Solar Energy, Vol. 19, pp. 539-548. Pergamon Press 1977. Printed in Great Britain

SOLAR ENERGY AND THE RESIDENCE-- SOME SYSTEMS ASPECTS

RICHARD C. NEVILLE Department of Electrical Engineering and Computer Science, University of California,

Santa Barbara, CA 93106, U.S.A.

(Received 12 January 1976; in revised form 1 December 1976)

Abstract--The feasibility, in an energy flow sense, of providing heating, cooling and electrical power for individual homes using some form of solar energy converter on the roof of each residence is considered. A model for home power requirements and solar insolation which reflects residence construction, local weather and geographic location is developed. This is used to demonstrate that 50-90 per cent of the homes in the U.S.A. could be self-powered from solar energy providing sufficient insulation is used and adequate energy conversion techniques are developed.

INTRODUCTION

Much has been written [1] about the use of solar energy to provide heating, cooling and power for both home and industrial use. Homes, with all or a significant fraction of their heating furnished by solar energy have been in existence for some time on a pilot basis. Electrical power schemes are either on the small scale (telephone repeaters or NASA type uses on space probes) or of the large 1000s of acres variety producing megawatts of power. Texts and government reports contain studies of the overall energy situation as applied to the world, the nation and the average home[2-4].

A significant fraction of the surface area of any city is covered by residence (single home and apartment) roofs, garage roofs and commercial and industrial roofs. This paper will consider the systems aspects of providing electrical power, heat and cooling to the family residence utilizing the roofs of garage and residence as the energy collecting area. Basically, we will consider the home as a total system. Given a particular city or location in the country, given the weather, temperatures and latitude of this location, what is the expected power usage of a home in that city? Not just power for heating and cooling but power for the use of dishwashers, electric lights, television, tooth brushes, etc. must be considered. Given the weather and roof area, roof orientation (inclined north or south, east or west and at what angle) what is the amount of solar insolation which is available to that particular residence?

Several sizes of homes are examined for 34 specific cities at selected locations around the country. Total energy requirements for each house are computed, total

tFor any particular city, particular residence and particular residents there will be significant local variations on an irregular schedule. For a general approach such as this study, one is constrained to use "average" or statistical data. It is for this reason that the choices made here (and in following sections) have been selected. The overall effect of these choices is somewhat conservative in the sense that household energy requirements are slightly over-estimated while solar insolation is under-estimated. With the human variable (at what temperature is the house kept?; what hours are spent awake?; etc.) present, it is not possible to be more specific.

solar energy-to-electrical energy or heat energy system is determined. The energy conversion system could be[l] sunlight to hot fluid (or gas) to a store (heat of fusion or a bed of hot rocks...)[2], or convert to electrical power with thermocouples, or it could be[3] sunlight to solar cells for storage in batteries or hydrogen with heating being resistance heating or burned hydrogen. Storage could be on site (i.e. in or near the residence) or in some central facility. For this study we want only to determine the overall efficiency of solar energy conversion system required to meet system (residence) energy demands. Any hardware system of energy conversion would then have a yardstick against which one could judge it.

WEATHER EFFECTS

Thirty-four cities in the continental United States, Alaska and Hawaii were selected as giving a represen- tative distribution of varying latitudes and climatic conditions. Data on hours of daylight, temperature and percentage of available sunshine were obtained from the literature [5-7].

Table 1 lists the product of time (in hr) times degrees Farhrenheit difference between interior and exterior temperatures of a residence in each of the 34 cities by month. Each "day" consists of a 68°F, 15 hr "active" period and a 60°F 9 hr "sleep" period.t In many locations high temperatures during summer months force interior cooling which is taken to commence at 78°F. These months are underlined in Table I.

HOUSE

In order to specify the actual energy load for heating and cooling one needs to have a model for a typical residence. Six house areas are considered ranging from 400 ft 2 (an apartment) to 4800 ft 2. Appendix A contains the assumptions used in computing the amount of energy loss from heating and cooling for each house as a function of construction (Type I construction being minimum insulation, Type II average insulation and Type III heavy insulation). In Table 2 the summary design data of each house are presented, including floor area, foundation dimensions and window area. In Table 3 the heat loss in

539

540 R. C. NEV1LLE

Table 1. Hour-°F/month (in 1000s)

Winter Spring Summer Fall City Nov. Dec. Jan. Feb. Mar. Apr. May June July Aug. Sept. Oct. Year Average

Caribou Burlington Concord Boston

25.2 36.46 40.18 34.94 31.25 20.88 11.60 0.12 0.37 0.65 7.92 15.84 225.41 18.78 19.44 31.25 34.97 30.91 26.78 15.84 6.48 0.3 0.0 0.28 3.60 11.90 181.75 15.15 19.44 29.76 32.74 28.22 24.55 15.12 7.20 0.73 0.53 0.68 4.32 11.90 175.19 14.60 14.40 23.81 26.04 23.52 19.55 12.24 4.46 0.0 0.63 0.11 0.20 7.44 132.40 11.03

Buffalo 18.72 28.27 29.26 27.55 24.55 15.12 7.44 0.20 0.09 0.0 2.88 10.42 164.50 13.71 Syracuse 18.00 27.53 30.50 27.55 23.81 13.68 5.23 0.18 0.36 0.17 2.16 9.67 158.84 13.24 New York City 12.96 21.58 23.06 20.83 17.86 10.08 2.23 0.42 0.63 0.63 0.0 4.46 114.74 9.56 Washington D.C. 12.24 20.09 20.83 18.14 14.88 6.48 0.25 0.63 1.95 1.30 0.0 4.46 101.25 8.44 Atlanta 10.08 15.62 14.63 12.10 9.67 2.88 0.17 2.16 2.19 2.08 0.46 1.21 73.27 6.11 Miami 0.08 0.0 0.09 0.0 0.08 0.54 1.45 2.16 2.88 2.88 2.16 0.63 12.96 1.08

Duluth Minneapolis Chicago Cincinnati Nashville New Orleans

27.36 37.96 41.66 36.29 32.29 32.74 11.90 4.32 0.54 0.0 7.92 14.88 235.73 18.81 24.48 34.97 39.43 32.93 27.53 14.40 5.21 0.26 0.58 0.31 2.88 12.65 195.64 16.30 18.00 26.78 29.08 24.86 21.58 11.52 3.72 0.09 1.03 0.43 0.0 7.44 144.53 12.04 13.68 20.93 21.58 18.82 15.62 6.48 0.25 1.09 2.16 1.46 0.17 3.72 105.96 8.83

I

11.52 17.86 18.60 15.46 11.90 3.60 0.0 2.16 3.02 2.73 0.74 2.23 89.82 7.49 3.60 7.44 7.44 5.38 2.98 0.0 0.76 2.94 3.15 3.15 1.66 0.0 38.50 3.21

Great Falls Omaha Denver Kansas City Albuquerque Fort Worth

22.32 28.27 31.99 27.55 25.30 15.12 8.93 3.60 0.60 0.22 5.76 12.96 182.62 15.22 18.72 27.53 31.99 26.21 20.83 9.36 1.49 0.76 2.72 1.55 0.0 6.70 147.86 12.32 19.44 24.55 26.78 22.18 21.58 13.68 6.70 0.54 1.49 1.15 1.74 10.42 150.25 12.52 14.40 21.58 24.55 19.49 16.37 6.48 0.16 1.11 4.24 3.04 0.39 2.42 144.23 9.52 12.96 20.83 24.55 16.80 14.14 6.48 0.75 1.80 2.60 2.08 0.25 5.21 108.45 9.04 7.20 12.65 14.14 10.75 6.70 0.50 0.49 3.78 5.43 5.43 2.11 0.0 69.18 5.77

Spokane Salt Lake City Flagstaff Phoenix

20.88 26.04 29.76 23.52 20.09 12.96 6.70 0.12 0.10 0.19 2.88 10.90 154.14 12.85 19.44 22.69 28.27 21.50 18.60 10.80 5.21 3.02 2.60 1.98 1.14 8.93 141.70 11.81 20.88 26.04 28.27 23.52 21.58 15.84 10.42 3.60 0.84 1.67 4.32 13.40 170.38 14.30

5.04 9.67 11.15 8.06 4.46 0.54 2.57 6.75 8.93 7.44 4.89 0.89 70.82 5.90

Seattle San Francisco Fresno Los Angeles Santa Barbara

15.12 17.86 20.09 16.13 15.62 11.52 6.70 3.60 0.46 0.18 3.60 9.67 120.55 10.13 7.20 11.16 11.90 9.41 8.93 5.48 5.23 2.88 1.49 1.49 0.72 2.98 69.87 5.82 7.92 13.39 14.14 14.14 7.44 2.88 0.61 1.89 5.21 4.60 2.06 1.53 75.81 6.32 2.89 5.95 8.18 6.72 5.95 5.04 0.78 0.0 0.0 0.0 0.0 0.21 35.72 2.97 5.04 8.18 5.64 7.39 6.70 5.04 2.97 0.90 0.0 0.0 0.0 0.0 41.86 3.49

Fairbanks Honolulu Brownsville

43.92 54.31 49.10 45.70 41.66 25.92 13.39 5.04 3.72 8.18 15.12 29.02 335.08 27.92 0.0 0.0 0.0 0.0 0.0 0.0 0.54 1.20 1.20 0.60 0.60 0.60 4.74 0.35 0.0 0.93 1.64 0.50 0.0 0.35 0.41 3.69 4.62 4.62 3.11 0.81 20.68 1.72

In calculating hour-°F/month, take a home heated to 68 ° for 15 hr during the day, at 60 ° for 9 hr during the night. In summer cooling comes on at 78°F automatically. Underline denotes cooling.

Table 2. Home design data

Area (ft 2) 400 1000 1400 2400 4800 4800 Configuration 16 x 25 ft 25 x 40 ft 25 x 56 ft 30 x 80 ft 30 x 160ft 30 x 80 ft Foundation length 82 ft 130 ft 162 ft 220 ft 380 ft 220 ft Window area (ft 2) 84 160 240 400 1000 1000

tTwo floors.

Table 3. Heat loss (Btu/hr°F) [10]

Area 400 1 0 0 0 1 4 0 0 2400 4800 4800 (2F)

Type I 340 610 840 1330 2660 1870 Type II 240 460 610 960 1870 1330 Type III 150 260 340 510 1050 840

Btu/hr°F is provided for the 6 different areas of houses for

the 3 types of insulation.

locations. These data are presented for a 1400 ft 2 house in

Table 4. In comput ing the total energy requi rement for a

residence, however , one mus t include the requi rement for

lights, cooking, hot water, washing, appliances, etc. The

amoun t of energy used for non-heat ing and cooling purposes can be approximated by Table 5 [2-4, 8, 9].

For locations and weather condit ions demanding

heating energy, En, one can utilize heat f rom a percentage

F rom Tables 1 and 3 one can calculate the energy of the appliance and lighting load, Ea, and the body heat ,

requi rement for home heating and cooling in the various E~, of the residents. Thus , in "winter" the total energy

Solar energy and the residence--some systems aspects

Table 4. Energy/year (kWh/year) for heating and cooling a 1400 ft ~ house

Location

(Type I) (Type II) (Type III) Inexpensive Moderate Expensive insulation insulation insulation

Caribou 55457 40272 22447 Burlington 44730 32482 18105 Concord 43117 31311 17452 Boston 32584 23662 13189

Buffalo 40488 29402 16388 Syracuse 39094 28389 15824 New York City 28240 20508 11431 Washington, D.C. 24923 18099 10088 Atlanta 18035 13097 7300 Miami 3192 2318 1292

Duluth 55558 40345 22488 Minneapolis 48149 34965 19489 Chicago 35574 25833 14399 Cincinnati 26082 18940 10557 Nashville 22109 16055 8948 New Orleans 9492 6893 3842

Great Falls 44940 32635 18190 Omaha 36389 26425 14729 Denver 36977 26852 14967 Kansas City 28123 20423 11383 Albuquerque 26695 19386 10835 Fort Worth 17027 12365 6892

Spokane 37934 27548 15354 S~tLake City 34868 25321 14113 Flagstaff 42664 30982 17269 Phoenix 17430 12657 7055

Seattle 29912 21722 11954 San Francisco 17195 12487 6960 Fresno 18656 13548 7551 Los Angeles 8795 6387 3560 SantaBarbara 10298 7479 4168

Fairbanks 82471 59890 33381 Honolulu 1042 756 422 Brownsville 5090 3697 2060

Table 5. Appliance and lighting energy

Residence area (ft 2) 400 I 0 0 0 1400 2400 4800 Energy(kWh) 18000 21000 24000 27000 30000

required is

where

~ = E. + EA- Ec (1)

Ec=O.7Ea + EB (0.7Ea + EB <O.8Eu)

Ec =O.8Eu (0.7Ea + EB >--O.8Eu).

The limitation on use of appliance and body heat to offset heating requirements arises as a result of the time distribution of heating loads and appliance use. It is assumed for the model that Es is 100 kWh/month in the 400ft 2 apartment and 200kWh/month in the other structures.

541

In those areas where no house heating or cooling is required no deductions or additions for the appliance and personal heat load are made. In those cases where cooling is a requirement then the air conditioning load is increased to account for the appliance and body heat losses. Since one can utilize night-time temperature drops and breezes, this extra air conditioning load is estimated as 80 per cent of the power dissipated (Ea + E~) for inland locations, 40 per cent for eastern and western coastal locations and 30 per cent for Honolulu and Miami.

Table 6 presents the total estimated energy requirement for a 1400 ft 2 house.

SOLAR INSOLATION

The solar constant, or power provided by the Sun at the earth's orbital distance, i s [ l l ]

S = 1.35 kW/m :. (2)

This value must be corrected for scattering losses as the Sun passes through the atmosphere. These losses are in turn dependent on time of day, latitude, month and

Table 6. Total energy requirement 1400 ft ~ house (kWh/year)

Area

Type I Type II Type Ill Inexpensive Moderate Expensive insulation insulation insulation

Caribou 70500 51100 33900 Burlington 58800 42700 31100 Concord 56800 42200 30300 Boston 50400 38000 29200

Buffalo 56300 42900 30800 Syracuse 56700 42900 32500 New York City 47200 35900 28500 Washington, D.C. 45300 34400 28300 Atlanta 44100 34300 31100 Miami 38400 30600 29600

Duluth 69700 51500 34700 Minneapolis 66000 49200 35200 Chicago 56500 45700 33900 Cincinnati 48500 39000 31800 Nashville 47500 36400 31600 New Orleans 42000 33400 32500

Great Falls 60800 45400 34200 Omaha 55100 43700 33000 Denver 54700 41000 30400 Kansas City 52800 40200 32600 Albuquerque 50800 38700 32800 Fort Worth 46200 36000 33100

Spokane 55600 41600 31200 Salt Lake City 53600 40400 30800 Flagstaff 56200 41900 30400 Phoenix 49700 38700 35600

Seattle 43300 32600 26400 San Francisco 34100 26600 25400 Fresno 47300 36400 31300 Los Angeles 31800 25300 24700 Santa Barbara 32200 25600 24900

Fairbanks 91400 67600 42500 Honolulu 34700 27700 27400 Brownsville 45400 36200 34500

SE Vol. 19, No. 5~H

542 R. C, NEVILLE

Table 7. Potential solar energy for selected cities--annual total

North latitude 21018 '

c~

• ~ ~ ~._~ ~ o ~ o ~ 0 ~ :~._ ..=_ ~.__.

z =~u

e~

r)

ea

..- z

25°47 ' 29051 ' 33°27 ' 34025 ' 35°12 ' 36°44 ' 38o54 ' 40°45 '

o )

m ~ c~

4204 ' 44o18 '

g

47°37 '

. ~ < rr~

64048 '

ETp (kWh/m 2 ) 3195 3177 3037 3004 2966 2957 2915 2862 2832 2795 2748 2678 2210 ETpw(kWh/m 2) 2085 2076 1817 2580 2163 2141 2401 1688 1721 1629 1370 1272 1073 EF~at (kWh/m 2 ) 1307 1235 1078 1476 1184 1198 1334 907 1003 849 716 634 423 E,o(kWh/m 2) 1532 1425 1276 1785 1450 1459 1627 1153 1119 1058 900 812 720 E2o (kWh/m 2 ) 1713 1852 1466 2050 1700 1675 1898 1311 1311 1236 1044 952 720 Ewx, o (kWh]m 2 ) 1987 1953 1701 2369 1935 1930 2203 1517 1511 1420 1194 1097 787

Table 8. Annual solar insolation and convertible energy

City

Solar insolation 1400 ft 2 house with Net

10 ° south roof, convertible energy tracking on east- system effectivity

west plane 15% 10% 5% (kWh) (kWh)

Honolulu Miami New Orleans Phoenix Santa Barbara

Flagstaff Fresno Washington, D.C. New York

Boston Burlington Seattle Fairbanks

384000 57,600 38 ,400 19,200 377000 56,500 37 ,700 18,800 328000 49,200 32 ,800 16,400 457000 68,500 45,70t3 22,800 574000 56,100 37 ,400 18,700

372000 55,800 37 ,200 18,600 425000 63,7000 42,500 21,200 293000 43,900 29 ,200 14.600 292000 43,800 2 9 , 2 0 0 14,600

273000 40,900 13,600 13,600 250000 34,500 23 ,000 11,500 212000 31,800 21 ,200 10,600 151000 22,600 15,100 7,500

character of the atmosphere [12, 13]. A major factor arises from non-alignment of the solar energy collector normal and the Sun. A perfectly tracking energy collector results in no losses from this source. A fixed collector yields a power output dependent on the cosine of the angle between Sun and collector normal. One can reduce this deleterious effect by tipping the collector towards the south (in the northern hemisphere)f13]. Table 7 presents the available energy in kW/m 2 for 13 cities selected to indicate latitude variation of the available energy,

Here, Exp is the maximum amount of solar energy available, ErPw is the energy available to an ideal tracking collector after correction for weather[5-7], EF~a, is the energy which a fiat collector will provide, Elo that of a collector inclined 10 ° to the south, E20 inclined 20 ° to south and Ewr.lO the energy supplied per m 2 by a collector inclined 10 ° to the south but with east-west tracking. You will note that weather losses are a major factor.

Table 8 lists, for 13 geographic locations, the incoming

tTracking systems appear to be an economic necessity if solar cells are to be used. The high cost of individual solar cells precludes their use with non-concentrated light[14]. Concen- tration requires tracking to work efficiently.

solar energy for a 1400 ft 2 home with a 10 ° south angled roof-mounted collector utilizing a tracking mechanism.t For a discussion of roof designs, the reader is referred to Appendix B. The power input data listed are given for 3 different system efficiencies (5, 10 and 15 per cent).

DISCUSSION

In considering system efficiencies, one must take into account the solar energy collector itself and must consider storage of the energy and reconversion into desired forms. Such operations yield a wide range of efficiencies, but a detailed discussion of methodology is not the aim of this paper. In general, the method of storage and reconversion used will range from 40-80 per cent in overall efficiency. Solar cells with efficiencies of 15-23 per cent have been reported in the literature [14-16]. At 40 per cent storage efficiency this yields an overall power conversion of 6-9 per cent, while at 80% per cent etliciencies the overall system would range from 12-18 per cent. It would seem that the system efficiencies chosen for discussion represent a pessimistic outlook, a conservative estimate and an optimistic view of system performance (the 15 per cent estimate).

Solar energy and the residence--some systems aspects

Consider the energy inflow-outflow for a residence. From Table 6 (total energy requirements for a 1400 ft: home) and Table 8 (potential influx of solar energy) one can estimate the required efficiency for a solar energy conversion system serving a 1400 ft: home.

Note that a 5 per cent system, while supplying a significant portion of the power available, does not supply the total needs of any single type of residence anywhere. On the other hand, a 10 per cent efficient conversion system satisfies the systems needs of a significant number of locations. A more general presentation of the data for a 1400 ft 2 home with a 10 ° angle roof is presented in Fig. 1.~ In this figure the available solar insolation for 34 cities is given for a 10 per cent efficient system (i.e. the value given is (E~_~o×0.10)×area of roof). Also provided is the energy required to operate the residence with Type I, 1I and III insulation.

In considering what kind of system is adequate, one must determine what one feels is a sufficient power level. Owing to the variances of weather and to the uncertainty of power loads, in order to adequately power a house the residence solar energy converter must supply the estimated needs plus a safety factor of 10 per cent. The 10 per cent efficient 10 ° roof with tracking system adequately powers residences in Honolulu, Santa Barbara, Los

tThe effective area of the roof has been reduced in each case to account for shadowing of one tracking assembly by another. The resulting insolation estimate is conservative.

543

Angeles, San Francisco, Fresno, Phoenix and Miami, if one considers only Type II insulated homes, Type IiI houses would add Salt Lake City, Flagstaff, Albuquerque, Fort Worth and New Orleans to the list of locations with system self-sufficiency. The Type 1 insulation home is satisfactory only for Los Angeles, Santa Barbara, and Honolulu. A 15 per cent efficient system would expand the number of solar-power locations for 1400ft: houses, adding locations as far north as New York. Figures 2-6 present data on energy flow for homes of 400, 1000, 2400 and 4800 ft.: (both 1 and 2 floor locations) and 10 ° angled roofs. As in Fig. 1, all three classes of home insulation are given as well as the insolation at a 10 per cent conversion efficiency. Persual of these figures indicates that: (1) the larger homes have an advantage in that energy require- ments increase more slowly than energy input; (2) two-story houses are a poor arrangement in terms of energy flow; (3) Type I (minimal insulation) homes are not economic except along the southern portion of the Pacific Coast and in Hawaii; and (4) Type III homes are required over most of the nation.

CONCLUSIONS

A significant fraction of the area of any city is composed of the roofs of the residences of its population. A model has been developed for the energy inflow and outflow for individual residences of varying size and degree of insulation. The model has been checked against reported regional results and found to be in agreement.

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AVAILABLE SOLAR EDERGY (I0~ SYSTEM) CARIBOU

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Fig. 1. 1400 ft 2 house. Yearly energy requirement (in thousands of kWh) for Type I, II and II] insulated homes and available solar energy for a l0 per cent system with east-west solar collector tracking and 10 ° angle (in thousands of

kWh).

544 R. C. NEVILLE

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Fig. 2. 1000 ft ~ house. Yearly energy requirement (in thousands of kWh) for Type I, II and III insulated homes and available solar energy for a 10 per cent system with east-west solar collector tracking and 10 ° angle (in thousands of

kWh).

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CARIBOU

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Fig. 3. 2400 ft 2 house. Yearly energy requirement (in thousands of kWh) for Type I, II and III insulated homes and available solar energy for a 10 per cent system with east-west solar collector tracking and 10 ° angle (in thousands of

kWh).

Solar energy and the residence--some systems aspects 545

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ENERGY REOUIREMEHTS AVAILABLE SOLAR Et, ERGY (101 SYSTEM)

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Fig, 4. 4800 ft 2 house (single floor). Yearly energy requirement (in thousands of kWh) for Type I, II and III insulated homes and available solar energy for a 10 per cent system with east-west solar collector tracking and 10 ° angle (in

thousands of kwh).

• FAIRBANKS 189.4/137.8/91,4

23.7 ENERGY RFOUIREMENT$

AVAILABLE SOLAR ENERGY (10% SYSTEI'I) CARIBOU 135.7/99.8/70.5

_ ~ BURLINGTON .'

42.8

GRF.AT FAHS / • BUFFALO

t~ 46.9 I 1 3 ~ ~ f / ~ 39 ",,(1)l, llfiN~mtlS //7 N ") ? - - ~~BOSTOr(

y -k \ (k N/J/ ~ S | SAi'i FRAI|C 1SCO ~ ~ "/ ~ aOlS/Sa.y,17.2 j I ~$0.4/4_0.g_/34.1 ~ CCAI T I AVI~ rlTV k .... / ~HICA.qO 45.5 j,) ~ . / 50 Z K I ~ I, p l l l • Olk~'mmA 102.5/76.2/56.5 96.2/75 1/55.6 7 - - 53"1 07.5 8.2 5 1 45 •

b ~ ~ ~ - - " 45.7 T

.2 $6.8 47.3 - - 49.1 g'~")

ANGELES "~. ~ ~.T / 81.4/~s/~0.8 ) ~.3 / - , 38/33.5/31.8 ~ f l 61.9 / ' . . . . . . . . {'

s7.1 • AII.AIWt PHOENIX 7 65.5/54.4/44.1 63 915 8/49 Z

. ~ , , ,~NEW ORLEANS~ N "t

" 3~ 0 lli~O~sU- 4LY 34.7 ~,~ f 5. ~

i t41A,~Z BROI.#ISVI LLE ,.3/~j135.4 ..7/~:o.~.4

Fig. 5. 4800 ft = house (two floor). Yearly energy requirement (in thousands of kWh) for Type I, I1 and III insulated homes and available solar energy for a 10 per cent system with east-west solar collector tracking and 100 angle (in

thousands of kWh).

546 R.C. NEVILLE

• FAIRBANKS 4z,s/~1.~gm.4

ENERGY REOUI REMENTS AVAILABLE SOLAR Er~ERGY (10% SYSTEr, I)

s _X _ _

6 ~ DULUTH ~ v _ ~ ,

{, fzs.V!9.O./le.6 - U) SALT ~ CITY ~ 1 .. . . . ," ~ ,n~ t~

. . . . ' T3':i , ' ' ~ ~ It33.0124.7J2Zl. 11.'~ W~

~- _ E J ' ~ DE~R ~ CINCINNAT] ,o,.,-.~ 30 9/2z .9/z1 3

• ' 1 " • 1 .8 23.6 22.8

BARBARA " • NASHV ~ J / ~ • FLA~TAFF ,..~_._ / • NASHVILLE LOS ~ ' -3o.41zz.~/zo.s P A I . B U ~ ~ 3)~:~/22.a ANGELES ~.. ~ 1 4 . 7 / 32.8/23.8/22.9 ) 12.9

74.7/13.S/13.3~ f ./ 15.6 1

' " ' t ) ( 17.9 t FORT WORTH ~ 13

~ t _ _ ~ ,,~ "lx)NEW ORLEANS

HONOLULU - ~ ~ 13.3 ~r.v~o:4/2o.s \

,s~ B ROWrlSV}I ~I~E

BURLINGTON

NEW YORK CITY q! 28,8 /21 .3 /20 .4

11.5 •

CARIBOU

Q . ,

BOSTOri

~.~ ~tlAMI 29.6 /22 .1 /21 .7

14.9

Fig. 6. 400 ft 2 residence. Yearly energy requirement (in thousands of kWh) for Type I, II and III insulated homes and available solar energy for a 10 per cent system with east-west solar collector tracking and 10 ° angle (in thousands of

kWh).

This model is used to examine the possibilities of completely satisfying the energy requirements for an individual home via a solar energy converter on the home roof. The model does not address itself to the technical nor to the economic details of the problem but does provide an answer as to its possibility. Study of power inflow-power outflow patterns indicates that, with good to excellent levels of insulation (defined herein) and an obtainable solar energy conversion system (10 per cent efficiency including storage), one third to one half of the country's residences could be powered by solar-con- verters on their roofs.

A solar energy conversion system operating at a 15 per cent efficiency level combined with an excellent level of residence insulation (see text for details) is capable of satisfying the energy requirements of in excess of 90 per cent of the country's homes.

REFERENCES 1. Many references exist for solar energy use in and about the

home. As a general background, and for some ideas on energy conversion and use, the reader is referred to: (a) Proc. of the World Symposium on Applied Solar Energy, Phoenix, Arizona, Johnson Reprint Corporation, 111 Fifth Ave., New York, NY 10003 (1955). (b) Introduction to the Utilization of Solar Energy (Edited by A. M. Zarem and D. D. Erway). McGraw-Hill, New York (1%3). (c) Eighth lntersociety Energy Conversion Engng Conf. Proc., University of Penn- sylvania, Philadelphia (1973). (d) Architectural Guidelines to

Promote Effcient Energy Use, Hearing before Energy Subcommittee of Committee on Public Works. (e) J. E. Small, P. R. Achenbach and S. R. Peterson, Science 192, 1305 (1976).

2. Federal Energy Administration, Project Independence Report (1974).

3. Energy Facts, Subcommittee on Energy, House Committee on Science and Astronautics, House of Representatives (1973).

4. Conservation and Efficient Use of Energy, 26th Report, Committee on Governmental Operations, House of Re- presentatives (1975).

5. The Weather Almanac (Edited by J. RuNner and F. E. Blair) Gale Research Co., Detroit, Michigan (1974).

6. The Weather Handbook (Edited by H. McKinley and L. Liston) Conway Research, Atlanta, Georgia (1974).

8. Energy Outlook for the 1980s, Joint Economic Committee, Congress (1973).

9. Research Development and the Energy Crisis, Committee on Science and Astronautics, House of Representatives (1973).

10. Lange's Handbook of Chemistry,, 8th Edn, p. 846, Handbook Publishers, Inc., Sandusky, Ohio (1952).

11. M. P. Thekaekara, Solar Energy 14, 109 (1973). 12. International Symposium on Solar Radiation Simulation,

Institute of Environmental Sciences (1965). 13. A. M. Zarem and D. D. Erway (editor) Introduction to the

Utilization of Solar Energy, Chap. 3, McGraw-Hill, New York (1963).

14. GaAs Concentrator Solar Cells (Edited by L. W. James and R. L. Moon) Photovoltaic Specialists Conference, Phoenix, Arizona, May 1975, Published by the Institute of Electrical and Electronics Engineers, Inc., 345 East 47th Street, New York, NY 10017.

15. J. L. Loferski, lAP 27, 777 (1956). 16. Electronics, p. 41 (1975).

Solar energy and the residence--some systems aspects 547

APPENDIX A

MODEL HOUSE DESIGN

In computing the energy requirements for heating and cooling a residence, a completely theoretical approach was taken. The end results were then checked with known local values (2), (4), (8) and found to be in agreement.

The rough outline of each size of home is given in Table 2. Three typical variations, having to do with degree of insulation of the home, of each home size were taken. A Type I home is a low-cost, low-insulation scheme, Type I1 is a medium-cost, medium- insulation scheme and Type III is a high-cost, high-insulation scheme. In greater detail:

Examination of Fig. B, indicates that, combining esthetic (consumer resistance to radical changes in housing appearance is a fact of life) and economic reasons, the 10 ° angle solar roof appears

Table B,. Useable roof area

House floor 400 1 0 0 0 1 4 0 0 2400 area (ft :)

Roof area 85 163 215 335 (M 2)

(2 floors) 4800

(1 floor) 4400

335 637

Type l II III

Roof Flat roof Peaked-air space Peaked insulation Walls Block Brick with Double-layer

insulation insulation Floor Slab Slab Wood-post and Beam Glass Standard Double-pane, storm Double-pane, storm

windows in winter windows in winter Doors Standard Heavy Insulated and

Heavy Foundation Reinforced concrete

Some description of the various terms above is in order. (1) Roo/s. A flat roof consists of an asphalt-like layer on wood, a 4 in. air space and the ceiling. The air space contains insulation and 2 x 4 in. boards on 12 in. centers. A peak roof contains a slanting roof with the shingles followed by approximately 3 ft of air space, 6 in. of insulation and the ceiling. In Type III houses the insulation in 2 ft thick in the air space.

(2) Walls. Block walls mean cinder block walls with interior plaster or wooden sheathing. Brick walls have an insulation-filled air space between the brick and interior house plasterboard wall. Double-layer insulation means an additional layer of wood (1 in. thick) between the outside brick (or stone) and the insulation-filled air space.

(3) bToors. All floors include a carpet. Slab floors are double concrete layers of total 6 in. thickness. The wooden floor is a minimum of 1 in. thick on posts at least 30 in. tall.

(4) Glass. Double-pane indicates 2 layers of 1/8 in. glass with an insulating dead-air space between. Storm windows would then be a third layer of glass.

(5) Doors. A heavy door has wood panels 0.5 in. thick surrounding a 1 in. air space. Insulating the air space converts to an insulated door.

(6) Foundations. Foundations include supports for fireplaces. The 1400 and 2400 ft 2 homes have 1 fireplace each and the 4800 ft 2 homes have 2 fireplaces each.

APPENDIX B

RESIDENCE DESIGN--ROOF

From Table 2 one can determine the configuration for the several home areas considered. The data in Table 7 consider five potential roof solar energy collecting systems (the top row--ideal potential energy is not feasible). The most inexpensive system would be a flat roof--it also is the least efficient for solar energy. Next in cost come the 10 and 20 ° angled roof systems. The 2 tracking systems (east-west with a 10 ° roof and the ideal tracking system) are both liable to be expensive systems, requiring sub- stantial engineering, Figure B , attached, gives profile views of the various roof configurations together with their areas. The tracking systems' areas should be reduced from the figures given in (B0, owing to interference between individual tracking units.t

tAssume that the entire roof is not a single tracking entity, as this would be poor economics and a complex piece of engineering.

Floor Area

25'x16'

(400 f t 2 )

Roof Angle 0 ° i0" 20 °

Roof Area 84 86 P. 9

(M 2 )

Floor Area

25'x40'

(1000 ft 2 )

25'x56'

(1400 ft 2 ) Roof ~ngle 0* i0 ° 20"

Roof Area (M 2 )

1000 ft 2 163 165 173

1409 ft 2 215 218 228

Floor Area

31'x80'

(2400 f t 2 a n d

2 story 4800 ft 2)

30'x160'

(4800 ft 2 )

-1 [ Roof Angle 0 ° i0" 20*

Roof Area (?~2)

2400 and 334 339 356

2 story

4~00 ft 2

4800 ft 2 631 642 670

1 story

- - Flat Roof ..... Twenty Degree Roof

__ __ __ Ten Degree Roof 5' overhangs assumed

Fig. B~. Roof profiles.

to be optimum. Note that 5 ft overhanges are used in all cases. The roof areas listed in Fig. B~ are total areas. If one excludes

the roof area which must be used for vent pipes, chimneys, TV aerials, drain pipes, etc. the effective roof area is that given in Table B,.

548 R, C. NEVILLE

Resumen--Se considera la factibilidad, en un sentido de flujo de energfa, de provisi6n de calefacci6n, enfriamiento y electricidad para casas individuales usando algunas formas de conversores de energfa solar sobre el techo de cada residencia. Se desarrolla un modelo para requerimientos domiciliarios de energia y la insolaci6n, que refleja la construcci6n de la residencia, el climalocal y la ubicaci6n geogrflfica. Este es usado para demostrar que entre el 50% y el 90% de las casas en los EE.UU. de America pueden ser autoenergetizadas solarmente con tal que se use suflciente aislaci6n y sean desarrolladas t6cnicas de conversi6n adecuadas.

R6sum6--On 6tudie la possibilit6, du point de rue 6nerg6tique, de produire la puissance de chauffage, de r6frig6ration et la puissance 61ectrique, pour des maisons individuelles utilisant une forme quelconque de convertisseur 6nerg6tique solaire sur le toit de chaque r6sidence. On d6veloppe un module qui tient compte des besoins domestiques en puissance, insolation, de la construction de la r~sidence, du temps m6t6orologique local et de l'emplacement g6ographique. Celui-ci est utilis6 pour d6monter que 5T ~ 90% des maisons aux USA pourraient 6tre autonomes 6nerg6tiquement gr~,ce/t l'6nergie solaire ~ la condition d'utiliser une isolation sutfisante et de d~velopper des techniques ad6quates pour la conversion de l'6nergie.