Parabolic Trough ReceiverParabolic Trough Receiver

Thermal PerformanceThermal Performance

Parabolic Trough Workshop

Golden, Colorado

March 9, 2007

NREL/PR-550-41422

Parabolic Trough Receiver or Heat Collection Element

Parabolic Trough Receiver orParabolic Trough Receiver or Heat Collection ElementHeat Collection Element

• Key to good performance at parabolic trough power plants – Problems with glass breakage appears to be resolved with new

designs and O&M procedures. – New receivers improve optical and thermal performance

Source: Solargenix – APS 1-MW Trough Plant

2

Parabolic Trough Receiver or Heat Collection Element

Parabolic Trough Receiver orParabolic Trough Receiver or Heat Collection ElementHeat Collection Element

Protective Shielding for

Glass-to-Metal Seal Solel UVAC

Bellows & Glass-to-Metal Seal

New Solel UVAC Receiver Borosilicate Glass Tube w/ Anti-Reflective Coating

Stainless Steel Tube w/ Cermet Selective Coating

Getters to Absorb Gases (Hydrogen)

New Schott Bellows

3

Parabolic Trough Receiver Thermal Testing

• Outdoor – Thermal Loop Tests – Use measurement of flow and temperature difference to

calculate energy gained or lost. – Sandia Rotating Platform, Plataforma Solar de Almería

EuroTrough Collector, SEGS Collector Test Loops

• Indoor – Electric resistance heating

• Heat receiver to steady state temperature • Electric power consumed is the thermal loss

– DLR, Schott, ENEA,NREL

4

Parabolic Trough Receiver Thermal Testing

• Receiver testing on AZTRAK rotating platform @ Sandia • Luz Black Chrome (1993) • Luz Cermet (1993) • Solel UVAC (2003) • Schott Cermet (2004)

• Advantages • 2-Axis Tracking • On-sun or off sun testing

• Disadvantages • Only one collector element tested & 2 receivers • Low precision on measurements

5

AC

Curve fit equation:

η = 78.59 - 0.0357T - 4.33x10-6T2

Eff

icie

ncy

(%)

Parabolic Trough Receiver Thermal Testing

Efficiency vs. Average Fluid Temperature Above Ambient for the LS-2/Schott HCE system

100

at about 1000 W/m2 DNI

LS-2/Schott HCE Efficiency Curve Fit for LS-2/Schott HCE

90 Curve Fit for LS-2/UV 2 HCE (1994) Luz

80

70

60

50

0 50 100 150 200 250 300 350 400

Average Fluid Temperature Above Ambient (oC)

6

Parabolic Trough Receiver Thermal Testing

• Receiver testing on EuroTrough Prototype @ Plataforma Solar de Almería • Solel UVAC • Schott Cermet

• Advantages • Full collector tested

(more receivers)

• Better precision • Disadvantages

• Single E/W axis tracking • Reduced test flexibility

7

Parabolic Trough Receiver Thermal Testing

• Receiver testing on ENEA Loop • Schott Receiver • ENEA Receiver (Summer 2007)

• Advantages • Molten Salt Test • Higher Temperatures • Two Collectors

8

Parabolic Trough Receiver Thermal Testing

• Loop Testing at the SEGS • Solel UVAC (SEGS VI) • Schott Cermet (SKAL-ET, SEGS V)

• Advantages • Field testing in normal operation • Full loop tested • Comparison to other loops

• Disadvantages • Many factors affect results • Limited control of test

9

UVAC / Cermet Comparision - SEGS VI

0%

20%

40%

60%

80%

100%

120%

5:00 7:00 9:00 11:00 13:00 15:00 17:00 19:00

Ther

mal

Effi

cien

cy -

%

0

200

400

600

800

1000

1200

Inso

latio

n - W

/m^2

UVAC Loop (3/4) Base Loop (5/6) Insolation 3/28/01

UVAC Test Loop Results @ SEGS VI Performance or 192 HCEs

10

Receiver Thermal LossIndoor Test Stand

Receiver Thermal LossReceiver Thermal Loss Indoor Test StandIndoor Test Stand

DLR Receiver Test Lab • Electric resistance heating• At steady state power consumption is equal to thermal losses

11

Receiver Thermal LossIndoor Test Stand

Receiver Thermal LossReceiver Thermal Loss Indoor Test StandIndoor Test Stand

Calvin Feik, Ray Hansen, Steve Phillips,NREL Receiver Test Lab Al Lewandowski, Carl Bingham, Judy Netter,• Electric resistance heating Chuck Kutscher, Frank Burkholder

• At steady state power consumption is equal to thermal losses

• Similar to approaches used by DLR & Schott

12

13

Receiver Test ResultsReceiver Test ResultsSolel UVAC 2Solel UVAC 2

0 50 100 150 200 250 300 350 400 4500

50

100

150

200

250

300

350

400

450

500

550

600

0

10

20

30

40

50

60

70

80

90

100

110

120

Sandia UVAC2 (2003)Sandia UVAC2 (2003)Loss (W/m)=0.47*∆T+6.11E-09*∆T4

T* - Tambie nt (°C)

The

rmal

Los

s (

W/m

HC

E le

ngth

)

in liquid cool-down tests, T* = Tfluidin electric resistance testing, T* = Tabsor ber

Ther

mal

Los

s (W

/m2 c

olle

ctor

ape

rture

)

EuroTrough UVAC (2002)EuroTrough UVAC (2002)Loss (W/m)=0.44*∆T+8.40E-09*∆T4Loss (W/m)=0.44*∆T+8.40E-09*∆T4

Thermorec UVAC (2004)Thermorec UVAC (2004)Loss (W/m)=0.32*∆T+9.38E-09*∆T4Loss (W/m)=0.32*∆T+9.38E-09*∆T4

Collector aperture area = 39.2 m2Collector holds 2 HCEs

HCE length = 4.08 m

NREL UVAC2 (2007) NREL UVAC2 (2007)

Loss(W/m)=0.41*∆T+1.11E-08*∆T4Loss(W/m)=0.41*∆T+1.11E-08*∆T4

14

Receiver Test ResultsReceiver Test ResultsSchott PTR70Schott PTR70

0 50 100 150 200 250 300 350 400 4500

50

100

150

200

250

300

350

400

450

500

550

600

0

10

20

30

40

50

60

70

80

90

100

110

120

Sandia PTR70 (2005)Sandia PTR70 (2005)

Loss (W/m)=0.26*∆T+9.50E-09*∆T4Loss (W/m)=0.26*∆T+9.50E-09*∆T4

T* - Tambient (°C)

The

rmal

Los

s (

W/m

HCE

leng

th)

in liquid cool-down tests, T* = Tflu idin electric resistance testing, T* = Tabsorber

Ther

mal

Los

s (W

/m2 c

olle

ctor

ape

rture

)

EuroTrough PTR70 (2004)EuroTrough PTR70 (2004)Loss (W/m)=0.33*∆T+1.54E-08*∆T4Loss (W/m)=0.33*∆T+1.54E-08*∆T4

Thermorec PTR (2004)Thermorec PTR (2004)

Loss (W/m)=0.33*∆T+1.16E-08*∆T4Loss (W/m)=0.33*∆T+1.16E-08*∆T4

Collector aperture area = 39.2 m2Collector holds 2 HCEs

HCE length = 4.08 m

NREL PTR70 (2007)NREL PTR70 (2007)Loss(W/m)=0.39*∆T+1.21E-08*∆T4Loss(W/m)=0.39*∆T+1.21E-08*∆T4

Receiver Field SurveyReceiver Field Survey For FPL EnergyFor FPL Energy

Receiver Field Survey

With Infrared Camera

Sky

Mirrors

Receiver

Cool Receiver

Hot Receiver

Temperature Varies

15

HCE Losses vs.HCE Losses vs. Glass TemperatureGlass Temperature

Rec

eive

r The

rmal

Los

ses

(W/m

)

1000

1200

1400

For a known wind speed and ambient temperature, …

400

600

800

• Receiver thermal losses are a function of the glass

200 temperature. 0

0 m/s 1 m/s 2 m/s 4 m/s 8 m/s

0 50 100 150 200

Glass Envelop -A mbient Air Temperature (C) • Receiver condition doesn’t

matter (vacuum, lost vacuum, hydrogen)

16

17

10 Cross-Sections

Max of Cross-section

Maximums107ºC

10 Cross-Sections

Sky Temperature

Mirror Glass Temperature

Temperature Profiles of Cross-Sections

Receiver Glass Temperature

Min ofCross section

Maximums93ºC

Top

of L

ine

Average ofCross-section

Maximums98ºC

Max Min ofCross-section

Maximum14ºC

Tem

pera

ture

(ºC

)

Bot

tom

of L

ine

IR Camera Analysis SoftwareIR Camera Analysis Software

-

–

Max of Cross-section

Maximums 107ºC

10 Cross-Sections

Sky Temperature

Mirror Glass Temperature

Temperature Profiles of Cross-Sections

Receiver Glass Temperature

Min of Cross-section

Maximums 93ºC

Top

of L

ine

Average of Cross-section

Maximums 98ºC

Max – Min of Cross-section

Maximum 14ºC

Tem

pera

ture

(ºC

)

Bot

tom

of L

ine

18

Solel UVAC2 Solel UVAC2 (2 years old) with Vacuum(2 years old) with Vacuum

Visible Image of Receiver – Not Tracking

Infrared Image – Not Tracking (Glass Temp. 63ºC-66ºC )

Infrared Image – Tracking (Glass Temp. 68ºC-71ºC)

Visible Image of Receiver – Not Tracking

Infrared Image – Not Tracking (Glass Temp. 63ºC-66ºC )

Infrared Image – Tracking (Glass Temp. 68ºC-71ºC)

19

Luz Cermet with VacuumLuz Cermet with Vacuum

Visible Image of Receiver – Not Tracking

Infrared Image – Not Tracking (Glass Temp. 124ºC-141ºC )

Infrared Image – Tracking (Glass Temp. 138ºC-267ºC)

Getter dust is causing hot spots on the glass

Visible Image of Receiver – Not Tracking

Infrared Image – Not Tracking (Glass Temp. 124ºC-141ºC )

Infrared Image – Tracking (Glass Temp. 138ºC-267ºC)

Getter dust is causing hot spots on the glass

Field Test ResultsSEGS VI

Field Test ResultsField Test Results SEGS VISEGS VI

Gla

ss E

nvel

op -

Am

bien

t Tem

p. (º

C)

50

100

150

200 Black Chrome w/ Getters Cermet w/ Hydrogen Remover Cermet w/ Getters

Hydrogen0

240 260 280 300 320 340 360

Heat Transfer Fluid - Ambient Temperature (ºC)

20

Receiver Field SurveyReceiver Field Survey ConclusionsConclusions

• IR camera provided a good approach for evaluating condition of a large number of receivers in the solar field. – A highly automated approach for imaging receiver and analyzing data

developed – Good agreement between IR camera and thermocouple measurements – Able to take measurement while collectors tracking – Approximately 12,000 images of receivers taken (out of ~90,000

receivers) • Results from testing:

– Able to evaluate performance of various generations of original and replacement receivers.

– Getter dust, dirt on glass, or fluorescent coating failure cause increased glass temperatures.

– Results indicate a potential hydrogen build-up in receivers in solar field

21

IR Camera SystemIR Camera System UpdatesUpdates

• Improved automation of image acquisition – Integration of GPS for automated acquisition of

images. GPS Antenna

GPS Heads-up Display

IR Camera

22

Infrared Camera Measurements through Glass

23

24

Absorber Surface Temperature Measurement Results

Spectrometer

Fiber optic cable

RF Power Supply

RF Antenna

Spectral Acquisition

NonNon--Invasive MeasurementInvasive Measurement of Gases in Trough Receiverof Gases in Trough Receiver

• Confined gases under low pressure emit characteristic spectra when a high voltage discharge is allowed to pass through the gases.

• The characteristic emission wavelengths provide the identity of the gas and the intensity of the emissions are proportional to the amount of gas.

25

Spectrometer

Fiber optic cable

RF Power Supply

RF Antenna

Spectral Acquisition

Developed by:

Bob Meglen Latent Structures

&

Ed Wolfrum NREL

1.4

Receiver Test ResultsReceiver Test Results Gas MeasurementGas Measurement

Getter

Fiber Optic and

RF Antenna

Hydrogen Emission ~250-350 mtorr

Tem

pera

ture

(C)

TI08 TI09 TI17 TI18 TI19 H-Pred(torr)

Thermal Test Results 3S (06-03-08)

450

400

350 1

300

0.8

250

0.6

200

0.4 150

0.2100

050 0 -0.2

8 9 10 11 12 13 14 15 16 17 18

time of day (hrs)

Hyd

roge

n E

stim

ate

(torr)

• Hydrogen detected above ~300ºC • Corresponds to Increase in Glass Temperature &

Increased Thermal Losses on Hot Receiver

26 1.2

27

Receiver Test ResultsReceiver Test Results

0 50 100 150 200 250 300 350 400 4500

200

400

600

800

1000

1200

Tabsorber - Tambient (°C)

HC

E h

eat l

oss

(W/m

HC

E le

ngth

) NREL test bed UVAC2NREL test bed UVAC2Loss (W/m)=0.41*∆T+1.11E-08*∆T4Loss (W/m)=0.41*∆T+1.11E-08*∆T4

NREL test bed Schott PTR70NREL test bed Schott PTR70Loss (W/m)=0.39*∆T+1.21E-08*∆T 4Loss (W/m)=0.39*∆T+1.21E-08*∆T 4

NREL test bed UVAC2 with H2 in annulusNREL test bed UVAC2 with H2 in annulus

hydrogen starts coming out of getters

Receiver

Receiver Test ConclusionsReceiver Test Conclusions ConclusionsConclusions

• Outdoor testing – 2-axis – Single collectors – Field Test Loops

• Indoor testing • Rapid Field Observations

28

Mirror Washing

High Pressure Spray with Demineralized water

29

Mirror Washing

Deluge wash with Demineralized water

30

31

Thank You