ~ t a b l e p r o g r e s s , had been made, bu t most s t u d i e s were immature a t t h e p e r i o d ' s e n d .

. T e c h n i c a l development w a s e f f e c t i v e l y i n t e g r a t e d w i t h c o s t . c o n s i d e r a t i o n s a s economic a n a 1 y s . i ~ work p r o g r e s s e d .

- .-.-

* I n . 1975 d o l l a r s .

A p l a n was completed t o r e v i s e t h e P r o j e c t o r g a n i z a t i o n s o a s t o p r o v i d e a more focused e f f o r t f o r each o f t h e t e c h n i c a l . a r e a s a s t h e scope o f P r o j e c t a c t i v i t i e s expanded. The Automated Array Task . .

was c o n s o l i d a t e d ' u n d e r a new Area i d e n t i f i e d . a s . P r o d u c t i o n P r o c e s s . . . and Equipment Development. The P r o j e c t A n a l y s i s and I n t e g r a t i o n , E n g i n e e r i n g , and O p e r a t i o n s Tasks were e l e v a t e d t o Area l e v e l , and t h e Large-Scale Procurement Task was a s s i g n e d under O p e r a t i o n s . A new Task was added f o r t h e i m p o r t a n t func t i0 .n o f c e l l development t o p r o v i d e emphasis o n a l l f a c e t s o f c e l l p r e p a r a t i o n and p r o c e s s i n g . A Deputy P r o j e c t Manager, a s s i g n e d t o f u n c t i o n e s s e n t i a l l y as g e n e r a l manager , was ' a d d e d . t o t h e P r o j e c t s t a f f .

. . . . . .... . : :. . Four t a s k . . r e p o r t i were. i s s u e d d u r i n g . t h e . q u a r t e r . C v c l i c ..

~ r e s s u r ' e - ~ o a d ' eve rob mental ' ~ ' e s t i n a o f S o l a r p a n e l s ( t h i s work was summarized i n LSSA Q u a r t e r l y Report 2 ) d e s c r i b e d t e s t i n g done w i t h aii a p p a r a t u s c r e a t e d a t JPL t o s i m u l a t e l o a d i n g o f winds o f up t o 100 mph. T e s t Program on Low-Cost Connector f o r S o l a r P a n e l s ( a l s o s e e LSSA Q u a r t e r l y Heport 2) d e s c r i b e s a n i n e x p e n s i v e d e v i c e developed f o r a u t o m o t i v e use which was found t o be p romis ing f o r s o l a r module a p p l i c a t i o n . A v a i l a b i l i t v o f U l t r a v i o l e t R a d i a t i o n Data ( f o r E ~ c ~ D s u - l a t i o n Svstem Design) r e l a t e s how d a t a r e g a r d i n g t h e s p e c t r a l compos i t ion of . the u l t r a v i o l e t p o r t i o n o f t o t a l i r r a d i a n c e a t v a r i o u s s i t e s i s p r e s e n t l y i n a d e q u a t e f o r P r o j e c t purposes . P r e l i m i n a r y A n a l v s i s o f I n d u s t r i a l Growth examined f a c t o r s t h a t a f f e c t i n d u s t r i a l growth r a t e s . a s t h e y might a p p l y t o t h e LSSA P r o j e c t .

'The P r o j e c t conducted . a . P r o j e c t I n t e g r a t i o n Meeting on J a n u a r y 1 7 t h and 1 8 t h i n San Diego. A key theme was t h e e m e r g e n c e . o f u s a b l e c o s t i n g d a t a and t h e i r i n t e g r a t i o w w i t h t h e t e c h n i c a l s p h e r e . During t h e PIM, p r e s e n t a t i o n showed t h a t c o s t v s . c e l l c o n v e r s i o n e f f i c i e n c y was t h e dominant tracle-off when t e c h n i c a l development was a n a l y z e d from a c o s t p e r s p e c t i v e . Also , a p r e s e n t a t i o n by t h e Economics and I n d u s t r i a l i z a t i o n A c t i v i t y concluded t h a t t h e i n i t i a l c o s t o f module8 i s t h e m o s t i m p o r t a n t c o n s i d e r a t i o n i n p h o t o v o l t a i c sys tem l i f e - c y c l e c o s t . -. - The. E n g i n e e r i n g Area o u t l i n e d t h e r e s u l t s o f i t s work t o d e f i n e . . . . t h e p a r a m e t e r s o f t h e c o s t v s . e f f i c i e n c y . . t r a d e - o f f , and p r e s e n t e d a ' fo rmuia ' t h a t i l l u s t r a ~ t e s t h e e f f e c t s o f e f f i c i e n c y changes on cos t : The theme was f u r t h e r emphasized i n d i s c u s s i o n s by t h e S i l i c o n M a t e r i a l

. . . . Task and t h e P r o d u c t i o n P r o c e s s and Equipment Area. . .

A uniform c o s t i n g methodology f o r m a n u f a c t u r i n g p r o c e s s e s , c a l l e d SAMICS, had . been .. completed b,y t h e . .time o f t h e .PIM, and was d i s c u s s e d . _ .._. . . . _ ..... ..

. . .. . .. . . SBM~C;S; ' is a s t a n d a r d fo rmat f o r axpreesj..ng,..+. Jgs,grSy:t&on o f ' t h e ecoilbmic" . . . c h a r a c t e r i s t ' i c s ' of . .e .ach manufac tu r ing p r o c e s s , and was c o n s i d e r e d t o .

be a n i m p o r t a n t p r o d u c t o f t h e P r o j e c t ' s c o s t a n a l y s i s f u n c t i o n . I n a f i n a l ' p r e s e n t a t i o n i n . , t h e a r e a ,of c . o s t , a l l o c a t i o n s f o r i n g o t and . : . .

.,. . . non- ingot t e c h n o l o g i e s were . s e t , . f o r t h , . .. .. and-, t h e a l l o c a t i o n s t r u c t u r e was shown gr%phioa l ly . Dramatic, imptlovements WMI~C? p r o j e c t e d i n i n g o t t e c h n o l o g y . f o r c r y s t a l growth and s l i c i n g , and f o r c e l l f a b r i c a t i o n and module assembly. . .

SECTION I1

A. PROJECT ANALYSIS AND INTEGRATION , . . .

During this a mission system interface analysis activity was started in an effort to enhance the information flow into the LSSA Project, particularly from the mission and systems contractors of -the ERDA program. A preliminary version of the SAMICS workbook was published, and its application to a realistic processing sequence was about 50% complete; application to a wafer-to-module sequence was initiated. A contractor was 3alect.ed to support the SAMICS program. Design of the SAMIS I11 computer program was about 75% complete at quarter's end . Brllce goal allocationo were updated several times during this period, and presented at the Project Integration Meeting in May. Computer modeling of the life-cycle cost of energy systems was essentially completed. A price/quantity study based upon manufacturing process contract data furnished by the Production Process and Equipment Area found that approximately 50 MW/year is the optimum manufacturing quantity for solar modules.

B. TECHNOLOGY DEVELOPMENT AREA

1. Silicon Material Task

Continued experimentation with the fluidized bed reactor for production of Si by Zn'reduction of Sic14 showed that 78% of theoretical conversion efficiency from SiC14 to Si was attainable using a hemi- spherical bed support, versus 68% when using the concise bed support. A smoother bed action was noted also; this is expected to result in higher reactant throughput. The high deposition rates demonstrated. provide experimental verification for the 7-inch reactor selected for the 25 MT/yr process system development.faci1ity. . A production rate 0.f 5 kg/hr was reached for about one minute in the free space reactor designed to produce Si from SiH4, and a pyrolysis efficiency of 99% was demonstrated. However, continuous operation has not yet been demonstrated. Another contractor concluded that semiconductor-grade Si can be produced by SiF2 transport from Simet at rates of up to 40 gm/hr for short runs. An economic analysis of the Zn/SiC14 process indicated'that'.a. $10,510;000 ''

fixed capital investment will be required for a 1000 MT/yr plant that will produce Si at $9.63/kg.

2. Large-Area Sil.icon Sheet Task

The EFG process is now producing 2-inch wide ribbon .at 2-3 inches per minute; however, conversion efficiencies remain low at 2%-3%. Work on the CAST process has stopped pending contract negotiation. Materials other than Si02 are being evaluated for the die used in the inverted Stepanov process. Erratic wetting of the Si02 die caused experiments using this material to be suspended. Problems associated with optimizing furnace geometry have created great problems with the web-dendritic

technique, ,but in the best furnace configuration found so far, ribbons 1 inch wide by 15 inches long were grown. In the investigation.of substrate materials for the CVD process, it was found during this quarter that re- firing crystalline aluminas results in only limited grain.growth in the . .

wafer surfaces in contact with another .surface. The heat exchanger method of casting large silicon ingots has demonstrated a crack-free ingot growth using crucibles which have been coated with sintered silica; the silica separates freely from the silicon ingot during cooldown and prevents cracking.

3. Encapsulation c ask

Developuerit of low-cost encapsulation materials and systems is continuing at Battelle (Study 31, Springborn, Simulation Physics, and Endurex. Battelle and Springborn have screened a large number of materials for encapsulation capability. These tests have included meohanical, physical, thermal, and electrical testa. Emphasis has been on radiation transmission, water vapor permeability, adhesion, and mechanical integrity. Battelle has performed a limited number of tests on single encapsulated active photovoltaic cells; this work will be continued under a contract extension with statistical numbers of samples and extended exposure to ultraviolet, temperature cycling, and high humidity. Springborn also began testing of encapsulated active photovoltaic cells. These are two-cell mini-modules assembled by Solar Power Corporation and encapsulated by Springborn; they are designed to test encapsulation materials combinations. Simulation Physics has produced electrically functioning four-cell electro-statically bonded (ESB) modules. These modules have shown no significant reduction in electrical output caused by the ESB process. No results were obtained from Endurex this quarter (the Endurex contract has just begun).

Development of life prediction methodology is being accomplished by Rockwell and Battelle. Rockwell has designed and is testing a universal test specimen (UTS) which shows promise of provid'ii-lg a low-cost method of

. . . . . . testing encapsulation materials and encapsulating materials systems. Significant progress.has been made in predicting ,degradation using mathematical models .(for example, the Weibull model). This work is continuing under a contract extension employing improved UTS designs. Battelle has completed a literature/theoretical study of life prediction methodology and.has developed an improved procedure for designing life

.. . pi?edic:tign. tests .. -This.. will . be ' giVer+'.'lri:'.'detail in the final report to be ( . . . . . . . . . . . . . .

fii~blished "in 'the next. qu~rt.ar.

Significant efforts were expended this quarter to support the - Engi'neering and Operations Areas by conducting failure analyses on modules ".in'tests, doing field repair work, taking part in design reviews, and participating in module design team efforts chaired by the Engineering 'Area. These efforts have become increasingly important in the Encapsulation Task and will receive increased emphasis in the,next quarter.

PRODUCTION PROCESS AND EQUIPMENT AREA c.

With Phase I a s s e s s m e n t conc luded , .emphasis. was s h i f t e d to.. t h e . . . . .. . . . . - . . c o s t - e f f e c t i v e n e s s o f p r o c e s s e s s t i l l b e i n g . c o n s i d e r e d , and , t o .-the . .

. .

. . '. s e n s i t i v i t y o f t h o s e p r o c e s s e s t o commercia l ly r e a l i s t i c t o l - e r a n c e s . . Three add-on c o n t r a c t s were i n i t i a t e d d u r i n g t h i s q u a r t e r f o r s t u d y o f t h e s e f a c t o r s . Ten cm/hr C z o c h r a l s k i c r y s t a l p u l l i n g was accom- p l i s h e d , a l t h o u g h a t t e m p t s a t p u l l i n g 12 cm/hr f a i l e d . During t h e s e

. . . t e s t s , though , t h e program g o a l o f an 80% y i e l d o f 12 cm-dia. c r y s t a l s ' f rom a 12 kg c h a r g e was demons t ra ted . A t e c h n i q u e f o r s p i n n i n g i n g o t s d u r i n g m u l t i b l a d e sawing was t r i e d , and showed c u t t i n g r a t e s o f a l m o s t 50 mm/hr. One c o n t r a c t o r t h i s q u a r t e r ' b e g a n t o s t u d y t h e e n t i r e proposed m a n u f a c t u r i n g sequence from t h e p e r s p e c t i v e o f "energy payback," a p p r a i s i n g t h e amount o f e n e r g y expended d u r i n g manufac tu re o f s o l a r a r r a y s v e r s u s t h e energy t h a t is expec ted t o be produced th roughout t h e l i f e of t h o s e a r r a y s .

D . E N G I N E E R I N G A R E A

E n g i n e e r i n g Area work d u r i n g t h e second q u a r t e r o f F i s c a l Year 1977 c e n t e r e d i n two p r imary a r e a s : ( 1 ) t h e f i n a l i z i n g o f a s u b s t a n t i a l l y updated module d e s i g n s p e c i f i c a t i o n , and ( 2 ) expanded a c t i v i t y i n t h e development o f env i ronmenta l d e s i g n r e q u i r e m e n t s .

The updated d e s i g n s p e c i f i c a t i o n is aimed a t t h i r d g e n e r a t i o n modules beyond t h e d e s i g n s a s s o c i a t e d w i t h t h e 130-kW Block 2 p rocure - ment. The new s p e c i f i c a t i o n emphasizes t h e needs o f l a r g e r power s y s t e m s i n t h e r a n g e from 10 t o 250 kW. P a r t i c u l a r a r e a s o f emphasis i n c l u d e minimizing f i e l d l a b o r and sys tem c o n s t r u c t i o n c o s t th rough t h e use o f s t a n d a r d i z e d e l e c t r i c a l c o n n e c t o r and mechan ica l a t t a c h m e n t i n t e r f a c e s . I n c r e a s e d emphasis is a l s o p laced on e f f i c i e n c y (minimum a l l o w a b l e is 7%) and on e l e c t r i c a l i s o l a t i o n and s a f e t y . I n c r e a s e d c o m p a t i b i l i t y w i t h t h e r e q u i r e m e n t s o f 1 2 - v o l t b a t t e r y c h a r g i n g h a s been a c h i e v e d w i t h a new v o l t a g e s p e c i f i c a t i o n based on t h e a c t u a l c e l l o p e r a t i n g t e m p e r a t u r e i n t h e f i e l d , r e f e r r e d t o a s Nominal O p e r a t i n g C e l l Temperature (NOCT)..

Thermal a n a l y s e s c o n t i n u e d d u r i n g t h e p a s t q u , a r t e r w i t h emphasis

. . 'on d e t e r m i n i n g t h e Nominal Opera t ing C e l l Temperature o f t h e Block 1 . . . . , . . . . . . . . . . . . . , . . and lock 2"module d e s i g n s . T e s t s were a l s o conduc ted to f u r t h e r ,ex.amine t h e e f f e c t o f f i n s and r e s i d e n t i a l r o o f t o p mounting ( i n s u l a t e d r e a r s i d e ) .

B u i l d i n g upon t h e q u a l i f i c a t i o n and f i e l d t e s t e x p e r i e n c e g a i n e d w i t h t h e Block 1 and 2 l a r g e - e c a l e p r o d u c t i o n modules , a number o f a c t i v i t i e s s u p p o r t i v e o f new env i ronmenta l r e q u i r e m e n t s a r e i n work. The p r i n c i p a l a c t i v i t y is a s s o c i a t e d w i t h t h e development o f an impact l o a d ( h a i l ) t e s t . Work is p r o g r e s s i n g bo th i n t h e t e s t i n g o f modules wi th s i m u l a t e d h a i l and i n t h e a c q u i r i n g o f h a i l impact p r o b a b i l i t y s t a t i s t i c s . The o b j e c t i v e s o f t h e e f f o r t i n c l u d e e v a l u a t i n g t h e c u r r e n t module c o n s t r u c t i o n approaches , d e v e l o p i n g d e s i g n and c o s t d a t a on approaches t o i n c r e a s e ruggedness , d e v e l o p i n g e a s i l y implemented t e s t p r o c e d u r e s , and d e f i n i n g c o s t - e f f e c t i v e ruggedness r e q u i r e m e n t s .

Another area o f e n v i r o n m e n t a l r e q u i r e m e n t g e n e r a t i o n is a d d r e s s e d toward o b t a i n i n g q u a n t i t a t i v e d a t a on . t h e mechan ica l f a t i g u e l o a d i n g a s s o c i a t e d w i t h f i e l d wind and t h e r m a l c y c l e env i ronments . T h i s a c t i v i t y , : u s e s computer a n a l y s i s o f c o n t i n u o u s t e m p e r a t u r e and wind h i s t o r i e s i n . ' . . . . c o n j u n c t i o n w i t h mechan ica l f a t i g u e l o a d i n g t h e o r i e s t o e s t i m a t e t h e t o t a l f a t i g u e l o a d i n g l e v e l a s s o c i a t e d w i t h a p r o j e c t e d p h o t o v o l t a i c p l a n t l i f e - time. These d a t a w i l l u l t i m a t e l y be f a c t o r e d i n t o upda ted s p e c i f i c a t i o n s f o r t h e c u r r e n t t h e r m a l c y c l e and c y c l i c wind l o a d i n g tests.

. . . . . . . . . .

I n c o n j u n c t i o n w i t h t h e c y c l i c l o a d i n g a n a l y s i s ' e f f o r t , work h a s ...

a l s o p r o g r e s s e d on t h e d e s i g n , f ' ab r i ca t ion . ; ' a n d . checkou t o f . a ' wind- load ing ' ' . '

s p e c t r o m e t e r . T h i s i n s t r u m e n t . e l iminat .es t h e ' problem o f d e t e r m i n i n g . t h e . .

f a t i g u e l o a d i n g c h a r a c t e r i s t i c s o f wind a t a p a r t i c u l a r s i t e b y , i n t e g r a t i n g . . . i n real time t h e number o f ' c y c l i c . l oads obse rved by t h e i n s t r u m e n t . . . Use'..'; ;: . . . . . . . . . .

.,. . . . . . . o f t h e i n s t r u m e n t a t . module t e s t s i t e s p r o v i d e s a n a c c u r a t e . e s t . i m ~ t e .of .:.: . . . . . " . .

. . t h e f a t i g u e env i ronment s e e n by t h e t e s t modules. . . . . . . . . .

I n t h e s u p p o r t o f a Department o f Defense p h o t q v o l t a i c r a n i e .A=- . . : . ' : . . . . . . . . . . . . . . . s u r i n g sys tem (RMS) a p p l i c a t i o n , work i s n e a r c o m p l e t i o n on t h e development; . . . . . . . . . .:::..%::. : , : . ..

. . . . . . . . ... o f i n s o l a t i o n d e f i c i t s t a t i s t i c s ~ a s s o c i a t e d w i t t i , c l i m a t i c v a r i a t i o n s ....... ., . '.. : . . . . . . . ( c l o u d y d a y s ) . A u n i q u e mettiodolog.y .has been deve loped : around. ' t ' t ie corn-. . . . . . . . . .

p u t e r a n a l y s i s o f hour-by-hour h i s t o r i c a l w e a t h e r . r e c o r d s ( t a p e s ) which: . : : ' ; " . . . a i d s i n t h e s e l e c t i o n o f t h e optimum c o l l e c t o r and s t o r a g e s i z e f o r a . .

g i v e n g e o g r a p h i c a l s i t e .

E . OPERATIONS AREA

The l a s t o f t h e Block 1 ( 15-kW add-on) modules was d e l i v e r e d e a r l y i n t h i s q u a r t e r f o r d e l i v e r y t o a DOD a p p l i c a t i o n . Approval f o r produc- t i o n was g i v e n t o a l l f o u r m a n u f a c t u r e r s f o r t h e Block 2 (130 kW), p r o c u r e - ment. Ninety-seven a d d i t i o n a l modules were i n s t a l l e d a t t h e JPL and T a b l e Mountain test s i t e s , f o r a total o f 218 a t a l l t h r e e s i t es . E i g h t o f t h e modules a t the" JPL s i t e were mounted f o r a test o f t h e e f fec t o f d i r t on module pe r fo rmance . Work on t h e Pasadena tes t s i t e automated d a t a a c q u i s i t i o n sys tem p e r i p h e r a l hardware was l a r g e l y c o m p l e t e d , and was a w a i t i n g d e l i v e r y o f t h e d a t a sys tem i t s e l f . A summary o f t h e i n t e r - l a b o r a t o r y s t a n d a r d s measurements was g i v e n a t t h e Semiannual Photovol- t a ic Program Review i n San Diego i n J a n u a r y . The s o l a r c e l l module p r o b l e d f a i l u r e r e p o r t i n g p r o c e d u r e document was r e v i s e d .

SECTION I11 . . .

PROJECT ANALYSIS AND INTEGRATION AREA

A. PLANNING AND INTEGRATION 'TASK

During t h i s q u a r t e r p l a n n i n g was i n i t i a t e d f o r a n expanded i n t e - g r a t i o n e f f o r t among t h e Technology Development Area t a s k s , P r o j e c t A n a l y s i s and I n t e g r a t i o n (PA&I) Area, and o t h e r ERDA program e lements . A - m i s s i o n sys tem i n t e r f a c e a n a l y s i s a c t i v i t y was s t a r t e d l a t e i n t h e q u a r t e r i n a n e f f o r t t o enhance t h e i n f o r m a t i o n f l o w i n t o t h e LSSA p r o j e c t , p a r t i c u l a r l y from t h e ' m i s s i o n and sys tems c o n t r a c t o r s o f t h e ERDA program. 'the Planni,ng and I n t a n g r a t i o n Task s u p p o r t e d t h e Program P lann ing Group* a t m e e t i n g s i n January a t S a n d i a C o r p o r a t i o n , i n Fcbruary a t MIT, and i n M a r c h . a t Aerospace C o r p o r a t i o n .

B. ARRAY TECHNOLOGY COST ANALYSIS TASK

A p r e l i m i n a r y v e r s i o n o f t h e SAMICS Workbook was p u b l i s h e d as , JPL Document 5101-15. Toward t h e - end o f t h e q u a r t e r , some o f t h e a r e a s i n which t h e Workbook w i l l b e r e v i s e d had been i d e n t i f i e d . A p p l i c a t i o n of t h e Workbook t o a r e a l i s t i c p r o c e s s i n g sequence was a b o u t 50% comple te . Meanwhile, t h e Automated Array Assembly Task i n c l u d e d a r equ i rement i n i t s technolog-y a s s e s s m e n t c o n t r a c t s t h a t t h e p r e l i m i n a r y v e r s i o n o f t h e Workbook's p r o c e s s d e s c r i p t i o n f o r m a t be used. I n a d d i t i o n , an a p p l i c a t i o n o f t h e p r e l i m i n a r y Workbook t o a wafer-to-module p r o c e s s i n g sequence was i n i t i a t e d .

Reques t s f o r e x p r e s s i o n s o f i n t e r e s t i n s e r v i n g a s t h e SAMICS . suppor t c o n t r a c t o r were s e n t t o o v e r 20 firms. A f t e r h e a r i n g two supp le - mentary p r e s e n t a t i o n s , t h e JPL A&E S e r v i c e s Board s e l e c t e d a firm; n e g o t i a t i o n s were a b o u t t o b e g i n a t t h e end o f t h e q u a r t e r .

Design o f t h e SAMIS I11 computer program was abou t 75% complete a t q u a r t e r ' s end , b u t cod ing had n o t y e t s t a r t e d . S e v e r a l submodels ' o f t h e methodology were c l a r i f i e d . The one-t ime c o s t s , f o r example, were shown t o be s i g n i f i c a n t c o n t r i b u t o r s t o p r i c e .

P r i c e g o a l a l l o c a t i o n s were reviewed and updated s e v e r a l t i m e s d u r i n g t h e q u a r t e r , and t h e fo rmat f o r p r e s e n t i n g t h e a l l o c a t i o n s was . r e v i s e d . Updated p r i c e g o a l , a l l o c a t i o n s were p repared f o r t h e P r o j e c t I n t e g r a t i o n Meeting i n May.

*The Program P l a n n i n g Group was e s t a b l i s h e d by ERDA H e a d q u a r t e r s . It c o n s i s t s o f r e p r e s e n t a t i v e s from a l l t h e P h o t o v o l t a i c Program e l e m e n t s , i n c l u d i n g JPL. The purpose of t h e g roup i s t o w r i t e t h e N a t i o n a l P h o t o v o l t a i c Energy Conversion Plan.

C . ECONOMICS AND INDUSTRIALIZATION ANALYSIS TASK . .

The l i f e - c y c l e c o s t o f e n e r g y s y s t e m s e f f o r t .was c o n t i n u e d a t . , .

0 . 5 person-inonth/month d u r i n g t h e q u a r t e r . .The m a j o r p r o g r e s s h a s . , . been t o c o n s o l i d a t e a c o l l e c t i o n o f a d , h o c . c o m p u t e r models i n t o one i n t e g r a t e d program s e t , and t o b e g i n n o n - o r i e n t e d d o c u m e n t a t i o n . The compute r mode l ing was n e a r l y c o m p l e t e a t q u a r t e r ' s end .

The P r o d u c t i o n P r o c e s s and Equipment Area produced a m a j o r summary o f t h e , m a n u f a c t u r i n g p r o c e s s c o n t r a c t s , and . t h i s . w a s . i n t e g r a t e d i n t o t h e PA.&I p r i c e / q u a n t i t y s t u d y . The most i m p o r t a n t c o n c l u s . i o n o f t h i s s t u d y t o d a t e was t h a t , b a s e d on modest e s t i m a t ' i o n s ' o f c u r r e n t t e c h n o l o g y , t h e minimum a v e r a g e c o s t o f rnanuf%.ct.uring moduleo seems at ; l ;a inabIe ; . -,

i n a f a c i l i t y s i z e d f o r ~ 5 0 MWpt/year o u t p u t . T h i s is. a n o r d e r o f . '.,

magni tude smaller tdhan t.ba 500 MW/yca~ p r o d u c t i o n goal ..pi'. 19@. . '-If c o r r e c t , this i m p l i e s t h a t 450 MW/year o f c i r c a 1986 p r o d u c t i o n ~ m u s t ... . : I

be j u s t i f i e d , i f a t a l l , on g r o u n d s o t h e r t h a n ' e conomies o f .. scal.e,: . . .' ' . . . . .. .

. . . .

It a p p e a r s t h a t t h e MIT Energy L a b o r a t o r y w i l i join ' . ' the ~ . r o g r a m , .. . s p e c i f i c a l l y t o p r o v i d e s u p p o r t i n t h e a r e a o f economic a n a l y s i s . ; : ' T h i s e f f o r t w i l l c o u p l e w i t h MIT/Lincoln L a b o r a t o r y r e s p + r i s 1 6 i l g t i e s . . f o r tes t and d e m o n s t r a t i o n a c t i v i t i e s , and w i l l p r o v i d e a s t r o n g a n a l y . s i s c o v e r a g e o f t h e demand s i d e o f t h e m a r k e t . Economics and ~ n d < s t r i ' a l ' i z ~ a $ i o n Task c o n d u c t e d s e v e r a l m e e t i n g s w i t h t h e ~ 1 ~ / ~ n e r 4 y : . ~ a b o r a t o r y s t a f f , and t h e ~ n e r ~ y L a b o r a t o r y s t a f f h a s c o l l e c t i v e l y d e v e l o p e d a work p l a n t h a t c o v e r s m a r k e t development a n a l y s i s much more t h o r o u g h l y t h a n a t any time i n t h e p a s t .

A f o r m a l workp lan h a s been d e r i y e d and s t a f f e d f o r JPL c o n t r i b u t i o n s t o t h e Program P l a n n i n g Group. A c o n t i n u i n g problem i s t h e l a c k o f a f i r m c o n t r a c t from t h e Program Office t o MIT/Energy L a b o r a t o r y . The s u b s t a n t i v e a n a l y t i c a l i s s u e s . have been r e s o l v e d , and work i s unde r way on t h e r e l e v a n t l i t e r a t u r e s e a r c h e s .

TECHNOLOGY DEVELOPMENT AREA . .

A . SILICON MATERIAL TASK

The o b j e c t i v e o f t h e S i l i c o n M a t e r i a l Task i s t o e s t a b l i s h by 1986, a n i n s t a l l e d p l a n t c a p a b i l i t y f o r p roduc ing s i l i c o n s u i t a b l e f o r s o l a r c e l l s .at a r a t e e q u i v a l e n t t o 500 megawatts ( p e a k ) o f s o l a r a r r a y s p e r y e a r a t a p r i c e o f less t h a n $10 p e r k i logram. The program f o r m u l a t e d t o a c h i e v e t h i s o b j e c t i v e is based on t h e c o n c l u s i o n t h a t t h e p r i c e g o a l c a n n o t be r eached i f t h e p r o c e s s used is e s s e n t i a l l y t h e same a s t h e p r e s e n t commercial

' . pl;aeejj"' f61- producing samiesnduetdr-giadc o i l i c o n Conooquontly , it i o . . .

n e c e s s a r y t h a t e i t h e r a d i f f e r e n t p r o c e s s be deve loped f o r p roduc ing semiconduc to r -g rade s i l i c o n o r a less p u r e and l e s s c o s t l y s i l i c o n m a t e r i a l ( i . e . , a s o l a r - c e l l - g r a d e s i l i c o n ) be shown t o be u t i l i z a b l e .

1. T e c h n i c a l Background

S o l a r ce l l s a r e p r e s e n t l y f a b r i c a t e d from semiconduc to r -g rade s i l i c o n , which h a s a marke t p r i c e o f abou t $65 p e r k i l o g r a m . A d r a s t i c r e d u c t i o n i n p r i c e o f m a t e r i a l is n e c e s s a r y t o meet t h e economic o b j e c t i v e s o f t h e LSSA P r o j e c t . One means f o r mee t ing t h i s r e q u i r e m e n t i.s t o d e v i s e a p r o c e s s f o r p roduc ing a s i l i c o n m a t e r i a l which is s i g n i f i c a n t l y less pure t h a n ,

semiconduc to r -g rade s i l i c o n ; t h e p r i c e g o a l f o r t h i s m a t e r i a l i s less t h a n $10 p e r k i l o g r a m . However, t h e a l lowance f o r t h e c o s t o f s i l i c o n m a t e r i a l i n t h e o v e r a l l economics o f t h e s o l a r a r r a y s f o r LSSA i s dependen t on o p t i m i z a t i o n t r a d e - o f f s , which c o n c o m i t a n t l y t r e a t t h e e f f e c t s o f t h e p r i c e o f s i l i c o n m a t e r i a l and t h e e f fec ts o f m a t e r i a l p r o p e r t i e s on t h e performance o f s o l a r c e l l s . Accord ing ly , t h e program o f t h e S i l i c o n M a t e r i a l Task i s s t r u c t u r e d t o p r o v i d e i n f o r m a t i o n f o r t h e o p t i m i z a t i o n t r a d e - o f f s c o n c u r r e n t l y w i t h t h e development o f h i g h volume and low c o s t p r o c e s s e s f o r producing d i f f e r e n t i m p u r i t y - g r a d e s o f s i l i c o n .

. . .

2. O r g a n i z a t i o n and C o o r d i n a t i o n o f t h e S i l i c o n M a t e r i a l Task E f f o r t . . . .. . . . . . . '

. . . ... . ,

The S i l i c o n M a t e r i a l Task e f f o r t is o r g a n i z e d i n t o f i v e p h a s e s . A s Tab le 4-1 i n d i c a t e s , Phase I is d i v i d e d i n t o f o u r p a r t s - . I n P a r t I t h e : ' t e c h n i c a l f e a s i b i l i t y and p r a c t i c a l i t y o f p r o c e s s e s f o r p roduc ing

..'. .-sem$conduc t o r - g r a d e s i l i c o n w i l l . - b e . d e m o n s t r a t e d . I n P a r t I1 t h e e f f e c t s . . o f . i m p u r i t i e s and o f v a r i o u s p r o c e s s i n g p r o c e d u r e s on t h e p r o p e r t i e s of o f s i n g l e - c r y s t a l s i l i c o n m a t e r i a l and t h e pe r fo rmance c h a r a c t e r i s t i c s o f s o l a r c e l l s w i l l be i n v e s t i g a t e d . T h i s body o f i n f o r m a t i o n w i l l s e r v e as a g u i d e i n d e v e l o p i n g p r c c e s s e s ' ( i n P a r t 111) f o r t h e p r o d u c t i o n o f s o l a r - c e l l - g r a d e s i l i c o n . The p r o c e s s developments i n P a r t s I and 111 w i l l be accompl ished t h r o u g h chemica l r e a c t i c n , chemica l e n g i n e e r i n g , energy- u s e , and economic s t u d i e s . I n P a r t I V o f Phase I , t h e r e l a t i v e commercial p o t e n t i a l s o f t h e v a r i o u s s i l i c o n - p r o d u c t i o n p r o c e s s e s deve loped under P a r t s I and I11 v i l l . b e e v a l u a t e d . Thus, a t t h e end o f Phase I a body

Table-4-1.. ' O r g a n i z a t i o n o f t h e S i l i c o n M a t e r i a l Task E f f o r t

. . . . . . . .

P h a s e / P a r t O b j e c t i v e . :

. . ..>

. Phase I ~ e m o ' n s t r a t e , t h e t e c h n i c a l f e a s i b i l i t y and p r a c t i - c a l i t y o f p r o c e s s e s f o r p r o d u c i n g , s i l i c o n . . ; . . . .

. . . . . . . . . . . .... . .

P a r t I . , E s t a b l i s h t h e p r a c t i c a l i t y o f a p r o c e s s c a p a b l e ...

. o f h i g h volume p r o d u c t i o h ' o f 'seniicontluctor-gyade ; . . . . . . . . . :...I . . . . . . . . . . . . . . . . . . . s i l i c o n a t a macked$y'..reduced . . . c o s t . . . " . : . . . . . . . . . . . . . . .

. . , $ . . . . :.. . . . . . . . . . . . . . . P a r t 11. ~ n v e s t i ~ a t e t h e e f f e c t d o f i m p u r i t i e s . . a n d . . . . . . of. : :vari-" +.' . . . % . . ... . . . :... ., ... . . . ous p r o c e s s i n g pro ,cedures on ' t h e . prop&.t'$es o f !:. .::,:. . .

s i n g l e - c r y s t a l s i l i c o n m a t e r i a l and the ..performance . . . ' . . . . ' . . . .. . . . . . . . . - .:. . . . . . . . . . . . . . . . . . . . . . . . . . . c h a r a c t e r i s t i c s ' of s o l a r c e l l s . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. : . . ... . . . . . . . . . . . P a r t I11 E s t a b l i s h t h e p r a c t i c a l i t y .of a p r o c e s s "ca;pabl:e of.-:' '.: . ' , :.

. . . . . . . . . . . . h i g h volume p r o d u c t i o n o f .solar-cell-grade.:'sil:icon. , : ::.- :. . . . . _ . . . . . . . . . . . . . . . . . . a t a p r i c e o f less t h a n $lO..:peri .kilogram..; :., . . . . . - . . . . . . . . ... . . . . . . . . . . . . . . . . . . . ... . . . . .

. . . . . . . P a r t I V E v a l u a t e t h e r e l a t i v e commercial p o t e n t i a l o f t h 6 :

s i l i c o n - p r o d u c t i o n p r o c e s s e s deve ioped under Phase I.

Phase I1 ' O b t a i n p r o c e s s sca le -up i n f o r m a t i o n .

Phase I11 Conduct, e x p e r i m e n t a l p l a n t o p e r a t i o n s t.o .nht .a in t e c h n i c a l and economic av.i.rlnnne o f l a r p - s o a l e p r o d u c t i o n p o t e n t i a l .

Phase I V Des ign , i n s t a l l , and o p e r a t e a f u l l - s c a l e commercial p l a n t c a p a b l e o f mee t ing t h e ' p r o d u c t i o n o b j e c t i v e .

of i n f o r m a t i o n k i l l have been ~ b t a i n e d f o r op t imiza t i .on tat-ad.-nf f s t u d i e s . . . . . . . . . . and t h e most p romis ing p r o c e s s e s . w i l l .have . .been. s e l e c t e d . . . . : . .

..... . . . . . .. : . . . . .

Phase . I1 w i l l be i n i t i a t e d t o o b t a i n scale- information. T h i s w i l l be d e r i v e d from e x p e r i m e n t s and a n a l y s e s i n v o l v i n g mass and e n e r g y b a l a n c e s , p r o c e s s f l o w s , k i n e t i c s , m a s s . t r a n s f e r , t e m p e r a t u r e and p r e s s u r e . e f f e c t s , and o p e r a t i n g c o n t r o l s . The b a s i c approach w i l l be t o p r o v i d e fundamenta l s c i e n t i f i c and e n g i n e e r i n g i n f o r m a t i o n from which v a l i d e x t r a p o l a t i o n s u s a b l e f o r p l a n t d e s i g n . c a n be made; a p p l i c a b l e s c a l e - u p c o r r e l a t i o n s w i l l a l s o be used. T h i s body o f sca1.e-up i n f o r m a t i o n w i l l t h e n p r o v i d e t h e n e c e s s a r y b a s i s f o r t h e d e s i g n , c o n s t r u c t i o n , and o p e r a t i o n of a l a r g e - s c a l e p roduc t i o n p l a n t .

S i n c e t h e i n s t a l l a t i o n and o p e r a t i o n o f a commercial chemica l p r o c e s s p l a n t t h a t i n c o r p o r a t e s a new p r o c e s s i n v o l v e s h i g h r i s k s , e x p e r i m e n t a l p l a n t s w i l l be used t o o b t a i n t e c h n i c a l and economic .ev idence -

o f l a r g e - s c a l e p r o d u c t i o n p o t e n t i a l . I n t h e e x p e r i m e n t a l p l a n t phase ( i . e . , Phase 1 1 1 ) t h e r e w i l l be o p p o r t u n i t i e s t o c o r r e c t d e s i g n e r r o r s ; t o d e t e r m i n e ene rgy consumpt ion; t o e s t a b l i s h p r a c t i c a l o p e r a t i n g proce- d u r e s and p r o d u c t i o n c o n d i t i o n s ; and t o more r e a l i s t i c a l l y e v a l u a t e t h e r e q u i r e m e n t s f o r i n s t r u m e n t a t i o n , c o n t r o l s , and o n - l i n e a n a l y s e s .

I n t h e f i n a l phase of t h e S i l i c o n Material Task ( i. e . , Phase I V ) , a f u l l - s c a l e commercial p l a n t c a p a b l e o f mee t ing t h e p r o d u c t i o n o b j e c t i v e w i l l be d e s i g n e d , i n s t a l l e d , and o p e r a t e d . The e x p e r i m e n t a l p l a n t and t h e commercial p l a n t w i l l be o p e r a t e d c o n c u r r e n t l y s o as t o p e r m i t t h e u s e o f t h e e x p e r i m e n t a l p l a n t f o r I n v e s t l g a L i o n s o f p l a n t o p e r a t l . o n s , i . e . , f o r problem s o l v i n g and f o r s t u d i e s o f p r o c e s s o p t i m i z a t i o n .

A d d i t i o n a l b a s i c chemica l and e n g i n e e r i n g i n v e s t i g a t i o n s t o respond t o p rob lem-so lv ing needs o f t h e S i l i c o n M a t e r i a l Task w i l l be conducted i n . s u p p o r t i n g e f f o r t s . These s u p p o r t i n g s u b t a s k s w i l l be accompl ished under c o n t r a c t and by an in-house JPL program.

3 S i l i c o n M a t e r i a l Task C o n t r a c t s

Nine c o n t r a c t s a r e i n p r o g r e s s : t h r e e f o r P a r t I , one f o r P a r t 11, f o u r f o r P a r t 111, and one f o r P a r t I V . These c o n t r a c t s were n e g o t i a t e d a f t e r c a r e f u l e v a l u a t i o n s o f r e s p o n s e s t o a Request f o r P r o p o s a l (RFP) and o f u n s o l i c i t e d p r o p o s a l s . The c o n t r a c t s are l i s t e d i n T a b l e 4-2. A d d i t i o n a l c o n t r a c t o r s f o r s u b s e q u e n t p h a s e s w i l l be s e l e c t e d from u n s o l i c i t e d p r o p o s a l s and from f u t u r e RFPs.

4. S i l i c o n M a t e r i a l . T a s k T e c h n i c a l A c t i v i t y

The o b j e c t i v e s o f Phase I o f t h e S i l i c o n Material Task a r e a s f o l l o w s :

( 1 ) P a r t I - E s t a b l i s h t h e p r a c t i c a l i t y of a p roceo3 o a p a b l e of ' t h e h i g h .volume p r o d u c t i o n o f semiconduc t o r - g r a d e s i l i c o n a t a markedly reduced c o s t .

( 2 ) P a r t I1 - I n v e s t i g a t e t h e e f fec ts o f i m p u r i t i e s and p r o c e s s - '

s t e p s on t h e p r o p e r t i e s o f s i n g l e - c r y s t a l s i l i c o n m a t e r i a l . . ..

and t h e performance c h a r a c t e r i s t i c s o f s o l a r ce l l s .

( 3 ) P a r t I11 - E s t a b l i s h t h e p r a c t i c a l i t y o f a p r o c e s s c a p a b l e o f t h e h i g h volume p r o d u c t i o n o f s o l a r - c e l l - g r a d e s i l i c o n a t a p r i c e o f less t h a n $10 p e r k i l o g r a m .

. ( 4 ) P a r t I V - E v a l u a t e t h e r e l a t i v e commercia l p r a c t i c a l i t y o f t h e s i l i c o n - p r o d u c t i o n p r o c e s s e s deve loped under Phase I o f t h e S i l i c o n M a t e r i a l Task.

Table 4-2. Si l icon Material Task Contractors

Contractor Technology Area

SEMICONDUCTOR-GRADE PRODUCTION PROCESSES (Par t I of Phase I )

E a t t e l l e Memorial I n s t i t u t e , S i from Sic14 reduction by Zn Columbus, Ohio (JPL Contract No. 954339)

4

Union Carbide, S i s t e r s v i l l e , S i from SiH4 derived by W . Virginia r ed i s t r i bu t i on process (JPL Contract No. 954334)

. . . . Motorola, Phoenix, Arizona S i using SiF4 react ion with 'metal- (JPL Contract No. 954442) l u rg i ca l grade S i and SiF2 . t r ans fe r .

SOLAR-CELL-GRADE SPECIFICATIONS (Par t I1 of Phase I )

Westinghouse E l e c t r i c , Pi t t sburgh, Pennsylvania (JPL Contract No. 954331)

Invest igat ion of e f f e c t s of impur- i t i e s on s o l a r c e l l performance

SOLAR-CELL-GRADE PRODUCTION PROCESSES (Par t I11 of Phase I )

Dow Corning, Hemlock, Michigan S i from purer source mater ia ls i JPL Contract No, 954559) us lng arc furnace processing

Stanford Research I n s t i t ~ ? t e S i by Na reduction 6f SiF4 Menlo Park, Californka (J1:'L ConLrlact' N 6 . 954471 )

Westinghouse E l e c t r i c Pi t t sburgh, Pennsylvania (JPL Contract No. 954589)

S i by plasma-arc-heater reduction of Sic14 w i t h H; and a l k a l i metala a3 reducing agents

AeroChem Research Laboratories, S i by use of a nonequilibrium Princeton, New Jersey plasma j e t (JPL Contract No. 954560)

. T a b l e 4-2. S i l i c o n Material Task C o n t r a c t o r s . ( c o n t i n u a t i o n '1 ) . .

C o n t r a c t o r Technology Area

COMMERCIAL POTENTIAL OF PROCESSES ( P a r t I V o f Phase I )

Lamar U n i v e r s i t y , Beaumont, Texas (JPL C o n t r a c t No. 954343)

E v a l u a t e r e l a t i v e commercial poten- t i a l s o f S i - p r o d u c t i o n p r o c e s s e s deve loped under t h e S i l i c o n M a t e r i a l Task

a . P r o c e s s e s f o r Producing Semiconductor-Grade S i l i c o n .

1 ) P r o d u c t i o n o f S i by Zn Reduc t ion o f S i c 1 4 - B a t t e l l e Memorial I n s t i t u t e . The c o n t r a c t w i t h Battelle Memorial I n s t i t u t e is f o r development o f t h e r e a c t i o n f o r t h e Zn r e d u c t i o n of S i c 1 4 u s i n g a f l u i d i z e d bed r e a c t o r a s an eccnomica l means f o r p roduc ing S i , Based on c a l c u l a t i o n s by B a t t e l l e and Lamar U n i v e r s i t y , t h i s p r o c e s s h a s t h e p o t e n t i a l f o r a t o t a l p r o d u c t c o s t between $9.12 and $9.68/kg S i f o r a 1000 metric t o n j y e a r p l a n t .

A d e t a i l e d f low s h e e t o f t h e p r o c e s s fo r a 25 m e t r i c t o n / y e a r p r o c e s s sys tem development f a c i l i t y was p r e p a r e d . The subsys tems o f t h e p r o c e s s a r e f o r S i d e p o s i t i o n , Zn r e c y c l e , S i c 1 4 w a s t e d i s p o s a l , C12 h a n d l i n g , and p e r i o d i c c h l o r i n a t i o n t o remove S i d e p o s i t e d on t h e walls o f t h e r e a c t o r . Purchased S i c 1 4 w i l l be p u r i f i e d i n t h e f irst s t e p o f t h i s f a c i l i t y . The d e p o s i t i o n p r o d u c t w i l l be coo led and removed p e r i o d i c a l l y . Zn r e c y c l i n g w i l l be accompl ished u s i n g a ZnC12 e l e c t r o l y s i s c e l l . The major by-product t o be d i s p o s e d of i s C 1 2 ; t h i s w i l l amount t o a b o u t 5 kg f o r e v e r y kg S i produced. The p l a n f o r t h i s f a c i l i t y is t o d i s p o s e o f i t by forming NaHC102, which is m a r k e t a b l e . The o t h e r o p t i o n s are t o u s e t h e C12 t o c h l o r i n a t e m e t a l l u r g i c a l g r a d e S i t o make S i c 1 4 and t o s e l l t h e C12. R e v i s i o n s o f t h e f l o w diagram w i l l f o l l o w c a l c u l a t i o n s o f e x p e r i m e n t a l d a t a and i t e r a t i o n s o f a n a l y s e s .

A rna t , e r i a l / ene rgy b a l a n c e s h e e t was c a l c u l a t e d u s i n g d a t a from t h e l i t e r a t u r e . The was te d i s p o s a l subsys tem was n o t i n c l u d e d a t t h i s time, s i n c e some p h y s i c a l d a t a a r e n o t y e t a v a i l a b l e . The b a s i s f o r t h e c a l c u l a t i o n s was an assumed p r o d u c t i o n r a t e o f 3 .6 kg /h r and an 80% on-stream o p e r a t i o n f o r 7000 h r / y r . The v a l u e s f o r t h e e f f i c i e n c i e s of r e a c t i o n and o f c o n d e n s a t i o n s were based e i t h e r on e x p e r i m e n t a l d a t a o r on e x t r a p o l a t i o n s . Other a s sumpt ions were : o p e r a t i o n a t t h e Zn/SiC14 r a t i o o f 2 : 1 ; a bed d e p o s i t i o n e f f i c i e n c y o f 60%; w a l l d e p o s i L i o r ~ and S i c a r r y o v e r o f 1.8 and 1 .25 , u s i n g e x p e r i m e n t a l l y o b t a i n e d v a l u e s ; a p r o d u c t o f 5% seed and 95% d e p o s i t , and an e l e c t r o l y s i s c e l l o p e r a t i o n

o f 100% c u r r e n t e f f i c i e n c y . The f l u i d i z e d bed r e a c t o r is p r a c t i c a l l y a d i a b a t i c . S i n c e t h e e x o t h e r m i c h e a t o f r e a c t i o n c a n n o t be used t o h e a t t h e SiC14, t h e s i m p l e s t o p e r a t i o n o f t h e f l u i d i z e d bed r e a c t o r was t a k e n t o be w i t h s e p a r a t e p r e h e a t e r ( e n d o t h e r m i c ) and r e a c t i o n ( e x o t h e r m i c ) s e c t i o n s . The e n e r g y b a l a n c e w i l l be r e v i s e d t o t a k e i n t o a c c o u n t f a c t o r s which were n o t i n c l u d e d i n t h e s i m p l e t r e a t m e n t .

.. The e x p e r i m e n t a l s t u d i e s were l i n k e d t o t h e f l u i d i z e d bed r e a c t o r d e s i g n , t h e by -p roduc t c o n d e n s a t i o n and r e c o v e r y , and t h e p r o d u c t pro- d u c t i o n ra te and y i e l d . I n a d d i t i o n , a series o f e x p e r i m e n t s was d i r e c t e d .

.

t o t h e deve lopmen t o f a d i f f e r e n t i n v a p o r i z e r and ' t o t h e d e t e r m i n a t i o n o f t h e c o n d i t i o n s f o r t h e Zn/SiCl4 , r e a c t i o n o t h e r t h a n i n - t h e FBR. The l a s t s t u d y was f o r t h e p u r p o s e o f e s t a b l i s h i n g c o n d i t i o n s f o r max- ' ,:'

i m i z i n g t h e d e p o s i t i o n on t h e s e e d material i n t h e f l u i d i z e d ' bed r e a c t o r . ' .

. . . . E x p e r i m e n t s i n v o l v i n g t h e o p e r a t i n g p a r a m e t e r s and r e a c t o r d e s i g n . " ,:" .,. . . ' . .

f a c t o r s l e d t o a s e r i e s o f t e n t a t i v e c o n c l u s i o r ~ s and i n f e r e n c e s . The . . i n s t i t u t i o n ot ' a h e m i s p h e r i c a i bed s u p p o r t g a v e an i n c r e a s e i n t h e . . . . . . . . . . . . . . . .

S i c l o - t o - S i c o n v e r s i o n e f f i c i e n c y ( 7 9 and 78% o f t h e o r y .as com.pared . . . - : . ..

w i t h 68% w i t h t h e c o n c i s e bed s u p p o r t ) . I n a d d i t i o n , t h e e f f i c i e n c y . .

.. . g a i n was accompanied by smoo the r bed a c t i o n , i n d i c a t i n g t h e c a p a b i l i t y f o r h i g h e r r e a c t a n t t h r o u g h p u t . Changing t h e i n l e t . p o s i t ion.,,, t o f l p w Zn t h r o u g h t h e a x i a l i n l e t e l i m i n a t e d S i g rowth a t . t h e Z n : l n l & t and r e d u c e d t h e amount o f S i d e p o s i t e d on t h e r e a c t o r wall, P r e l i m i n a r y r e s u l t s i n d i c a t e t h a t o p e r a t i o n as a g r a d e d t e m p e r a t u r e bed w j , l l e a d t o improved c o n v e r s i o n e f f i c i e n c y . I n c r e a s e d f e e d s l e d t o enhanced y i e l d s ; an i n c r e a s e i n t o t a l t h r o u g h p u t i n m o l e s o f gas p e r hour of 42% g a v e a bed d e p o s i t i o n ra te o f 344 gm/hr , t h e h i g h e s t a c h i e v e d s o f a r . The o v e r a l l o p e r a b i l i t y o f t h e e x p e r i m e n t a l f a c i l i t y was c o n s i d e r a b l y improved. With minor de ' s ign c h a n g e s t h e by -p roduc t c o n d e n s a t e c o l l e c t i o n s u b s y s t e m p e r f o r m s s a t i s f a c t o r i l y . The f l u i d i z e d bed r e a c t o r wall d e p o s i t , which h a s been shown t o b e - a s low as 3% of t h e Si p r o d u c t , is e x p e c t e d t o d e c r e a s e marked ly w i t h i n c r e a s e d r e a c t o r s i z e . While S i d u s t , which was r e d u c e d t o 2.4% o f t h e S i p r o d u c t , i s u n d e s i r a b l e , i t is b e l i e v e d t h a t t h i s i s c o n t r o l l a b l e , a l l o w i n g economic 'al o p e r a t i o n . The h i g h d e p o s i t i o n ra tes p r o v i d e a n e x p e r i m e n t a l v e r i f i c a t i o n f o r t h e 7 - inch r e a c t o r s e l e c t e d f o r t h e 25 mettc.ic: t .on /ysar p r o c e s s syst.em deve lopmen t f a c i l i t y .

2 P r o d u c t i c r i ~ of 3i Fiuu SiHlr PreDared bv H e d l s t r i b u t i o n - o f . ; . ' . ' . "-

C h l o r o s i l a n e s - Union C a r b i d e C o r ~ o r a t i o n . The Union C a r b i d e c o n t r a c t is f o r t h e deve lopmen t o f p r o c e s s e s f o r t h e p r o d u c t i o n o f SiH4 and f o r t h e d e p o s i t i o n of S i from SiH4. The SiH4 p r o c e s s i n c l u d e s s y s t e m s f o r t h e r e d i s t r i b u t i o n o f c h l o r o s i l a n e s and t h e h y d r o g e n a t i o n o f t h e by-product S i c 1 4 t o SiHC13, which c a n be used as a f e e d f o r r e d i s t r i b u t i o n . The free s p a c e r e a c t o r and t h e f l u i d i z e d bed r e a c t o r are t e c h n i q u e s b e i n g i n v e s t i g a t e d a s t h e means f o r S i d e p o s i t i o n .

After a s a f e t y c e r t i f i c a t i o n , t h e SiH4 e x p e r i m e n t a l f a c i l i t y was t o d e t e r m i n e t h e o p e r a t i o n a l l i m i t s and t h e p u r i t y - y i e l d c h a r a c t e r i s t i c s o f t h e u n i t . A maximum P u r i t y of 97 mole % SiH4 was o b t a i n e d w i t h o u t t h e u s e o f t h e S i c 1 4 o r C p u r i f i c a t i o n t r a p s u s i n g SiH2C12 as t h e f e e d . When t h e S i c 1 4 a b s o r b e r was p u t on stream, t h e e x p e c t e d p u r i f i c a t i o n

- . . .

d i d n o t o c c u r owing t o a n i n a b i l i t y t o overcome t h e h e a t l o s s o f t h e s y s t e m . A c c e p t a b l e p u r i f i c a t i o n c a n be o b t a i n e d w i t h a r e d e s i g n e d , h i g h e r c a p a c i t y u n i t o r by i n c r e a s i n g t h e s i z e o f t h e C - p u r i f i c a t i o n s y s t e m .

The economic o f t h i s SiH4 p r o c e s s depends i n l a r g e p a r t on t h e c a p a b i l i t y o f h y d r o g e n a t i n g t h e by-product S i c 1 4 t o SiHC13 a c c o r d i n g t o t h e r e a c t i o n 3SiC14 + 2H2 + S i m e t = 4 SiHC13 where S ime t is m e t a l l u r g i c a l g r a d e S i . T h i s r e a c t i o n is n o t s t r o n g l y e x o t h e r m i c , is p r o b a b l y s u r f a c e area d e p e n d e n t , r e q u i r e s a c a t a l y s t , s u c h as Cu, f o r t h e h i g h r e a c t i o n ra tes , and is f a v o r e d by h i g h p r e s s u r e . From a s e r i e s o f e x p e r i m e n t s i n a f i x e d bed r e a c t o r , it was c o n c l u d e d t h a t

,

t h i s t y p e o f r e a c t o r is n o t s u i t a b l e , b e c a u s e o f low r e a c t i o n rates and impropc r operating f o a t u r . e s . Expe r imen t s i n a f l i ~ i d i zed bed r e a c t o r showed t h a t t h e ra tes o f r e a c t i o n , b u t n o t t h e f i n a l c o m p o s i t i o n , were g r e a t l y a f f e c t e d by t e m p e r a t u r e o v e r t h e r a n g e of 400 t o 5 0 0 ' ~ ; a t 5 0 0 ~ ~ t h e y i e l d of 13.7% SiHC13 was r e a c h e d i n a b o u t 10 s e c o n d s . A t t empt s t o h y d r o g e n a t e SiHC13 t o form SiH2C12 were u n s u c c e s s f u l . A f l u i d i z e d bed r e a c t o r f o r t h e S iC14-hydrogena t ion r e a c t i o n w i t h a t h r o u g h p u t o f 7 k g / h r was d e s i g n e d f o r u s e i n t h e e x p e r i m e n t a l f a c i l i t y .

An a l t e r n a t i v e p r o c e s s f l o w scheme h a s been d e v i s e d f o r t h e i n t e - g r a t e d e x p e r i m e n t a l f a c i l i t y . O r i g i n a l l y t h i s f a c i l i t y f o r c o n v e r t i n g SiHC13 t o SiH4 used t h r e e d i s t i l l a t i o n co lumns , two r e d i s t r i b u t i o n r e a c t o r s , a n a b s o r b e r - s t r i p p e r e n r i c h m e n t s e c t i o n , and a C- t r ap f o r f i n a l p u r i f i c a t i o n . The alternative.configuration would u s e less equipment and r e q u i r e less e n e r g y . The f e e d would be e i t h e r p u r e SiHC13 o r a SiHC13/SiC14 m i x t u r e r e s u l t i n g from t h e h y d r o g e n a t i o n r e a c t i o n ; t h e SiHC13/SiC14 would first be p u t t h r o u g h a s t i l l . The s e q u e n c e would be : SiHC13 i n t o t h e f i r s t r e d i s t r i b u t i o n r e a c t o r ; t h e m i x t u r e o f c h l o r o s i l a n e s i n t o a s t i l l t o s e p a r a t e o u t t h e SiC13; and t h e d i s t i l l a t e of s ~ H ~ c ~ ~ / s ~ H c ~ ~ i n t o a s t i l l t o s e p a r a t e o u t t h e SiHC13 f o r r e c y c l i n g t o t h e first r e d i s t r i b u t i o n r e a c t o r , t h e SiHC12 i n t o a s e c o n d r e d i s t r i b u t i o n r e a c t o r f o r t h e f d r m a t i o n of S iH4 , and a c a r b o n t r a p t o remove c h l o r o s i l a n e i m p u r i t i e s from t h e p r o d u c t . The h e a t b a l a n c e c a l c u l a t i o n s f o r t h i s scheme are n o t c o m p l e t e ; t h e t h e r m a l e n e r g y n e e d s s h o u l d be lower d u e 'tb t h e d e c r e a s e in u ~ a l e r ~ i a l fo r v a p o r i z a t i o n .

The n a t u r e o f t h e r e s i n c a t a l y s t f o r t h e r e d i s t r i b u t i o n r e a c t i o n and t h e mechanism o f t h e r e a c t i o n were s t u d i e d u s i n g d e u t e r i u m - l a b e l e d

. . . , compounds t o t e s t . E a r l y e x p e r i m e n t a l d a t a had been i n t e r p r e t e d as ........ i n d i c a t i n g t h a t t h e a c t i v e form o f t h e c a t a l y s t f o r t h e r e d i s t r i b u t i o n . . . . . ' ' . ' ' . '

r e a c t i o n . i s . t h e amine h y d r o c h l o r i d e . The e x p e r i m e n t a l d a t a were s u r p r i s i n g , i n d i c a t i n g t h a t t h e amine h y d r o c h l o r i d e is n o t t h e a c t i v e form o f t h e c a t a l y s t . The a p p a r e n t a c t i v a t i o n by H C 1 i n p r e v i o u s work r e m a i n s u n e x p l a i n e d . . ... . .

. ,

The economic ' f e a s i b i l i t y o f u s i n g e i t h e r a f l u i d i z e d bed r e a c t o r o r a f r e e s p a c e r e a c t o r f o r t h e d e p o s i t i o n o f S i from SiH4 is b e i n g i n v e s t i g a t e d . One o f t h e o r i g i n a l c o n c e p t s was t o u s e t h e small p a r t i c l e s produced i n t h e f r e e s p a c e r e a c t o r as t h e s e e d f o r g rowth i n t h e f l u i d i z e d bed r e a c t o r . S u b s e q u e n t l y , e x p e r i m e n t a l r e s u l t s showed t h a t t h i s p r o c e d u r e was n o t p r a c t i c a l , and t h e p r e s e n t program p l a n i n v o l v e s t h e c o n c u r r e n t deve lopmen t s o f e a c h r e a c t o r .

I n t h e p r e s e n t s t u d y o f t h e f r e e s p a c e r e a c t o r t h e o p e r a t i n g c h a r a c t e r i s t i c s a r e b e i n g exp lo red a s f u n c t i o n s o f t h e i m p o r t a n t param- e t e r s . A p r o d u c t i o n r a t e o f 5 kg/hr was reached f o r a b o u t one minu te and a t a h i g h g a s v e l o c i t y a p y r o l y s i s e f f i c i e n c y o f o v e r 99% was a t t a i n e d . However, c o n t i n u o u s o p e r a t i o n h a s n o t y e t been d e m o n s t r a t e d . The S i powder p r o d u c t i s composed o f submicron-s ize p a r t i c l e s . C o n s o l i d a t i o n o f t h e powder by m e l t i n g and compaction t e c h n i q u e s i s b e i n g i n v e s t i g a t e d . M o d i f i c a t i o n s o f t h e r e a c t o r , which is c a p a b l e o f p roduc ing 1.5 kg o f S i powder p e r r u n , a r e be ing des igned s o a s t o i n c r e a s e p roduc t p u r i t y and t o a l l o w a u t o m a t i c p roduc t t r a n s f e r from t h e r e a c t o r chamber. Chemical a n a l y s e s o f t h e p roduc t a r e p lanned f o r t h e n e x t q u a r t e r .

3 ) f i o d u c t i o n of S i bv SiF4/SiFp T r a n s p o r t - Motorola C o r p o r a t i o n . The Motorola c o n t r a c t is f o r t h e development o f . a p r o c e s s f o r t h e con- v e r s i o n o f m e t a l l u r g i c a l - g r a d e S i i n t o semiconductor-grade S i u s i n g t h e S i F 2 t r a n s p o r t p u r i f i c a t i o n r e a c t i o n s t e p s . I n a s e r i e s o f e x p e r i m e n t s

, it was shown t h a t ( 1 ) 75% of t h e SiF4 r e a c t s w i t h S i m e t a t 1 2 5 0 ' ~ and a t 1350°c, ( 2 ) t h e r a t e o f S i g p fo rmat ion is n o t a f f e c t e d by t h e p r e s e n c e o f i m p u r i t i e s and ( 3 ) a t 1350 C t h e SiF2/SiF4 r a t i o i s c o n s t a n t a t f lows g r e a t e r than 100 SCCM. No g r e a t d i f f e r e n c e s i n t h e S iF2 /S iF4 r a t i o s were obse rved when comparing r e a c t i o n s u s i n g p u r i f i e d and u n p u r i f i e d S iF4 . The t h e r m a l decompos i t ion o f S iF2 polymer was c h a r a c t e r i z e d between 20 and 1 3 0 0 ~ ~ , and a s e r i e s o f p r o d u c t s was p o s t u l a t e d t o e x p l a i n mass s p e c t r o m e t r i c d a t a . The c o n v e r s i o n o f amorphous S i t o d e n d r i t i c S i a t a b o u t 7 3 0 ' ~ e v o l v e s S i F 4 , FeSiOSiF3, and p o s s i b l y A1F3. The c o n v e r s i o n o f t h e S i F 2 polymer r e l e a s e s v o l a t i l e S i f l u o r i d e s and forms S i - r i c h polymers which c o n v e r t i n t o S i a t abou t 930'~. Motc ro la h a s conc luded t h a t semiconduc to r -g rade S i can be produced by S i F 2 t r a n s p o r t from S i r n e t a t r a t e s o f up t o 40 gm/hr f o r s h o r t r u n t i m e s .

b . D e t e r m i n a t i o n o f t h e E f f e c t s o f I m p u r i t i e s and Process -S teps on P r o ~ e r t i e s o f S i and t h e Performance o f S o l a r C e l l s - Westinnhouse E l e c t r i c C o r p o r a t i o n . Phase I1 of t h i s c o n t r a c t c o n s i s t s of f i v e t a s k s : ( 1 ) The e f f e c t s o f p r o c e s s i n g - s t e p s , such as h e a t t r e a t m e n t , g e t t e r i n g , and c r y s t a l growth p a r a m e t e r s , w i l l be de te rmined i n con . junc t ion wit,h t h e i m p u r i t y e f f e c t s . (2) The combined e f f e c t s o f i m p u r i t i e s and h i g h B c o n c e n t r a t i o n s on s o l a r c e l l performance w i l l be examined. ( 3 ) The e f f e c t s o f i m p u r i t i e s on n- type, P-doped S i w i l l be d e t e r m i n e d ; t h e s e d a t a w i l l be compared wi th t h o s e f o r p - type , B-doped S i m a t e r i a l . ( 4 ) The m p u r i t y m a t r i x f o r n- type S i w i l l be expanded, e s p e c i a l l y i n two a r e a s : measurement and modeling f o r m a t e r i a l c o n t a i n i n g two o r more i m p u r i t i e s and s t u d y o f i m p u r i t i e s which may c o n t a m i n a t e t h e S i d u r i n g t h e S i p r o d u c t i o n p r o c e s s . ( 5 ) The e f f e c t s o f oxygen and c a r b o n i n t e r a c t i o n s w i t h t h e i m p u r i t i e s w i l l be s t u d i e d .

The 'growth of i n g o t s f o r t h e s t u d i e s p roceeded . O b s e r v a t i o n s i n d i c a t e d a r e l a t i v e l y l a r g e v a r i a t i o n i n r e s i s t i v i t y a l o n g t h e l e n g t h o f t h e n-type i n g o t s due t o t h e s m a l l e r e f f e c t i v e s e g r e g a t i o n c o e f f i c i e n t o f P compared t o B. S e v e r a l o f t h e i n g o t s were f r e e o f d i s l o c a t i o n s , as was shown by a l a c k o f e t c h p i t s . The c a l c u l a t e d i n g o t c o n c e n t r a t i o n s o f i m p u r i t i e s , based on melt a n a l y s i s , were i n e x c e l l e n t agreement w i t h t h e t a r g e t e d v a l u e s . The measured c o n c e n t r a t i o n s were i n good

. . agreement e x c e p t f o r t h e Mn-doped i n g o t . A d d i t i o n a l measurements by s p a r k s o u r c e . mass. s p e c t r o m e t r y and by. , n e u t r o n , a c t i v a t ' i o n . a n a l y s i s . a r e .. . .

. . ' . s c h e d u l e d .

. , - . .

. . . D i f f i c u l t i e s were encoun te red i n t h e a n a l y s e s o f ' d e n d r i t e s .and

c e n t r a l web s e c . t i o n s i n . t h e d e n d r i t i c web c r y s t a l e f f o r t ; t h e r e were no problems w i t h t h e m e l t measurements. The d a t a f o r t h e d e n d r i t i e s i n d i c a t e a n o n u n i f o r m i t y i n t h e i m p u r i t y d i s t r i b u t i o n . S i n c e p r e v i o u s d a t a showed t h a t t h e i m p u r i t y c o n c e n t r a t i o n s i n t h e web s e c t i o n were lower than in t h e d e n d r i t e s , . . t h e p r e s e n t v a l u e s f o r t h e d e n d r i t i e s may be assumed t o be upper l i m i t s f o r t h e c o n c e n t r a t i o n s i n t h e webs.

The p l a n f o r t h e low r e s i s t i v i t y s t u d i e s is t o d e t e r m i n e t h e e f f e c t s o f r e s i s t i v i t y on c e l l performance, u s i n g a r e l i a b l e , b u t non- o p t i m i z e d , p r o c e s s f o r c e l l f a b r i c a t i o n and t h e n t o a s s e s s t h e e f f e c t s o f added i m p u r i t i e s c o n c o m i t a n t l y w i t h r e s i s t i v i t y changes . I n t h e f irst e x p e r i m e n t s i t was found t h a t h e a v i l y doped s u b s t r a t e s were more s e n s i t i v e t o m e t a l l i z a t i o n s i n t e r i n g c o n d i t i o n s , t h e c e l l b i l l f a c t o r d e g r a d a t i o n i n c r e a s i n g w i t h i m p u r i t y c o n c e n t r a t i o n s . These r e s u l t s s u g g e s t t h a t i t i s n e c e s s a r y t o o b t a i n d a t a on l o n g term r e l i a b i l i t y , a d h e r e n c e , s t a b i l i t y o f m e t a l l i z a t i o n and on l o n g term c e l l performance.

Measurements were made on n+p c e l l s u s i n g d i f f e r e n t C z o c h r a l s k i and f loa t -zoned S i t o e s t a b l i s h a n ypper l i m i t t o t h e B dop ing c o n c e n t r a t i o n f o r r e a s o n a b l e . c e l l performance. These d a t a a r e shown i n F i g u r e s 4-1, 4-2, and 4-3, which g i v e open c i r c u i t v o l t a g e , s h o r t c i r c u i t c u r r e n t , and c e l l e f f i c i e n c y as f u n c t i o n s o f r e s i s t i v i t y . . Vo, d a t a show a broad maximum i n t h e r a n g e o f 1016 t o 1017 atoms/cm3; Isc d e c r e a s e s g r a d u a l l y wi th i n c r e a s e d B c o n c e n t r a t i o n and t h e n d e c r e a s e s r a p i d l y above 1017 atoms/cm3. The d a t a f o r c e l l e f f i c i e n c y do , n o t i d e n t i f y t h e maximum range as s h a r p l y . However, i t a p p e a r s t h a t c e l l s w i t h e f f i c i e n c i e s comparable t o c e l l s f a b r i c a t e d from 4 ohm/cm m a t e r i a l can be f a b r i c a t e d from m a t e r i a l hav ing r e s i s t i v i t i e s n e a r 0.2 ohm/cm u s i n g TiPAg c o n t a c t s and a reduced s i n t e r i n g t e m p e r a t u r e . Thus, t h e nominal 0 .2 ohm/cm m a t e r i a l ' w i l l be t h e b a s e l i n e m a t e r i a l f o r t h e s u b s e q u e n t ' impur i ty ' -ef f e c t s t u d i e s .

. The c o n c l u s i o n from a s e r i e s o f exper iments f o r ' t h e p /n c e l l s

was t h a t s low c o o l i n g o f t h e w a f e r s af ter B d i f f u s i o n a p p e a r s n e c e s s a r y t o m a i n t a i n good l i f e t i m e and ISc v a l u e s . Some v e r y good c e l l s have been: prepa'red ; 16% e f f i c i e n c i e s i n p+/n/n+ b a s e l i n e c e l l s ( w i t h a n t i r e - f l e c t i o n c o a t i n g ) have b e e n o b t a i n e d u s i n g BBr3 d i f f u s i o n a t 875 '~ .

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c. P r o c e s s e s f o r Producina Solar-Cel l -Grade S i l i c o n .

1) P r o d u c t i o n o f 'S i Using Submerged Arc Furnace and ~ n i d i r . e c t i o n a 1 . . . . .. . . . . ... ' . . . a U i f i c a t i o n P r o c e s s e s - Dow Corning C o r d o r a t i o n . The D0.w C o r n i n g . ; . ..

C o n t r a c t is f o r t h e development o f a p r o c e s s f o r improving t h e p u r i t y o f S i produced i n t h e a r c f u r n a c e by u s i n g p u r e r raw m a t e r i a l s and f o r t h e f u r t h e r ' p u r i f i c a t i o n o f t h e S i p r o d u c t by u n i d i r e c t i o n a l s o l i d - i f i c a t i o n . Tasks under t h e c o n t r a c t are raw m a t e r i a l s s e l e c t i o n and p r e p a r a t i o n , a r c f u r n a c e s t u d i e s , and u n i d i r e c t i o n a l s o l i d i f i c a t i o n , and S i . a n a l y s i s .

S i n c e t h e major amounts o f i m p u r i t i e s i n commercial m e t a l l u r g i c a l - g r a d e S i a r e from t h e ca rbonaceous r e d u c i n g m a t e r i a l s , a l a r g e e f f o r t 1s be ing d i r e c t e d toward t h e p r e p a r a t i v e means o f a s s u r i n g a s u p p l y o f s u i t a b l e C-material, e . g . , p u r i f i e d c h a r c o a l . P u r i f i c a t i o n o f a r e l a t i v e l y p u r e c h a r c o a l by t r e a t m e n t w i t h a f l u o r o c a r b o n m i x t u r e a t t e m p e r a t u r e s o f 1500, 2000, and 2 5 0 0 ' ~ produced a v a r i e t y o f r e s u l t s . The c o n c e n t r a t i o n s o f Ca, Mg, Mn, and P were g r e a t l y r educed a t each t e m p e r a t u r e . The c o n c e n t r a t i o n o f B was s i g n i f i c a n t l y reduced o n l y a t 2500'~. S i n c e a t e m p e r a t u r e below 2 2 0 0 ~ ~ would be p r e f e r a b l e , t o p r e v e n t g r a p h i t i z a t i o n and reduce energy u s e , t h e dependence o f C-pur i ty on s o u r c e m a t e r i a l was r e s e a r c h e d . The r e s u l t s a g a i n v a r y w i t h t h e e lement ; back-free c h a r c o a l c o n t a i n s much l e s s B and l e s s P , b u t t h e P c o n c e n t r a t i o n remains r e l a t i v e l y h i g h after f l u o r o c a r b o n t r e a t m e n t a t 2 0 0 0 ~ ~ and a t 2 5 0 0 ~ ~ .

Ana lyses showed t h a t q u a r t z i t e would be t h e main s o u r c e o f A l , B, and Fe i f p u r i f i e d c h a r c o a l were used i n t h e a r c f u r n a c e . Many l a r g e d e p o s i t s have been surveyed f o r c o s t , a v a i l a b i l i t y , s i z e o f s o u r c e , and p u r i t y .

A development-s ize , a r c f u r n a c e a t Elkem, Norway, h a s been used t o e v a l u a t e t h e u s e of p u r e r raw m a t e r i a l s . No r u n s were made d u r i n g t h e l a s t q u a r t e r .

. . I n - - t h e . u n i d i r e c t i o n a l s o l i d i f i c a t i o n s t u d i e s , t h e e f f e c t o f poly- c r y s t a l l i n e growth on t h e e f f e c t i v e s e g r e g a t i o n c o e f f i c i e n t s was inves - t i g a t e d p r i o r t o t h e o n s e t . o f c o n s t i t u t i o n a l s u p e r c o o l i n g o f t h e m e l t . I n t h e s e e x p e r i m e n t s Cu and Mn were used as d o p a n t s , and C z o c h r a l s k i i n g o t s were p u l l e d u s i n g s i n g l e c r y s t a l and p o l y c r y s t a l s e e d s . Composit ion a n a l y s e s were made by n e u t r o n a c t i v a t i o n a n a l y s i s from samples t a k e n from j u s t below t h e s e e d , j u s t above t h e p o i n t where c o n s t i t u t i o n a l s u p e r c o o l i n g o c c u r r e d , and from t h e t a n g end. The r e s u l t s were t h a t t h e e f f e c t i v e s e g r e g a t i o n c o e f f i c i e n t s f o r t h e s e r e g i o n s were p r a c t i c a l l y i d e n t i c a l f o r t h e two i n g o t s . R e l a t i v e l y l a r g e c o n c e n t r a t i o n and c o e f f i c i e n t v a l u e s were o b t a i n e d f o r t h e p o i n t s j u s t p r i o r t o c o n s t i - t u t i o n a l s u p e r c o o l i n g where v e r y r a p i d changes i n compos i t ion o c c u r . R e l a t i v e l y l a r g e c o n c e n t r a t i o n and c o e f f i c i e n t v a l u e s were d e r i v e d f o r t h e samples from t h e t ang ends . The c o n c l u s i o n was t h a t t h e r e a r e e s s e n t i a l l y no d i f f e r e n c e s i n t h e v a l u e s f o r t h e e f f e c t i v e s e g r e g a t i o n c o e f f i c i e n t s f o r s i n g l e c r y s t a l and p o l y c r y s t a l growth p rov ided t h e i n g o t s are grown ' from reasonabf y d i i u t e m e l t s . The . b e n e f i t s o f u s i n g p o l y c r y s t a l l i n e i n g o t s f o r p u r i f i c a t i o n by u n i d i r e c t i o n a l s o l i d i f i c a t i o n

are h i g h e r growth y i e l d s , reduced s e e d i n g problems, and t h e use o f l a r g e r d i a m e t e r s e e d s .

- The s u i t a b i l i t y o f t h e Bridgeman t y p e t e c h n i q u e f o r p u r i f i c a t i o n , by u n i d i r e c t i o n a l s o l i d i f i c a t i o n ( s o l i d i f i c a t i o n from t h e bottom t o t h e t o p o f a c r u c i b l e by c o n t r o l l a b l y d e c r e a s i n g t h e t e m p e r a t u r e s o t h a t t h e s o l i d - l i q u i d i n t e r f a c e moves upward) was e x p l o r e d f u r t h e r . I n e x p e r i m e n t s u s i n g Al-doped S i , t h e e f f e c t o f A 1 s e g r e g a t i o n was shown. More e x p e r i m e n t s a r e t o be performed t o e s t a b l i s h t h e c a p a b i l i t y o f t h i s p r o c e d u r e .

. ..

2 Production of S i from NapSIFh Source M a t e r i a l Usim Na Reduc t ion o f S i F 4 and S iFh T r a n s ~ o r t P r o c e s s e s - S t a n f o r d Research

-- ~

I n s t i t u t e . The c o n t r a c t w i t h Stant 'ord Kesearch l n s t i t u t e is f o r t h e development of a two s t e p p r o c e s s f o r t h e p r o d u c t i o n o f S i . The s t e p s a r e ( 1 ) t h e r e d u c t i o n of SiF4 by Na t o produce h i g h p u r i t y S i and ( 2 ) t h e f u r t h e r p u r i f i c a t i o n o f t h i s p roduc t by r e a c t i o n w i t h SiF4 t o form S i F 2 fo l lowed by t h e d i s p r o p o r t i o n a t i o n o f t h e S i F 2 t o y i e l d S i w i t h t h e r e g e n e r a t i o n o f t h e SiF4. The work t o d a t e h a s d e a l t e n t i r e l y w i t h t h e f i r s t r e a c t i o n .

. . . P r o c e d u r e s f o r c o n t r o l l i n g t h e r e a c t i o n were s t u d i e d . To avo id . . . .. . . . . c a r r y i n g u n r e a c t e d NA i n t o t h e r e a c t i o n p r o d u c t , t h e l i q u i d NA and

S i F 4 g a s were p u l s e f e d i n t o t h e r e a c t i o n v e s s e l . An a v e r a g e t e m p e r a t u r e of 6 0 0 ' ~ was m a i n t a i n e d by c a r e f u l r e g u l a t i o n o f t h e p u l s e t i m e s . B a t c h e s o f p r o d u c t o f up t o 250 g c o n t a i n i n g 25 t o 30 g o f S i were o b t a i n e d . The by-produc t s were N ~ F and Na2SiF6.

Owing t o t h e impor tance of Na2SiF6 bo th as a r e a c t i o n p r o d u c t and as a p o s s i b l e i n t e r m e d i a t e f o r SiF4 g e n e r a t i o n , t h e e q u i l i b r i u m pres - s u r e of S i F q ( g ) above Na2SiF6 and d u r i n g decompos i t ion i n t h e temper- a t u r e r a n g e o f 585 t o 6 5 0 ' ~ was s t u d i e d by a n e f f u s i o n method. The d a t a were e x t r a p o l a t e d t o g i v e an e q u i l i b r i u m p r e s s u r e v a l u e o f 1 atom a t 734 '~ . The S i F 4 was ana lyzed by mass s p e c t r o m e t r y t o d e t e r m i n e t h e n a t u r e and amount o f v o l a t i l e i m p u r i t i e s . The major c o n s t i t u e n t s were found t o be s i l i c o n o x y f l u o r i d e s ( a b o u t 4 % ) , s u l f u r o x y f l u o r i d e s ( a b o u t 0 . 1 % ) , and S02 ( a b o u t 0 . 0 5 % ) .

A l e a c h p r o c e d u r e t o s e p a r a t e S i from t h e o t h e r r e a c t i o n p r o d u c t s , NaF and Na2SiFg is under way. It .is e x p e c t e d t h a t t h e s e r e s u l t s w i l l g i v ? . a n i n d i c a t i o n o f . t h e s u i t a b i l i t y .of using...thi.s..procedure .for e x k r a c t i n g - . : . . . '.". . . . S i from t h e Na r e d u c t i o n and w i l l p r o v i d e i n f o r m a t i o n f o r u s e i n t h e s u b s e q u e n t p u r i f i c a t i o n s ' t e p .

. . .

3) P r o d u c t i o n of S i Usina Arc I l e a t e r P r o c e s s f o r Reduct ion '

gf S i c 1 4 by Na. Ma. o r H? - W e s t i n ~ h o u s e E l e c t r i c C o r p o r a t i o n . T h i s c o n t r a c t w i t h Westinghouse is f o r t h e development o f a n e l e c t r i c a r c h e a t e r f o r t h e p r o d u c t i o n o f S i u s i n g r e a c t i o n s f o r t h e r e d u c t i o n o f S i c 1 4 by e i t h e r Na, Mg,, H o r Zn. The f i r s t phase c o n s i s t s o f a r e v i e w o f t h e chemica l and e n g i n e e r i n g f e a s i b i l i t y and t h e d e s i g n i n g o f a sys tem f o r e x p e r i m e n t a l v e r i f i c a t i o n ; it i n c l u d e s f o u r s u b t a s k s :

r e a c t i o n a n a l y s i s , . plasma r e a c t o r , r e a c t o r s t o r a g e and i n j e c t i o n , . a n d p roduc t ' c o l l e c t i o n and e f f l u e n t d i s p o s a l . . . . .

. . The r e a c t l o n a n a l y s i s s u b t a s k h a s been completed. . C a l c u l a t i o n s were performed u s i n g t h e developed model t o p r e d i c t v a p o r i z a t i o n l e n g t h s .

f o r l i q u i d sodium d r o p l e t s . Based.on t h e o p e r a t i n g p a r a m e t e r s and t h e a s s u m p t i o n s o f t h e model, t h e r e s u l t s o f t h e s e a n a l y s e s i n d i c a t e t h a t d r o p l e t v a p o r i z a t i o n can o c c u r i n a v e r y s h o r t d i s t a n c e ( e . g . , 7 cm). A method which i n c o r p o r a t e s t h e e f f e c t o f t u r b u l e n t g a s f low on s i l i c o n p a r t i c l e growth was e v a l u a t e d , s i n c e a p r e v i o u s a n a l y s i s o n l y c o n s i d e r e d s i l i c o n p a r t i c l e growth under q u i e s c e n t c o n d i t i o n s . (Turbu lence is known t o be p r e s e n t i n t h e proposed a r c h e a t e r sys tem and shou ld enhance p a r t i c l e g rowth , t h u s a i d i n g s i l i c o n s e p a r a t i o n . ) R e s u l t s o f t h e t u r - bulence . model i n d i c a t e c o n s i s t e n t growth times and l e n g t h s when compared

. . . t o t h e r e a c t o r d e s i g n .

Heat t r a n s f e r a n a l y s e s were conducted t o s u b s t a n t i a t e bo th t h e d e s i g n and m a t e r i a l s s e l e c t i o n f o r t h e r e a c t o r / s e p a r a t o r . I n a d d i t i o n , a h e a t t r a n s f e r a n a l y s i s was performed f o r t h e r e a c t o r based upor, hydrogen r e d u c t i o n of SiC14. P r e v i o u s e q u i l i b r i u m c a l c u l a t i o n r e s u l t s f o r t h e H2/SiC14 r e a c t i o n were used i n t h i s a n a l y s i s . Based upon t h e h e a t t r a n s f e r a n a l y s i s , t h e e s t a b l i s h e d r e a c t o r d e s i g n i s a d e q u a t e f o r e i t h e r sodium o r hydrogen r e d u c t i o n o f SiC14.

System drawings f o r t h e components o f t h e r e a c t o r / s e p a r a t o r were completed and c o s t e s t i m a t i o n s are i n p r o g r e s s . System s a f e t y c o n s i d e r a t i o n s f o r t h e r e a c t o r / s e p a r a t o r were deve loped .

F i n a l d e s i g n s f o r bo th t h e S i c 1 4 and t h e Na s t o r a g e and i n j e c t i o n sys tems were completed. For t h e S i c 1 4 s y s t e m , h a n d l i n g , s a f e t y , and r e q u i r e m e n t s f o r c o n t r o l o f p o t e n t i a l h a z a r d s r e l a t i n g t o S i c 1 4 s y s t e m s were d e f i n e d . Commercial ly a v a ' i l a b l e h y d r a u l i c a t o m i z i n g n o z z l e s f o r . . . .

Sic14 i n j e c t i o n were s e l e c t e d . P r o g r e s s on t h e sodium system p a r a l l e l e d t h a t on t h e . S i C 1 4 sys tem; Based upon sys tem r e q u i r e m e n t s , a son ic - . .

t y p e a t o m i z i n g n o z z l e &s s e l e c t e d f o r sodium i n j e c t i o n . Subsystem camponeats and s p e c i f i c a t i o n s have been d e f i n e d f o r t h e sodium system. A r e v i e w o f bo th l i q u i d m e t a l s a f e t y and h a n d l i n g r e q u i r e m e n t s was conducted and o p e r a t i o n a l g u i d e l i n e s were e s t a b l i s h e d .

. . . . . . . . . . . . . . . . .. . . . . . .

The s i l i c o i i . c o l l e c t i o n and t h e by-product ( e f f l u e n t ) d i s p o s a l ' ' , :"'.' ' " " "

sys tems have undergone e x t e n s i v e d e s i g n r e f i n e m e n t s . A t e r n a t i v e d e s i g n s f o r t h e s i l i c o n c o l l e c t i o n system d e s i g n u s e ' a t h e r m a l l y - c o n t r o l l e d v a l v e o f f u s e d s i 1 i.ca t o c o n t r o l t h e f l o w from t h e c y c l o n i c ' s e p a r a t o r , .,

o r a q u a r t z - l i n e d s l i d i n g g a t e v a l v e . A-water-cooled c a s t i n g c a r o u s e l . .

w i l l he used t o form i n ~ o t s o f t h e s i l i c o n p r o d u c t . Both h e a t t r a n s f e r and the rmal p r o f i l e a n a l y s e s were performed f o r t h e s i l i c o n c o l l e c t i o n d e s i g n . The by-product d i s p o s a l sys tem was comple ted ; t h e d e s i g n c o n s i s t s of two water- j a c k e t e d c o n d e n s e r s t o s e p a r a t e t h e NaCl . e f f l u e n t from t h e Ar-H2 g a s m i x t u r e . T h i s approach was f a v o r e d o v e r . . t h e compet ing water-spray chamber f o r r e a s o n s o f s a f e t y , r educed p roduc t c o n t a m i n a t i o n , .

and d i r e c t a p p l i c a t i o n t o a f u l l s c a l e p r o c e s s , i n .which t h e NaCl would be r e c y c l e d t o form Na and C12 v i a e l e c t r o l y s i s . Both h e a t t r a n s f e r and c o n d e n s a t e (NaC1) t h i c k n e s s c a l c u l a t i o n s were performed t o a i d condense r s i z i n g and d e s i g n . A r e v i e w o f s a f e t y c o n s i d e r a t i o n s was

conducted f o r t h e c o n d e n s e r s and a s s o c J a t e d equipment . F i n a l e n g i n e e r i n g d r a w i n g s were comple ted and c o n t a c t s w i t h s u p p l i e r s f o r c o s t . e s t i m a t i o n s

. . . . a r e in p r o g r e s s . . .

4 1 P r o d u c t i o n of SiHb o r S i us in^ a Noneau i l ib r ium Plasma Je t f o r t h e Reduc t ion o f S ic14 - AeroChem Research C o r ~ o r a t i o n . The

. o b j e c t i v e o f t h i s program is t o d e t e r m i n e t h e f e a s i b i l i t y o f h i g h volume, low-cost p r o d u c t i o n o f h i g h p u r i t y s i l a n e o r s o l a r - c e l l - g r a d e s i l i c o n .

. . u s i n g a n o n e q u i l i b r i u m hydrogen atom plasma j e t . R e a c t i o n s o f hydrogen a t o m s i n t h e plasma jet w i t h c h l o r o s i l a n e s ( a d d e d ' e i t h e r t o t h e d i s c h a r g e

. . . . . . . . . . . . . . . . . . . . . . . . . . . . : . o r t o t h e hydrogen a tom. s t ream). a r e be ing s t u d i e d .

. . . . . . . . . . . < . . . ., . . : . . . . . . . . . . . During t h i s q u a r t e r c a l c u l a t i o n s were made t o d e f i n e t h e e x p e r i m e n t a l

l i m i t s w i t h i n which gas-phase r e a c t i o n s would be most l i k e l y t o o c c u r . These show t h a t H-atom - recombina t ion does n o t compete s i g n i f i c a n t l y w i t h t h e . o t h e r r e a c t i o n s as a s i n k f o r H , and t h a t , i f t h e H/SiC14 o v e r a l l r e a c t i o n h a s an a c t i v a t i o n energy , t h e p r e s s u r e r a t i o a c r o s s '

t h e n o z z l e and t h e . t e m p e r a t u r e i n t h e d i s c h a r g e become v e r y i m p o r t a n t p a r a m e t e r s . Most i m p o r t a n t l y , t h e maximum o p e r a t i n g p r e s s u r e was. shown t o be l i m i t e d by t h e p r e s s u r e a t which t h e glow d i s c h a r g e c a n b e main ta ined o r t h e p r e s s u r e a t which t h e hydrogen atom y i e l d s become s m a l l .

S o l i d p r ,oduc t s o f t h e H/H2/SiC14 r e a c t i o n were r e c o v e r e d . Depending upon e x p e r i m e n t a l c o n d i t i o n s , t h e s e were ( t e n t a t i v e l y ) i d e n t i f i e d a s a po lymer ic m a t e r i a l , amorphous s i l i c o n and p o l y c r y s t a l l i n e s i l i c o n . The p o l y c r y s t a ' ~ l i n e m a t e r i a l was shown by X-ray f l u o r . e s c e n c e a n a l y s i s t o have n i c k e l p r e s e n t a t ppm l e v e l s ; c o n s p i c u o u s l y a b s e n t a t t h e ppm l e v e l were the heavy metals Fe, C r , Pb, ~ n , Cu, and Zn, m a t e r i a l s o f c o n s t r u c t i o n o f t h e a p p a r a t u s .

Q u a n t i t a t l v e a n a l y s i s o f s o l i d and gas-phase m a t e r i a l r e c o v e r e d i n a s y n t h e s i s . e x p e r i m e n t gave p roduc t y i e l d s o f 12% SiHC13, 1% SiH4, and 1.4% s i l i c o n , w i t h 80% S i c 1 4 s t a r t i n g m a t e r i a l c o l l e c t e d and 6% unaccounted f o r . The low y i e l d s a r e p robab ly d u e t o less-than-optimum mix ing o f t h e H/.H2 j e t w i t h SiC14.

. . . . . . . . . . . . . ...

A new n o z z l e w i t h S i c 1 4 i n j e c t i o n i n t h e n o z l e i t s e l f h a s been . , d e s i g n e d and p r e l i m i n a r y E e s t s i n d i c a t e improved 'mix ing w i t h less d i s -

t u r b a n c e t o t h e , s t r e a m t h a n f o r t h e p r e v i o u s mix ing s y s t e m s .

. , , . . ;d.., ,,. E v a l u a . t i o n o f S i P roduc t ion P r o c e s s e s - Lamar U n i v e r s i t v . ' T h e o b j e c t i v e . o f ' t h i s c 0 n t r a c . t i s t o e v a l u a t e t h e p o t e n t i a l s o f t h e p r o c e s s e s be ing deve loped i n t h e program o f t h e S i l i c o n M a t e r i a l Task. .The. economic e v a l u a t i o n s w i l l be based upon a n a l y s e s o f process-sys tem p r o p e r t i e s , chemica l e n g i n e e r i n g c h a r a c t e r i s t i c s , and cost ing-economics . he e v a l u a t i o n s w i l l be performed d u r i n g a l l p h a s e s o f t h e Task, u s i n g i n f o r m a t i o n which becomes a v a i l a b l e from . t h e v a r i o u s p r o c e s s development c o n t r a c t s .

1 ) P r o c e s s System P r o ~ e r t i e s . Major a c t i v i t i e s were c o n t i n u e d on p r o c e s s sys tem p r o p e r t i e s o f s i l i c o n s o u r c e m a t e r i a l s under c o n s i d e r a t i o n

f o r s o l a r - c e l l - g r a d e s i l i c o n p r o d u c t i o n . In p r o p e r t y c o r r e l a t i o n e f f o r t s , p r o p e r t y d a t a r e s u l t s were o b t a i n e d f o r h e a t o f v a p o r i z a t i o n , g a s h e a t c a p a c i t y , l i q u i d h e a t c a p a c i t y , l i q u i d d e n s i t y , s u r f a c e t e n s i o n and . g a s v i s c o s i t y o f s i l a n e ( S i ~ 4 ) as a f u n c t i o n o f t e m p e r a t u r e .

The c o r r e l s t i o n r e s u l t s f o r g a s h e a t c a p a c i t y c o v e r bo th t h e low and h igh t e m p e r a t u r e r a n g e s which w i l l be encoun te red i n t h e s p e c i f i c p r o c e s s t echno logy ( l o w t e m p e r a t u r e r a n g e - s i l a n e p r o d u c t i o n ; h i g h t e m p e r a t u r e r a n g e - s i l i c o n p r o d u c t i o n from s i l a n e ) . These r e s u l t s w i l l be used i n pe r fo rming t h e chemical e n g i n e e r i n g a n a l y s i s o f t h e s i l a n e p r o c e s s (Union C a r b i d e ) .

. .

2 ) Chemical E n n i n e e r i n ~ . Major chemica l e n g i n e e r i n g a n a l y s i s ' . . .

a c t i v i t i e s a r e b e i n g devoted t o p r e l i m i n a r y p r o c e s s d e s i g n f o r 'a s i l a n e (SiH4) p l a n t t h a t w i l l produce 1000 m e t r i c t o n s / y e a r o f s o l a r - c e l l - g r a d e s i l i c o n . The t echno logy developed by Union Carb ide f o r t h e p r o d u c t i o n o f s i l a n e u s e s hydrogen and m e t a l l u r g i c a l - g r a d e s i l i c o n as raw m a t e r i a l s . A p r e l i m i n a r y p r o c e s s f low diagram and base c o n d i t i o n s have been deve loped .

A p r e l i m i n a r y p r o c e s s d e s i g n was i n i t i a t e d f o r t h e c o n v e n t i o n a l p o l y s i l i c o n p r o c e s s now used i n t h e Uni ted States t o produce semiconductor- g r a d e s i l i c o n from SiHC13) .

3 ) Economic A n a l v s i s . Economic a n a l y s i s a c t i v i t i e s . focused on development o f a computer model t o a i d i n e s t i m a t i o n o f p roduc t and p l a n t i n v e s t m e n t c o s t s f o r t h e a l t e r n a t e s o l a r - c e l l - g r a d e s i l i c o n p r o c e s s e s . A p p l i c a t i o n o f t h e computer model t o t h e B a t t e l l e p r o c e s s (Zn/SiClq ) i n d i c a t e d a $1 0 ,510,000 f i x e d c a p i t a l i n v e s t m e n t and a $9.63/kg p r i c e o f s i l i c o n f o r a 1000 m e t r i c t o n / y e a r p l a n t .

Economic a n a l y s i s a c t i v i t i e s a l s o c e n t e r e d on d e v e l o p i n g c o s t s t a n d a r d i z a t i o n t e c h n i q u e s f o r a p p l i c a t i o n t o t h e a l t e r n a t e p r o c e s s e s . Thaw techniques and t h e i n f o r m a t i o n p r e s e n t e d w i l l a l l o w v a l i d compar isons

. . between p r o c e s s e s on a s t a n d a r d i z e d b a s i s .

.e . J P L In-House A c t i v i t i e s . The c u r r e n t computer model was t e s t e d a g a i n s t e x p e r i m e n t a l f l u i d i z a t i o n d a t a . The agreement is good c o n s i d e r i n g t h e s i m p l i f i c a t i o n s i n t h e model.

. . . . . . . . , . . . The d r a f t o f t h e JPL r e p o r t on f l u i d i z e d bed model ing was r e v i s e d .

and has been s~lhrnit . t .~rl f o r p u b l i c a t i o n . The s e c t i o n on t h e computer program h a s been expanded and i n c l u d e s t h e l a t e s t compar ison r e s u l t s .

. . The first d r a f t o f t h e t e c h n i c a l r e p o r t on t h e fundamental r e e c t i o n . . . . .

a s p e c t s o f s i l i c o n chemica l vapor d e p o s i t i o n h a s been t y p e d . and d i s t r i b u t e d f o r comments .

The f l u i d i z e d bed e x p e r i m e n t a l sys tem r e c e i v e d some f i n a l m o d i f i c a t i o n . E l e c t r o n i c p r e s s u r e t r a n s d u c e r s were i n s t a l l e d t o moni to r t o t a l bed p r e s s u r e and d i f f e r e n t i a l p r e s s u r e s w i t h i n t h e bed. The sys tem i s

undergo ing f i n a l l e a k t e s t i n g and c a l i b r a t i o n s i n p r e p a r a t i o n f o r f l u i d - i z a t i o n t e s t i n g . A c a p a c i t a n c e probe h a s been d e s i g n e d f o r measur ing bubb le s i z e i n t h e bed. Th i s d e v i c e is b e i n g t e s t e d . Other ins t rumen- t a t i o n improvements , i n c l u d i n g a d i g i t a l d a t a - a c q u i s i t i o n sys tem and p a r t i c l e s i z e a n a l y s i s equipment , were o r d e r e d . Design work and equipment procurement f o r t h e r e a c t i o n sys tem were a l s o conduc ted . A purge sys tem was i n s t a l l e d on t h e p r e s s u r e t a p s o f t h e f l u i d i z e d bed a p p a r a t u s . A d i f f e r e n t i a l p r e s s u r e probe was des igned and is b e i n g i n s t a l l e d t o h e l p measure bed v o l t a g e and p a r t i c l e s i z e i n t h e bed. P r e s s u r e t r a n s - d u c e r and c a p a c i t a n c e p robe sys tems a r e b e i n g t e s t e d and i n s t a l l e d i n t o t h e f l u i d i z e d bed r e a c t o r t o improve t h e i n s t r u m e n t a t i o n f u n c t i o n .

P r e l i m i n a r y e x p e r i m e n t a l d a t a on t h e s t age-? f l i l i d i z e d bed was o b t a i n e d u s i n g c o a r s e s i l i c o n p a r t i c l e s and a r g o n g a s . The e x p e r i m e n t a l s e t u p a p p e a r s t o be o p e r a t i n g p r o p e r l y . D i f f e r e n t . i a 1 p r e s s u r e d r o p measurement t e c h n i q u e t o o b t a i n i n t e r n a l f l u i d i z e d bed d a t a was chosen .

A i l iu iLlal flu1dlzat16ti exper iment was conduc ted t o check f o r . . .

equipment f l a w s and t o s e t up o p e r a t i n g p r o c e d u r e s . The d a t a compared . .

r e a s o n a b l y well w i t h p r e d i c t e d r e s u l t s , b u t a few improvements were i n d i c a t e d i n t h e purge sys tem and p r e s s u r e d e v i c e s .

The f l a n g e - g a s k e t method t o e f f e c t c o m p l e t e l y l e a k - p r o o f s e a l s , f o r t h e s i l a n e p y r o l y z e r ( i n c l u d i n g a way t o seal i n t h e q u a r t z s i g h t t u b e ) was f i n a l i z e d . The sys tem f o r s i l a n e p y r o l y s i s - s e p a r a t i o n - c o l l e c t i o n h a s been p r o c e e d i n g t h r o u g h s t a g e s o f l e a k - t e s t i n g , r e v i s i o n s , and c o r r e c t i o n s t o f a b r i c a t i o n , and i n s t a l l a t i o n i n t h e fume hood. The e l e c t r o s t a t i c p r e c i p i t a t o r is be ing s l i g h t l y m o d i f i e d and p repa red f o r p o w e r / e f f i c i e n c y t e s t i n g . I n s t r u m e n t s were i n s t a l l e d i n t h e c o n t r o l p a n e l . I n t h e p r e s e n t e x p e r i m e n t a l sys tem, t e s t i n g and development o f a n e l e c t r o s t a t i c p r e c i p i t a t o r t o f u n c t i o n w i t h hydrogen g a s and s i l i c o n d u s t a r e i n p r o g r e s s . Because o f t h e n a t u r e o f t h e s e m a t e r i a l s ( d i e l e c t r i c c o n s t a n t s , e t c . ) , a s p e c i a l u n i t h a s been d e s i g n e d and

. . . . t e s t e d .

An i n v e s t i g a t i o n was made i n t o v a r i o u s t y p e s o f d i g i t a l d a t a a c q u i s i t i o n s y s t e m s f o r u s e wi th t h e f l u i d i z e d bed and t h e p y r o l y s i s r e a c t o r sys tem t o enhance d a t a r e d u c t i o n and p r o c e s s c o n t r o l . These s y s t e m s r a n g e from small computer sys tems w i t h i n s t r u m e n t a t i o n i n t e r - f a c e s t o d a t a l o g g e r s f o r r e c o r d i n g d a t a f o r a l a r g e computer such a s t h e Univac 1108. Recommendations by D r . F i t z g e r a l d , t h e f l i ~ i d i z a t i o n i n s t r u m e n t a t i o n c o n s u l t a n t , and o t h e r s i n d i c a t e t h a t t h e small computer system has t h e most f l e x i b i i i t y . An i n v e s t i g a t i o n was a l s o made i n t o hydrogen d e t e c t o r s , p a r t i c l e s i z e a n a l y z e r s , and g r i n d i n g equipment.

B. LARGE-AREA SILICON SHEET TASK

The o b j e c t i v e o f t h e Large-Area S i l i c o n S h e e t Task is t o d e v e l o p and d e m o n s t r a t e t h e f e a s i b i l i t y o f s e v e r a l a l t e r n a t i v e p r o c e s s e s f o r p roduc ing l a r g e a r e a s o f s i l i c o n s h e e t m a t e r i a l s u i t a b l e f o r low-cost , h i g h e f f i c i e n c y s o l a r p h o t o v o l t a i c energy c o n v e r s i o n . To meet t h e o b j e c t i v e o f t h e LSSA P r o j e c t , s u f f i c i e n t r e s e a r c h and development must be performed on a number of p r o c e s s e s t o d e t e r m i n e t h e c a p a b i l i t y

of each for p roduc ing l a r g e areas o f c r y s t a l l i z e d s i l i c o n . The f i n a l sheet -growth c o n f i g u r a t i o n s must be s u i t a b l e f o r d i r e c t i n c o r p o r a t i o n i n t o an automated s o l a r - a r r a y p r o c e s s i n g scheme.

1. T e c h n i c a l Background

c u r r e n t s o l a r c e l l techno.logy. is based on t h e u s e o f s i l i c o n wafe r s o b t a i n e d by s l i c i n g l a r g e C z o c h r a l s k i o r f l o a t - z o n e i n g o t s ( u p t o 12.5 cm i n d i a m e t e r ) , u s i n g s i n g l e - b l a d e inn.er-diameter '(ID) diamond saws. T h i s method o f o b t a i n i n g s i n g l e c r y s t a l l i n e s i l i c o n w a f e r s i s . t a i l o r e d t o t h e ' needs . o f l a r g e volume semi-conduc t o r pro.ducts ( i .e . , i n t e g r a t e d . c i r c u i t s ~ : p l : u s : d i s c r e t e power and c o n t r o l d e v i c e s ' . - o t h e r t h a n s o l a r c e l l s ) . Indeed , t h e small .market o f f e r e d By p r e s e n t s u l a i - c e l l u s e r s d o e s n o t j u s t i f y t h e development o f s i l i c o n " r e a l e s t a t e n produ.ct ion .. . .. .:

.. . t e c h n i q u e s which would r e s u l t i n low-cost e l e c t r i c a l energy. . , , . . . . . .. . . . .. .. .. ... . . . . .

Growth o f s i l i c o n c r y s t a l l i n e m a t e r i a l i n a geometry which does n o t r e q u i r e c u t t i n g t o a c h i e v e p roper t h i c k n e s s is a n obv ious way t o e l i m i n a t e c o s t l y p r o c e s s i n g and m a t e r i a l was te . Growth t e c h n i q u e s such a s edge-def ined f i lm- fed growth (EFG), web-dendr i t i c g rowth , chemica l vapor d e p o s i t i o n (CVD) , e t c .. , a r e p o s s i b l e c a n d i d a t e s f o r t h e growing o f s o l a r c e l l m a t e r i a l . The growing of l a r g e i n g o t s w i t h optimum s h a p e s f o r s o l a r ce l l n e e d s ( e . g . , hexagonal c r o s s - s e c t i o n s ) , r e q u i r i n g v e r y l i t t l e manpower and machinery would a l s o a p p e a r p l a u s i b l e . However:, . .

it a p p e a r s t h a t t h e ' c u t t i n g o f t h e l a r g e i n g o t s i n t o . w a f e r s must be done u s i n g m u l t i p l e r a t h e r than s i n g l e b l a d e s i n o r d e r . t o be c o s t - e f f e c t i v e .

Research and development o n . r i b b o n , s h e e t , and i n g o t growth . , .

p l u s m u l t i p l e - b l a d e and m u l t i p l e - w i r e c u t t i n g , i n i t i a t e d i n 1975-1976 is i n p r o g r e s s .

2. O r g a n i z a t i o n and Coord ina t ion o f t h e Large-Area . . S i l i c o n S h e e t T a s k . E f f o r t

A t t h e time t h e LSSA ~ r o j e c t " w s i n i t ' i a t e d ( J a n u a r y 1975) a ' number of methods p o t e n t i a l l y s u i t a b l e f o r growing s i l i c o n c r y s t a l s f o r s o l a r c e l l manufac tu re were known. Some o f t h e s e . were under develop-

. m e n t ; o t h e r s e x i s t e d o n l y i n concep t . Development work on t h e most promis ing methods i s now be ing funded. A f t e r a p e r i o d o f a c c e l e r a t e d

... dcy.elopment, t h e varj.o~.l.s metheds w i l l be e v a l u a t e d and t h e b e s t s e l e c t e d . . . . . . . . . . f o r advanced development . A s t h e growth methods a r e r e f i n e d , manu- f a c t u r i n g p l a n t s w i l l be developed from which t h e most c o s t - e f f e c t i v e s o l a r c e l l s c a n be manufactured.

The Large-Area S i l i c o n S h e e t Task e f f o r t is o r g a n i z e d i n t o f o u r phases : r e s e a r c h and development on s h e e t . g r o w t h methods , (1975-77) ; advanced development o f s e l e c t e d . growth methods ( 1977-80 ); prototype . .

p r o d u c t i o n development (1981-82); development , f a b r i c a t i o n , and' o p e r a t i o n of p r o d u c t i o n growth p l a n t s ( 1983-86 1.

3. Large-Area S i l i c o n S h e e t Task C o n t r a c t s

Resea rch and development c o n t r a c t s awarded f o r growing s i l i c o n c r y s t a l l i n e m a t e r i a l f o r s o l a r c e l l p r o d u c t i o n are shown i n T a b l e 4-3. T h i s work w i l l c o n t i n u e th rough t h e end o f FY 1977, by which t ime i t is e x p e c t e d t h a t t e c h n i c a l f e a s i b i l i t v w i l l have been d e m o n s t r a t e d . S e l e c t i o n o f " p r e f e r r e d " growth methods f o r f u r t h e r development d u r i n g FY 1978-80 is planned f o r l a t e FY 1977 o r e a r l y FY 1978. By 1980, b o t h t e c h n i c a l and economic f e a s i b i l i t y shou ld b e demons t ra ted by i n d i v i d u a l growth methods.

An economic a n a l y s i s o f C z o c h r a l s k i i n g o t growth p r o c e s s was performed t o a s s e s s i ts p o t e n t i a l t o meet near- term and 1986 g o a l s . The s t u d y was made w i t h t h e i n t e n t i o n o f i d e n t i f y i n g key f e a t u r e s of t h e p r o c e s s t h a t a r e making t h e p r o c e s s c o s t l y a t t h e p r e s e n t t i m e . The a n a l y s i s , conduc ted a t JPL and e l s e w h e r e , shows t h a t c o n t i n u o u s g rowth p r o c e s s is t h e key. It was dec ided t o s o l i c i t p r o p o s a l s t o d e v e l o p an advanced C z o c h r a l s k i p r o c e s s , s p e c i f i c a l l y one a c h i e v i n g c o n t i n u o u s i n g o t g rowth th rough m u l t i p l e use o f c r u c i b l e s , and i n c o r - p o r a t i n g improved sawing t e c h n i q u e s . These t e c h n i q u e s , when s u c c e s s - f u l l y d e v e l o p e d , w i l l r e d u c e c o s t s a s s o c i a t e d w i t h c r u c i b l e s , p r o c e s s i n g , and sawing l o s s e s .

RFPs were s t a r t e d d u r i n g t h i s q u a r t e r t o i n v e s t i g a t e t h e s e two a r e a s . Two o r t h r e e c o n t r a c t s a r e expec ted t o r e s u l t from t h e c o n t i n u o u s growth i n t e r e s t , one o r two f o r t h e sawing work. It is i n t e n d e d t h a t b o t h t h e s e e f f o r t s w i l l become a c t i v e i n FY78.

4. Large-Area S i l i c o n S h e e t Task Techn ica l A c t i v i t y

8. S i l i c o r i Ribburl Growth: EFC Method--Mobil-Tvco S o l a r Enernv C o r ~ o r a t i o n . The edge-def ined f i lm-fed growth (EFG) t e c h n i q u e is based on f e e d i n g mol ten s i l i c o n th rough a s l o t t e d d i e ( a s i l l u s t r a t . e d i n F i g u r e - 4 - 4 . I n t h i s t e c h n i q u e , t h e shape o f t h e r i b b o n is de te rmined by t h e c o n t a c t o f mol ten s i l i c o n wi th t h e o u t e r edge o f t h e d i e . The d i e is c o n s t r u c t e d from m a t e r i a l which is wet ted by mol ten s i l i c o n ( e . g . , g r a p h i t e ) . E f f o r t s under t h i s c o n t r a c t a r e d i r e c t e d toward e x t e n d i n g t h e c a p a c i t y o f t h e EFG arocess t a a speed of 7 ; 5 crn/min and a w i d t h o f 7.5 cm. , I n a d d i t i o n t o t h e development o f EFG machines and t h e growing o f r i b b o n s , t h e program i n c l u d e s economic a n a l y s i s , c h a r a c t e r i z a t i o n o f t h e r i b b o n , p r o d u c t i o n and a n a l y s i s o f s o l a r c e l l s , and t h e o r e t i c a l a n a l y s i s o f the rmal and s t r e s s c o n d i t i o n s .

The EFG p r o c e s s , which had been d i r e c t e d toward p roduc ing w i d e r r i b b o n s f a s t e r , i s now r o u t i n e l y o p e r a t i n g . Two-inch-wide r i b b o n i s

. be ing produced a t somewhat f a s t e r than 2 i n c h e s p e r m i n u t e , wi th o c c a s i o n a i o u t p u t a t c l o s e t o 3 i n c h e s p e r m i n u t e . Three-inch-wide d e s i g n s are b e i n g produced, as are c a r t r i d g e s . Convers ion e f f i c i e n c i e s o f c e l l s on EFG r i b b o n s remain r a t h e r low, i n t h e . r a n g e o f 2% t o 6 5 , owing p r i m a r i l y t o i m p u r i t i e s i n t r o d u c e d by t h e r e s i s t a n c e f u r n a c e s . Var ious p o s s i b i l i t i e s a r e be ing exp lo red t o r a i s e c e l l e f f i c i e n c y . A p lanned e x t e n s i o n o f t h i s work w i l l be aimed a t machines c a p a b l e of growing f i v e r i b b o n s s i m u l t a n e o u s l y , e a c h 2 i n c h e s wide.

Table 4-3. Large-Area:Silicon Sheet Task Contractors. . . ; .. .

. . ..

Contrac tor Technology Area

Mobil-Tyco, Waltham, Massachu- . .

Edge-defined , f i lm-fed growth s e t t s

(JPL Contraot No. 954355)

IBM , Hopewell J u n c t i o n , New 'York Edge-defined , fi lm-fed growth (JPL 'Contract No. '9541 44)

R C A , P r ince ton , New J e r s e y Inver ted Stepanov growth (JPL Cont rac t No. 954465)

Univ. of So. Ca ro l ina , Columbia, Web-dendritic growth So. Carol ina (JPL c o n t r a c t No. 954344)

Motorola, Phoenix, Arizona (JPL Cont rac t No. 954376)

Laser zone r i bbon growth

SHEET GROWTH PROCESSES . . -. d

Honeywell, Bloomington, Minnesota

(JPL Cont rac t No. 954356

Dip-coating of low-cost sub- s t r a t e s

Hockwell, Anakielm, C a l i f o r n i a Chcmioal vapor depos i t ion nn (JPL Cont rac t No. 954372) low-cost s u b s t r a t e s

General E l e c t r i c , Schenectady, Chemical. vapor .depos i t ion on New York f l o a t i n g s i l i c o n s u b s t r a t e

(JPL Cont rac t No. 954350) . .

, ,. ... . Univ. o f Pennsylvania , Phi la- Mot-forming of e i l i o o n shee t

d e l p h i a , Pennsylvania (JPL, Cont rac t N U . 954506 )

INGOT GROWTH PROCESS

Crys t a l Systemo, Salem, . Massachuset ts

(JPL Cont rac t No. 954373)

Heat-exchanger ingot c a s t i n R g

Table 4-3. Large-Area S i l i c o n Sheet Task Con t r ac to r s . . .

(Cont inua t ion 1 ) . .

Cont rac to r Technology Area - -- - -

INGOT CUTTING

. . C r y s t a l Systems, Salem ; Mult ip le wi re sawinga

Massaohuoet t o . .

. .

(JPL Con t r ac t No. 954373) . . . . . . . . . .: : . .;.;:. . . . . . . .

Varian, Lexington, Massachuset ts Breadknife sawing . . . . . . . . . . (JPL Con t r ac t No. 954374) . . . . . .

. . . . . . . . . . .-

. . . . . . . . . . . . . . : . . . . . . . . . .

*Single c o n t r a c t p rovides f o r both i n g o t c a s t i n g and m u l t i p l e w i r e . : . . . . . . . . . ; : . . . . . . . . . . . . . . . . . . . . . . sawing. . , . . . .

. . .

MOLTEN SILICON

Figure 4-4. Cap i l l a ry Die Growth (EFG and CAST) - Mobil-Tyco and IBM

b. S i l i c o n Ribbon Growth: ' CAST Method - IBM. . The c a p i l l a r y a c t i o n . .

shaping technique (CAST) .is based on t h e - same p r i n c i p l e a s .EFG growth. , : . .

(F igu re 4-4); i .e., i t . u t i l i z e s a d i e cons t ruc t ed from m a t e r i a l wh2c.h is wetted by molten s i l i c o n . Work under . t h i s contract:is d i r e c t e d . ,. .

toward e v a l u a t i o n o f t h e t e c h n i c a l and economic p o t e n t i a l of CAST f o r . , . .

t h e p repa ra t i on o f s i l i c o n r ibbon. The e f f o r t c o n c e n t r a t e s on ( 1 ) understanding and e x t r a p o l a t i n g t h e e f f e c t s o f growth c o n d i t i o n s , ( 2 )

y c h a r a c t e r i z a t i o n o f t h e r ibbon , with s p e c i a l emphasis on . t he c o r r e l a t i o n of s t r u c t u r e and e l e c t r i c a l performance, and ( 3 ) economic . . a n a l y s i s .

of s i l i c o n growth b y . t h i s and o t h e r growth techniques . .. . . . . . . .

When a d m i n i s t r a t i v e and o the r problems a r e overcome i n renewal: ' . .

of t h e CAST process program, work w i l l advance t o develop g r e a t e r in-: :.. . .

s i g h t i n t o t h i s r i b b o n process ; these underotandings w i l l a lao aid '

t h e EFG technique exp lo ra t i on . Growth a n a l y s i s , r ibbon c h a r a c t e r i z a t i o n , and economic a n a l y s i s w i l l .be looked i n t o . It is n o t p r e s e n t l y . . . c l e a r when t h e program extens ion w i l l be nego t i a t ed . . . .

. .

. . . . .. . . .. .

. . . c . S i l i c o n Ribbon Growth : Inver ted S t e ~ a n o v Techniaui? - :"R'cA. I n t h i s program extiphasis is placed on developing a technique for"g,rowing ribbon-shaped s i l i c o n using a "nonwettedn d i e (F igu re - 4-5 1.. .. The. use of t h e I1nonwetted1' d i e provides t h e p o s s i b i l i t y o f minimizing t h e r e a c t i o n between t h e molten s i l i c o n and t h e d i e .ma te r i a l . Reaction between molten s i l i c o n and wetted d i e s is one source o f degrada t ion i n t h e c r y s t a l l o g r a p h i c q u a l i t y o f s i l i c o n grown us ing a wetted d i e ( i . e . , t h e edge-defined fi lm-fed growth method). The i n t r o d u c t i o n of t h e feed from above and t h e growth of t h e s i n g l e c r y s t a l i n a down- ward d i r e c t i o n ( t h e i n v e r t e d Stepanov technique) i n . p a r t compensates f o r t h e hydrodynamic d rag i n t h e s l o t and f o r t h e l a c k o f c a p i l l a r y rise. (The c a p i l l a r y rise f eeds t h e m a t e r i a l t o t h e d i e , e d g e i n t h e EFG method.) The inve r t ed geometry a l s o l e a d s t o cons ide rab l e f l ex - i b i l i t y i n t h e growth con f igu ra t i on when t h e ' f e e d i s in t roduced from a molten zone a t t h e end o f a s o l i d s i l i c o n rod .

Work on t h e i n v e r t e d Stepanov process i s still being held up because of e r r a t i c we t t i ng of t h e Yi02 d i e . The SiO2 exper imenta t ion has been suspended and o t h e r m a t e r i a l s a r e being eva lua ted f o r t h e i r s u i t a b i l i t y f o r growing r ibbons with t h e process .

d . S i l i c o n Ribbon Growth: Web-Dendritic Method - Univers i tv af South Caro l ina . Web-dendritic growth makes i ts own gu ides of s i l i c o n , whereas most o t h e r r ibbon processes must r e l y on m a t e r i a l s o t h e r than s i l i c o n f o r t h e gu ides ( i . e . , d i e s ) (F igure 4-6). The gu ides a r e t h i n d e n d r i t e s t h a t grow ahead o f t h e shee t and suppor t t h e molten s i l i c o n between them t o form the shee t . The d e n d r i t e gu ides grow i n a very p r e c i s e o r i e n t a t i o n d i c t a t e d by t h e i r unique growth h a b i t . Thus t h e o r i e n t a t i o n o f t h e s h e e t which grows between them t a k e s on t h i s p r e c i s e o r i e n t a t i o n . The twin plane r e e n t r a n t edge mechanism (TPREM) c o n t r o l s t he growth of t h e edge d e n d r i t e s , g i v i n g them t h e i r unique and i n t e r n a l l y - c o n t r o l l e d growth d i r e c t l u n , a l lowing thcm t o grow ahead of t h e s h e e t and thus a c t a s gu ides .

FEED

NON-

POLYCRYSTAL FEEDSTOCK

. . . .

. .

ORIFICE

........ - . . . . . . ' . . 2 . . . . . . . . . . _............... : . . . . . .,,, ..:: .,,. :,,:~~,:~'~~';?."" .. '.'.' . . . . . . . . .. .,:. ..>, . . . . . . . . . . . . . . . .: ,..,,. I.. . . . . . ... ,: :: ;::, : . . . . " ...: . . . . . . . . . . . . . . ,. ,: ;.- .,:... > ?','.' ;, . . . . . . . . . . . . . . . . . . . . . . . . . . . . ,..:., ...... . . . .:.. . . . $. . . . . . . . . . .

. . . . . . . . . . . . . . . . : . . . . . . . . ./.. . . . . . . . . . . . . . PU.LL . , " ' '

. . . . . . . . . . . . . . . . . . : . . . . . . . . . . . . . . . . . ... I

. ,. ..: .7 . . . . . : . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ... . . . . . . . . . . . . .:, . . - . .. , . , .: . . . . . . . . . . . . . . . . . i... . . . . . . .

F i g u r e 4-5. I n v e r t e d S tepanov Technique - RCA

The w e b - d e n d r i t i c e f f o r t is r i d d l e d w i t h problems i n o p t i m i z i n g f u r n a c e geometry . I n t h e b e s t f u r n a c e c o n f i g u r a t i o n s o far d e v e l o p e d , r i b b o n s 1 i n c h wide by 15 i n c h e s l o n g have been grown. The t h e r m a l : r a d i a t i o n a n a l y s i s w a s completed d u r i n g t h i s q u a r t e r . \

. . . . . . . . . . . . . . . . . .

e. S i l i c o n Ribbon Growth : ' Laser Zone Growth i n ' a Ribbon-to-Ribbon P r o c e s s - Mo.torola. The r ibbon- to - r ibbon p r o c e s s i s b a s i c a l l y a f l o a t - z o n e c r y s t a l growth method i n which t h e f e e d s t o c k is a p o l y c r y s t a l l i n e s i l i c o n r i b b o n . ( F i g u r e 4-7). The ~ o l y a i l i c o n r i b b o n i.s f e d i n t o a p r e h e a t e d r e g i o n which is a d d i t i o n a l l y h e a t e d by a f o c u s e d laser beam, m e l t e d , and c r y s t a l l i z e d . The l i q u i d s i l i c o n is h e l d i n p l a c e by i t s own s u r f a c e . t e n s i o n . The s h a p e o f t h e r e s u l t i n g c r y s t a l is d e f i n e d by t h e s h a p e o f t h e f e e d s t o c k and

. . . . . t h e orientation i s d e t e r m i n e d by t h a t o f a s e e d s i n g l e - c r y s t a l r i b b o n .

The machine b e i n g used f o r t h e RTR p r o c e s s was s h u t down f o r most of' t h i s q u a r t e r b e c a u s e o f problems with,the.transporit'system.. To d a t e , 2-1 /2 cm-wide , r i b b o n s . have been grown. 'Owin8 t o l a s e r ' gowe P.. anh, s c a n l i m i t a t i o n s , g rowth s p e e d s have been l i m i t e d t o 0 .25 cm/min. 'The high- t e m p e r a t u r e p o s t h e a t e r was i n s t a l l e d , and t h e r i b b o n s grown have been shown t o have n e g l i g i b l e t h e r m a l stresses. T e s t i n g . i n d i c a t e s t h a t t h e RTR r i b b o n s a r e still 20% t o 30% lower i n c o n v e r s i o n e f f i c i e n c y t h a n t h e e q u i v a l e n t s i n g l e c r y s t a l ce l l s . It i s c o n s i d e r e d v e r y i m p o r t a n t t h a t t h i s d e g r a d a t i o n mechanism be u n d e r s t o o d . A fo l low-on c o n t r a c t is b e i n g prepa red t o f u r t h e r t h i s .

Figu re 4-6. Web-Dendritic Growth - . U n i v e r s i t y o f South Caro l ina . .

f . S i l i c o n Shee t Growth: Chemical V a ~ o r ' D e p o s i t i o n on LQw- Cost S u b s t r a t e s - Rockwell I n t e r n a t i o n a l . The purpose o f t h i s c o n t r a c t is t o exp lo re t h e chemical vapor depos i t i on (CVD) method f o r t h e growth

'

of s i l i c o n s h e e t on inexpens ive s u b s t r a t e m a t e r i a l s ( Figure 4-8 ) . A s a p p l i e d t o s i l i c o n s h e e t growth, t h e method invo lves p y r o l y s i s , o r r e d u c t i o n , 0 f . a s u i t a b l e sil icon.compound a t e l e v a t e d temperature and approximately atmospheric pressure . A l abora tory- type CVD r e a c t o r system wi th a flow-through (open-tube) v e r t i c a l d e p o s i t i o n chamber is used f o r t h e s e i n v e s t i g a t i o n s . The s u b s t r a t e i s mounted on a s i l i c o n carbide-coated carb0.n pedes t a l heated by an RF c o i l ex t e rna l . . t o t h e . . . . . . . .

chamber. ~ h e " r e a c t o r system has been e x t e n s i v e l y modified by i n s t a l l a t i o n of mass flow c o n t r o l l e r s , automatic process sequence timers, and s p e c i a l bellows-sealed a i r -ope ra t ed va lves . This system, which has a c a p a c i t y of 30 cm2, is used a s a r e sea rch v e h i c l e i n an a t tempt t o reach t h e . .

g o a l s of 100,pm g r a i n s depos i ted 20 t o 100 ;pm t h i c k on inexpensive s u b s t r a t e s a t r a t e s up t o 5 ,pm per minute.

During ' t h i s q u a r t e r , 20 d i f f e r e n t s u p p l i e r s were i n v e s t i g a t e d : f o r s u b s t r a t e m a t e r i a l s , which included g l a s se s ; ce ramics , g lass -ceramics , and composites. It was found t h a t r e - f i r i n g p o l y c r y s t a l l i n e aluminas . r e s u l t s i n on ly l i m i t e d g r a i n growth i n t h e wafer s u r f a c e s i n c o n t a c t with another s u r f a c e . There haa been repea ted evidence o f contaminat ion of f i l m s depos i ted on va r ious g l a s s s u b s t r a t e s .

THIN, SINGLE -CRYSTAL / RIBBON

\ \

COORDINATED

.<. ..

ZONE OF RECRY STAl

MELTING .LIZATION

AND

. . . . .. '.- .AUXILIARY HEATING

ROLLER TRANSPORT SYSTEM

SLOW SPEED IN T . . . .. . . . .. .: .. ....,

. . ... . , . , .

. . . i: . . . . . . . . . . .

. . . . . .

' . : .... .. , .

F i g u r e 4-7. L a s e r Zone C r y s t a l l i z a t i o n - Motorola

g . S i l i c o n S h e e t Growth: Hot-Forminn o f S i l i c o n - U n i v e r s i t y of P e n n s v l v a n i a . T h i s c o n t r a c t is des igned t o d e t e r m i n e t h e f e a s i b i l i t y o f hot- forming s i l i c o n i n a c o s t - e f f e c t i v e manner. The p rocedure t o be fo l lowed is h i g h - s t r a i n - r a t e ( i > I ) , high-compress ion d e f o r m a t i o n of s i l i c o n . From t h i s i n f o r m a t i o n , one can c o n s t r u c t t h e hot-forming d iagram f o r s i l i c o n and make some e x t r a p o l a t i o n s o f t h e economics o f t h e p r o c e s s . The program a l s o i n c l u d e s e v a l u a t i o n s o f m e t a l l u r g i c a l p r o p e r t i e s such a s hot-forming t e x t u r e , r e c r y s t a l l i z a t i o n t e x t u r e and g r a i n s i z e , and o f e l e c t r i c a l p r o p e r t i e s .

Dur ing t h i s q u a r t e r , s t r e s s and s t r a i n r a t e s i n t h e h o t r o l l i n g program have been i n c r e a s e d up t o 5 / s e c a t 1 3 8 0 ' ~ and a t 1 3 0 0 ~ ~ .

Th: s t r e s s e s i n c r e a s e d p r e c i p i t o u s l y w i t h i n c r e a s i n g s t r a i n rate a t 1100 C , but f o r h igh t e m p e r a t u r e s t h e i n c r e a s e is r a t h e r s low. A p r e l i m i n a r y economic a n a l y s i s was performed w i t h t h e g o a l o f i d e n t i f y i n g t h e most i m p o r t a n t c o n t r o l l i n g pa ramete r s .

h . I n a o t Growth: Heat Exchanger Method - C r y s t a l Svstems. The Schmid-Vicchnicki t e c h n i q u e (hea t -exchanger method) h a s been developed t o grow l a r g e s i n g l e - c r y s t a l s a p p h i r e ( F i g u r e 4-51). Heat is removed from t h e c r y s t a l by means o f a h igh- tempera tu re h e a t exchanger . The h e a t removal i s c o n t r o l l e d by t h e f low o f hel ium g a s ( t h e c o o l i n g medium) t h r o u g h t h e h e a t exchanger . T h i s e l i m i n a t e s t h e need f o r mot ion o f t h e c r y s t a l , c r u c i b l e , o r h e a t zone. I n e s s e n c e t h i s method i n v o l v e s

Figure 4-8. Chemical Vapor Deposi t ion on Low-Cost S u b s t r a t e s - 'Rockwell I n t e r n a t i o n a l

d i r e c t i o n a l s o l i d i f i c a t i o n from t h e melt where t h e tempera ture grad ' ient i n t he ' s o l i d might be c o n t r o l l e d by..the hea t exchanger and t h e g r a d i e n t . .

i n t h e l i q u i d c o n t r o l l e d by t h e furnace temperature . . . ,

. . . . . . . . .

The o v e r a l l g o a l uf Lhis .y~.ugr~aiu IB t o Jetei3iuine i f t h e h e a t s exchanger i n g o t c a s t i n g method.can grow l a r g e s i l i c o n c r y s t a l s ( 6 i nches i n diameter by 4 i nches i n he igh t ) i n a form s u i t a b l e f o r t h e even tua l f a b r i c a t i o n o f s o l a r c e l l s . Th i s goa l i s t o be accomplished by t h e

... . . . t r a n s f e r o f s apph i r e growth technology (50-pound i n g o t s have a l r eady - been grown), and t h e o r e t i c a l c o n s i d e r a t i o n s o f s eed ing , c r y s t a l l i z a t i o n k i n e t i c s , f l u i d dynamics, and hea t flow f o r s i l i c o n .

The Heat Exchanger Method o f c a s t i n g l a r g e s i l i c o n i n g o t s has demonstrated a c r ack - f r ee i ngo t growth using c r u c i b l e s which have been coated with s i n t e r e d s i l i c a . The s i n t e r e d s i l i c a s e p a r a t e s f r e e l y from t h e s i l i c o n i n g o t dur ing cooldown and p reven t s c r ack ing .

h. I nao t C u t t i m : M u l t i ~ l e Wirina Sawing - C r y s t a l Systems. Today moot o i l i c o n is s l i o e d i n t o wafers with an i n s i d e d iameter saw, one wafer a t a time being c u t from t h e c r y s t a l . Th i s is a b ig c o s t f a c t o r in producing s o l a r c e l l s . The lesser -used mu l t i b l ade s l i c e r

COVER 7

CRUCI BLE.

START I NG MATER l AL

SEE HEAT-. . . .

EXCHANGER ( 8 )

L l Q U l LEVEL

L l Q U l D

l NTERFACE , c l

. . . . : . . . . . . . . . . . ": .:- . . . . . . Growth of a crystal :by the heat exchanger method:. .,. ; . .

( a ) Crucible, -cover, starting material, and seed prior to mel.tirig. . . . . . . . . . . . . . ( b ) Starting, material melted. . ' . . . . . . . . . . . . . .

. . ( c ) 'Seed partially melted to insure good nucleation. ( d ) Growth of crystal commences. ( e ) Growth of crystal covers crucible bottom. ( f ) Liquid-solid interface expands in nearly ellipsoidal fashion. ( ) Liquid-solid interface breaks liquid surface. ( f ) CV sta l growth completed.

Figure 4-9. Crystal Growth Using the Heat. Exchanger Method - Crystal Systems

. . . . . . . . . . . . _ . . . . . . . . . . . .

can be c t i l i z e d to s l i c e s i l i con . The multiblade s l i c e r has not been developed for the semiconductor industry s ince t h i s method produces bow and taper unacceptable fo r in tegrated-ci rcui t appl icat ions .

The overa l l goal of the s l i c ing program is t o optimize multiblade (wire) s i l i con s l i c i n g , invest igat ing the following parameters in par t i cu la r : . .

( 1 ) Rate of material removal and k e r f removal.

. . (2) Sl i ce . thickness, wire blade dimensions, cu t t ing forces, ' ...

wire'/blade tens ion , and other machine .va r iab les . . . . . . . .

(3) Wires versus blades a s a cu t t ing too l .

( 4 ) Variation of rocking motion.

( 5 ) Introduction of abrasive during s l i c i n g operation.

( 6 ) Effect of surface condition of t o o l , including consideration of hardness and method of p la t ing.

( 7 ) E f f e c t o f diamond a b r a s i v e p a r t i c l e s i z e and type,. . . . .

( 8 ) ~ f f k c t ' o f c u t t i n g f l u i d , composition. . . . . . . . .

.The s l i c i n g ' o p e r a t i o n employs a rocking motion and u t i l i z e s '50 8-mil wires. These are 6-mil s t e e l w i r e s surrounded by a 1-mil copper s h e a t h , which i s impregnated with diamond a s an a b r a s i v e . The shape o f t h e a b r a s i v e s and t h e i r i n t e r a c t i o n with t h e copper and steel is an unknown v a r i a b l e and w i l l be i n v e s t i g a t e d . The i n d i v i d u a l wi res wi th in a m u l t i p l e wire package a r e . equi tens ioned by t h e use o f a s i n g r e j i g i n t h e form o f a weaving machine.

The v a r i a b l e s f o r s l i c i n g have been s p e c i f i c a l l y i d e n t i f i e d . The independent. v a r i a b l e s are feed f o r c e , speed , rocking a n g l e , and .

phase ang le ; t h e dependent v a r i a b l e s are c u t t i n g r a t e , d e f l e c t i o n , deg rada t ion o f diamond, and c u t p r o f i l e o f y ve r sus x .

Wire wander has been i d e n t i f i e d a s t h e most important problem a f f e c t i n g t h e .wire sawing process . This wandering has been reduced by an o r d e r o f magnitude by i n s t a l l i n g a grooved r o l l e r suppor t and a gu ide system f o r t h e wires . During the q u a r t e r , more than 12 runs were made with one s e t o f tungs ten wires impregnated with diamond without caus ing degrada t ion o f wire f a i l u r e .

C. ENCAPSULATION TASK

The o b j e c t i v e o f t h e Encapsulat ion Task is t o develop and q u a l i f y a s o l a r a r r a y module encapsu la t i on system t h a t has a demonstrated high r e l i a b i l i t y and a 20-year l i f e t i m e expectancy i n t e r r e s t r i a l environments, and is compatible with t h e low-cost o b j e c t i v e s o f t h e P r o j e c t .

The scope o f t h e Encapsulat ion Task i n c l u d e s developing t h e t o t a l system requ i r ed t o p r o t e c t t h e o p t i c a l l y and e l e c t r i c a l l y a c t i v e elements o f t h e a r r a y from t h e degrading e f f e c t s o f t e r r e s t r i a l environments. The most d i f f i c u l t t e c h n i c a l problem i s expected t o be developing t h e element o f t h e encapsu la t i on system f o r t h e s u n l i t s i d e ; t h i s element must main ta in high t ransparency f o r t h e 20-year l i f e t i m e , while a l s o provid ing p r o t e c t i o n from adverse environments. In a d d i t i o n , s i g n i f i c a n t t e c h n i c a l problems a r e a n t i c i p a t e d a t i n t e r f a c e s between t h e p a r t s o f t h e encapsu la t i on system, between t h e encapsu la t i on system and t h e a c t i v e a r r a y e lements , and a t p o i n t s where t h e encapsu la t i on system is pene t r a t ed f o r e x t e r n a l e l e c t r i c a l connec t ions . S e l e c t i o n of t h e element f o r t h e r e a r s i d e ( i . e . , t h e s i d e oppos i t e t o t h e s u n l i t s i d e ) of t h e encapsu la t i on system w i l l be based p r i m a r i l y on c o s t , f u n c t i o n a l requi rements , and c o m p a t i b i l i t y with t h e o t h e r p a r t s o f t h e encapsu la t i on system and wi th t h e s o l a r c e l l s .

Depending on t h e f i n a l s o l a r a r r a y des ign implementat ion, t h e encapsu la t i on system may a l s o s e r v e o t h e r f u n c t i o n s , e . g . , s t r u c t u r a l , e l e c t r i c a l , e t c . - i n a d d i t i o n t o provid ing t h e e s s e n t i a l p r o t e c t i o n .

A t p r e s e n t , o p t i o n s are being kept open a s t o what form t h e t r a n s - pa ren t element o f t h e encapsula t ion system w i l l t a k e - ' g l a s s o r polymer

s h e e t , . polymer f i l m , sp rayab le polymer', c a s t a b l e polymer, e t c . The t r a n s p a r e n t e lement may conta ' in more than one m a t e r i a l . a n d may.be i n t e g r a l wi th t h e pho tovo l t a i c dev ice , o r be bonded t o i t , o r i n s t a l l e d , a s a . . - window o r l e n s remote from t h e dev ice ; . . . . , . ..

1. Technical Background

Pho tovo l t a i c d e v i c e s ( s o l a r c e l l s ) and t h e a s s o c i a t e d e l e c t r i c a l conductors which t o g e t h e r c o n s t i t u t e s o l a r a r r a y s must be p ro t ec t ed . . .

from exposure t o t h e environment. Exposure would cause s eve re deg rada t ion o f e l e c t r i c a l performance a s a r e s u l t o f c o r r o s i o n , contamina t ion , and mechanical damage. . .. . .

. .. . :.. .. . . . .. , :

I n t he p a s t , test exper ience by government organiza t ions ' . and : ... : .

i n d u s t r y has confirmed t h a t s p a c e c r a f t s o l a r a r r a y s a r e poor ly des'ign.$d:. .., . . .. . . . ... ,,

t o s u r v i v e t h e e a r t h environment. Arrays designed for . t e r r e s t r i ' a l . : '.- .. ' .. . . .. use have shown mixed r e s u l t s . These ' r e s u l t s , and' ana lyses performed"

. . as p a r t o f t h i s t a s k , sugges t t h a t l o n g - l i f e , low-cost encapsul'at.Lon "' ' , .. . . .

is p o s s i b l e under t e r r e s t r i a l ' c o n d i t f o n s ; however, a t p r e s e n t , s u c c e s s f u l . . :

p r o t e c t i o n from deg rada t ion by t h e environment is a s s o c i a t e d wi th ' . . .

. . . . encapsu la t i on materials and process ing c o s t s which a r e excess ive . . f o r .:.'. - , - - .

l a r g e s c a l e , low-cost use. Thus ,' a n accep tab l e encapsu la t i on system .-. .',. '"

one t h a t pos se s se s t h e r e q ' u i r e d ' . p u a l i t i e s and i s .compati.ble wi th 'low-dost , . . high-volume s o l a r a r r a y process ing - has y e t ' to be developed, , ' . . . .. . , .

. . . . ... .

2. Organiza t ion and Coord ina t ion o f t h e Encapsula t ion ask , ~ f f o r t

The approach being used t o ach ieve t he o v e r a l l o b j e d t i v e o f t h e Encapsula t ion Task i n c l u d e s an a p p r o p r i a t e combination of c o n t r a c t o r and JPL in-house e f f o r t s . 'Me c o n t r a c t o r e f f o r t s w i l l be c a r r i e d ou t i n two phases. Within each phase some p a r a l l e l i n v e s t i g a t i o n s w i l l be conducted t o assur.e t ime ly accomplishment of o b j e c t i v e s .

During Phase I t h e c o n t r a c t o r and t h e JPL in-house e f f o r t s c o n s i s t p r i m a r i l y of a sys t ema t i c assessment and documentation o f t h e fo l lowing items:

( 1 ) P o t e n t i a l candida te encapsulan t m a t e r i a l s based on pas t exper ience wi th t h e encapsu la t i on of s i l i c o n and ot.her semiconductor dev i ce s and on a v a i l a b l e in format ion on the p r o p e r t i e s a~id Y L a b i l i t y of o t h e r ' p o t e n t i a l encapsulan t m a t e r i a l s and processes .

( 2 ) The environment which t h e encapsu la t i on system must with- s t a n d .

( 3 ) The p r o p e r t i e s , environmental s t a b i l i t y , and p o t e n t i a l i m - provement of p o t e n t i a l encapsulan t m a t e r i a l s and processes .

( 4 ) T e s t and a n a l y t i c a l methods r equ i r ed t o e v a l u a t e performance and p r e d i c t and/or v e r i f y l i f e t i m e o f encapsulan t m a t e r i a l s and encapsu la t i on systems.

'The r e s u l t o f . t h i s e f f o r t w i l l . t h e n be used . t o s p e c i f i c a l l y d e f i n e a d d i t i o n a l , . .

r e s e a r c h , development , and e v a l u a t i o n . : r e q u i r e d d u r i n g t h e subsequent . phase . - . . .

~ h r o u ~ h o u t t h e t a s k a t y p i c a l o r u n i q u e . approaches t o . ' so lv ing t h e e n c a p s u l a t i o n sys tem p r o b l e m - w i l l be sough t and e v a l u a t e d . . . F o r example , Phase I w i l l i n c l u d e an e v a l u a t i o n o f t h e f e a s i b i l i t y of u t i l i z i n g e l e c t r o s t a t i c a l l y - b o n d e d i n t e g r a l g l a s s c o v e r s as p a r t of t h e e n c a p s u l a t i o n sys tem.

I n Phase 11, c o n t r a c t o r and .JPL in-house e f f o r t s w i l l be conducted t o i d e n t i f y a n d / o r d e v e l o p one o r more p o t e n t i a l l y s u i t a b l e e n c a p s u l a t e d s y s t e m s ,and t h e n . v e r i f y t h e expected. l i f e t i m e and r e l i a b i l i t y o f t h e s e sys tems . Depending on t h e r e s u l t s o f Phase I , t h e c o n t r a c t o r e f f o r t i i r tnis phase w i l l It ' lclude a11 appropriatc combina t ion of some af the f o l l o w i n g i t e m s :

( 1 ) E v a l u a t e , d e v e l o p , and /o r modify test and a n a l y t i c a l methods and t h e n v a l i d a t e t h e s e methods.

(2) Perform m a t e r i a l s and i n t e r a c t i o n t e s t i n g , u s i n g t h e s e . .

methods t o e v a i u a t e c a n d i d a t e s and d e m o n s t r a t e t h e r e l i a b i l i t y o f e n c a p s u l a t i o n sys tems .

( 3 ) Modify materials and p r o c e s s e s used. i n e n c a p s u l a t i o n sys tems t o improve au tomat ion and c o s t p o t e n t i a l .

( 4 ) Modify p o t e n t i a l e n c a p s u l a t i o n sys tem m a t e r i a l s t o o p t i m i z e m e c h a n i c a l , t h e r m a l and a g i n g p r o p e r t i e s .

( 5 ) Implement r e s e a r c h and development on new e n c a p s u l a n t .,. . . - . .

materials. . . . ' , ...

- , '. . . . . ... . . . . . , ... .

3 E n c a p s u l a t i o n Task C o n t r a c t s

E n c a p s u l a t i o n Task c o n t r a c t s a r e shown i n T a b l e ' 4 - 4 . I n a d d i t i o n , P r o f e s s o r C h a r l e s Rogers , Department o f Macromolecular S c i e n c e , Case Western Reserve U n i v e r s i t y , s e r v e s as a c o n s u l t a n t t o t h i s t a s k (JPL C o n t r a c t No. 954738) and w i l l a l s o implement s e l e c t e d s u p p o r t i n g exper- i m e n t a l i n v e s t i g a t i o n s i n t h e l a b o r a t o r i e s a t Case.

. . . . . C o n t r a c t u a l n e g o t i a t i o n s i n p r o g r e s s i n c l u d e follow-on c o n t r a c t s t o the f o u r major c o n t r a c t o r s , a c o n t r a c t w i t h t h e Rockwell S c i e n c e Cen te r t o s t u d y t h e s u r f a c e c h a r a c t e r i s t i c s o f s o l a r c e l l s , a c o n t r a c t w i t h t h e Motorola S o l a r ' Energy Department t o i n v e s t i g a t e t h e f e a s i b i l i t y o f d e v e l o p i n g a n t i r e f l e c t a n c e c o a t i n g s f o r g l a s s , and a c o n t r a c t w i t h Endurex o f Mesqu i t e , Texas , t o s t u d y i o n p l a t i n g c o a t i n g t e c h n i q u e s . A l l o f t h e above c o n t r a c t s a r e schedu led f o r e x e c u t i o n i n t h e t h i r d and f o u r t h . q u a r t e r - s o f FY 1977.

I n a d d i t i o n , c o n s i d e r a b l e e f f o r t h a s been expended i n p r e p a r i n g two Phase I1 s t a t e m e n t s o f work. These a r e e s s e n t i a l l y comple te , b u t may be h e l d up pending r e l e a s e o f t h e B a t t e l l e S tudy 4 r e p o r t on l i f e p r e d i c t i o n methodology.

. Table. 4-4. Encapsulation Task ont tractors . . .

Contractor Technology Area

~attelle Memorial Institute Columbus', . Ohio . '

(JPL Contract No. 954328) . . . . . . . . . . . .

ROckwell International Anaheim, California (JPL Contract No. 954458)

Simulation rhyaicv Burlington, Massachusetts (JPL Contract No. 954521)

. .

Springborn Laboratories Enfield, Conneotiout (JPL Contract 'NO. 954527)

Endurex Dallas, Texas (ITPL C ~ n t r ~ a u l ; No. 954'128) . .

Study 1: Identification of candidate encapsulant materials

. . . . . based on a review of (a) world- . .

. . . wide experience:w.ith encapsulant systeni,s;::for. ..siS:icon solar cells ... . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . and ',related .dPvioeo and (b) the . . . . . .

properties of other available mat.erials.

Study 2: Definition of environmental conditions for qualifying encapsulant materials.

Study 3: Evaluation of encapsulant material 'properties and test mst,hods,

Study 4: Analysis of accelerated/ .abbreviated encapsulant test methods.

Experimental evaluation of accelerated/abbreviated encapsulant test methods, .

Electrostatically-bonded glass covers.

. , . . , , , . . . . . . . . . . . . .

Polymer properties and aging.

Ion plating procesa and testing.

. . . . . . . . . . . . . . . . . . . . . . . . . . .

4. Encapsulat ion Task Technica l ' A c t i v i t i e s . .

Program e f f o r t s t o d a t e have provided - a n assessment.- o f t h e s t a t e -o f - . .:. :- . . i . ...

. . . . . . t h e - a r t and a . de f in i . t i on .o f t h e po.tentia1.. environmental and opera t ion ,a l s t r e s s e s . - . . imposed on t h e encapsu la t i on system. A d a t a base.. o f cand ida t e m a t e r i a l s and t h e i r responses t o t h e s e stresses i s being accumulated and analyzed. Tech- nology d e f i c i e n c i e s a r e being exper imenta l ly exposed .and documented.

a. Studv 3 * : Evaluat ion of Encapsulant Ma te r i a l s P r o p e r t i e s and Tes t Methods--Battelle. The experimental e v a l u a t i o n s under Study 3 were completed du r ing t h i s q u a r t e r and t h e d r a f t of t h e f i n a l r e p o r t was begun. E f f o r t s d i r e c t e d toward ach iev ing t h e o b j e c t i v e s o f t h e s tudy woro broken down i n t o several s ~ ~ b a t u d i e s encompassing both polymeric m a t e r i a l s and g l a s s e s . Subs tudies i d e n t i f i e d wi th t h e l e t t e r "PI1 r e l a t e t o polymeric m a t e r i a l s ; those i d e n t i f i e d with "Gw r e l a t e t o s t u d i e s i n which g l a s s i s a major component.

Substudv P-1: Measurement o f P r o p e r t i e s o f Polvmeric Ma te r i a l s

This s tudy provides in format ion on t h e t e n s i l e p r o p e r t i e s (modulus, s t r e n g t h , and e l o n g a t i o n ) , thermal c o e f f i c i e n t s of expansion, mois ture ,

b a r r i e r p r o p e r t i e s , and l i g h t t r ansmi t t ance o f cand ida t e polymer m a t e r i a l s i n t he as - rece ived o r prepared cond i t i on and a f t e r exposure t o a c c e l e r a t e d weather ing ( u l t r a v i o l e t (UV) o r thermai c y c l i n g ) . Th i s in format ion was used t o he lp e s t a b l i s h t h e ag ing r e s i s t a n c e o f t h e i n d i v i d u a l m a t e r i a l s . The product of t h e t e n s i l e modulus and thermal c o e f f i c i e n t o f expansion was used , be fo re and after ag ing , t o e s t i m a t e stress l e v e l s i n m a t e r i a l s l amina t e s , a s de sc r ibed by C a r r o l l , Cuddihy, and Sa lana ,** and i n d i c a t e p o s s i b l e de lamina t ion a t t h e e n c a p s u l a n t / c o v e r / a d h e s i ~ ( o r p o t t a n t ) , . .

and adhes ive ( o r p o t t a n t ) / c e l l i n t e r f a c e s . Moisture b a r r i e r in format ion ' was used i n t h e s e l e c t i o n o f i n d i v i d u a l m a t e r i a l s f o r use i n encapsulan t de s igns where b a r r i e r p r o p e r t i e s o f t h e s i n g l e component is c r i t i c a l . Light t r a n s m i t t a n c e be fo re and a f t e r environmental exposure was used t o provide a measure o f t h e u t i l i t y o f s p e c i f i c m a t e r i a l s f o r cover a p p l i c a t l o a u .

U l t r a v i o l e t and temperature c y c l i n g exposures through 1000 hours have been completed on polymer f i l m s o f "Teflonw FEP, weatherable Mylar, UV-stabilized Lexan, Korad A , Tedlar , F l ex iga rd , Ha la r , and Aclar and

F i n a l r e p o r t s on S t u d i e s 1 and 2 under t h e B a t t e l l e c o n t r a c t (refer t o Table 4-4) have been publ ished. Work on Study 4 was completed e a r l y i n t h e p re sen t q u a r t e r , and t h e f i n a l r e p o r t i s scheduled f o r p u b l i c a t i o n e a r l y i n Ju ly .

* * c a r r o l l , W . , Cuddihy, E., and Salama, M . , M a t e r i a l s .and Desian Con- ., . . .

s i d e r a t i o n s of E n c a ~ s u l a n t s f o r Pho tovo l t a i c Arravs i n T e r r e s t r i a l A ~ ~ l i c a t i o n S , IEEE Photovol ta ic S p e c i a l i s t s Conf., Baton Rouge, LA, Nov. 1976.

o n A c r y l i t e , Lexan, and Sun-Lite polymer s h e e t m a t e r i a l s . . Water-vapor . . t r a n s m i s s i o n r a t e measurements a r e c u r r e n t l y .being performed on unexposed, . ,

s a m p l e s of e a c h and' on samples which have been exposed. t o UV o r t e m p e r a t u r e c y c l i n g . Data w i l l be i n c l u d e d i n t h e . f i n a l r e p o r t .

T e s t samples of "Tef lonu FEP, Korad A , Sun-Li te , T e d l a r , and Halar f i l m and s h e e t m a t e r i a l s and f r e e f i l m s o f t h e A c r y l o i d B-7, S i l g r i p SR-573, and Scotch-Weld 2216 B/A a d h e s i v e s were e x o s e d t o 8 U V , t e m p e r a t u r e c y c l i n g , and h igh humid i ty (100% R . H . , 100 F ( 3 8 ' ~ ) . These samples were used i n s t u d i e s o f t h e e f f e c t s of t h e v a r i o u s exposure c o n d i t i o n s on normal l i g h t t r a n s m i t t a n c e . The work . a l s o i n c l u d e s measurements o f t h e t r a n s m i t t a n c e o f f i l m ' a n d s h e e t subsys tems w i t h t h e s e v e r a l a d h e s i v e s b e f o r e and a f te r exposures . '

Subs tudv P-2: E v a l u a t i o n s o f Polvmer Subsvstems and I n t e r f a c e s

Subs tudv P-2.1: ' Polvmer F i lm Bondinst. T h i s s t u d y p rov ided a n e v a l u a t i o n o f a d h e s i v e m a t e r i a l s and t h e manner i n which t h e y a r e t o be a p p l i e d f o r use w i t h t h e d i f f e r e n t polymer f i l m material c a n d i d a t e s ( f o r t h e f i l m - l a m i n a t i o n e n c a p s u l a t i o n d e s i g n ) , i n o r d e r t o r e v e a l subsys tems t h a t are r e s i s t a n t t o d e l a m i n a t i o n and t o m o i s t u r e t r a n s p o r t a f t e r test e x p o s u r e s to UV and t o t e m p e r a t u r e , c y c l i n g from -40 t o 90°c.

Subs tudv P-2.2: Polvmer S h e e t Bonding. T h i s s t u d y p rov ided f o r polymer s h e e t c a n d i d a t e s a n o u t p u t o f t h e t y p e d e s c r i b e d i n Subs tudy P-2.1.

Subs tudv P-3.3: C e l l Bondina/Seal inq. T h i s s t u d y p rov ided a n i d e n t i f i c a t i o n o f a d h e s i v e s and conformal c o a t i n g s t h a t a r e e f f e c t i v e i n p r o t e c t i n g t h e metallic components of t h e sys tem f o r mois tu re - induced c o r r o s i o n . The e f f e c t s o f exposure o f t h e m a t e r i a l s t o UV and tempe18atur8e c y c l i n g a r e i n c l u d e d i n t h i s s u b s t i ~ d y .

S t u d i e s of f i l m - t o - f i l m a d h e s i v e bond ing , de te rmined by l ap -shear - s t r e n g t h measurements b e f o r e and af ter t h e r m a l and UV e x p o s u r e s were computed. Data were r e p o r t e d e a r l i e r f o r subsys tems o f "Teflonv1 FEP, w e a t h e r a b l e Mylar , and UV-stabi l ized Lexan f i l m s bonded w i t h v a r i o u s a d h e s i v e s t h r o u g h 1000 h o u r s o f UV and t e m p e r a t u r e c y c l i n g e x p o s u r e s . S i m i l a r e v a l u a t i o n s have been completed f o r Korad A and T e d l a r subsystems. F i v e hundred-hour e x p o s u r e s o f F l e x i g a r d ( s h e e t m a t e r i a l ) subsys tems have been comple ted . S e l e c t e d a d h e s i v e s f o r Korad A f i l m th rough 1000 h o u r s o f t e m p e r a t u r e cynl ing showed no signi f ican t d e o r c a o c in b o n d i ~ l g pe r fo rmance . After 1000 h o u r s o f UV e x p o s u r e , two a d h e s i v e s , Scotch-Grip 4475 and 4693, d i d show bond s t r e n g t h d e c r e a s e . Cohesive f a i l u r e o c c u r r e d w i t h t h e 4693; b r e a k i n g o f t h e film a d j a c e n t t o t h e bonded a r e a o c c u r r e d w i t h 4475. N e i t h e r subsystem had f a i l e d after a 500-hour exposure . No s i g n i f i c a n t d e c r e a s e i n bonding performance was n o t e d f o r t h e o t h e r a d h e s i v e s e v a l u a t e d .

E v a l u a t i o n s o f a d h e s i v e s f o r bonding T e d l a r f i l m af ter 1000-hour e x p o s u r e s t o t h e r m a l c y c l i n g and UV showed no s i g n i f i c a n t d e c r e a s e i n bonding performance. Bond s t r e n g t h v a l u e s o b t a i n e d w i t h t h e Cavalon 3100s ( u s i n g benzoyl pe rox ide a s t h e c a t a l y s t ) s u g g e s t t h a t c u r e was irnccmplete. Thermal c o n t r o l s and e x p e r i m e n t a l samples a l l

had h i g h e r bond s t r e n g t h v a l u e s . Benzoyl p e r o x i d e was used in o r d e r t o e l i m i n a t e t h e d a r k c o l o r noted w i t h c a t a l y s t s 3300s and 33033. The a d h e s i v e area d o e s have some m i l k i n e s s which might be overcome by a p p r o p r i a t e c o m b i n a t i o n s o f c a t a l y s t c o n c e n t r a t i o n , c u r e t i m e , and

i t e m p e r a t u r e . Data on a l l o f t h e f i l m / s h e e t and a d h e s i v e materials w i l l be p r e s e n t e d i n t h e f i n a l r e p o r t .

Water vapor t r a n s m i s s i o n r a t e measurements o f A c r y l i t e , Lexan, and Sun-Li,te ( f i b e r g l a s s r e i n f o r c e d p o l y e s t e r ) s h e e t - a d h e s i v e subsystems

. . were performed. ... .... . . . . . . . , . . . . . . . . .

Bubble f o r m a t i o n o c c u r r e d d u r i n g l a m i n a t i o n s i n v o l v i n g t h e thermo- plaat..i.c a c r y l i , ~ a d h e s i v e ( A c r y l o i d B-7) and t h e Acrylite and Lexan s h e e t m a t e r i a l s . It i s l i k e l y t h a t s o l v e n t i n t h e a d h e s i v e f o r m u l a t i o n was absorbed . on t h e s u r f a c e 'of t h e s e s h e e t m a t e r i a l s and was r e l e a s e d t o produce bubb les when h e a t and p r e s s u r e a r e a p p l i e d . A number o f f a i l u r e s ( h i g h r a t e of water-vapor t r a n s m i s s i o n d e p l e t i n g t h e d e s i c c a n t ) were observed i n t h e unexposed and t empera tu re -cyc led samples. " NO.

bubb les were n o t e d w i t h t h e Sun-Lite Acry lo id B-7 subsystem.

. . The A c r y l o i d B-7 and Scotch-Grip 4693 perform b e t t e r t h a n S i l g r i p SR-573'with t h e Sun-Li te m a t e r i a l . With t h e A c r y l i t e and Lexan m a t e r i a l s t h e Scotch-Grip 4693 and S i l g r i p SR-573 a r e s u p e r i o r t o A c r y l o i d B-7.

Adhesives , c o a t i n g s , and p o t t a n t m a t e r i a l were c o n f o r m a l l y c o a t e d on s o l a r ce l l s , and t h e subsystems were e v a l u a t e d f o r r e s i s t a n c e t o h igh h u m i d i t y , u s i n g v i s u a l o b s e r v a t i o n s and e l e c t r i c a l measurements. I n t h i s work, seven c o a t i n g s , n i n e a d h e s i v e s , and one p o t t a n t were .

a p p l i e d d i r e c t l y t o s i l i c o n c e l l s . The e l e c t r i c a l r e s p o n s e s o f t h e c e l l s were measured a f t e r high-humidity exposure ( 100% R . H . , 3 8 ' ~ ) and .were compared w i t h t h o s e o f t h e uncoated c e l l . Four o f t h e seven conformal c o a t i n g s took on a mi lky appearance a s a r e s u l t o f t h e high- humid i ty e x p o s u r e . Three of s i x a d h e s i y e s on t e s t a l s o showed some d e g r e e o f m i l k i n e s s . Thus f a r t h e m i l k i n e s s h a s been r e s t r i c t e d t o

' two c l a s s e s o f m a t e r i a l s , t h e a c r y l i c s and t h e p o l y v i n y l b u t y r a l r e s i n s . The Scotch-Grip a d h e s i v e s 4693 and 4475 showed some e f f e c t s o f t h e h igh-humidi ty exposure . The e l e c t r i c a l c h a r a c t e r i z a t i o n s w i l l be d i s - cussed i n t h e f i n a l r e p o r t .

Substudv P-3 : Polvmer E n c a p ~ ~ l a t i o n Svs tems Development and . E v a l u a t i o n . . . ..

Subs tudv P-3.1: ~ o l v m e r Film Laminat ion Design. Subs tudy P-3.1

I prov ided i n f o r m a t i o n on c a n d i d a t e m a t e r i a l s and p r o c e d u r e s f o r t h e f i lm- lamina t ion type* o f e n c a p s u l a t i o n d e s i g n , which h a s s i g n i f i c a n t p o t e n t i a l f o r f u t u r e low-cost a r r a y s . The i n v e s t i g a t i o n i n c l u d e d d e t e r - m i n a t i o n o f ( 1 ) t h e e f f e c t s o f U V , humid i ty , and t e m p e r a t u r e c y c l i n g e x p o s u r e s on t h e o u t p u t c h a r a c t e r i s t i c s of t h e e n c a p s u l a t e d c e l l s and (2)

I * ~ a r m i c h a e l , D.C. , G a i n e s , G.B., S l i e m e r s , F.A., and K i s t l e r , C.W.,

M a t e r i a l s f o r E n c a p s u l a t i o n Systems f o r T e r r e s t r i a l P h o t o v o l t a i c A r r a v s , I E E E . P h o t o v o l t a i c S p e c i a l i s t s Conf . , Baton Rouge, L A Nov. 1976.

t h e e f f e c t s of ':.eric.apsulation m a t e r i a l s and ' .p rocess ing on t h e e l e c t r i c a l , . ,

. pe'rformance o f .emcapsulated c e l l s . : . . . .

. . - 2 . . . .. ~ u b s t u d v P-3.2. ..' Polvmer Sheet Bonding. .Design. '.. Thi s s tudy . provided . .. . .. . .. .

f o r . s h e e t . iamiimtes an o u t p u t of t h e type desc r ibed i n Substudy. P-3. 1.

Substudv P-3.3. Polvmer Conformal Coat ings Design. Th i s .s tudy provided f o r conformal c o a t i n g s an output o f t h e t ype desc r ibed i n Substudy P-3.1.

Encapsulated ce l l s f a b r i c a t e d by l amina t ing us ing s e l e c t e d f i l m s , s h e e t s , conformal c o a t i n g s , and adhes ives have been prepared f o r e v a l u a t i o n be fo re and a f t e r exposure t o e l eva t ed tempera ture /h igh humidi ty , temperature c y c l i n g , and UV exposure. The e f f e c t s of' encapsu la t i on and of ag ing on ce l l e l e c t r i c a l performance were emphasized.

S p e c i f i c c e l l parameters were measured i n t h e as-received c o n d i t i o n , a f t e r c l e a n i n g , a f t e r i n i t i a l encapsu la t i on , and a f t e r exposures t o v a r i o u s environments ( t he rma l c y c l i n g , U V , e t c . ) f o r a measured l e n g t h of t ime. The parameters determined were

( 1 ) Open-c i rcu i t v o l t a g e , Voc.

( 2 ) S h o r t - c i r c u i t c u r r e n t , Isc.

( 3 ) Maximum power, Pmx.

( 4 ) Curren t a t maximum power, Imax.

(5) Voltage a t maximum power, Vmax.

( 6 ) F i l l - f a c t e r ( e l e c t r i c a l ) , F.F.

( 7 ) S e r i e s r e s i s t a n c e , RS,

( 8 ) Shunt r e s i s t a n c e , Rsh.

( 9 ) E f f i c i e n c y , i n percent .

Because t hey rorm p a r t o f t h e o p t i c a l pa th t o t h e c e l l , encapsulan ts can a f f e c t profoundly t h e e f f e c t i v e conversion e f f i c i e n c y o f t h e photo- v o l t a i c module. Moreover, t h e s e r v i c e l i f e o f t h e c e l l is determined i n a l a r a e measure by t h e chnine of t.he encapsulan t system. Thc c r i t i c a l measure o f t h e u t i l i t y o f an encapsulan t i s i t s e f f e c t s on t h e e l e c t r i c a l ou tpu t o f t h e ce l l s , i n i t i a l l y and a f t e r exposure t o s e r v i c e environments.

Sho r t -C i r cu i t Cur ren t , IS,: With regard t o t h e encapsulan t t op c o v e r , t h e s h o r t - c i r c u i t c u r r e n t obvious ly is l i m i t e d by how much l i g h t o f t h e proper -wavelength i s allowed t o reach t h e c e l l . L ight can be r e f l e c t e d a t any one of t h e i n t e r f a c e s i n t h e op t i , c a l , pa th , i t can . .

be absorbed i n t h e . o p t i c a l pa th , o r it .can be s c a t t e r e d i n such a way t h a t i t w i l l .not be absorbed i n t h e c o l l e c t i o n zone o f t h e c e l l . I n a common encapsu la t ed -ce l l c o n f i g u r a t i o n , t h e o p t i c a l pa th can c o n s i s t o f a t o p cover , an adhes ive , and the a n t i r e f l e c t i o n (AR) coa t ing of

t h e c e l l . The amount o f l i g h t r e f l e c t e d depends upon t h e index of r e f r a c t i o n o f t h e v a r i o u s l a y e r s and on t h e i r t h i c k n e s s . I n t h i s s t u d y , some of t h e e n c a p s u l a n t sys tems i n c r e a s e d Isc over t h a t measured when t h e c e l l had o n l y t h e AR c o a t i n g a p p l i e d ( u n e n c a p s u l a t e d ) . That i s , t h e i n d i c e s were such t h a t a b e t t e r o p t i c a l c o u p l i n g was o b t a i n e d . I n o t h e r c a s e s , IS, d e c r e a s e d .

C l e a r l y , t h e t r a n s m i t t a n c e o f t h e m a t e r i a l s i n t h e o p t i c a l p a t h a l s o a f f e c t s Is,. Transmi t t ance is a f u n c t i o n o f wavelength , and a s e n s i t i v e one a t some wavelength r a n g e s f o r some p o l y m e r i c . m a t e c i a 1 s . I n t h i s program, t h e normal t r a n s m i t t a n c e was measured f o r s o m e - s i n g l e m a t e r i a l s . . ,In d e s i g n jng t h e u l t i m a t e e n c a p s u l a t i o n sy.st.em.,,..th,e.,, t r a n s -

. . . . . . , . . . . m i t t a n c e shou ld be known f o r combina t ions o f materials i n , - ' t h e . o p t i c a l p a t h , and as a f u n c t i o n o f wavelength . For composi te m a t e r i a l s e s p e c i a l l y , t h e d i f f u s e and s p e c u l a r p o r t i o n s o f t r a n s m i t t a n c e should a l s o be known. With such i n f o r m a t i o n , t h e " i d e a l m j u n c t i o n dep th can be d e t e r m i n e d , o r o p t i c a l c h a r a c t e r i s t i c s can be t a i l o r e d t o a g iven j u n c t i o n d e p t h .

Open-Circuit Vol tage , Voc: For t h e i d e a l s i l i c o n c e l l , t h e fundamental l i m i t a t i o n o f Voc is t h e S c h o t t k y d i f f u s i o n c u r r e n t . Voc is t h e n 'a f u n c t i o n of IS,, t h e d a r k c u r r e n t , and t empera tu re . E n c a p s u l a n t s might affect t h e j u n c t i o n t e m p e r a t u r e and t h e j u n c t i o n " p e r f e c t i o n f a c t o r " , Ao. They a l s o can change t h e s u r f a c e recombina t ion v e l o c i t y and space-charge recombina t ion c u r r e n t , t h e r e b y a f f e c t i n g Voc.

Series R e s i s t a n c e , RS: An i m p o r t a n t e f f e c t t h e e n c a p s u l a n t has on t h e c e l l o u t p u t is t h e p r o t e c t i o n , o r l a c k o f i t , t h a t t h e e n c a p s u l a n t sys tem g i v e s t o t h e c o l l e c t i n g metal g r i d . Gr id c o r r o s i o n and weakening of t h e m e t a l l i z a t i o n bond can l e a d t o i n c r e a s e d RS. If t h e e n c a p s u l a n t e lement ( a d h e s i v e , f o r example) i n t e r a c t s e x c e s s i v e l y w i t h t h e A R coat2ng- s i l i c o n i n t e r f a c e , t h e c o l l e c L i o n e f f i c i e n c y o f t h e j u n c t i o n can be d e c r e a s e d .

Shunt R e s i s t a n c e , Rsh: Shunt ing c u r r e n t a l s o can be i n c r e a s e d . ... " 'wi thin- t h e area of t h e c e l l if t h e . i n t e r a c t . i o n o f t h e e n c a p s u l a n t com-

p o n e n t . i s e x c e s s i v e . I n t h e . a b s e n c e o f h igh- tempera tu re . p r o c e s s e s invo lved i n t h e a p p l i c a t i o n o f t h e ' e n c a p s u l a n t e l e m e n t s , t h e p r i n c i p a l

'. . source o f a change in s h u n t i n g ' c u r r e n t i s probab ly t h e d e g r e e t o which : t h e e n c a p s u l a n t p a s s i v a t e s t h e exposed j u n c t i o n around t h e edge o f t h e ( c o n v e n t i o n a l ) ce l l . It is l i k e l y t h a t t h e s h u n t i n g c u r r e n t s can be decreased by e n c a p s u l a t i o n ; which, o f c o u r s e , l e a d s t o a more e f f i c i e n t

. . . . . . . . .-:. cell:. ."'The e l e c t r i c a l c o n d u c t i v i t y o f t h e e n c a p s u l a n t ' can a l s o ' lead: . . t o a .change i n s h u n t i n g c u r r e n t s , b u t c o n d u c t i v i t y , p e r se, is n o t . .

I ' l i k e l y t o be a l a r g e f a c t o r i n t h e r e s u l t s i n t h i s s t u d y . However, keeping water vapor away from t h e j u n c t i o n edge is , o f course; an advantage.

. .. . .

b. h ~ e r i m e n t a l E v a l u a t i o n o f Acce le ra ted /Abbrev ia ted E n c a ~ s u l a n t T e s t Methods--Rockwell I n t e r n a t i o n a l . A 1 . l m a t e r i a l s degrade , . . however s l o w l y , on exposure t o the' wea ther . To meet t h e g o a l s o f t h e LSSA program, s o l a r c e l l e n c a p s u l a n t s must p r o v i d e p r o t e c t i o n o r 20 y e a r s . Consequent ly , t h e o b j e c t i v e o f t h e p r e s e n t program is t o deve lop methodology f o r making c o n f i d e n t p r e d i c t i o n s o f e n c a p s u l a n t performance

a t any exposure s i t e i n t h e U.S. The i n h e r e n t w e a t h e r a b i l i t y f a c t o r s o f i n s o l a t i o n , . t empera ture , and mois ture must be cons idered .

To p r e d i c t how lorig and how well t h e encapsu lan t s can perform, i t is necessariy t o have a mathematical model which. d e s c r i b e s t h e de- g r a d a t i o n processes . I n p r i n c i p l e , by i n s e r t i n g measured va lues f o r deg rada t ion r a t e c o n s t a n t s i n t o a s u i t a b l e e q u a t i o n , any p rope r ty can be p red i c t ed a s a f u n c t i o n o f time.

Phoenix, Arizona and M i a m i , F l o r i d a , were s e l e c t e d a s s u i t a b l e s i t e s f o r t h e weather ing tests. Complete weather d a t a and outdoor exposure s e r v i c e s are a v a i l a b l e a t both l o c a t i o n s . Encapsulated Universa l Tes t Specimens (UTSs) were placed outdoors o n ' r a c k s and were r e tu rned for examination a t a p p r o p r i a t e time i n t e r v a l s . Upon r e c e i p t , t hey were examined chemica l ly , p h y s i c a l l y , and e l e c t r i c a l l y t o e s t a b l i s h deg rada t ion rates. Based on t h i s d a t a , probable f a i l u r e mechanisms a r e being developed.

S i m i l a r test specimens were exposed i n a weather ing chamber. The f a c t o r s t u d i e d were l i g h t i n t e n s i t y , t empera ture , and humidity. There were 24 combinat ions o f t he se . Degradation r a t e s were measured and are being compared wi th ' those found f o r outdoor exposure.

The indoor tests have been concluded and t h e outdoor tests a r e proceeding a s planned. One mode of d e t e r i o r a t i o n is a p rog re s s ive yel lowing of t h e encapsulan t f i l m s due t o photochemical r e a c t i o n s nea r t h e s u r f a c e . This change i n o p t i c a l t r ansmi t t ance is p r e c i s e l y measurable and t h e r e f o r e e s p e c i a l l y u s e f u l f o r mathematical modeling. Other f a i l u r e modes o f polymeric m a t e r i a l s observed included l o s s o f c l a r i t y , formation o f s u r f a c e carbonyl groups by ox ida t ion , l o s s o f t e n s i l e p r o p e r t i e s , and lowering of t h e g l a s s t r a n s i t i o n tempera ture . Mois ture- re la ted f a i l u r e s o f t h e s o l a r c e l l s themselves a r e now being analyzed. So f a r , t h e s e c e l l f a i l u r e s have been confined t o t h e a c c e l e r a t e d test .

S t a t i s t i c a l a n a l y s i s o f t h e r e s u l t s e v e n t u a l l y w i l l permit t h e development of a p r e d i c t i v e model f o r t h e i n h e r e n t w e a t h e r a b i l i t y o f encapsu lan t s . E f f e c t s o f complex c o n d i t i o n s , such a s r a p i d temperature changes, w i l l be superimposed on t h e b a s e l i n e e s t i m a t e du r ing t h e follow-up program. The con t inu ing abbrev ia ted t e s t i n g program, i nvo lv ing de t e rmina t ion o f s ea sona l model equa t ion parameters , is a necessary complement t o a c c e l e r a t e d t e s t i n g i n t h e methodology.

The Uiiivcrocll Tes t SpecJ,mens"(UT3s) showed unly ''sI&$it reduction (ave rage 4%) i n s o l a r c e l l power ou tput a f t e r 150 days o f outdoor exposure, i nc lud ing exposure on t h e EMMA and EMMAQUA sun l igh t - concen t r a to r s . I n t h e a c c e l e r a t e d test a t cont inuous high humidi ty , mo i s tu re - r e l a t ed deg rada t ion of some c e l l s was observed. F a i l u r e a n a l y s i s is i n p rog re s s .

The yel lowing o f Lexan f i l m was a t t r i b u t e d t o l i g h t a t 290-300 nanometers. The e f f e c t was g r e a t l y a c c e l e r a t e d by Py rex - f i l t e r ed xenon l i g h t . A s expec ted , I

t h e yel lowing r a t e dropped with age o f t h e lamp. T h i s e f f e c t was due t o t h e s o l a r i z a t i o n of t h e lamp envelope and/or f i l t e r . On t h e o t h e r hand, t h e yel lowing of po lys ty rene f i lm was due t o l i g h t o f h igher wavelengths (319 nanometers accord ing t o t he l i t e r a t u r e ) . Consequently, t h e yel lowing

rate i n t h i s c a s e was u n a f f e c t e d by lamp a g i n g . Yellowness of t h e f i l m r e p r e s e n t s a d e c r e a s e i n t h e t r a n s m i t t a n c e o n l y f o r v i o l e t l i g h t . It h a s n e g l i g i b l e e f f e c t on s o l a r c e l l performance. T h i s i s because t h e c e l l h a s a low r e s p o n s e a t t h e lower ( v i o l e t ) end o f t h e v i s i b l e spec t rum.

Because t r a n s m i t t a n c e a t 360 nanometers c a n be measured q u i c k l y , n o n d e s t r u c t i v e l y , and p r e c i s e l y , i t h a s been g i v e n most o f t h e a t t e n t i o n i n t h e development o f model e q u a t i o n s . T h i s p r o p e r t y i s n o t i t se l f c r i t i c a l t o c e l l pe r fo rmance , b u t i t might be ' c o r r e l a t e d w i t h a more s i g n i f i c a n t p r o p e r t y such as t e n s i l e s t r e n g t h . However, t h i s c o r r e l a t i o n must be made a d v i s e d l y . For example, under xenon l i g h t t h e ye l lowing r a t e was u n u s u a l l y r a p i d compared w i t h t h e r a t e o f c h a i n s c i s s i o n ( t e n s i l e

. . . . . l o s s ) . . . . . . . . . . . . . . . . . . . . . . . . . . . . , . . . . . . . :. . , . . . . . . . . . . . . . . . .

Other f i l m p r o p e r t i e s s t u d i e d were t e n s i l e s t r e n g t h and e l o n g a t i o n , ''.' " ' ' : ' '

c a r b o n y l f o r m a t i o n by a t t e n u a t e d t o t a l r e f l e c t a n c e - - i n f r a r e d , t r a n s m i t t a n c e o f 600 nanomete r s , g l a s s t r a n s i t i o n t e m p e r a t u r e by t h e r m a l mechanical a n a l y s i s ( o r d i f f e r e n t i a l scann ing c a l o r i m e t r y ) , and t h e r m a l s t a b i l i t y by t h e r m a l g r a v i m e t r i c a n a l y s i s . A s t u d y o f a s e r i e s o f weathered p o l y s t y r e n e f i l m s by e l e c t r o n s u r f a c e chemica l a n a l y s i s i s pending.

Proposed a b b r e v i a t e d t e s t i n g methodology i n c l u d e s ou tdoor exposures b e g i n n i n g on t h e s u m e r and w i n t e r s o l s t i c e s t o g e t s e a s o n a l p a r a m e t e r s f o r model e q u a t i o n s . A much h i g h e r r a t e o f d e g r a d a t i o n ( as judged by t r a n s m i t t a n c e a t 360 nanometers) was obse rved f o r Lexan when exposure began e a r l y i n September t h a n when it began on t h e w i n t e r s o l s t i c e ' (December 22). Model e q u a t i o n s w i l l be d i s c u s s e d a t l e n g t h i n t h e , .

f i n a l r e p o r t . No g e n e r a l c o n c l u s i o n s o r recommendations a r e a p p r o p r i a t e a t t h e p r e s e n t t i m e .

c . Electrostaticallv-Bonded I n t e g r a l Glass Covers--Simulation P h v s i c s . T h i s is a program t o deve lop i n t e g r a l g l a s s e n c a p s u l a t i o n f o r t e r r e s t r i a l s o l a r c e l l s , u s i n g e l e c t r o s t a t i c bonding. The f e a s i b i l i t y of t h i s t e c h n i q u e h a s been shown and f u n c t i o n a l d e m o n s t r a t i o n modules have been d e l i v e r e d t o JPL f o r t e s t i n g .

E l e c t r o s t a t i c bonding is a p r o c e s s th rough which a v a r i e t y o f d i s s i m i l a r m a t e r i a l s may be permanent ly j o i n e d w i t h o u t u s e o f a d h e s i v e s . With e l e v a t e d t e m p e r a t u r e t o produce i o n i c c o n d u c t i v i t y and a n e x t e r n a l l y a p p l i e d e l e c t r i c f i e l d t o d r i v e t h e mobi le i o n s , i r r e v e r s i b l e chemica l hnnds a r e formed a t the i n t e r f a c e of the piecea being . jo'ined. The p r o c e s s i s a p p l i c a b l e t o j o i n i n g b a r e s o l a r c e l l s o r t h o s e w i t h a v a r i e t y of antireflective c o a t i n g s t o g l a s s and t o j o i n i n g alass t o g l a s s w i t h t h e a i d o f i n o r g a n i c i n t e r f a c e l a y e r s . C o m p a t i b i l i t y of t h e p r o c e s s w i t h s o l a r c e l l s and w i t h a s s o c i a t e d a r r a y h a r d k r e h a s been f u l l y demons t ra ted . Developmental modules have shown no d e g r a d a t i o n o f s o l a r c e l l performance caused by e l e c t r o s t a t i c bonding.

By t h e end o f t h e p r e v i o u s q u a r t e r , f u n c t i o n i n g bonded s o l a r c e l l modules had been f a b r i c a t e d f o r t h e first time. P r o c e s s o p t i m i z a t i o n was be ing conducted i n p r e p a r a t i o n f o r f a b r i c a t i o n o f d e l i v e r a b l e demon- s t r a t i o n modules of t h e first t y p e . These s i n g l e . g l a s s s h e e t (Type 1 )

modules have been d e l i v e r e d and are undergoing tests a t JPL. Two more module t ypes (Types I1 and 111) a r e t o be produced a s p a r t o f t h e c u r r e n t e f f o r t . Both of t h e s e des igns w i l l provide f r o n t and back g l a s s encapsu- l a t i o n . Development o f both s e r i e s is n e a r l y completed. S i n g l e c e l l p ro to types have demonstrated most o f t h e des ign f e a t u r e s t o be i nco rpo ra t ed i n t o t h e s e modules. F a b r i c a t i o n of both t ypes should begin i n t h e n e a r . f u t u r e .

E f f o r t s o f t h e l a s t 3 months have inc luded:

( 1 ) Bonding of meta l f o i l s with a p p l i c a t i o n t o module ou tput t e r m i n a l s and c e l l i n t e r connec t ion .

( 2 ) Major deforniat ion bonding with evaporated f i l m m e t a l l i z a t i o n .

( 3 ) Bonding t o s i lk -screened in t e r connec t ion p a t t e r n s app l i ed t o g l a s s .

( 4 ) Hot p re s s ing o f g l a s s t o produce major deformation a s would be used i n preshaped g l a s s forms.

( 5 ) Bonding t o ground g l a s s s u r f a c e s .

( 6 ) P r e p a r a t i o n of bonded evaporated f i l m and s i lk -screened l a p shea r t e s t samples; e v a l u a t i o n o f shea r s t r e n g t h t e s t r e s u l t s .

( 7 ) Del ivery o f t h e f i r s t s e r i e s o f demons t ra t ion modules produced with e l e c t r o s t a t i c bonding.

( 8 ) Development o f module c o n f i g u r a t i o n s t o be f a b r i c a t e d as pare 4t' t h i s program.

d . Polvmer P r o ~ e r t i e s and Aninn--S~rinnborn Labora to r i e s . The g o a l of t h e program is t o develop and test m a t e r i a l s and encapsu la t i on o r c o a t i n g p roces se s s u i t a b l e f o r t h e p r o t e c t i o n o f s o l a r c e l l s . t o p rov ide a minimum 20-year s e r v i c e l i f e i n a t e r r e s t r i a l cnvironment. The work is being conducted a t Spr ingborn ' s f a c i l i t i e s i n E n f i e l d , Coarlect icut , wi th c e l l performance being eva lua ted by S o l a r Power Cor- p o r a t i o n of B r a i n t r e e , Massachuse t t s , under subcon t r ac t . The o v e r a l l program is s t r u c t u r e d t o i nc lude four o t h e r t e c h n i c a l endeavors: c o s t a n a l y s i s , s e l e c t i o n of p r imers and enhancement o f adhes ion , upgrading u l t r a v i o l e t s t a b i l i t y , and process ing r e p a i r s t u d i e s .

E f f o r t s du r ing t h e q u a r t e r involved t h e fo l lowing s t u d i e s :

( 1 ) The i r ic lus ion of 24 p o t e n t i a l l y u s e f u i encapsulan t m a t e r i a l s i n t o a program of acce l e r a t ed . ag.ing and e v a l u a t i o n .

( 2 ) Tabula t ion and c o r r e l a t i o n o f t h e changes i n o p t i c a l c h a r a c t e r i s t i c s a f t e r 120 days o f a c c e l e r a t e d ag ing .

( 3 ) T a b u l a t i o n and c o r r e l a t i o n o f c h a n g e s . i n . m e c h a n i c a 1 ' . . . .

p r o p e r t i e s . . . af ter 120 d a y s o f a c c e l e r a t e d . a g i n g . . . . . . . . . . . . . . . . . . . .

( 4 ) Measurement o f t h e e f f e c t s o f 6 :months. . o f sail a c c u m u l a t i o n ;

( 5 ) C o n t i n u a t i o n of an adhes ion s t u d y i n v o l v i n g t h e s c r e e n i n g o f commercia l ly a v a i l a b l e p r i m e r s , a d h e s i v e s , and p r o c e s s e s t o bond c a n d i d a t e e n c a p s u l a n t m a t e r i a l s t o s o l a r c e l l s and s u b s t r a t e s . " < ....

. . .* . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . , . (6.) E v a l u a t i o n o f fungus a t t a c k on c a n d i d a t e materials. . . " . .

. . . . . . . . . .

......... ..., : . . . . . . . _ . . . . . . . . . . . . . . . . . . . . . . ( 7 ) C o n s i d e r a t i o n s o f p r o c e s s i n g and d e s i g n p a r a m e t e r s . , .. . . . . . . . . . . . I . . . . . . . . . . . . . . . . . . ' . . . . . . . . . 4. , ,

. . . . . . . . : . . . . : : ' . . . . . . . . . . . . . . , . . . . _ . ,

. . , . . . . . . . . ..< . . . . . .. ,.. ..... -. . . . . . . . . . . . . . . . . . . _ _ . . . a . . . . . . . . . . . . , . . . . . . (8 ) P r e p a r a t i o n o f t e s t modules (mini-modules) by S o l a r . Power . , ' . . , . . ' -

:.::.: . . . . . . . . . . . . . . . . . . ; . . . . . " . . . ......... .......... :,...:s.i..::....::I ,.. .. :i.-j... .I::; . . . . C o r p o r a t i o n . . .... .... . . . . . . ..1, :... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .; ..; . - . <;. ....-... . . . . . . . . . .:. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . , ......... :.. . . - . The r e s u l t s o f o p t i c a l t e s t i n g o v e r t h e v i s i b l e r a n g e a f t e r t h e ...................... . . . . . . . . . . . . . . . . . . 120-day exposure p e r i o d i n d i c a t e t h a t a l l m a t e r i a l s d e c r e a s e i,n t r a n s - ., ,.;::, . . .., .:. m i s s i o n from t h e i r c o n t r o l v a l u e s . The most d r a m a t i c changes can , be:: .i' :..: ::...

. . . . . . . . . . . s e e n i n t h e most s e v e r e c o n d i t i o n s (Weather-Ometer, ~ ~ - 4 / 1 0 0 ~ ~ ~ ) . ~ ~ . ' a r ; ' a

. . d e g r a d a t i o n t o t h e p o i n t o f d i s i n t e g r a t i o n was obse rved i n ~ e d l & ,:" C-4 .:.-- \ ,

p o l y c a r b o n a t e , and T e n i t e 479. The wors t d e c r e a s e s i n t r a n s m i s s i o n 'were bound f o r Udel 1700 ( p o l y a r y l s u l f o n e ) , T e d l a r , S y l g a r d 184, and RTV 615 after Weather-Ometer exposure . The l e a s t a f f e c t e d were PFA, CR-39, P l e x i g l a s DR-61K, and P l e x i g l a s V-811.

~ r a n s m i s s i o n s measured o v e r t h e u l t r a v i o l e t r a n g e ( a f t e r 120 days e x p o s u r e ) showed g e n e r a l l y d e c r e a s i n g v a l u e s w i t h no p a r t i c u l a r c o n n e c t i o n t o t h e t y p e o f exposure c o n d i t i o n . Uniform i n c r e a s e s i n u l t r a v i o l e t t r a n s m i s s i o n s were found f o r Kynar 460 and T e n i t e 479.

An ~ ~ - 4 / 5 5 ' ~ c o n d i t i o n was set up w i t h p r o v i s i o n s f o r m a i n t a i n i n g 70% relative. h u m i d i t y , t h e purpose be ing t o f u r t h e r 'exiimine h y d r o l y t i c . .

i n s t a b i l i t i e s . .No. g r e a t d i f f e r e n c e s . w e r e obse rved . between t h e s e r e s u l t s and those o f t h c Wcather--Ometer, except i n t.he cases nf Tldel 1700, RTV 61 5 , and S y l g a r d 184, which appeared t o ' b e ' less s e v e r e l y a f f e c t e d . The o v e r a l l t r e n d was t o d e c r e a s e i n t r a n s m i s s i o n v a l u e , a s u s u a l .

U l t r a v i o l e t t r a n s m i s s i o n s o f t h e RS-4/55OC, 70% RH e x p o s u r e appeared t o d e c r e a s e t o a c e r t a i n v a l u e a f t e r 30 d a y s and change l i t t l e w i t h i n c r e a s i n g time. T e d l a r showed t h e g r e a t e s t l o s s , r e t a i n i n g o n l y 7% o f c o n t r o l measurement.

, A t a b l e o f " M a t e r i a l Transmiss ion Indexn v a l u e s was compiled by m u l t i p l y i n g t h e c o n t r o l v a l u e ($ ) by t h e e x p o s u r e v a l u e (%) f o r t h r e e c o n d i t i o n s ; ~ ~ - 4 / 5 5 O c , Weather-Ometer and RS-4/55'~, 70% R H . The v a l u e s a r e i n d i c a t i v e o f o v e r a l l m a t e r i a l performance and s u i t a b i l i t y . The b e s t performance is found f o r CR-39, PFA, and bo th P l e x i g l a s f o r m u l a s . Again, no g r e a t d i f f e r e n c e was n o t i c e d between Weather-Ometer and RS-4 h i g h humid i t y exposures .

R e s u l t s o f h a r d n e s s (ASTM D-2240) e v a l u a t i o n s d e m o n s t r a t e t h e t endency f o r a l l m a t e r i a l s t o d e c r e a s e i n s u r f a c e h a r d n e s s w i t h t ime

i n a i l cond i t i ons . The on ly excep t ions . are t h e two s i , l i c o n e rubbe r s , Sy lgard 1 84 and ' RTV 6 1 5, which s t e a d i l y , i n c r e a s e i n hardness .

Mechanical p r o p e r t i e d were determined. by. conve.nti.ona1 I n s t r o n . . . . . . . t e s t i n g ; va lues f o r t e n s i l e s t r e n g t h and elonga. t ion were obta ined a f t e r . .

ag ing 30, 60, and 120 days. The r e s u l t s f o r t e n s i l e s t r e n g t h . were v a r i a b l e bu t showed t endenc i e s t o i n c r e a s e i n most c a s e s . Some m a t e r i a l s appeared t o be una f f ec t ed . Gene ra l l y , t h e v a r i a t i o n s were more pronounced with i n c r e a s i n g s e v e r i t y o f cond i t i on .

Elongat ion a t break appears t o be t h e most s e n s i t i v e i n d i c a t i o n o f polymer deg rada t ion , showing t h e widest changes i n v a l u e s as aging proceeds. I n c r e a s e s i n e longa t ion were found f o r some m a t e r i a l s , (Kynar, Ha la r , PFA, T e f z e l ) i n c e r t a i n c o n d i t i o n s bu t i n some i n s t a n c e s (h igh t empera tu re ) a dec rease was found. Fluorocarbnns tended t o gain i n t h i s p rope r ty and most o t h e r m a t e r i a l s l o s t . Again, t h e most d ramat ic v a r i a t i o n s were no t i ced i n t he most s eve re c o n d i t i o n s .

Because- o f poor o v e r a l l performance and p o t e n t i a l t h e fo l lowing m a t e r i a l s have been dropped from the program and w i l l undergo no f u r t h e r e v a l u a t i o n :

Resin Reason f o r Re i e c t i o n

T e f z e l 280

Udel 1.700

CR-39

( 1 ) Low o p t i c a l t r ansmis s ion .

( 2 ) Poor o p t i c a l s t a b i l i t y .

( 3 ) U l t r a v i o l e t deg rada t ion .

( 4 ) Foor p r o c e u u a b i l i t y ,

( 5 ) High coot .

( 1 ) Very poor mechanical s t a b i l i t y .

( 2 ) Low flow tempera ture .

( 3 ) High c o s t . . . . . .

( 4 ) . Very poor o p t i c a l s t a b i l i t y . . . . .

(5) Very pool- mechanicai s t a b i l i t y .

( 1 ) Decay o f t e n s i l e . s t r e n g t h ,

( 2 ) Development o f f r a c t u r e s .

( 3 ) Completely unprocessab le .

S o i l accumulat ion specimens a l l l o s t a smal l percentage o f t h e o r i g i n a l o p t i c a l t r ansmis s ion (except f o r Udel 1700 which degrades) but r e t a i n e d r e l a t i v e l y c l ean s u r f a c e s . RTV 615, Sylgard 184, and

Viton AHV were t h e o n l y materials t h a t , w e r e . s e v e r e l y a f f e c t e d :and. w i l l . .

have t o be used o u t d o o r s w i t h p r o t e c t i v e ( h i g h modulus) coat ings . ' . . . . . .

-Fungus t e s t i n g demonstra ted t h a t most o f t h e , r e s i n s s u p p o r t e d . -; .

o n l y l i g h t growth and were g e n e r a l l y u n a f f e c t e d . . . O n l y RTV 615 and . . . .

T e n i t e 479 showed p e r s i s t e n t s p l o t c h e s o f fungus and s u r f a c e a t t a c k .

e . I o n Pla t im P r o c e s s and Testinn--Endurex. Work under t h e Endurex c o n t r a c t began d u r i n g t h i s q u a r t e r . Endurex h a s developed a h igh-energy- leve l i o n p l a t i n g p r o c e s s which h a s proven t o be a c o s t - e f f e c t i v e means o f a p p l y i n g c o a t i n g s t o bo th p l a s t i c and m e t a l l i c p a r t s . The e n c a p s u l a t i o n o f s i l i c o n s o l a r c e l l s a p p e a r s t o be a c h i e v a b l e by means of t h e i o n ' p l a t i n g p r o c e s s . Both c o s t - e f f e c t i v e n e s s and f u n c t i o n a l improvement are a n t i c i p a t e d .

S i n c e v i r t u a l l y any m a t e r i a l can be d e p o s i t e d , t h e major o b j e c t i v e o f t h i s e f f o r t w i l l be t h e d e t e r m i n a t i o n o f which o f s e v e r a l c a n d i d a t e m a t e r i a l s i s optimum f o r t h i s a p p l i c a t i o n . Concur ren t w i t h t h e material s e l e c t i o n w i l l be a d e t e r m i n a t i o n o f i ts r e s p o n s e t o v a r i a t i o n o f param- e t e r s o f t h e i o n p l a t i n g p r o c e s s . B i a s v o l t a g e , d e p o s i t i o n r a t e , and chamber' p r e s s u r e w i l l have s i g n i f i c a n t e f f e c t s upon . compos i t ion h a r d n e s s and growth morphology. These w i l l , i n t u r n , a f f e c t such impor- t a n t c e l l p a r a m e t e r s as a c t i v e band w i d t h , a n t i r e f l e c t i o n , e l e c t r i c a l c o n d u c t i o n , a b r a s i o n r e s i s t a n c e , t h e r m a l c y c l i n g , and env i ronmenta l

. . s t a b i l i t y . These e f f e c t s w i l l be measured and n o t e d .

f . " JPL In-House A c t i v i t i e s . B a s i c s t u d i e s o f a d h e s i v e bonding from a - f r a c t u r e mechanics s t a n d p o i n t a r e b e i n g c o n t i n u e d by D r . W . Knauss o f Cal t e c h .

Ongoing in-house a c t i v i t i e s a r e c o n c e n t r a t e d on f a i l u r e a n a l y s e s o f modules from t h e 46 kW (Block 1 ) proc.urement, a l i m i t e d amount o f .. . . _ . .. .

materials t e s t i n g t o s u p p o r t c o r r e c t i v e a c t i o n o r d e s i g n change . . %

s e c ~ m e n d a t i o n s , and f i e l d r e p a i r s .

SECTION V

PRODUCTION PROCESS AND EQUIPMENT AREA . . . . . . . . - .

The o v e r a l l o b j e c t i v e o f t h e P r o d u c t i o n P r o c e s s and Equipment Area i s t o d e v e l o p t h e t e c h n o l o g y n e c e s s a r y t o a c h i e v e h igh-volume, l ow-cos t p r o d u c t i o n o f s i l i c o n s o l a r a r r a y modu le s . The g o a l o f t h i s t a s k i.s t o . . d e v e l o p . t h e c a p a b i l i t y t o f a b r i c a t e s o l ' a r a r r a y m o d u l e s o f 10% o r b e t t e r c o n v e r s i o n e f f i c i e n c y a.t a s e l l i n g p r i c e o f $ 0 . 5 0 / w a t t o r . .les.s:,::.a.t . . . ,a,, rate: , o f . 500. megawa t t s p e r .year , with: . a 2 0 r y e a r o p e r a t i n g l i f e . Many .o ' f . ' t he"dec i s ions t h a t mus t b e made d u r i n g the t a s k . e f f o r t canrlvL be illadt i n d e p e n d e n t l y and w i l l rcsi.11 t. f m m " t r a d e - o f f s w i t h o t h e r ' ..

d e c i s i o n s t h a t a r e made b o t h w i t h i n t h i s t a s k and i n c o n j u n c t i o n w i t h , , . .

o t h e r t a s k s o f t h e p r o j e c t .

A . TECHNICAL BACKGROUND

The m a n u f a c t u r e o f s o l a r c e l l s and a r r a y s i s p r e s e n t l y .accompl ished u n d e r t h e judgment and d . i r e c t c o n t r o l o f i n d i v i d u a l o p e r a t o r s . Because o f t h e l i m i t e d q u a n t i t i e s o f s o l a r c e l l s and a r r a y s produced' , . ... c o s t s

. .. are h i g h . Automated s o l a r c e l l p r o d u c t i o n , a s p r o p o s e d , w i l l l e a d

. . . . . . . . . . . ..

t o s i g n i f i c a n t r e d u c t i o n s i n m a n u f a c t u r i n g c o s t . I n a d d i t i o n , a u t o m a t i o n . . .. . , . . . wi~l:.:r .esqTt:; ' : ln . .... u n i f o r m i t y o f c e l l p r o c e s s i n g w i t h a r e d u c t i o n o f waste :a u.& .:to'. 'r'.6' jc<ted product .

B. ORGANIZATION A N D COORDINATION OF' THE PRODUCTION PROCESS A N D EQUIPMENT AREA EFFORT

The P r o d u c t i o n P r o c e s s and Equipment Area e f f o r t i s d i v i d e d i n t o f i v e p h a s e s , o c c u r r i n g o v e r a 10-year p e r i o d o f time ( F i g u r e 5-1 ) . The p h a s e s are

11. P r o c e s s deve lopmen t . . ,

111. F a ~ i l ~ t y a n d e q u i p m e n t d e s i g n . . ....

IV.: - . E x p e r i m e n t a l p l a n t c o n s t r u c t i o n . . . .

V. C o n v e r s i o n t o mass p r o d u c t i o n p l a n t ( b y 1986) . . , .. . .

. .

. . . Phase I , which was i n i t i a t e d i n F e b r u a r y 1976, h a s ' t h e s e s p e c i f i c . , . , ,, o b j e c t i v e s :

( 1 ) To i d e n t i f y t h e r e q u i r e m e n t s f o r e c o n o m i c a l m a n u f a c t u r i n g p r o c e s s e s and f a c i l i t i e s .

( 2 ) To a s s e s s t h e t e c h n o l o g y c u r r e n t l y u sed i n t h e m a n u f a c t u r e and a s s e m b l y p r o c e s s e s t h a t c o u l d b e a p p l i e d t o s o l a r a r r a y s .

CY 76 CY n CY 78 1 I C Y U 1 CY 84 CY 85 CY 86

4 *I V v v 'PHASE i : TECHNOLOGY PHASE 11: DEFINE, .l.EcT, AND PHASE I 11 PHASE Iv PHASE v

ASSESSMENT DEMONSTRATE MANUFACTURING TECHNOLOGY EXPERIMENTAL MASS PRODUC~ION PROCESSES READY PLANT I N PLANT READY FOR

OPERATION OPERATION

ANALYZE EXISTING TECHNOLOGIES .

IDENTIFY COSTS OF PROCESSING AND TESTING STEPS

DETERMINE PRIORIIY FOR PROCESS DEVELOPMENT

8 IDENTIFY AREAS WERE NEW TECHNOLOGY MUST BE DEVELOPED

DEVELOP COST-EFFECTIVE ' DEVELOP PROCESSES AND APPROACHES AND IDENTWY DEMONSTRATE TECHNOLOGY OPTIONS AVAILABLE READINESS

8 IDENTIFY COST/ i IDENTIFY THE MANUFACTURING OBSTACLES MANUFACTURING EQUIPMENT

AND FACILITIES REn2U.RED

8 CONCEPTUAL SOLUTIONS - TO THESE OBSTACLES UPDATE CONCEPTWL DESIGN

DEVELCPED I N PHP.SE I ' . . . . . . DEMONSTFATE COST- . . I EFFECTIVENESS OF SOLUTIONC_ UPDATE THE COST ANALYSIS . .

. . . . . . . . .;. . . DEFINE THE CONCEPTUAL . ..

. . . . APPROACH1 THAT APPEARS , . ... . .. MOST COSI-EFFECTIVE FOF .

% . . FABRICATION/ASSEMBLY 0- SOLAR CELVARRAY M O D g E S . . . * .

. .

F i g . x e 5-1. ~ r o d u c t - l o r P r o c e s s and Equipment Area S c h e d u l e

( 3 ) To d e t e r m i n e t h e l e v e l o f t e c h n o l o g y r e a d i n e s s t o a c h i e v e high-volume, low-cost p r o d u c t i o n . , -

( 4 ) To propose p r o c e s s e s f o r development . .. . . ., , . I ; . - . . . . . . . , . . .

. . . .

C. PRODUCTION PROCESS A N D EQUIPMENT AREA CONTRACTS

Under Phase I c o n t r a c t s , t h r e e c o n t r a c t o r s ( M o t o r o l a , R C A , and Texas I n s t r u m e n t s ) are p e r f o h i n g p a r a l l e l e f f o r t s ( T a b l e 5-1 1 . The

. .. , t h r e e - c o n t r a c t o r p a r a l l e l - e f f o r t ' p h i l o s o p h y was s e l e c t e d t o o b t a i n . . . t h e - b r o a d e s t p o s s i b l e view o f recommendations and c o n c l u s i o n s upon

. . . . . which t o b a s e t h e c o n t r a c t u a l e f f o r t s o f Phase I1 ( F i g u r e 5-1) . Durin'g., ' . . . . . . . ' , ' - Phase I , t h e s e c o n t r a c t o r s a r e d e f i n i n g t h e r e q u i r e m e n t s f o r a n automated .. . . . . .:... . . , . s o l a r c e l l manufac tu r ing sequence by e v a l u a t i n g p r o c e s s e s now used

. :. .:. .:. . . . :.:.bg:, t h e semiconductor i n d u s t r y and t h e ways i n which t h e s e p r o c e s s e s . . .. ... , . ., . . . . .

. - " ' : :can. .be.- m o d i f i e d / s e l e c t e d f o r high-volume, low-cost p r o d u c t i o n o f s o l a r .,., .i'i. . . . . .. . . . . . .: . . . c e l l modules. Cost a n a l y s e s a r e b e i n g conducted t o p r o v i d e economic . ... . .

... . g u i d e l i n e s t o m a i n t a i n a n o v e r a l l view o f LSSA P r o j e c t o b j e c t i v e s . . ..

. .

The Phase I c o n t r a c t o r s n e a r l y completed t h e t echno logy a s s e s s m e n t : . . . . .

. . . a c . t i v i t i e s d u r i n g t h e 0 c t . - ~ e c . 1976 q u a r t e r Under: t h e b a s i c c o n t r a c t , ,,, . i t . - ' w a s . .planned t h a t t h e s e s t u d i e s would conc lude i n ' January ; however, . .

. . s e l e c t e d c o n t r a c t s a r e b e i n g ex tended a p p r o x i m a t e l y 6 months t o pursue " a n a l y s i s o f key p r o c e s s v a r i a b l e s .

S e v e r a l u n s o l i c i t e d p r o p o s a l s were r e c e i v e d f o r advanced s o l a r p a n e l d e s i g n s . C o n t r a c t s a r e be'ing n e g o t i a t e d f o r most o f them. These i n c l u d e unique c e l l s h a p e s , c o n t a c t i n g methods , e n c a p s u l a t i o n t e c h n i q u e s , and v a r i o u s means o f a c h i e v i n g h i g h e r e l e c t r i c a l e f f i c i e n c i e s .

Two c o n t r a c t s were l e t f o r advanced pane l d e s i g n s a ~ ~ ~ f a l l o u t ' ~ from t h e 130 kW pane l procurement. One o f t h e s e , g i v e n t o Lockheed M i s s i l e s and Space Company, i s f o r i n v e s t i g a t i o n o f , a , h i g h t r a n s m i s s i o n g l a s s s t r u c t u r e . The o t h e r , w i t h Xerox E l e c t r o - O p t i c a l Systems, i s for study of a pane l f a b r i c a t e d o f s o l a r c e l l s w i t h h o l e s i n t h e c e n t e r s which accomodate f a s t e n e r s s e r v i n g b o t h mechan ica l and e l e c t r i c a l f u n c t i u n u .

T a b l e 5-1. P r o d u c t i o n P r o c e s s and Equipment Area C o n t r a c t o r s

C o n t r a c t o r Type C o n t r a c t Technology Area

Motorola Phase I Manufac tu r ing p r o c e s s e s Phoen ix , Arizona a s s e s s m e n t (JPL C o n t r a c t No. 954363)

RCA Phase I M a n u f a c t u r i n g - p r o c e s s e s P r i n o e t o n , New J e r s e y a s s e s s m e n t (JPL C o n t r a c t No. 954352)

Texas I n s t r u m e n t s Phase I Manufac tu r ing p r o c e s s e s .. D a l l a s , .Texas a s s e s s m e n t

(JPL . C o n t r a c t No. 954405)

Texas I n s t r u m e n t s Suppor t ' L a r g e a r e a C z o c h r a l s k i D a l l a s ; Texas s i l i c o n i n g o t growth (JPL C o n t r a c t .No. 954475) and w a f e r i n g improvements

S o l a r e x R o c k v i l l e , Maryland (JPL C o n t r a c t No. 954606)

P r o c e s s i n q e n e r g y s t u d y

D. PRUDUCTION PROCESS AND EQUIPMENT AREA TECHNICAL ACTIVITIES

1. ' Manufac tu r ing ~ r o c e s s e s Assessment -- Motoro la , R C A , and Texas I n s t r u m e n t s .

Phase I a s s e s s m e n t o f s t a t e - o f - t h e - a r t s i l i c o n s o l a r a r r a y t e c h - nology was f o r m a l l y conc luded d u r i n g this q u a r t e r . The Task's predominant a c t i v i t y d u r i n g t h e q u a r t e r was t o beg in t o m a n i p u l a t e t h e d a t a r e s u l t i n g from t h o s e s t u d i e s i n t o i n c r e a s i n g l y p r a c t i c a l forms. Much o f t h i s w i l l , i n t u r n , form a b a s e f o r t e c h n o l o g y and i n d u s t r y development a c t i v i t i e s when Phase I1 procurements come i n t o e f f e c t .

A s was s e t f o r t h a t t h e 5 t h P r o j e c t I n t e g r a t i o n Meeting i n January; ".. '

Phase I produced some key u n d e r s t a n d i n g s r e l a t e d t o t h e c o s t o f manufac tu r ing p r o c e s s e s . One o f t h e most i m p o r t a n t was t h a t , because o f a u t o m a t i o n , l a b o r c o s t s i n s o l a r module manufac tu r ing w i l l b e minor . It was found t h a t t h e major p r i c e d r i v e r w i l l be t h e c o s t o f . m a t e r i a l s and s u p p l i e s consumed d u r i n g f a b r i c a t i o n . T h i s p u t s t h e f o c u s on t h e c o s t - e f f e c t i v e n e s s o f p r o c e s s e s and t h e s e n s i t i v i t y o f t h o s e p r o c e s s e s t o t o l e r a n c e v a r i a b l e s i n commercial p r o d u c t i o n .

It was t h e s e two f a c t o r s t h a t were a d d r e s s e d i n t h e 6-month add-on p rocurements i n i t i a t e d d u r i n g t h i s q u a r t e r . Motoro la , R C A , and Texas I n s t r u m e n t s were c o n t r a c t e d t o a s s e s s t h e c o s t e f f e c t o f m a n u f a c t u r i n g

t o l e r a n c e s r e g a r d i n g t h e d e c r e a s e d c e l l e f f i c i e n c y t h a t may r e s u l t ' . . . . . ,

from t h e t o l e r a n c e s . They w i l l t h e n recommend t h e most promis ing sequences . . . . . . .

. ' f o r p o t e n t i a l development . Allowance .was 'made f o r d i s c r . e t e p r o c e s s ..

e m p h a s i s , . s o t h a t s t e p s from t h e c a n d i d a t e sequences -may b e commingled' . . ..

t o form a f ine - tuned m a s t e r sequence o r sequences .

2. Large-Area C z o c h r a l s k i S i l i c o n I n g o t Growth and Wafering Improvements - Texas I n s t r u m e n t s

The purpose o f work under t h i s c o n t r a c t i s t o o p t i m i z e c u r r e n t proven semiconduc to r t e c h n i q u e s s o a s t o produce s i l i c o n w a f e r s i n t h e most c o s t - e f f e c t i v e manner. Accord ing ly , t e c h n i c a l a c t i v i t y h a s p r i m a r i l y c e n t e r e d on e s t a b l i s h i n g a c c e p t a b l e s i l i c o n c r y s t a l p u l l i n g and s l i c i n g r a t e s .

C r v s t a l P u l l i n g

Cont inu ing e x p e r i m e n t a t i o n a t Texas I n s t r u m e n t s showed t h a t a n averag,e growth r a t e . o f 12 cm/hr f o r 12-cm-dia. C z o c h r a l s k i c r y s t a l s c a n n o t be c o n s i s t e n t l y s u s t a i n e d , b u t t h a t 10 cm/hr c a n be . A t t h e 10-cm/hr growth r a t e , t h e program g o a l o f a n 80% y i e l d o f 12-cm-dia. c r y s t a l s from a 12-kg c h a r g e was d e m o n s t r a t e d . Modified m e l t r e p l e n i s h - ment t o o l i n g was completed a t Texas I n s t r u m e n t s and was i n s t a l l e d on a 12-kg p u l l e r . It was though t t h a t t h i s would a l l o w t h e s i l i c o n po ly t o be added from an a i r t i g h t f e e d sys tem and t h a t t h i s would r e d u c e t h e o x i d e problem t h a t had plagued p r e v i o u s m e l t r e p l e n i s h m e n t a t t e m p t s . However, m e l t r e p l e n i s h m e n t t e c h n i q u e s f o r growing t h r e e c r y s t a l s from one h e a t c y c l e were u n s u c c e s s f u l .

C r v s t a l S l i c i n q

Texas I n s t r u m e n t s a l s o began working on a new concep t f o r c u t t i n g i n g o t s on m u l t i b l a d e a b r a s i v e saws which c a l l e d f o r t h e i n g o t t o be ro ta ted d u r i n g c u t t i n g t o i n c r e a s e t h e speed o f t h e a b r a s i v e a c t i o n . Sawing e x p e r i m e n t s u s i n g diamond b l a d e s i n t h e m u l t i b l a d e saw and s p i n n i n g t h e i n g o t have r e s u l t e d i n c u t t i n g r a t e s approach ing 50 mm/hr.

3. P r o c e s s i n g Energy S tudy - S o l a r e x

During t h i s q u a r t e r , S o l a r e x began t o s t u d y t h e e n e r g y consumed d u r i n g s o l a r module manufac tu r ing . The e n t i r e sequence o f p r o c e s s e s i s b e i n g examined from t h i s p e r s p e c t i v e , s t a r t i n g w i t h t h e chemica l r e d u c t i o n o f s i l i c o n and f i n i s h i n g w i t h t h e f a b r i c a t e d module. The energy r e q u i r e m e n t s a r e b e i n g d e a l t w i t h i n r e g a r d t o "energy paybackl1 by r e l a t i n g t h e e n e r g y consumed d u r i n g manufac tu re t o t h e . e n e r g y e x p e c t e d t o be g e n e r a t e d d u r i n g t h e l i f e . o f t h e . s o l a r module.

SECTION V I

ENGINEERING AREA

A . FUTURE MODULE REQUIflEMENTS

During t h i s q u a r t e r , work on f u t u r e module r e q u i r e m e n t s c e n t e r e d on f i n a l i z i n g t h e d r a f t r e q u i r e m e n t f o r t h i r d g e n e r a t i o n l a r g e - s c a l e p r o d u c t i o n modules. T h i s r e q u i r e m e n t was o r i g i n a l l y s l a t e d f o r t h e 150-kk procurement and h a s been under development s i n c e e a r l y FY77. M o d i f i c a t i o n s t o p r e v i o u s r e q u i r e m e n t s t y p i f i e d by t h e Block 2 Large- S c a l e Procurement S p e c i f i c a t i o n , 5-342-1, Rev. B, were c o n s i d e r e d i n a r e a s which a d d r e s s t h e needs o f f u t u r e l a r g e r - s c a l e p h o t o v o l t a l c a p p l f - c a t i o n s . I n p a r t i c u l a r , t h e n e e d s f o r l o n g e r l i f e t i m e , i n c r e a s e d s t a n d a r d - i z a t i o n , c o m p a t i b i l i t y w i t h h i g h e r o p e r a t i n g v o l t a g e s , minimum i n s t a l l a t i o n c o s t s , and improved performance were c o n s i d e r e d .

. .

1. ~ l e c t r . i c a l Performance

Based on t h e a n a l y s i s r e p o r t e d d u r i n g t h e p r e v i o u s q u a r t e r , t o s e l e c t a s u i t a b l e module o u t p u t v o l t a g e w i t h r e s p e c t t o c h a r g i n g r e q u i r e m e n t s f o r l ead-ac id b a t t e r i e s , t h e module v o l t a q e a t S tandard O p e r a t i n g C o n d i t i o n s was s e l e c t e d a 15.0 Vdc. T h i s v a l u e makes p r o v i s i o n f o r . i n c l u s i o n o f a d i o d e i n small b a t t e r y - c h a r g i n g a p p l i c a t i o n s b u t i s a l s o compat ib le w i t h t h e u s e o f modules i n s e r i e s - c o n n e c t e d h iqher - o p e r a t i n g - v o l t a g e a p p l i c a t i o n s . A concern h a s been e x p r e s s e d t h a t l a r g e d i f f e r e n c e s i n t h e measured power o f i n d i v i d u a l modules i n c o r p o r a t e d i n s e r i e s s t r i n g s c o u l d reduce o v e r a l l system o u t p u t because o f mismatch l o s s e s . During t h e q u a r t e r , p r e l i m i n a r y a n a l y s e s o f t h e e f f e c t o f such l o s s e s were conduc ted . A s a r e s u l t , t h e a l l o w a b l e v a r i a n c e o f module o u t p u t power f o r a minimum a c c e p t a b l e module h a s been reduced

.. . . . . . t o 10% below t h e a v e r a g e module power. That is, Pmin = 90.0 pa,%.

2 . Module Interc~nnections/~erminations

Near-term p l a n n i n g f o r ERDA d e m o n s t r a t i o n s i n d i c a t e s t h a t modules w i l l be employed i n a p p l i c a t i o n s where o p e r a t i n g v o l t a g e s a r e a t l e a s t 250 Vac. Thus, i t i s i m p o r t a n t t h a t t h e modules b e e a s i l y c o n n e c t e d , when i n s t a l l e d , i n t o s e r i e s s t r i n g s . F u r t h e r , i t i s n e c e s s a r y t o r educe i n s t a l l a t i o n t i m e i n t h e f i e l d , and minimize t h e need f o r f i e l d - i n s t a l l e d in te r -module c a b l i n g . For f u t u r e module d e s i r n s , a n i n e x p e n s i v e quick- d i s c o n n e c t c o n n e c t o r p a i r has been proposed. By hard-mounting t h e c o n n e c t o r r e c e p t a c l e on t h e module n e a r one e d g e , and a t t h e o p p o s i t e edge znd t h e same end o f t h e module, p r o v i d i n g a s h o r t p i g t a i l c a b l e w i t h t h e mat ing p l u g , i t 2 s p o s s i b l e t o d i r e c t l y connec t modules t o g e t h e r i n t o s e r i e s s t r i n g s . A f u r t h e r advan tage t o t h e use o f t h e q u i c k d i s c o n n e c t i s t h a t p e r s o n n e l s a f e t y i s enhanced by n o t hav ing t o work w i t h exposed c o n t a c t s o r s t u d s . A number o f c o n n e c t o r t y p e s were a c t i v e l y i n v e s t i g a t e d a s d e s i g n c a n d i d a t e s d u r i n g t h e q u a r t e r . The b a s e l i n e c o n n e c t o r s e l e c t i o n is a two-contact c o n n e c t o r manufac tu red by I T T Cannon f o r u s e by t h e a u t o m o t i v e i n d u s t r y . T e s t e x p e r i e n c e w i t h t h i s c o n n e c t o r was o b t a i n e d

d u r i n g t h e q u a r t e r th rough a JPL test program, t h e r e s u l t s o f which were p u b l i s h e d i n LSSA Task Repor t 5101-20, and t h r o u g h t h e u s e o f t h e c o n n e c t o r on one o f t h e Block 2 modules.

3. Mechanical C o n f i g u r a t i o n ~erquirernen.ts

An a s s e s s m e n t o f a v a r i e t y o f p lanned a p p l i c a t i o n s , e x p e r i m e n t s , t e s t s , and d e m o n s t r a t i o n s i n t h e FY77-79 time frame and c o n c e p t u a l sys tem d e s i g n s t u d i e s have,shown a r e q u i r e m e n t f o r s t a n d a r d i z a t i o n o f module c o n f i g u r a t i o n s . P r e v i o u s LSSA procurements have r e q u i r e d t h a t modules o f any s i z e be c o n f i g u r e d w i t h i n a 46 i n c h by 46 i n c h s u b a r r a y . T h i s r e q u i r e m e n t h a s r e s u l t e d i n t h r e e t o e i g h t modules per. s u b a r r a y . Ubviously , t h e l a r g e r ' t h e number o f modules . i n a n a r r a y , t h e g r e a t e r t h e s y s t e m - r e l a t e d c o s t s f o r t r a n ~ p n r ~ a t i o n , handling, . . i n s t a l l a t i o n , and e l e c t r i c a l i n t e r c o n n e c t s .

To d e c r e a s e h a n d l i n g and i n s t a l l a t i o n c o s t s a s s o c i a t e d w i t h m u l t i - . :'.

k i l o w a t t p h o t o v o l t a i c i n s t a l l a t i o n s ' , i t h a s . been proposed t h a t a l l f .u tu re . ' modules have t h e same l e n g t h (48 i n c h e s ) and a uniform mounting h o l e s p a c i n g ( 4 7 i n c h e s between rows, wid th s p a c i n g i n i n c r e m e n t s o f 3/11 i n c h ) . ..

The wid th o f t h e module would be s e l e c t a b l e i n i n c r e m e n t s - o f 3/4 i n c h up t o a maximum o f 48 i n c h e s t o a l l o w t h e m a n u f a c t u r e r s f l e x i b i l i t y i n . .

c h o o s i n g c e l l s i z e s and packing schemes t o p r o v i d e . t h e r e q u i r e d v o l t a g e , - .

and improved pack ing f a c t o r . The 3/4 i n c h v a r i a b l e wid th p r o v i d e s i n t e r c h a n g e a b i l i t y o f m a n u f a c t u r e r ' s modules t h r o u g h t h e u s e o f s t a n d a r d prepunched s t e e l and aluminum f o r mounting modules i n t o a r r a y s .

*ro accommodate t h e 50 l b / f t 2 s t r u c t u r a l l o a d i n g r e q u i r e m e n t , a d e p t h of 2 i n c h e s below t h e mounting p l a n e i s a l lowed f o r s t i f f e n i n g r i b s o r o t h e r s t r u c t u r a l members. The module mounting i n t e r f a c e i s d e s i g n e d t o a l l o w f r o n t and back s i d e a c c e s s t o t h e a t t a c h m e n t f a s t e n e r s . I n t h e d e s i g n o f s p e c i f i c modules , e f f i o i e n t packing a l l o w s fo r mounting h o l e s o n l y a t t h e r e a r s i n c e t h e c e l l s c o v e r t h e e n t i r e 48 i n c h l e n g t h . I n t h i s c a s e , t h e mounting h o l e s may b e a c c e s s i b l e o n l y a t t h e r e a r i f t h e module i s c a p a b l e o f b e i n g a t t a c h e d from t h e f r o n t by c1.arnpi.n~ a t foup c o r n e r s . T h i s c o n f i g u r a t i o n i s t y p i c a l o f i n s t a l l a t i o n s on t h e r o o f of ' a r e s i d e n c e , where o n l y f r o n t s i d e a t t a c h m e n t is a v a i l a b l e .

4. Module E f f i c i e n c y Requirements

Recause o f t h e i m p n r t . ~ n e . e o f n~odult , e f f l c i c n c y to o v e i - a l l sys le~n a r e a - r e l a t e d c o s t s , i n c r e a s e d emphasis h a s been p l a c e d on p r o v i d i n g a s t a n d a r d method f o r s p e c i f y i n g , compar ing, and d i s c u s s i n g module e f f i c i e n c y . Module e f f i c3 .ency i s t h e module peak power o u t p u t a t a n i n s o l a t i o n l e v e l of 100 mh/cm2 and c e l l t e m p e r a t u r e e q u a l t o t h e Nominal O p e r a t i n g C e l l Temperature (NOCT), d i v i d e d by t h e i n s o l a t i o n l e v e l (100 mw/cm2) and t h e g r o s s module a r e a . * G r o s s modu1.e a r e a i s d e f i n e d a s t h e maximum o v e r a l l l e n g t h t i m e s t h e maximum o v e r a l l wid th .

*For a d i s c u s s i o n o f t h e d e f i n i t i o n o f t h e Nominal Opera t ing Cell Tempera- t u r e , s e e t h e LSSA P r o j e c t Q u a r t e r l y Repor t .

T h i s d e f i n i t i o n h a s t h e advan tage o f p r o v i d i n g a c c u r a t e performance i .,

compar isons a t expec ted . f i e l d c o n d i t i o n s f o r . v a r i o u s ~ m o d u ~ e d e s i g n s . . . . . . .

w i t h d i f f e r e n t t h e r m a l performance and c e l l I-V.:temperat.ure, c h a r a c t e r i s t i c s . . - .

It a l s o p r o v i d e s a n i n c e n t i v e t o o p t i m i z e - t h e module. - cel l , ' performance . . . . ' . : .

and c o s t s f o r a c t u a l f i e l d c o n d i t i o n s .

Module e f f i c i e n c y i s c o n s i d e r e d t o be t h e p roduc t o f two major e f f i c i e n c y t e r m s , o p e r a t i n g c e l l e f f i c i e n c y and module packing e f f i c i e n c y :

where

q , = module e f f i c i e n c y

qoc = , o p e r a t i n g c e l l ' e f f i c i e n c y a t NOCT, 100 rnw/cm2

q, = module packing e f f i c i e n c y

O p e r a t i n g c e l l e f f i c i e n c y i s c a l c u l a t e d as a n a v e r a g e w i t h i n a n e n c a p s u l a t e d module w i t h t h e c e l l s a t .NOCT and 100 m~/cm2 i n s o l a t i o n :

module peak power Toc =

number c e l l s x p r o j e c t e d c e l l a r e a x i n s o l a t i o n 100 mw/cm2, NOCT

Module pack ing e f f i c i e n c y i s t h e r a t i o o f p r o j e c t e d c e l l a r e a and g r o s s module a r e a :

number o f c e l l s x p r o j e c t e d c e l l a r e a QP = --

g r o s s module area

Obviously , t h e s e e f f i c i e n c y t e r m s can be expanded i n t o a p r o d u c t o f s e v e r a l s u b - e f f i c i e n c i e s . A second s t u d y i s under way t o d e f i n e t h e s e s u b - e f f i c i e n c i e s and p r o v i d e t y p i c a l examples f o r c u r r e n t s t a t e - o f - t h e - a r t modules manufactured d u r i n g Block 1 ( 46 kW) , lock 2 ( 130 kW) , and r e s e a r c h and development procurements .

To d e t e r m i n e a n a p p r o p r i a t e minimum e f f i c i e n c y l e v e l f o r f u t u r e t h i r d g e n e r a t i o n procurements , a s t u d y was conducted u t i l i z i n g a c r o s s - s e c t i o n o f e x i s t i n g s o l a r - c e l l and e n c a p s u l a t i o n t e c h n o l o g i e s t o g e t h e r w i . t h ' t h e proposed mechanical c o n f i g u r a t i o n requirements-.descr,ibed above. Key assumpt ions used i n t h e s t u d y were..

( 1 ) The module maximum power v o l t a g e e q u a l s 15 . v o l t s a t 100 mW/cm2, NOCT. T h i s i s c o n s i s t e n t w i t h t h e c h a r g i n g r e q u i r e m e n t s

o f ' c o n v e t i t i o n a l 12 v o l t l e a d - a c i d b a t t e r i e s and c o r r e s p o n d s . . . - - t o a p p r o x i m a t e l y 36 s e r i e s s o l a r c e l l s .

. .

( 2 ) The module geometry i s c o n s t r a i n e d t o 48 i n c h e s i n l e n g t h by any wid th from 10 t o 48 i n c h e s . .

( 3 ) Based on Block 1 and Block 2 procurements and minor improvements by s e v e r a l manufacturei-s , a n o p e r a t i n g c e l l e f f i c i e n c y

. . of 10.35% a t a n NOCT o f 4 5 O ~ was assumed. T a b l e 6-1 summarizes . . . t h e c e l l e f f i c i e n c i e s of t h e Block 1 and Block 2 procurements .

. . ,... . . . .Assuming a ~ . % / O C c e l l maximum-power . t empera tu re c o e f f i c i e n t , a n . e . n c a p s u l a t e d c e l l e f f i c i e n c y o f 11.5% i s expec ted a t

. . . . . .. . ST^. (28QC)'.. . .

.. . . ( 4 ) S i n c e s e v e r a i m a n u f a c t u r e r s have e x p r e s s e d r i s k / y i e l d c o n c e r n s . . . . :.. . . . - , , .... .. . . .. . . . . . . ' .. . . . fo.r modules e x c e e d i n . $500, t h e c o n f i g u r a t i o n s were h e l d t o

a p p r o x i m a t e l y 50 watts.

. .

Table 6-1'. C e l l C h a r a c t e r i s t i c s f o r Block 1 and Block 2 Modules

Module ~ n c ' a p s u l a t e d NOCT O p e r a t i n g Mfg . C e l l E f f . , .STC E f f . C e l l E f f . Procurement

B l a c k . 1 Block 2

Block 1 Block 2

Block 1 Block 2

0 .105 0.87* 0.09 1 Block 1 0 .108 . 0. 90 0: 097 Block 2

. , . . . . . . . .. .

*Es t imated Value

. . i l l ' - . . .

AT .(NOCT - 28) NOCT Eff. = . . .

P 0 2 8 ' ~

(5) To p r e c l u d e e l i m i n a t i n g any e x i s t i n g p r o d u c t i o n f a c i l i t i e s o r m a n u f a c t u r e r s , t h e module c o n f i g u r a t i o n s used t h e s i x s t a n d a r d round c e l l s i z e s . Obviously , s p e c i a l c e l l s i z e s . w i l l n e s t more e f f i c i e n t l y i n t h e s p e c i f i e d enve lope and t h e r e f o r e produce a h i g h e r module e f f i c i e n c y .

T a b l e 6-2 summarizes t h e c h a r a c t e r i s t i c s o f c a n d i d a t e module c o n f i g u r a t i o n s w i t h e f f i c i e n c i e s g r e a t e r t h a n 7%. A s shown i n Tab le 6-2, by e l i m i n a t i n g s e v e r a l module c o n f i g u r a t i o n s , a minimum e f f i c i e n c y o f a p p r o x i m a t e l y 7 .5% is a c h i e v a b l e w i t h any s t a n d a r d c e l l s i z e . A s shown i n t h e t a b l e , each module c o n t a i n s from 72 t o 216 c e l l s , a p r a c t i c a l number o f c e l l s a s e x p r e s s e d by t h e i n d u s t r y c o n s i d e r i n g r e l i a b i l i t y and c o s t r i s k s . C e l l n e s t i n g l e n g t h s o f l e s s t h a n 46 i n c h e s p r o v i d e , a d e q u a t e room f o r module end f e a t u r e s , bus b a r s , and t e r m i n a t i o n f e a t u r e s . Each c e l l l a y o u t c o n f i g u r a t i o n use's a 30° s t a g g e r e d p a t t e r n spaced 0 .080. i n c h a p a r t . T h i s c e l l s e p a r a t i o n d i s t a n c e i s a d e q u a t e f o r normal v a r i a - t i o n s i n c e l l d i a m e t e r and i n t e r c o n n e c t d e s i g n .

T y p i c a l l y , g l a s s s t y l e modules have a l a r q e r b o r d e r t h a n pan s t y l e modules s i n c e a 1/8 i n c h s h e e t o f g l a s s r e q u i r e s a f rame b i t e o f 0.5 i n c h beyond t h e c e l l n e s t i n g enve lope as compared t o 0 . 3 i n c h f o r t h e pan s t y l e modules. Based on t h e r e s u l t s o f t h i s s t u d y , a.minimum module e f f i c i e n c y a t s t a n d a r d o p e r a t i n g c o n d i t i o n s o f 7% i s proposed f o r f u t u r e p rocurements .

B. THERMAL TEST RESULTS .

Thermal t e s t i n g c o n t i n u e d . d u r i n g t h e p a s t q u a r t e r w i t h emphasis on d e t e r m i n i n g t h e Nominal Opera t ing C e l l Temperature (NOCT) o f t h e .

Block 1 ( 4 6 kW) and Block 2 (130 kW) p rocurements modules. T e s t s were completed on a l l o f t h e Block 2 modules and two o f t h e f i v e Block 1 modules. Two s p e c i a l t e s t s were a l s o conducted t o f u r t h e r examine t h e e f f e c t o f f i n s and r e s i d e n t i a l r o o f t o p mounting ( ,enclosed r e a r ) . A summary o f t h e measured NOCT and c e l l o p e r a t i n g t e m p e r a t u r e e f f i c i e n c y ("lNOCT) v a l u e s i s g i v e n i n Tab le 6-3.

The r e s u l t s show t h a t t h e modules w i t h ' n o n m e t a l l i c , n o n t r a n s p a r e n t s u b s t r a t e s ( 130 kW - Y ,Z and 46 kW - Y) have t h e h i g h e s t NOCT (46Oc t o 48OC). The modules w i t h a m e t a l l i c s u b s t r a t e ( w i t h and w i t h o u t f i n s ) o r a t r a n s p a r e n t n o n m e t a l l i c s u b s t r a t e o p e r a t e a t a lower tempera-

. . .. . . . t u r e ..( 41.!?6 .:to 43OC) . A l l o f t h e s e modules have good the rmal . c o n f i g u r a t i o n s . . . . . .

and as a r e s u l t t h e s p r e a d i n NOCT is o n l y 8 ' ~ .

. . I n g e n e r a l , a l l of t h e modules u t i l i z e t h i n s u b s t r a t e s which ,' . . ,

have a h i g h i n f r a r e d e m i t t a n c e . Very l i t t l e a d d i t i o n a 1 , t h e r m a l improve- m e n t ' . i s p o s s i b l e w i t h t h e s e f l a t p l a t e c o n f i g u r a t i o n s . T h i s i s made '

e v i d e n t by ' o b s e r v i n g t h e ?NOCT d i s p l a y e d i n Tab le 6-3 and t h e two pa ra - m e t e r s whose p r o d u c t r e s u l t s i n TNOCT. For t h e Block 2 modules , ~ N O C T is between 0.90 and 0 .93. If t h e l o w e s t power t e m p e r a t u r e c o e f f i c i e n t i s combined w i t h t h e l o w e s t t e m p e r a t u r e d i f f e r e n c e (NOCT-28 '~) t h e n a TNOCT o f 0.94 i s o b t a i n e d . I f , a s s u s p e c t e d , 0.94 r e p r e s e n t s a p r a c t i c a l upper l i m i t f o r TNOCT f o r a f l a t p l a t e module, t h e n . a l l of t h e Block 2 modules a r e w i t h i n 4% o f t h e t h e r m a l l y optimum d e s i g n .

T a b l e 6-2. C h a r a c t e r i s t i c s o f Cand ida te Mod.ules w i t h ' .

E f f i c i e n c i e s ~ r e a t e r Than 7% . . . . .

. . . : <. . . . . -. .

C e l l No. Wat ts / B e s t i n g Module Width Module ~f f i c i e n c v Dia . Cells Module Length Pan G l a s s Pan Glass

Notes :

( 1 ) E n c a p s u l a t e d cell e f f i c i e n c y 10.352 @ ,NOCT ; 45OC.

( 2 ) C e l l s p a c i n g i s 0.. 080 i n c h .

(3) 36 c e l l s e q u a l s 15 v o l t s @ NOCT = 45OC.

( 4 ) Min. pan s t y l e b o r d e r 0.35 i n c h ; min. g l a s s s t y l e bor;cler8 8.5 i n c h .

. . . . . . . .. . . . . . . . . . . . .... .

( 5 ) 3/4 i n c h s u p p o r t . s t r u c t u r e h o l e s p a c i n g . '

Table 6-3. NOCT and "-INOCT Summary

NOCT Max. Pwr. No. o f T e s t s Module OC Coef f . NOCT-28OC q~~~~ Performed

V 39 0 Not meas. N / A N / A 6

Y 47.5 Not meas. N / A N / A 10

To f u r t h e r e x p l o r e t h e u s e f u l n e s s o f c o o l i n g f i n s on t h e rear s u r f a c e o f modules , a number o f tests were conducted u s i n g module V , which h a s a f i n n e d m e t a l s u b s t r a t e . After o b t a i n i n g a NOCT v a l u e f o r t h i s module ( t h r e e d i f f e r e n t t e s t s ) , t h e f i n a were machined o f f o f

. . . . . . . . . . . . . t h e module and t h e NOCT rede te rmined ( t h r e e d i f f e r e n t . t e s t s ) . . .

Removing t h e f i n s . i n c r e a s e d , t h e NOCT a p p r o x i m a t e l y 2.a°C. .Assuming a maximum-power t e m p e r a t u r e c o e f f i c i e n t o f O.SS/'C, t h e et't'ect of the

'

f i n s i s " t o i n c r e a s e . t h e power o u t b f t h e modu.le..by a b o u t 1.4%.

I n a t h i r d t e s t , des igned t o e v a l u a t e t h e e f f e c t o f a r o o f i n s t a l - . . . . . . . . . . . . . . . . l a t i o n , t h r e e B l o c k 2 S o l a r Power C o r p o r a t i o n modules were mounted . . . . . . . . . . . . ':.'.' ' " '"i'n a 4 x 1, f o o t a r r a y w i t h the ' b c k s i d e e n c l o s e d . Ba.sed on two tests,

, t h e NOCT i n c r e a s e d from t h e normal 4 6 . 0 ' ~ (open back s i d e ) t o 5 5 . 5 ' ~ f o r t h e r o o f .mount s i m u l a t i o n . T h e r e f o r e , a b o u t a 5% r e d u c t i o n i n . . . .

. . . . . . . , . . . . power is i n d i c a t e d fo r . a r o o f i n s t a l l a t i o n a s compared t o a f i e l d i n s t a l - l a t i o n which h a s t h e back s i d e open. ....

C. IMPACT LOADING (HAIL) TEST DEVELOPMENT .

Ddscuss ions wi th ' env i ronmenta l t e s t p e r s o n n e l around t h e c o u n t r y have i n d i c a t e d a l a c k o f s u i t a b l e p r o c e d u r e s f o r a n impact ( h a i l ) l o a d i n g

test f o r p h o t o v o l t a i c modu les . * F u r t h e r m o r e , t h e i m p a c t t o l e r a n c e ( f r a g i l i t y ) o f t h e c u r r e n t s t a t e - o f - t h e - a r t modules was unknown. Dur ing t h i s p a s t q u a r t e r a n a l y s e s h a v e been per formed and deve lopmen t tests i n i t i a t e d t o p r o v i d e i n f o r m a t i o n f o r s p e c i f y i n g a n i m p a c t l o a d i n g t e s t r e q u i r e m e n t f o r t h e n e x t s o l a r a r r a y p rocuremen t as w e l l a s recommendat ions f o r impac t l o a d i n g t o l e r a n c e .

The i m p a c t l o a d i n g tes t deve lopmen t h a s c o n c e n t r a t e d on h a i l s t o r m s b e c a u s e o f t h e i r h i g h damage p o t e n t i a l t o s o l a r a r r a y s t h r o u g h o u t t h e c o u n t r y , b u t e s p e c i a l l y i n t h e h a i l b e l t o f t h e c e n t r a 1 . U . S : O t h e r o b j e c t s s u c h . as rocks . , t o y b a i l s , and fall in^ t o o l s c a n a l s o c a u s e i m p a c t damage t o . s o l . a r a r r a y s . Damage a s s o c i a t e d w i t h ' t h e s e types o f d i s c r e t e e v e n t s , a l t h o u g h p o t e n t i a l l y s i q n i f i c a n t , may' n o t b e as c a t a s t r o p h i c as a h a i l s t o r m . The u l t i m a t e g o a l o f t h e i ~ i ~ p a c t l o a d i n q e f f o r t i s t o p r o v i d e d a t a s o t h a t c o s t t r a d e - o f f s be tween t h e r e p l a c e - ment c o s t s o f damaged sa1a . r a r r a y s and t h e c o s t s o f s . t ~ - e l i ~ l ; h e n i n g t h e p r o t e c t i v e s y s t e m c a n be p e r f o m e d .

E f f o r t s f o r t h i s program are d i r e c t e d toward a c c o m p l i s h i n g f o u r o b j e c t i v e s :

( 1 ) Develop a ? r o b a b i l i t y model f o r p r e d i c t i n g t h e p r o b a b i l i t y o f a s o l a r a r r a y b e i n g h i t by a h a i l s t o n e o f a damaging s i z e d u r i n g i t s l i f e t i m e .

( 2 ) E s t a b l i s h h a i l impac t s t r e n g t h and f a i l u r e modes o f c u r r e n t s t a t e - o f - t h e - a r t p h o t o v o l t a i c modules .

( 3 ) Develop s i m p l i f i e d t e s t methods t o be used f o r q u a l i f i c a t i o n t e s t i n g by m a n u f a c t u r e r s .

( 4 ) Develop i m p a c t - r e s i s t a n t d e s i g n c o n c e p t s .

1 . H a i l s t o n e P r o b a b i l i t y Model and Data A c q u i s i t i o n

The p r o b a b i l i t y model drzvcloped f o r t h o h a i l e n v i ~ - s r l ~ l u e ~ ~ t 1s based m a i n l y o n t h e u s e of t h e P o i s s o n d i s t r i b u t i o n . T h r e e q u a n t i t i e s are u s e d i n t h e model . T h e s e a r e t h e a v e r a g e a n n u a l number o f h a i l s t o r m s a t a g i v e n l o c a l i t y , the p r o b a b i l i t , ~ o f o o a u r r o n o o o f a ha i l s t c r i i c ,ur a g i v e n s i z e o r l a r g e r , g i v e n t h a t a h a i l s t o r m o c c u r s , and t h e number o f h a i l s t o n e q o f . a .g iven . . . s i z e . , o r . l a r g e r per u n i t area. . . " > : - " ' ' ' .

If the a v e r a g e riumber o f h a i l s t o r m s p e r y e a r i s A , t h e p r o b a b i l i t y o f o b t a i n i n g n h a i l s t o r m s i n a g i v e n i s (e-h /n! )An, a s s u m i n g a P o i s s o n d i s t r i b u t i o n . If Q ( d ) is t h e p r o b a b i l i t y o f o b t a i n i n g hailstones o f a g i v e n d i a m e t e r d o r l e s s , t h e p r o b a b i l i t y o f o b t a i n i n g h a i l s t o n e s o f d i a m e t e r d o r less i n a y e a r i s

'Ross, R . G . J r . , "Des ign C o n s i d e r a t i o n s o f S o l a r A r r a y s for T e r r e s t r i a l A p p l i c a t i o n s , " P r o c e e d i n g s o f t h e 1976 S o l a r E n e r a v S o c i e t v C o n f e r e n c e , Winn ipeg , Canada, Aug. 15-20, 1976, Vo l . 6 , pp. 48-56.

where N i s chosen s u f f i c i e n t l y l a r g e s o t h a t subsequen t t e r m s are i n s i g - n i f i c a n t i n c o n t r i b u t i n g t o t h e t o t a l p r o b a b i l i t y ; f o r t h i s a p p l i c a t i o n

.. . . N = 20 h a s been found t o be s u f f i c i e n t l y l a r g e . T h e r e f o r e , t h e p r o b a b i l i t y o f o b t a i n i n g ' h a i l s t o n e s of a d i a m e t e r d o r p r e a t e r i n K yea , r s i s g i v e n by

The p r o b a b i l i t y o f hav ing a n a r e a A , impacted by h a i l s t o n e s o f d i a m e t e r d o r g r e a t e r , g i v e n t h a t such h a i l s t o n e s o c c u r , i s g i v e n by

where M(d) is t h e a v e r a g e number o f s t o n e s o f s i z e d o r g r e a ' t e r p e r u n i t a r e a and t h e P o i s s o n d i s t r i b u t i o n i s used t o d e t e r m i n e t h e proba-

. b i l i t y o f a h i t . T h e r e f o r e , t h e p r o b a b i l i t y o f a n a r e a A b e i n g impacted by h a i l s t o n e s o f d i a m e t e r d o r g r e a t e r i n K y e a r s i s g i v e n by t h e p roduc t o f t h e s e two ~ r o b a b i l i t i e s : .

With t h i s model e s t a b l i s h e d , t h e t a s k o f a s s e s s i n g t h e p r o b a b i l i t y o f h a i l damage r e d u c e s t o t h e a c q u i s i t i o n o f t h e q u a n t i t i e s needed t o e x e r c i s e t h e model. The a v e r a g e number o f h a i l s t o r m s , A , i s w e l l known f o r most o f t h e U.S. T h i s i r u a n t i t y h a s been measured by t h e Weather Bureau and o t h e r a g e n c i e s , i n many l o c a l i t i e s f o r o v e r 60 y e a r s . The o t h e r two q u a n t i t i e s , Q ( d ) and M(d) , a r e n o t as w e l l de te rmined . Some d a t a e x i s t s , b u t i t becomes v e r y s p a r s e f o r d i a m e t e r s o f 1 i n c h o r g r e a t e r . For d i a m e t e r s l e s s t h a n t h i s , t h e r e i s d a t a f o r a few s e l e c t e d l o c a l i t i e s . Values o f M(d) are more d i f f i c u l t t o o b t a i n t h a n Q ( d ) . The l i t e r a t u r e h a s been c o n s u l t e d a l o n g w i t h s e v e r a l h a i l e x p e r t s , i n c l u d i n g D r . S t a n l e y Changnon o f t h e I l l i n o i s S t a t e Water Survey i n Champaign, I l l i n o i s and D r . P e t e r Summers of t h e N a t i o n a l C e n t e r f o r At.moapherin Research i n Boulder , Colorado,

The r e m a i n i n g p a r t o f . t h e h a i l a s s e s s m e n t . e f f o r t w i l l i n v o l v e a n a t t e m p t t o o b t a i n a s much d a t a a s p o s s i b l e f o r t h e above v a l u e s . . One o f t h e main d i f f i c u l t i e s i s t h e g r e a t v a r i a b i l i t y i n t h e v a l u e s o f t h e i m p o r t z n t h a i l p a r a m e t e r s w i t h ' l o c a l i t y . The . v a l u e s .o.f t h e h a i l p a r a m e t e r s ' f o r a g i v e n r e g i o n are de te rmined p r i m a r i l y by t h e m e t e o r o l o g i c a l c o n d i t i o n s p r e v a l e n t i n t h a t r e g i o n . T h e r e f o r e , q e n e r a l i - ' z a t i o n from one r e z i o n t o a n o t h e r may n o t be v a l i d .

Tab le 6-4 g i v e s t h e p r o b a b i l i t y o f a n a r e a 10 f t 2 b e i n g h i t by h a i l s t o n e s o f d i a m e t e r e q u a l t o o r g r e a t e r t h a n 1 i n c h i n 20 y e a r s u s i n g t h e p r o b a b i l i t y model d e s c r i b e d above.

2. Ha i l T e s t i n g . . ... .

I n s i m u l a t i n g impact phenomena, p a r a m e t e r s p e r t a i n i n g t o w e i g h t , v e l o c i t y , m a t e r i a l p r o p e r t i e s ( h a r d n e s s , strength, s t i f f n e s s , e t c . ) and g ~ n m e t ~ r y n f both t h e t a rgo t and prejectile a1.e ilupu~.LanL. To e s t a b l i s h t h e h a i l impact s t r e n g t h o f c u r r e n t s t a t e - o f - t h e - a r t modules , i t w a s d e c i d e d , t h e r e f o r e , t a d u p l i c a t e a l l o f t h e above p a r a m e t e r s a s c l o s e l y a s p o s s i b l e by i m p a c t i n g molded i c e s p h e r e s on a c t u a l p h o t o v o l t a i c p a n e l s a t v e l o c i t i e s c o r r e s p o n d i n g t o t h e t e r m i n a l v e l o c i t y o f n a t u r a l l y o c c u r r i n g h a i l . F i v e module d e s i g n s o f t h e 46 kW procurement and t h e f o u r module d e s i g n s o f t h e 130 kW procurement were t e s t e d u s i n 3 s i m u l a t e d h a i l s t o n e s r a n g i n g from 1/2 t o 2 i n c h e s i n d i a m e t e r . Tab le 6-5 shows t h e w e i g h t , v e l o c i t y , and k i n e t i c ene rgy f o r v a r i o u s h a i l s t o n e d i a m e t e r s .

A mold f o r making i c e s p h e r e s was o b t a i n e d from a p r e v i o u s J P L program o f t h e mid-1960s where h a i l impac t on a n t e n n a r e f l e c t i n g s u r f a c e s had been s t u d i e d . T h i s mold as a h e m i s p h e r i c a l c a v i t y o f t h e a p p r o p r i a t e s i z e i n each o f t h e aluminum mold h a l v e s . The mold i s opened , a p i e c e o f i c e somewhat l a r g e r t h a n d e s i r e d h a i l s t o n e i s i n s e r t e d , and a combi- r i a t ion o f h e a t and p r e s s u r e i s used t o mold t h e i c e i n t o a n i c e s p h e r e a s t h e mold is c l o s e d .

T a b l e 6-4. The P r o b a b i l i t y of a 10 F t 2 Area B e i k H i t by a H a i l s t o n e of Diameter 1 I n c h o r G r e a t e r i n 20 Yearo

Avcroge Number of! H a i l s t o n e s P e r Year

P r o b a b i l i t y o f ,, . . . . . . . a H i t " . '

. .

Table 6-5. H a i l s t o n e C h a r a c t e r i s t i c s as a Func t ion o f Diameter : , , ,

Dia. Weight ( i n . ) ( l b )

Terminal V e l o c i t y (mph)

K i n e t i c Energy . (ft - , l b )

. . . .... A pneumatic gun ( s e e F i g u r e 6-1) was c o n s t r u c t e d t o f i r e t h e

s i m u l a t e d h a i l s t o n e s a t t h e s o l a r p a n e l s . To s impl i fy ' . aim.ing , the . . . . . . . . . . . - . . .

. . . . . . . . . . . . . . . . gun fires v e r t i c a l l y upward a t t h e target s o l a r p a n e l , which . " t s mounted . . . . . . . . . . . . . . . o v e r h e a d . The gun c o n s i s t s o f a l a r g e r e s e r v o i r which .is p r e - p r e s s u r i z e d

t o t h e d e s i r e d f i r i n g p r e s s u r e . A s i m u l a t e d h a i l s t o n e i s ' d r o p p e d . i n t o t h e v e r t i c a l b a r r e l , and a f a s t - o p e n i n g v a l v e i s opened which a d m i t s . t h e p r e s s u r e i n t h e r e s e r v o i r t o t h e b a r r e l , t h u s p r o p e l l i n g t h e i c e . .

s p h e r e a t t h e d e s i r e d v e l o c i t y . To v e r i f y t h a t t h e s i m u l a t e d h a i l s t o n e . a c h i e v e s t h e d e s i r e d vela.-ity , a .photo-e lec t r o n i c v e l o c i t y measur ing sys tem i s i n s t a l l e d between t h e muzzle o f t h e gun and t h e t e s t a r t i c l e as shown i n F i g u r e 6-1. T e s t s u s i n g t h i s a p p a r a t u s a r e c u r r e n t l y i n p r o g r e s s .

. . . . . . . . . . . . >

. . . ... D . CYCLIC LOADING ANALYSIS . . . . . . . .

1 . O b j e c t i v e . .

A s o l a r a r r a y i n t h e f i e l d w i l l be s u b j e c t e d t o v a r i o u s c y c l i c . . . . s t r e s s e s , p r i m a r i l y c y c l i c t h e r m a l s t r e s s e s and c y c l i c wind l o a d i n g

. . . . . . . s t r e s q e s . : , The r e s u l t . o f t h i s c y c 1 . i ~ . lpad.ing .enviror?ment, .gen,eral~y,. . ' . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. ' ' 'mani.festS it 'seI 'f '"lri t h e '.form .of mechanical f a t i g u e o f v a r i o u s m a t e r i a l s . . w i t h i n t h e module. 'The s o . l a r c e l l e l e c t r i c a l i n t e r c o n n e c t i o n s t r i p '

is o f t e n t h e weakest component wi th . r e s p e c t t o t h i s environment . , , ; . ,.. . . . . . . . . . . . . . . . . . .

. . C u r r e n t a t t e m p t s . t ~ . ' ~ u a i i f ~ modules w i t h r e s p e c t t o . - the . c y c l i c " .:.' . . l o a d i n g environment u t i l i z e two t y p e s , o f t e s t i n g : t h e r m a l c y c l e t e s t s '

-

and mechan ica l uni form l o a d (wind) c y c l i c l o a d i n g t e s t s . ~ l t h o u g h t h e chosen l o a d i n g l e v e l s and number of l o a d c y c l e s have been e s t i m a t e d on t h e b a s i s of t h e - b e s t env i ronmenta l and f i e l d performance d a t a a v a i l a b l e t h e c u r r e n t l e v e l s must be c o n s i d e r e d p r e l i m i n a r y a t b e s t .

. .

. .

MODULE

-VELOCITY MEASURING SYSTEM . PHOTOELECTR lC

INTERCHANGEABLE BARRELS

' '

.

.

I I / SOLENO I D VALVE LARGE, FAST OPENING

.. :TEST CAGE . : REGULATOR :

RCSCRVOIR SHOP A I R

F i g u r e 6-1. Schemat ic o f .Ha i l T e s t S e t u p

To o b t a i n improved q u a l i f i c a t i o n t e s t methods , a s t u d y h a s been i n i t i a t e d t o ( 1 ) a c c u r a t e l y c h a r a c t e r i z e t h e t e r r e s t r i a l t h e r m a l and wind c y c l i c l o a d i n g env i ronment , and ( 2 ) d e r i v e a p p r o p r i a t e t h e r m a l and mechan ica l t e s t env i ronments . These test env i ronments w i l l be chosen t o r e c r e a t e t h e same l e v e l o f m a t e r i a l f a t i g u e e x p e c t e d i n t h e f i e l d i n a power p l a n t l i fet ime, and i f p o s s i b l e w i l l b e d e f i n e d s o a s t o minimize t e s t i n g t i m e , c o m p l e x i t y , and expense .

2 . Program Development

The f i r s t s t e p i n t h e t a s k was t o d e v e l o p a oomputer iocd approach f o r c o u t ~ t i n g t h e r m a l c y c l e s o v e r a n annua l p e r i o d . The approach involves t-eaafng wea the r t a p e s c o n t a i n i n g h o u r l y t e m p e r a t u r e and i n s o l a t i o n d a t a and model ing t h e c a l c u l a t e d module tamperat.11re h i s t o r y as a sequonoo o f d i s c r e t e l o a d i n g c y c l e s o f f i x e d a m p l i t u d e and mean v a l u e . The approach t o c o u n t i n g c y c l e s i n v o l v e s t h e c o n c e p t o f a system o f e q u a l l y s p a c e J g r i d l i n e s a g a i n s t which t h e a c t u a l t e m p e r a t u r e d a t a i s compared. C y c l e s a r e coun ted i n terms o f t h e g r i d l i n e s which a r e c r o s s e d , as i l l u s t r a t e d i n F i g u r e 6-2. Small c y c l e s which d o n o t i n v o l v e t h e c r o s s i n g o f a t l e a s t two g r i d l i n e s a r e n o t coun ted ( s e e S e c t i o n A o f F i g u r e 6 - 2 ) . A t r a d e - o f f d e v e l o p s i n d c t e r m i n i n q t h e f i n e n e s s o f t h e g r i d sys tem between n e g l e c t i n g small c y c l e s and o p t i m i z i n g t h e i n v o l v e d i n computer a n a l y s i s .

SECTION A CYCLES NOT COUNTED (TOO SMALL)

F i g u r e 6-2. Use o f Gr id System t o Determine Temperature Cyc les

By u s e o f t h i s t e c h n i q u e , t h e c y c l i c v a r i a t i o n s f o r a s i t e o v e r a g i v e n t ime p e r i o d a r e c a t e g o r i z e d based on t h e g r i d sys tem s e l e c t e d . T h e r e f o r e a l a r g e number o f c y c l i c v a r i a t i o n s a r e c o l l e c t e d i n t o d i s c r e t e c a t e g o r i e s and coun ted as members o f t h e s e c a t e g o r i e s . Lumped i n t o a g i v e n c a t e g o r y are c y c l e s which may have d i f f e r e d i n a m p l i t u d e by a n amount s l i g h t l y l e s s t h a n t h e d i s t a n c e between two g r i d l i n e s .

A f t e r t h e a r r a y t e m p e r a t u r e h i s t o r y i s modeled a s a c o l l e c t i o n o f d i s c r e t e l o a d i n g c y c l e s , t h e l o a d i n g c y c l e s a r e f u r t h e r a g g r e g a t e d i n t o a l i m i t e d number o f c a t e g o r i e s a c c o r d i n g t o t h e f a t i g u e s t r e s s l e v e l a s s o c i a t e d w i t h t h e p a r t i c u l a r t y p e o f c y c l e . S o d e r b e r g ' s l aw is u t i l i z e d t o q u a n t i f y t h e a t i g u e s t r e s s l e v e l o f c y c l e s w i t h d i f f e r e n t c y c l i c stress and mean s t r e s s l e v e l s . To d e t e r m i n e . the t o t a l f a t i g u e l o a d i n g imposed on t,he module, t h e c y c l e - r a t i o t h e o r y i s used t o combine t h e f a t i g u e damage p o t e n t i a l o f each o f t h e f i n a l l o a d i n g l e v e l s based on an e s t i m a t e d stress-level/number-of-cycles-to-failure ( s - n ) r e l a t i o n s h i p f o r t h e p h o t o v o l t a i c module o f i n t e r e s t .

Uord t o d a t e h a s invo lved debugging t h e c y c l e - c o u n t i n g program and d i g i t i z i n g a c t u a l wind d a t a r e c o r d s f o r a n a l y s i s by t h e same program.

E. WIND-LOADING SPECTROMETER DEVELOPMENT

Complementing t h e c y c l i c l o a d i n g a n a l y s i s d e s c r i b e d i n t h e p r e c e d i n g s e c t i o n , t h e same methodology f o r c o u n t i n g f a t i g u e l o a d i n g c y c l e s h a s

been i n c o r p o r a t e d d u r i n g t h e p a s t q u a r t e r i n t o a n i n s t r u m e n t f o r d i r e c t l y c h a r a c t e r i z i n g t h e c y c l i c l o a d i n g l e v e l o f i n s i t u winds . Recogniz ing t h a t a l a r g e number o f c y c l e s o f low i n t e n s i t y wind l o a d i n g can e v e n t u a l l y c r e a t e as much f a t i g u e damage a s a r e l a t i v e l y few c y c l e s o f h i g h i n t e n s i t y wind i t was d e c i d e d t o c o n s t r u c t a l lwind-loading s p e c t r o m e t e r " which would r e c o r d t h e f u l l spec t rum o f wind l o a d i n g . F u r t h e r m o r e , it was d e s i r e d t o measure , n o t t h e wind v e l o c i t y , b u t t h e e f f e c t i v e normal l o a d i n g a p p l i e d t o s o l a r p a n e l s r e s u l t i n g from t h e wind. These c o n s i d e r a - t i o n s d i c t a t e d t h e d e s i g n o f t h e "wind-loading s p e c t r o m e t e r " shown s c h e m a t i c a l l y i n F i g u r e 6-3.

The wind- loading s p e c t r o m e t e r automatically.constructs a wind- l o a d i n t e n s i t y spec t rum a s f o l l o w s : The s t r a i n - g a g e d p a n e l p roduces a s i g n a l p r o p o r t i o n a l t o t h e e f f e c t i v e wind p r e s s u r e normal t o t h e pane l . Eaoh t imo $he wind intensity f l u c t u a t e s : betweer1 ariy Lwu pr'e- s e t l e v e l s , a c o u n t i s r e c o r d e d by o n e o f t h e 28 e l e c t r o m e c h a n i c a l c o u n t e r s p rov ided . The s e t - p o i n t s a t which t h e c o u n t e r s a r e t r i p p e d a r e a d j u s t a b l e . T h i s d e v i c e h a s been comple ted , checked o u t , and i n s t a l l e d i n t h e J P L p h o t o v o l t a i c f i e l d t e s t f a c i l i t y .

F i g u r e 6-4 shows t h e 28 c a t e g o r i e s i n t o which t h e e f f e c t i v e normal . . . . .. . wind i n t e n s i t y i s c a t e g o r i z e d and r e c o r d e d . The c o u n t s which would

be r e c o r d e d f o r t h e sample a n a l o g t r a c e o f wind i n t e n s i t y are a l s o shown.

F. CLOUDY-DAY ANALYSIS

1 . Summary

The impe tus f o r pe r fo rming t h e t a s k d e s c r i b e d h e r e was d e r i v e d f'rom Department o f Defense r e q u i r e m e n t s f o r c r i t e r i a f o r s e l e c t i n g t h e optimal a r r a y / s t o r a g e s i z e f o r a g i v e n l o a d . I n t h e p r e s e n t work t h e mean i n s o l a t i o n d e f i c i t , based on 10 y e a r s o f wea the r d a t a , h a s been de te rmined f o r v a r i o u s numbers o f c o n s e c u t i v e d a y s , up t o 60.

SOLAR FANEL ELECTROMECHA IdICAL MC)I.INTINF FRAME COl-INTERS (28)

. . EEFECTIVE NORMAL COMPONENT OF WIND PRESS. SIGNAL LEAD 01311-1n

C = 3 0 " ' 0

[ I 0 0 0

( 3 0 0 0 0

STRAIN-GAGED PANEL REMOTE READOUT INSTRUMENT

F i g u r e 6-3. Schemat ic o f Wind-Load S p e c t r o m e t e r

EFFECTIVE NORMAL WIND VELOCITY

MPH CATEGORIES OF WIND INTENSITY

...... . .... . ANALOG TRACE OF HYPOTHETICAL 1 / I 1 1 IN EFFECTIVE WIND COUNTS PRODUCED

BY HYPOTHETICAL EFFECTIVE WIND-

. .

F i g u r e - 6-4. 'w ind-~oad S p e c t r o m e t e r ( I l l u s t r a t i o n o f F u n c t i o n ) . ,.

T h i s approach a l l o w s a compar ison .-~f t h e e f f e c t o f a m a l l number o f h i g h d e f i c i t d a y s v e r s u s a l a r g e r number o f low-to-moderate d e f i c i t d a y s i n s u c c e s s i o n . 'An e q u a t i o n g i v i n g t h e amount o f b a t t e r y and a r r a y r e q u i r e d t o a m e l i o r a t e a g i v e n d e f i c i t was d e r i v e d f o r a c o o r d i n a t e system r e p r e s e n t i n g i n s o l a t i o n . d e f i c i t and .number of cons .ecu t ive days . From t h i s e q u a t i o n f a m i l i e s o f c u r v e s were d e r i v e d and p l o t t e d . These c u r v e s may be used t o d e t e r m i n e t h e op t imal"a r ' r ay1s to rage s i z e .

2.. P r e l i m i n a r y R e s u l t s . . . . . . . . . . . . . ................

. . . . . . . . . . . The " a c t u a l i n s o l a t i o n d e f i c i t f'or p e r i o d s o f N c o n s e c u t i v e d a y s

.(where N = 1 , 2 , 3 , ... 60) was determined f o r s i x b imonthly ' p e r i o d s based on 10 year.3 o f s o l a r i n s o l a t i o n d a t a . The a n a l y s i s was performed f o r 3 1 cont ' i 'nenta l U.S. . .sites. : The l a r g e s t d e f i c i t s were f o r s h o r t p e r i o d s . . . . . . . . . . o f t fme ; ( inso ' i . a t ion .down 90-90% from t h e 10 y e a r a v e r a g e ) ; . t he d e f i c i t s f o r l o n g e r p e r i o d 3 t:&hded toward v a i u e s of 0-10%.

R e s u l t s from each o f t h e 10 g i v e n b imonth ly p e r i o d s ( b a s e d on 10 y e a r s ) were combined t o g i v e a 10-year wors t -case composi te . An a v e r a g e was de te rmined by w e i g h t i n g each p e r c e n t a g e d e v i a t i o n by t h e number o f o c c u r r e n c e s i n 10 y e a r s . The a v e r a g e v a l u e s were p l o t t e d a s a f u n c t i o n o f t h e g i v e n number o f d a y s f o r which t h e d e f i c i t o c c u r r e d . F i g u r e 6-5 shows t h e a v e r a g e and t h e a v e r a g e p l u s 2u p l o t t e d f o r S e a t t l e f o r t h e b imonthly p e r i o d c e n t e r e d i n A p r i l

0 - I I I I I 1 I I I I I

-

. .. . . . .

-

-

80 - 1 = 10 YEAR MEAN OF M A X I M U M DEFICIT I N APRl L -

2 = MEAN M I N U S 2 STANDARD DEVIATIONS 90 - -

F i g u r e 6-5. I n s o l a t i o n D e f i c i t Versus P e r i o d Length f ~ r S e a t t l e i n A p r i l

The c u r v e s shown i n F i g u r e 6-5 c a n be s c a l e d t o d e m o n s t r a t e s e v e r a l e f f e c t s . The c u r v e s can be normal ized t o t h e y e a r l y a ,verage and each bimonthly Zurve p l o t t e d t o t h i s s c a l e . Another t y p e o f e c a l i n g which can be a p p l i e d is t h e i n c r e a s e o r d e c r e a s e o f i n s o l a t i o n o v e r t h e h o r i z o n t a l - f l a t - p l a t e e x p e c t e d v a l u e due t o t h e t i l t i n g o f t h e r e c e i v i n g p l a n e . The combined e f f e c t o f t h e two t y p e s o f s c a l i n g can be s e e n i n F i g u r e . 6-6, which shows t h e r e s u l t s Por S e a t t l e f o r a 60° t ilt . . . .... .

Comparison of r e s u l t s from d i f f e r e n t s i t e s shows t h a t t h e a v e r a g e and a v e r a g e p l u s 2 r c u r v e s a r e g e n e r a l l y s i m i l a r , a 1 thouqh fhe:.$evels, :. ..

m a y . d i f f e r . It can a l s o be s e e n which sites a r e more c l o u d y tkian o t h e r s ; compar ison a l s o i n d i c a t e s which s i t e s have s tormy p e r i o d s i n s u k e r and which s i t e s have them i n w i n t e r .

LONG TERM YEARLY AVERAGE l NSOLATION LEVEL = 309 LANGELYSIDAY

1001 I 1 I I 1 1 1 1 1 1 1 1 J 0 5 10 15 20 25 30 .35 40 45 50 55 60

PERIOD LENGTH (DAYS)

Figure 6-6. Ten-Year Mean o f Maximum D e f i c i t s During Each Bimonthly Per iod (60° T i l t , S e a t t l e )

. . . , . . Figure '6-7 shows one o f a fami ly o f paramet r ic p l o t s ' g i v i r i g t h e

amount o f b a t t e r y and a r r a y r equ i r ed t o s a t i s f y a g i v e n . d e v i a t i o n from t h e average ( 100 i n d i c a t e s a 100% d e f i c i t o r 'no"sun) . . This p l o t is cons t ruc t ed f o r a p a r t i c u l a r f i x e d ba t te ry- to-ar ray r a t i o ; t h u s each curve r e p r e s e n t s a d i f f e r e n t s i z e system with . the same b a t t e r y t o a r r a y r a t i o . The number t o t h e r i g h t o f each curve i s t h e r a t i o of t h e ' r e q u i r e d system s i z e t o t h e s i z e r equ i r ed i f t h e system were s i a e d . f o r t h e mean . . . . . . . . . . . . . . . . inso1a tcof i ' - l eve l wi'th no d e f i c i t s . S imi l a r cu rves f o r o t h e r b a t t e r y - to -a r ray r a t i o s a l low s e l e c t i o n o f t h e optimum system t o s a t i s f y t h e expeoted o r 2r r inscr la t ion d e f i c i t for the s i t e o f i n t e r e s t .

. . . . . . .

. . . A .cnmplat! r e p o r t u i t h data f o r each o f t h e bimonthly pe r iods (Feb, A p r , . J u n , Aug, Oct, Dec) and each o f t h e 11 geographic s i t e s

'

is i n p repa ra t i on .

Figure 6-7. System Size Vervuv DeficlL Cuver.iri~r Capability f o r a Fixed B a t t e r y / A r r a y Hatio = 50 kW-ll/kW

0 I I I I I I . . . . . . -

- . .

1,Ol

1.10 2 -1.20 z -1,30 . O -1.40 2 -1.50 ;g .1.60=z

& = 1 . 8 0 ~ 0 -.2.00 2 2 2.25" >

a -2.50 >, -3.00 2.2' 4.00 .s

-5.00 = 6.00

& 8.00

r! V)

I lrn6. I :O 1: 0 2: 35 415 50 55 I

60 PERIOD LENGTH (Bays)

SECTION V I I . .

OPERATIONS AREA

A . LARGE-SCALE PRODUCTION TASK

The l a s t Block 1 ( 1 5 kW add-on) modules were d e l i v e r e d by S o l a r Power i'n mid-January t o Lewis Research C e n t e r f o r ' ~ e ~ a r t m e n t o f Defense . a p p l i c a t i o n s .

. . . . .% . . . .

. . ..... , - . F i n a l d e s i g n r e v i e w s w e r e c o n d u c t e d - f o r t h r e e lock 2. ( 130, kW) .

. .... . . . . . . : " & n u f a c t u r & r a d ' u r i n g . t h i s q u a r t e r , and a p p r o v a l f o r p r o d u c t i o n ' w a s . ., .

. . . g i v e r i r t o a l l f o u r . P r o d u c t i o n d a t a as o f t h e end o f March.: . . /'.. ' : ' . . . . . : . . , . . . . ,.. . .

. . . . . . . . . .:. . . . . . . . . ... . . . . . . . . . . . . . . . . . . . . . . . ' . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . , . : . , .:. . . ..:. . . . . : . .

. . . . . . . . . . . . . F i n a l P r o d u c t i o n P r o d u c t i o n Modules

. . . ..::.: .: :. . . . . - . . . . . . . . . . . . . . . . . . . . . .,,: ,:.., ... ,: . Design Review Go-Ahead Shipped . . . . . . . . . . . . . . . . . . . . . . . _. . '

. . . . . . . . . . . . Sensor Technology 01/31/77 02/07/77 . . . 2 . 5 kW'

. . ,

. "':i:S61 ar : Pow " , ,. , e r 03/22/77 03/22/77 0

So 1 a r e x 0 1 /26/77 02/ 16/77 0.86 kW

S p e c t r o l a b 11/05/76 03/18/77 0

A t t h e r e q u e s t o f ,MITfs ~ i n c o l n L a b o r a t o r y , Sensor Technology module d e s i g n was changed from 42 ce l ls t o 44 cel ls i n mid-March.

Some d e l a y s . w e r e e x p e r i e n c e d i n t h e i n i t i a t i o n o f p r o d u c t i o n . Prime f a c t o r s i n t h e s e d e l a y s i n c l u d e d t h e time r e q u i r e d t o implement d e s i g n changes r e s u l t i n g from d e s i g n r e v i e w s , t o implement r e v i s e d p r o v i s i o n s o f t h e JPL d e s i g n and t e s t . s p e c i f i c a t i o n (5-342-1) , t o o b t a i n needed t o o l i n g and materials from s u p p l i e r s , . a n d t o overcome p r o d u c t i o n problems a s s o c i a t e d w i t h new moduls d e s i g n s . ..

Top p r i o r i t y o n Sensor 'Techno logy and S o l a r e x module sh ipments i s b e i n g g i v e n t o d e l i v e r i e s t o MIT1s L i n c o l n L a b o r a t o r y f o r t h e a g r i -

, c u l t u r a l pumping a p p l i c a t i o n i n Nebraska s l a t e d f o r turn-on i n J u l y . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . B. ENVIRONMENTAL TESTING

. . . 1.. . Block 1 (46 kW)

E s s e n t i a l l y a l l o f t h e p lanned Block 1 t e s t i n g was completed : . .

by t h e .end o f the . q u a r t e r . Tab le 7-1 shows t h e tests performed and , .

t h e r e s u l t s o b t a i n e d . L a t e p r o d u c t i o n , m o d u l e s (Phase 2) were .used f o r most o f t h e e x p l o r a t o r y t e s t i n g . ,The fungus test was performed .

. . on o l d e r n o n o p e r a t i n g modules from t h e i n i t i a l pr6duct. lon ,101;. . 1i1 . . . . a d d i t i o n , samples from t h e 15 kW add-on were r u n t h r o u g h q u a l i f i o a t i o n .

tests. T a b l e s 7-2 and 7-3 summarize t h e test r e s u l t s .

Table 7-1. B r i e f ~ e s c r i p t i o n o f ~ x ~ l o r a t o r ~ . T e s t P roced .wes

Humidity/ f r e e z i n g Two t e m p e r a t u r e c y c l e s , .from 23 t o 6 5 O ~ , a t . .

95% r e l a t i v e humid i ty (R.H.) fo l lowed by 3 h o u r s a t -10 '~ ; . 10 t i m e s .

Hard r a i n . . R o t a t e t h e module i n a w a t e r s p r a y from- .. n o z z l e s s e t t o p rov ide 17 m / $ v e l ' o c i t y . : a t a n a v e r a g e 2. mm d r o p l e t s i z e , d e i o n i z e d w a t e r , 15 'min .

S a l t fog

Fungus

Heat i n s u n l i g h t ( o r under h e a t lamps) t o t y p i c a l warm, midday t e m p e r a t u r e s . Then s p r a y with d e i o n i z e d w a t e r a t 2 .5 cm/hr o r more s i m u l a t e d r a i n u n t i l s t a b l e temp- e r a t u r e s a r e r e a c h e d ; 5 times.

S a t u r a t e modules w i t h m o i s t u r e o v e r n i g h t (40°C, 95% R H . ) ; t h e n , q u i c k l y move modules under h e a t lamps set t o t h e e q u i v a l e n t o f 100 m~/cm* u n t i l t e m p e r a t u r e s s t a b i l i z e ; 10 t i m e s .

Concen t ra ted s a l t s p a r y f o r two d a y s 2n a chamber at 35OC ?.nd h i g h h u m i d i t y .

I n o c u l a t e modules w i t h 5 t y p e s o f f u n g i . Place i n a o b a m h ~ r at. 2g°C and 952 R . H. f o r 28 d a y s ,

Table 7-2. 46 kW, Phase 2 - E x p l o r a t o r y T e s t R e s u l t s

Note's :

(1) Anomalous i n c r e a s e o f . about 5% observed i n e l e c t r i c a l o u t p u t a f t e r h a r d r a i n .

(2) A d e c r e a s e i n power o u t p u t of about 8.5% a f t e r h e a t I r a i n .

'

(3) De lamina t ion , J-box d e g r a d a t i o n .

' (4) One cm of encapsular- t p e e l e d o f f one c e l l .

Fungus

' p h y s . Change

(5)

(5)

(5)

(5 )

H u m i d i t ~ l ~ e a t

( 5 ) No fungus growth ( e l e c t r i c a l d e g r a d a t i o n n o t measured) .

E l e c t . Degrad.

1.2%

3.0%

< 1%

2.3%

~ l e c t r i c a l d e g r a d a t i o n i s average p e r c e n t d e c r e a s e .

Phys. Change

( 4 ) '

0

0

0

Humidi ty/Freee .

0 No o b s e r v a b l e p h y s i c a l change.

-

i Vendor

I I i I v

w

E l e c t . Degrad.

-

-

-

1.8%

HeatIRain NO. of Modules

4

4

Y

Z .

Phys. Change

-

-

-

(3)

E l e c t . Degrad.

1 .5%

1.5%

<1%

(2

4'

4

S a l t Fog

Phys. Change

0

0

0

0

Hard Rain

E l e c t . Degrad.

< 1%

< 1%

-

-

E l e c t . Degrad.

0

0

1 .6%

( 1 )

Phys. Change

0

0

-

-

Phys. Change

0

0

0

0

Table 7-3. Add-On Procurement - Q u a l i f i c a t i o n T e s t R e s u l t s . ..

Temperature Humidity C v c l i n a

Module Number E l e c t . Phys . E l e c t .

Degrad . Change Degrad . P h y s i c a l Change

1 . 8 . 7 % 0 0 E n c a p s u l a n t s p l i t t i n g

2 3-05 0 < I % 0

3 ( 1 ) 0 ( 2 1 J-Sox c o v e r o f f

Notes : . . .

( 1 ) E r r a t i c e l e c t r i c a l o u t p u t . 12% a v e r a g e d e g r a d a t i o n .

( 2 ) Output stil.1 e r r a t i c ..

2. Block 2 (130 kW)

Q u a l i f i c a t i o n t e s t i n g o f t h e . remaining Block 2 modules was e s s e n t i a l l y comple te a t t h e end o f t h e q u a r t e r ( s e e Tab le 7 -4 ) . Modules from t h e first o f t h e f o u r s u p p l i e r s had been q u a l i f i c a t i o n t e s t e d i n t h e p r e v i o u s q u a r t e r . The o n l y t e s t i n t h i s q u a r t e r on t h e s e modules (W t y p e ) was h u m i d i t y / f r e e z i n g . No d e g r a d a t i o n was o b s e r v e d .

Modules from one s u p p l i e r ( Z ) showed e v i d e n c e s o f c e l l c r a c k i n g , e n c a p s u l a n t d e l a m i n a t i o n , and c e l l l i f t i n g a f t e r a chamber m a l f u n c t i o n . The chamber dropped i n t e m p e r a t u r e abou t 20% f a s t e r t h a n t h e s p e c i f i e d r a t e . The t e s t was d i s c o n t i n u e d , and two more s u b a r r a y s were assembled and s t a r t e d a g a i n t h r o u g h t h e t e s t . s e r i e s . A f o u r t h s u b a r r a y i n which ,

t h e c e l l - t o - s u b s t r a t e a d h e s i v e h a s been e l i ~ ~ ~ i r i a t e d i s also u n d e r ~ g o i n ~ t e s t s . None o f t h e s e l a t e r t e s t s have shown t h e c e l l l i f t i n g problem, a l t h o u g h e n c a p s u l a n t d e l a m i n a t i o n h a s been no ted

I n a problem u n r e l a t e d t o environrr~el l ta l t e s t i n s , t h e W-type modules have shown a t e n d e n c y t o degrade e l e c t r i c a l l y w i t h t i m e , even when s t o r e d i n a n a i r - c o n d i t i o n e d l a b o r a t o r y . A f t e r 3 t o 4 months , a l o s s o f power of a b o u t 3 t o 4% i n most c a s e s ( b u t around 7% f o r two modules) h a s been o b s e r v e d .

. ' T a b l e 7-4. Block 2 (130 kW) Modules - Q u a l i f i c a t i o n . T e s t R e s u l t s . .

. . . . . .

. , , . . -

Temperature Humidity ~ e c h a ' n i c a l C v c l i n a - C v c l i n a I n t e a r i t v (Wind)

No. o f S u p p l i e r Modules E l e c t . Phys. E l e c t . Phys. E l e c t . Phys .

Degrad . Change Deqrad . Change Degrad . Change

Z 6 ( 1 ) (6 )D, ( 1 (5)D 0 0 ( cement ) (3)CC

Z ( n o 3 (1 (2 )D, - - - - cement) (1)CC

Notes :

( I D Number o f modules showing e n c a p s u l a n t d e l a m i n a t i o n .

( ) VB Number o f modules showing high-vol t a g e breakdown.

( )CC Number o f module's showing one o r more c r a c k e d s o l a r c e l l s .

0 No p h y s i c a l change.

. . . .I 1 ) .Stored modules o f t h e s e types showed e r ra t i c o r d r i f t i n . e l e c t r i c a l ' o u t p u t . ' E l e c t r i c a l d e g r a d a t i o n .from envi,r'on- m e n t a i t e s t n o t s i g n i f i c a n t l y more t h a n obse rved w i t h

. . u n t e s t e d modules.

FIELD TESTING C. . . . . . . . . . . . . . . . . . . . . . . .

During t h i s q u a r t e r , 81 a d d i t i o n a l modules were p l a c e d i n t h e f i e l d a t JPL and 16 a t Tab le Mounta in , p r o v i d i n g a t o t a l o f 218 i n t h e f i e l d a t t h e t h r e e si tes. The d i s t r i b u t i o n f o r t h e Block 1 ( 4 6 kW) moduies was .as' f o l l o w s : . . . .;'. .

<, .: ': . . . . .. .. ., ;..:, .:. . . . . . . . :. ....

Table d& Mountain . Golds tone

S o l a r Power

S p e c t r o l a b

S o l a r e x

S e n s o r Technology

, _ . . . . . . . . . .

It is a n t i c i p a t e d t h a t by t h e end o f A p r i l , t h e p lanned 'dep. ioyment . . .

o f Block 1 modules w i l l be complete . . E i g h t o f . t h e module's .deployed . .

a t t h e JPL s i t e -- one S o l a r Power, two S p e c t r o l a b , t h r e e So la rex . , . . . .. . .. .

and two Sensor Technology -- were m.?unted on a "long-term d i r t s u b a r r a y " f o r t h e purpose o f i n v e s t i g a t i n g t h e prolonged e f f e c t . o f d i r t on performance. I n a d d i t i o n t o t h e s e modules , a s u b a r r a y c o n t a i n i n g t h r e e . . .

130 kW S p e c t r o l a b modules was deployed a t t h e JPL s i t e and t h e Tab le . .

Mountain s i t e .

Thir ty- two a d d i t i o n a l t e s t s t a n d s have been . d e l i v e r e d . Seven were i n s t a l l e d a t t h e JPL s i t e , forming t h e second column o f s t a n d s ( S t a n d s 9 t o 1 5 ) . , E a r l y i n A p r i l a f a c i l i t i e s work o r d e r w i l l be i n i t i a t e d t o i n s t a l l t h e r e m a i n i n g 18 s t a n d s t o comple te t h e JPL s i t e . Work o r d e r s w i l l a l s o be i n i t i a t e d t o add f o u r more s t a n d s a t b o t h t h e Tab le Mountain and Golds tone s i t e s t o complete t h o s e s i t e s .

The p r o c e s s o f o b t a i n i n g a p e r i o d i c Large-Area Pulsed S o l a r S i m u l a t o r (LAPSS) I - V r e c o r d f o r e a c h module i n t h e f i e l d a t Pasadena was c o n t i n u e d d u r i n g t h e q u a r t e r . . The r e c o r d i n g and t a b u l a t i o n o f t h e d a t a were mechanized w i t h t h e a i d o f a computer program. F i g u r e 7-1 is a r e p r e s e n t a t i v e computer t a b u l a t i o n f o r one module i n t h e f i e l d . B a s i c performance d a t a and t r e n d s a r e d i s p l a y e d . ,

The T a b l c Mountain modules were a l s o r e c y c l e d back t o JPL . f o r f l a s h i n g d u r i n g t h e q u a r t e r . A computer r e c o r d o f t h o s e I-V d a t a i s a l s o b e i n g m a i n t a i n e d , and a s i m i l a r r e c o r d o f t h e Golds tone modules w i l l b e i n i t i a t e d when t h e y a r e r e c y c l e d i n A p r i l .

. . Work c o n t i n u e d in ocvcral arcaa i n connection with t h e automated

d a t a a c q u i s i t i o n sys tem f o r t h e Pasadena s i t e : work a t t h e sys tem c o n t r a c t o r on t h e a c t u a l d a t a s y s t e m , . m o d i f i c a t i o n o f t h e t r a i l e r t o accommodate t h e s y s t e m , . i n s t a l l a t i o n o f t h e e l e c t r i c a l w i r i n g c o n n e c t i n g t h e modules and s e n s o r s t o t h e d a t a sys tem, i n s t a l l a t i o n o f t h e m e t e o r o l o g i c a l equ ipment , and f o r m u l a t i o n and imp. lementa t ion o f t h e s o f t w a r e . These i n d i v i d u a l e f f o r t s w i l l come t o g e t h e r n e x t q u a r t e r when t h e d a t a system

. i s d e l i v e r e d . The schedu led d e l i v e r y t o J P L , i s d u r i n g t h e . l a s t week i n A p r i l .

Voc p n , , ~ F A C T O R DEL ISC DEL Y O E D ~ L rwrhx Fr . .

A V E R A G E D E L T A 1S.C .531 A v ~ R A G E . D E L T A wuc - * a 1 9 A V E R A G E O E C T A P-RAX 1.571

F i g u r e 7-1. R e p r e s e n t a t i v e Computer T a b u l a t i o n o f LAPSS I-V Data f o r a Module i n t h e F i e l d :at Pasadena

D . PERFORMANCE MEASUREMENTS AND STANDARDS

A summary r e p o r t o f t h e i n t e r l a b o r a t o r y s t a n d a r d s measu remen t s , pe r fo rmed l a s t q u a r t e r , was made a t t h e . Semiannua l P h o t o v o l t a i c ,Program . . .

: . Heview i n San Diego i n J a n u a r y .

I n t e r m e d i a t e s t a n d a r d c e l l s f o r t h e 130 kW procuremen t have been d e l i v e r e d t o t h e l a r g e - s c a l e p rocu remen t m a n u f a c t u r e r s . P r i o r t o d e l i v e r y , c h a r a c t e r i z a t i o n tests and compar i son tests w i t h t h e 46 kW s t a n d a r d s

. . were c o m p l e t e d . . .

S p e c t r o l a b p r o t o t y p e modu les r e d / b l u e r a t i o s h a v e been compared t o t h e s t a n d a r d c e l l s t o v e r i f y t h a t t h e s t a n d a r d s a r e s p e c t r a l l y r e p r e - s e n t a t i v e o f t h e p r o d u c t i o n modu les . The f i n d i n g s o f t h e c o m p a r i s o n t e s t s i r l d i c a t e t h a t t h e s p e c t r a l mat,chingrl . is a d e q u a t e for p r o d u o t i o n t e s t i n g .

T e s t i n g o f Lewis R e s e a r c h C e n t e r and JPL r e f e r e n c e c e l l s i n . s u n - l i g h t was c o n t i n u e d d u r i n g t h i s q u a r t e r and i s e x p e c t e d t o b e c o n t i n u e d t h r o u g h t h e n e x t q u a r t e r .

Des ign and f a b r i c a t i o n o f a l a b o r a t o r y water v a p o r / t u r b i d i t y pho tomete r was c o m p l e t e d ; f i n a l c h e c k o u t and c a l i b r a t i o n w i l l t a k e p l a c e d u r i n g t h e n e x t q u a r t e r . A hand-held b a t t e r y - p o w e r water v a p o r / t u r b i d i t y p h o t o m e t e r w i t h s e l f - c o n t a i n e d r e a d o u t d i s p l a y h a s been d e s i g n e d . F a b r i c a t i o n o f t h i s u n i t i s i n p r o g r e s s and w i l l b e comple t ed d u r i n g t h e n e x t q u a r t e r .

Dur ing t h i s q u a r t e r 1 , 7 1 2 module tests and 86 c e l l t e s t s were r u n on t h e JPL LAPSS. The same l e v e l o f e f f o r t i s e x p e c t e d t o c o n t i n u e . t h r o u g h t h e n e x t q u a r t e r .

. ..

E. FAILURE ANALYSIS

The s o l a r c e l l module p r o b l e m / f a i l u r e r e p o r t i n g p r o c e d u r e document d r a f t h a s been r ev iewed and r e v i s e d . The r e l e a s e d document ( JPL 5101-26) is e x p e c t e d t o be a v a i l a b l e i n e a r l y May. The document w i l l p r o v i d e a u n i f i e d r e p o r t i n g s y s t e m f o r p r o b l e m / f a i l u r e s r e s u l t i n g from environ-

. . ... . m e n t a l . t e s t i n g .and" . f i . e l d appf + e a t i o n .. . . .. . . . . . . . . .

Dur ing t h i s q u a r t e r p r o b l e m / f a i l u r e r e p o r t (P /FRs) and a n a l y s i s a c t i v i t y o c o u r r e d a8 o u t l i n e d , i n Table. 7-'J fo r B l o c k s 1 and 2. The P/FR r e p o r t i n g h a s been s o l e l y from JPL e n v i r o n m e n t a l and f i e l d t e s t i n g .

The Block 1 f a i l u r e a n a l y s i s showed p rob lems w i t h i n t e r c o n n e c t s f o r Vendors V , Y , and Z C a b l e and t e r m i n a l p rob lems i n Vendor Z modules c a u s e d power i n p u t d e g r a d a t i o n d u r i n g add-on q u a l i f i c a t i o n t e s t i n g . Vendor W module power d e g r a d a t i o n ' a f t e r . n a m i d i t y t e s t i n g was found t o be c a u s e d by m o i s t u r e p e n e t r a t i o n t o ' t h e c e l l m e t a l l i z a t i o n , c a u s i n g c o n t a c t p rob lems .

Table 7-5. Summary o f P/FR A c t i v i t y

New Closed Enyironmental F i e l d vendor Procurement P/FRs P/FRs T e s t T e s t

V Block 1 1 7 . 1 Block 2 6 1 7 1

ki Block 1 9 Dlock 2

Y .Block 1 1 13 13 1 Block 2 13 1

Z Block 1 7 17 33 4 Block 2 10 3 3 3 4

Block 2 p r o b l e m / f a i h r e a n a l y s i s e x p e r i e n c e w i t h Vendor V modules r e l a t e s t o c racked c e l l s and d e l a m i n a t i o n o f e n c a p s u l a n t from t h e s u b s t r a t e a f t e r env i ronmenta l q u a l i f i c a t i o n t e s t i n g . A n a l y s i s shows a l a c k o f bond between l a y e r s o f s i l i c o n e r u b b e r . A materials s t u d y o f t h e problem' is i n p r o g r e s s . Other 'module problems observed were c r a c k s i n t h e m e t a l s u b s t r a t e r e i n f o r c i n g r i b s caused by forming-die c l e a r a n c e . The vendor h a s reworked t h e s e d i e s t o p r e v e n t damage t o f u t u r e modules '

S o l d e r j o i n t s were found t o e x h i b i t c r a c k i n g a t t h e t e r m i n a l s due t o hand l ing . The vendor h a s changed h i s assembly p rocedure t o p r e v e n t e x c e s s i v e working o f ' s o l d e r e d w i r e i n t h e assembly p r o c e s s .

From a n a n a l y s i s o f Vendor Y modules, it was found t h a t t h e v o l t a e e breakdown was caused by n icked e g r e s s wires, which r e s u l t e d i n a d e c r e a s e i n i n s u l a t i o n r e s i s t a n c e when s u b j e c t e d t o h u m i d i t y o r s a l t f o g tests. These :>roblems are a t t r i b u t a b l e t o workmanship.

Vendor Z modules have exper ienced c r a c k i n g o f c e l l s , d e l a m i n a t i o n of e n c a p s u l a n t and changes i n e l e c t r i c a l o u t p u t af ter env i ronmenta l t e s t i n g . The vendor h a s changed h i s p r o t o t y p e d e s i g n by e l i m i n a t i n g t h e u s e o f a d h e s i v e s t o f i x c e l l s t o t h e s u b s t r a t e ( o t h e r t h a n s i l i c o n e r u b b e r ) t o r e d u c e c e l l c r a c k i n g t e n d e n c i e s . A n a l y s i s is c o n t i n u i n g t o d e t e r m i n e o t h e r c a u s e s o f ce l l c r a c k i n g and s h i f t i n g o f e l e c t r i c a l o u t p u t .

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