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REGIONAL CONCEPTUAL DESIGN AND

ANALYSIS STUDIES FOR

SAND78-7039 DOCUMENT NO. 78SDS4239

JANUARY 1979

RESIDENTIAL PHOTOVOLTAIC SYSTEMS

CUSTOMER:

CONTRACT:

FINAL REPORT

EXECUTIVE SUMMARY VOLUME I

SANDIA LABORATORIES

P.O. NO. 05-6177

s,·uoY PERIOD: SEPTEMBER 1977 THROUGH SEPTEMBER 1978

ADVANCED ENERGY PROGRAMS

GENERAL. ELECTRIC SPACE DIVISION

Valley Forge Space Center

P. 0. Box 8555 • Philadelphia, Penna. 19101

NOTICE

This report was prepared as an account of work sponsored by the United States Government. Neither the United States nor the United States Department of Energy, nor any of their employees, nor any of their contractors, subcontractors, or their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy completeness or usefulness of any information, apparatus, product or process disclosed, or represents that its use would not infringe privately owned rights.

Printed in the United States of America Available from

National Technical Information Service U. S. Department of Commerce

5285 Port Royal Road Springfield, Virginia 22161

Price: Printed Copy $5.25; Microfiche $3.00

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Section

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TABLE OF CONTENTS

INTRODUCTION AND OBJECTIVES o •

CON CL US IONS • • • • • • • • • o • • • • 0 • • • •

APPROACH • • • • • 0 . . . . . . . . . . WEATHER REGION DETERMINATION •

RESIDENCE DESCRIPTION • • • • •

. . . . . . . . . . e e O e e e e e e 0

SPACE CONDITIONING LOADS e e e a e e O e e e e O e

OTHER HOME ENERGY DEMANDS • 0 e e • e D

SYSTEM DEFINITION • • • • • o • • • • • • e e O 0

ANALYTICAL MODELS • • • • • o • • • • 0 • • • • •

ECONOMIC MODEL •

COST DATA • • o . . . . . . .

• • • 0 . . SUBSYSTEM PERFORMANCE • o • • o • • • • o

SUMMARY OF ECONOMIC VIABILITY o • • • • • ..

COMPARISON OF PV SYSTEM PERFORMANCE • •

CORRELATION OF PV-ONLY SYSTEM OUTPUT. • •

0 • 0 0

SIDE-BY-SIDE SYSTEMS • • • • • • • • • • • • • • 0

COMBINED PV /THERMAL SYSTEMS • • •

ECONOMIC PARAMETRIC VARIATIONS

EXTENSIONS OF PERFORMANCE AND ECONOMIC RESULTS •

COMPARISON OF WEATHER DATA • •

HABITABLE HOUSE DESIGN • • • •

RESIDENTIAL TEST FACILITY •

• • • • • 0

. . . . . . 0 0 e

. . . .

PV AND THERMAL TEST SYSTEM DESIGN • e O e O O O e e

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ABSTRACT

Conceptual. design and analyses of photovoltaic (PV) systems were performed for residences applicable to various regions of the United States during the mid-1980 time period. A wide range of roof-mounted array systems was studied including PV-only systems and combined and separate PV /thermal collection systems which provide heat for space conditioning and domestic hot water. The attractiveness of the system options were assessed in terms of performance and economic competitiveness based on hourly weather data for twelve desig­nated regions of the U.S. representing a broad spectrum of climatic characteristics.

The study determined that if PV economic goals are achieved, PV-only solar energy systems for residential use should be emphasized because of their potential economic viability in all regions. On the basis of the costs and benefits used in the analysis, residential systems without batteries are preferred over systems with batteries assuming utility feedback ac­ceptance at some differential buy-back rate such as 40 to 50 percent of the sell rate. Side­by-side PV /thermal systems become more viable across the nation with a PV system cost to thermal system cost ratio of 1. The combined PV /thermal collector systems were eco­nomically unattractive due to the projected performance and costs assumed in the study.

Based on the study results, 'the immediate implementation of a residential test program is recommended. The test program is required to provide early system installation and oper­ating experience, to provide subsystem evaluations, to promote general public acceptance of PVsystems andtostimulatethepotentialPV residential market. Both test-bed facilities and habitable residences should be implemented. Test-bed facilities with PV-only systems with and without battery storage should be considered initially. These facilities would have pro­visions for installing solar thermal collectors at a later time. Parallel efforts with habitable residences having PV-only systems without storage is also recommended.

As part of the study, designs were developed for a habitable test house and a residential test­bed facility to the requirements of the test program. These facilities should be considered in the Southwest, Northeast and Southeast regions of the country in that order.

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1 . INTRODUCTION AND OBJECTIVES

This report presents the results of a comprehensive study on residential solar energy systems which include photovoltaic (PV) solar arrays for electrical power generation and PV /thermal systems. The study was conducted by the General Electric Co./ Ad­vanced Energy Programs for Sandia Laboratories with Dr. Gary Jones of Sandia providing program direction and guidance. The study was carried out over a twelve­month period starting in September, 1977.

The objectives of this study were to assess the technical and economic performance of residential solar energy systems and to select the most attractive systems for future testing. These systems encompassed both photovoltaic generation for residential elec­trical needs, and thermal energy collection for heating, cooling and domestic hot water needs. The technical and economic evaluations were completed based on residence de­signs and cost scenarios projected for the mid-1980's. The analyses were conducted on a regional basis to reflect significant climatic and economic differences. A final ob­jective was to prepare a residential test-bed facility design and a habitable residence de­sign and recommend an order for their implementation leading to systematic long-term development of residentif:I.]. PV and thermal solar energy systems.

In attaining these objectives, the study has developed many generalized results which can be utilized to change economic scenarios assumed in the study and to extend the results to other climatic regions.

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GENERAL ELECTRIC COMPANY Space Division

• • • •

Advanced Energy Programs Valley Forge, Pennsylvania

Project Management

Regional Identification

Load Determination

System Definition

PROJECT TEAM

• Performance and Economic Analyses

• System Cost Evaluation

• System Ranking

• Test Facility Design Features

MASSDESIGN ARCHITECTS AND PLANNERS CENTER FOR GOVERNMENTAL RESPONSI­BILITY

Cambridge, Massachusetts

•

•

•

• •

Residential Energy Conservation Measures

Residential Test Facility Architectural Design

Habitable Test Residences Architectural Design

Test Facility Cost Estimates

Building Code Implications

Gainesville, Florida

• •

Institutional Factor Considerations

Legal Issue Review

7

. IL-__ 2_. c_o_N_c_Lu_s_i_o_N_s __ --1.. _______________ _

The study has led to the following principal conclusions:

1. Most sites studied indicated that residential PV systems show economic viability in the 1986 time frame at 50 ¢ /peak Watt array costs.

2. Immediate implementation of a residential test program is recommended to support technical development needed to assure the projected economic viability of photovoltaic (PV) systems for the 1986 time frame.

3. PV-only solar energy systems for residential use should be emphasized since their potential economic viability was as good as or better than other solar energy options evaluated in all regions.

4. On the basis of costs and benefits assumed, residential systems without batteries are preferred over systems with batteries. Systems without batteries, however, require that utilities accept excess PV output with sell-back rates in the range of 40 to 50 per­cent of the electricity buy rate.

5. Present cost projection for solar thermal systems, and required costs for PV sys­tems to achieve economic viability, indicate a thermal to PV system cost ratio of about 2 to 1. Under this condition, side-by-side systems in the Southwest are eco­nomically viable with low thermal collector areas. At a cost ratio of 1 or less, side­by-side systems become more viable in most regions with thermal collectors occupy­ing more than 30 percent of the roof area.

6. Combined PV/thermal collector systems must show improved performance and reduced costs over those assumed in this study to show economic viability.

7. Test-bed facilities should be initially implemented with simple PV-only systems, both with and without battery storage. Some provision should be included for installing solar thermal collectors at a later time, should cost reductions encourage their use. Be­cause of the relative simplicity of the PV-only approach, particularly without storage, consideration should be given to concurrently erecting several PV-only habitable re­sidences with the test facilities thereby addressing non-technical issues and producing early results and experience. In order of economic preference, the facilities should be considered for the Southwest, Northeast and Southeast regions of the country. An appropriate program would consist of locating separate test facilities in the Southwest and Northeast and habitable residences in each of the three regions.

8. Fixed-panel, roof-mounted, passively-cooled PV solar arrays are the most suitable systems for residential use.

9. PV -only system performance can be correlated as a function of annual insolation levels and heating and cooling degree days to provide estimates of system performance for microclimates. Economic nomographs can also be used to estimate economic viability for these microclimate regions.

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DC/AC GENERAL INVERTER LOADS

FURNACE

VAPOR COMPR.

HEATING

HOT WATER

REPRESENTIVE PV- ONLY SCHEMATICS

RESIDENTIAL TEST FACILITY

HABITABLE TEST RESIDENCE FOR SUNBELT STATES

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3. APPROACH

To implement this study, the following approach to key issues was taken:

1. Weather Data: Performance analyses were based on hourly SOLMET tapes obtained from the National Climatic Center. From the years of record for a particular loca­tion, the most suitable one was selected representing the best average of the signifi­cant variables involved.

2. Regionalization: Analyses were performed at thirteen sites considered to be repre­sentative of various climates within the continental U. S.

3. Residence Characteristics: Residence desi.gns for median-income families of aver­age size (4 to 5 members) used in establishing heating and cooling loads were rep­resentative of those projected for 1986 which incorporate energy conservation fea­tures. Building styles reflected those prevalent in the selected regions.

4. Loads: The magnitude and temporal characteristics of the residence loads were de­fined in detail to assure the acceptance and validity of the final results.

5. Photovoltaic Systems: Conceptual designs were based on current technology regard­ing solar cell efficiencies. Costs reflected those projected for the mid-1980's or those required to achieve overall system economic viability.

6. Solar Thermal Systems: Conceptual designs were based on current technology regard­ing solar collectors and supporting subsystems. Cost projections to the mid-1980's were used in the economic evaluations.

7. Economics: Economic analyses were based on 20-year payback periods with start of operations assumed to be in 1986. Appropriate projections of electricity and fuel esca­lations were taken into account. Resident ownership of the solar energy system was assumed. For those systems involving the sell-back of electricity to the local utility, sell-back rates were treated parametrically in establishing economic break-even levels.

8. System Ranking: The primary system ranking criteria was the system cost-to-benefit ratio which reflects system costs and performance. This system ranking along with non-technical evaluation factors such as region population and growth rates, institu­tional issues and market stimulation was used to define the order for regional test programs.

With this approach, the study flow plan shown on the next page was followed.

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ANALYSIS

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TEST HOUSE DESIGN AND COST

,, TEST PROGRAM

RANKING

TEST FACILITY DESIGN AND COSTS

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4. WEATHER REGION DETERMINATION

The definition of regional weather characteristics for the study was directed toward two primary objectives. The first of these objectives was to provide a division of the conti­nental U. s. into climatic regions. The regions defined contiguous areas having similar solar system performance and residential. energy demand for convenient generalization of study results. The second objective was to select weather data for each of the regions for use in the detailed analysis of system performance and load demand.

Three premises were assumed for initiating the specific selections of sites and regions:

1. Regions could be climatically represented by specific sites.

2. PV system performance could be represented by the available insolation.

3. Residential energy demand could be represented by the space heating and cooling load.

Within the framework of the above premises, the following factors were considered to be of primary importance in the selection of sites and the expansion of site specific data to represent a region of similar climate.

1. Selected sites had to have measured hourly radiation and meteorological data records for a period of several years.

2. Sites had to be geographically dispersed across the U. s.

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3. Sites had to be typical of populated areas, population being a key factor in the potential ~

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for widespread PV usage.

Consideration of these premises and factors with the detailed insolation and heating and cooling degree-day data resulted in the selection of twelve regions with thirteen sites. One region, the Southwest, was represented by two sites, Phoenix and Albuquerque, to recog­nize the major shift in heating and cooling loads created by changes in site elevation vari­ations in this part of the country. Certain areas, particularly in the West, have been cross­hatched to indicate large climatic variability where the use of the representative site weather data may result in significant errors. Variations in weather patterns may be en­countered in these areas due to major changes in elevation, directions of wind patterns created by mountain ranges and valley orientations, other topographic features, and seasonal mixture patterns of polar and maritime air masses.

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. REGIONAL DIVISION

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15. RESIDENCE DESCRIPTION I

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Two basic residence designs were configured by Massdesign for the application of solar energy systems. A one-story wrlt, reflecting the architectural styles in the Swibelt region of the cowitry, has a living area of 141 m2 (1520 ft2) and a roof area suitable for solar array installations of 121 m2 (1300 ft2). A two-story wrlt, reflecting the traditional styles more prevalent in the Northern region of the cowitry, has a similar living area and a steeper roof for snow-shedding with a roof area of 102 m2 (1100 ft2). Both designs have reduced living space projected for future housing, no basement, and a single car garage. Energy conservation features are incorporated such as six-inch fiberglass insulation in the walls, eight-inch fiberglass in the ceilings and double glazing on southern windows and triple glazing on north-facing windows. Aside from the use of a slab, construction was as light as possible because of the projected high cost of materials and the control problems experienced in temperate climates by high-mass buildings. The ceilings of the upstairs rooms in the northern home and wherever practical in the swibelt house are open to the sloping roof. Careful design of the heating system, effective use of insulation and inno­vative application of a clerestory have been combined to assure optimal summer and winter comfort with minimal energy uses.

The floor plans have been arranged to have maximum flexibility and can readily be mod­ified to permit end-to-end contiguous placement. This feature allows an analysis of town houses in the Northern portion of the cowitry. The houses were also designed to permit entry, with minor alterations, from either the north or south side to allow placement on either side of an east-west street.

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RESIDENCE FOR SOUTHERN

(SUNBELT) STATES

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RESIDENCE FOR NORTHERN STATES

ENERGY- SAVING CONSTRUCTION DETAILS OF RESIDENCES

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6. SPACE CONDITIONING LOADS

The architectural sketches were used to identify the thermal characteristics of the various building elements for each exposure and to delineate isothermal zones within the residences. Typical energy conserving behavior patterns by the occupants were modeled to the extent practical. To compute the thermal loads that would exist for the residences, General Elec­tric' s Building Thermal Transient Load (BTT L) program was employed using the model of the building thermal characteristics together with the hourly meteorological and radi­ation data from the SOLMET tapes. Hourly profiles were generated for two dwellings in each of the representative sites chosen. These hourly profiles were then summed for a complete year to obtain annual thermal loads.

For these analyses, it was found that there is, in general, a linear relationship between the seasonal thermal load and the heating and cooling degree days. The slopes of the cor­relation curves are approximately equivalent to adjusted UA factors which include effects of solar gain, internal heat generation and infiltration as compared to the basic UA factor which accounts only for conductance (U) and area (A).

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REGIONS

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PHOENIX

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HEATING DEGREE DAYS (BASED ON 18.3°C)

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SINGLE FAMILY RESIDENCE HEATING LOADS AND HEATING DEGREE DAYS CORRELATION

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REGIONS

1. BOSTON 2. WASHINGTON, D.C. 3. CHARLESTON 4. MIAMI 5. BISMARCK 6. MADISON 7. OMAHA 8. FT. WORTH 9. NASHVILLE

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SINGLE FAMILY RESIDENCE COOLING LOADS AND COOLING DEGREE DAYS CORRELATION

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I 7. OTHER HOME ENERGY DEMANDS

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Energy loads for other than space conditioning were divided into three categories. The first category was that of diversified demand and includes lights and many miscellaneous applications in the modern home. The second group was cooking and clothes drying and the third grouping was heating of water for domestic use. Profiles of the integrated amount of energy used during each hour of the day for the various categories of energy usage were developed for 1977 by utilizing a wide variety of references and are shown on the opposite page. From the data examined, it was hypothesized that an annual usage of 5540 kWh would be representative of the diversified energy usage by a typical family of four persons in 1977. Since lights and some appliances ( e. g. , refrigeration equipment and HVAC auxiliaries) do have seasonal variations in their use, profiles for four seasons were developed. No significant regional variations were found. The cooking and clothes drying profile was found to have negligible seasonal and regional variations, and their annual load was determined to be 1980 kWh for the 1977 time period. An annual hot water load was similarly determined at 4940 kWh/year but a regional correction was applied to both the hourly profile and the annual value to account for difference in ground temper­ature across the countcy. Seasonal variations were again negligible.

All the profiles and annual values developed for 1977 were modified for projected usage trends in 1986 according to the rationale indicated below. The table below summarizes the annual projections for the thirteen sites for the 1986 time period.

ANNUAL ELECTRICAL LOAD PROJECTIONS FOR 1986

1986 PROJECTION DIVERSIF1ED COOKING CLOTHES DHW EFFECTS REGION LOAD LOAD DRY LOAD LOAD

kWh kWh kWh kWh DIVERSIF1ED, USAGE DECREASED

~ 1 BOSTON 5040 821 983 4813

DEMAND BY 1%/YR = 9% 2 WASHINGTON, D. C. 5040 821 983 4667 3 CHARLESTON 5040 821 983 4000

COOKING& COOKING DOWN 1. 5%/YR 4 MIAMI 5040 821 983 4267 CLOTHES DRYING DRYING DOWN 1/2%/YR 5 BISMARCK 5040 821 983 4546

TOTAL: 9. 3% DECREASE 6 MADISON 5040 821 983 4711 7 OMAHA 5040 821 983 4534

DOMESTIC CONSERVATION

~ 8 FORT WORTH 5040 821 983 3699

HOT WATER MEASURES REDUCE 9 NASHVILLE 5040 821 983 4011 BY 10% 10 PHOENIX 5040 821 983 3689

11 ALBUQUERQUE 5040 821 983 4800 12 SEATTLE 5040 821 983 4133 13 SANTA MARIA 5040 821 983 4145

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8. SYSTEM DEFINITION

The candidate systems for detailed performance and economic analysis were screened from a large number of possible concepts developed from various subsystem combin­ations. All cases included photovoltaic generation, either alone or in combination with solar heating and cooling systems. When solar thermal energy collectors were consider­ed, they were incorporated into side-by-side configurations with photovoltaic collectors, or were combined with the photovoltaic elements into a single collector design. In addition to defining system categories according to their solar collector configurations, other attributes were considered '\\hi ch included: (1) residential load characteristics; (2) elec­trical and fossil energy alternatives for meeting these loads; (3) the types of equipment available for heating and cooling; (4) the use of energy storage or, alternatively, the sell­back of excess PV generation to the local utility; and (5) different fwictional arrangements of the equipment.

The systems selected for detailed performance analysis as a result of the screening process are listed in the table on the top of the opposite page.

The screening process eliminated systems or subsystems on the basis of previous ex­perience and engineering judgment. In some instances, limited performance analyses were completed and systems showing similar performance were dropped. The table on the bottom of the opposite page summarizes many of the systems and subsystems dropped and the reason for their elimination.

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,-SYSTEM SCREENING 1 •

RESULTS

SYSTEMS SELECTED FOR DETAILED ANALYSIS

APPLICABLE SOLAR ARRAY POWER CLIMATE

TYPE STORAGE CONDITIONING COOLING HEATING HOT WATER TYPE

PV-ONLY (FLAT PANEL) YES DIRECT CHARGE HEAT PUMP (HP) HEAT PUMP (HP) ELECTRIC HOT/COLD

YES DIRECT CHARGE PLUS HP HP ELECTRIC HOT/COLD NIGHT-TIME CHARGE

YES MAX PWR TRACK HP HP · ELECTRIC HOT/COLD

NO MAX PWR TRACK HP HP ELECTRIC HOT/COLD

• NO MAX PWR TRACK HP FOSSIL FOSSIL HOT/COLD

PV-ONLY (2-AXISCONCENTRATOR) NO MAX PWR TRACK HP HP ELECTRIC HOT/COLD

' NO MAX PWR TRACK HP FOSSIL FOSSIL HOT/COLD

SIDE-BY-SIDE PV & THERMAL NO MAX PWR TRACK HP HP/SOLAR ELEC/SOLAR COLD

NO MAX PWR TRACK HP FOSSIL/SOLAR FOSSIL/SOLAR COLD

NO MAX PWR TRACK SOLAR DRIVEN HP HP/SOLAR ELEC/SOLAR HOT

NO MAX PWR TRACK FOSSIL/SOLAR FOSSIL/ SOLAR FOSSIL/SOLAR HOT ABSORPTION

COMBINED PV /THERMAL NO MAX PWR TRACK HP HP/SOLAR ELEC/SOLAR COLD

NO MAX PWR TRACK HP FOSSIL/SOLAR FOSSIL/SOLAR COLD

SYSTEM AND SUBSYSTEM OPTIONS ELIMINATED

SYSTEM REASON DROPPED ·-

SOLAR-DRIVEN HEAT ENGINES FOR ELECTRICITY • TOO COMPLICATED FOR RESIDENTIAL APPLI-CATIONS

OFF-ROOF MOUNTED COLLECTOR ARRAYS • ROOF IS CONVENIENT AVAILABLE AREA WHICH DOES NOT USE MORE REAL ESTATE

• PIPING & ELECTRICAL WIRING REQUIREMENTS ARE LESS REDUCING COSTS, MAINTENANCE, AND LOSSES

STAND-ALONE SYSTEMS • HIGHER CAPITAL COSTS AND MAINTENANCE REQUIREMENTS

• POTENTIAL PROBLEMS WITH ENERGY MANAGE-MENT TO MEET PEAK POWER CAPABILITY

DIRECT DC EQUIPMENT • MAJORITY OF HOME EQUIPMENT REQUIRES AC

NIGHTTIME BATTERY CHARGING • NEGLIGIBLE IMPROVEMENTS IN BENEFITS SHOWN FOR CLIMATE EXTREMES, PHOENIX AND BOSTON

MAXIMUM POWER BATTERY CHARGE • NEGLIGIBLE DIFFERENCES WITH DIRECT CHARGE BATTERY SYSTEM

LO-HI TEMPERATURE COLLECTORS IN SERIES • PRE-HEAT NOT USEFUL --TEMP. DROP IN RANKINE OR ABSORPTION EQUIPMENT ONLY 5. 6°C(l0°F) I LO-TEMP HI-TEMP

COOLING COLLECTOR COLLECTOR

HEATING & HOT WATER

SIDE-BY-SIDE PV & COMBINED PV/THERMAL • COMBINED PV /THERMAL COLLECTOR CAN BE EVALUATED INDEPENDENTLY

SIDE-BY-SIDE THERMAL & COMBINED PV/THERMAL • COMBINED PV /THERMAL COLLECTORS CAN BE EVALUATED INDEPENDENTLY

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9. ANAL VTICAL MODELS

22

Photovoltaic and solar thermal system models utilized in the study were developed by General Electric on previous programs and were combined as necessary. They are dis­cussed briefly on these two pages.

PHOTOVOLTAIC SYSTEM PERFORMANCE

The PV system performance was evaluated with a series of similar models. Each of the models determine the performance on an annual basis using hourly insolation and weather data tapes as input. The analysis methodology determines the instantaneous system operating point as a function of individual subsystem characteristics by iterative numer­ical calculations satisfying Kirchoff's Law at each node within the system. System models include direct charge battery systems, utility feedback systems with maximum power tracking and total energy systems. Several subsystem options are also available.

PV SYSTEM INPUT

HOURLY WEATHER DATA

BTTL PV-ONLV BUILDING PV/THERMAL ELECTRICAL THERMAL LOAD - LOADS FROM - ELECTRICAL LOADS SYSTEM SYSTEMS SOLAR THERMAL INPUT SYSTEM

---,, PV CELL

THERMAL& EXCESS DUMP ELECTRICAL

MODEL

UTILITY FEEDBACK/ BATTERY STORAGE

BACKUP

ELECTRICAL -LOAD SUPPLY -

PV SYSTEM PERFORMANCE

OUTPUT

[77) ~

~ ~

rry ~

C CJ

'

.

' C C .

C '

C C C

C

r i

ANALYTICAL MODELS

SOLAR THERMAL SYSTEM PERFORMANCE

The Solar System Simulation (SSS) program simulates the performance of thermal systems through mathematic models of the system components and appropriate logic to model the inter­action of these components within the specified system on an hour-by-hour basis. Hourly solar radiation, meteorological. data, building energy requirements from tapes and system configu­ration data are input to the program.

Several space heating, cooling and domestic water heating system options are available in the program. The cooling options consist of a solar Rankine-driven heat pump system and an ab­sorption air conditioner system. The performance of each system is calculated from actual unit performance curves. The heating mode is modeled as a conventional air-cooled heat exchanger system. All parasitic power requirements are taken into accollllt in the program and the appropriate portions of the pumping energy are utilized in meeting the building heating demand. All solar heating and cooling control schemes have auxiliary back-up systems with either an electric heat pump or fossil fuel system.

SYSTEM INPUT

HOURLY WEATHER AN 01.J.R RADIATION DAT

BUILDING HEATING/COOLING

DEMANDS

COLLECTOR MODELS VACUUM TUBE/FLAT PLATE

(AIR OR LIQUID)

THERMAL STORAGE UNIT

HEATING COOLING

HEAT EXCHANGER

SYSTEM

ABSORPTION AIR CONDITIONER

SYSTEM

HEAT PUMP OR FOSSIL FUEL

AUXILIARY SYSTEM

HOURLY, DAILY, MONTHLY AND YEARLY SYSTEM

PERFORMANCE PRINTOUT

SOIJ.R RANKINE DRIVEN HEAT

PUMP SYSTEM

23

10. ECONOMIC MODEL

24

True life cycle cost analysis must necessarily consider the timing of costs and benefits as well as the magnitude. A method employed in previous General Electric solar and wind energy programs is to compare Levelized Annual Benefits (LAB), representing system energy savings, with the Levelized Annual Cost (LAC), the levelized dollar amount re­quired to own, operate, and maintain a system during each year of the life of the system. Specifically, the levelized annual cost accounts for:

1. "Paying off' system capital costs (mortgage principal)

2. Paying mortgage interest

3. Paying property taxes and insurance

4. Paying operating and maintenance expenses

The levelized annual cost, illustrated graphically below, is the product of the capital recovery factor (CRF), which is equivalent to the Fixed Charge Rate (FCR) in the study since no property taxes were included, and the present value of the year-by-year cash requirements throughout the system life. The capital recovery factor is the uniform periodic payment, as a fraction of the original principal, that will fully repay a loan (including all interest) in yearly periods over the loan lifetime at a specified yearly interest rateo The interest rate used to calculate CRF is called the discount rate and is equal to the weighted average after-tax cost of capital.

The present value is analogous to that amount which, if deposited in an account bearing interest at the discount rate, would permit annual withdrawals to pay all system costs and diminish to zero at the end of system life.

Variable system costs include operation and maintenance which would most likely tend to increase with inflation and component replacement and overhaul which would depend on servicing schedules.

CAPITALIZATION OF ANNUAL COSTS

PRESENT WORTH LEVELIZED

---------- EQUIVALENT YEAR

F1 ~

F' ~

C '

Fl ~

~ ~

r kd

~ ~

~ bid

Fl ~

~ ~

F1 ~

Fl ~

F ~

r b0

~ ~

f9 I

ECONOMIC MODEL

Levelized annual cost can be computed in constant or current year dollars. The former is more meaningful since comparisons with present data are easier. It is very often more rep­resentative of the actual costs - that ls, they are more likely to stay constant in constant year dollars then in current year dollars. The constant dollar levelized annual cost is com­puted from a capital recovery factor which is based on the real, or inflation adjusted, dis­count rate.

The comparison of the energy cost savings of the solar system to the levelized annual cost is accomplished by computing the levelized annual benefits (LAB) for the energy savings. LAB is inherently a function of present and projected energy prices. It is simply the product of the price of energy with the annual energy saved by the solar system together with a multiplier defined as the levelized value of an escalating cost stream in constant year dollars. This last term accounts for the rate of energy price escalation over the lifetime of the system.

The economic viability of a system can be measured through the use of the cost-to-benefit ratio which is defined as the ratio of the levelized annual cost to the levelized annual benefits. The system becomes economically viable when the cost-to-benefit ratio is less than unity. The break-even system cost occurs when the ratio is exactly unity; i.e., when LAC and LAB are equal.

25

1.

26

11. COST DATA

Costs for the various systems analyzed were developed in 1975 dollars based on actual manufacturer data, whenever possible, or on cost estimates using available drawings and assuming large quantity manufacturing production. Variations in the costs existed for many of the subsystems, so a set of governing assumptions was made for comparison between the systems and regions of the country. These assumptions included inputs re­quired for the economic model such as inflation rate, fuel price escalation rate and oper­ating and maintenance costs. These are summarized in the table below. No property taxes were included, assuming state or federal tax credits for solar systems available in 1986. The projected thermal system costs and combined system costs were assumed at two times the projected PV system costs. These assumptions were used in the cost­to-benefit ratio comparison between systems and regions but results were developed for various sets of economic assumptions to allow for different economic scenarios.

BASIC RANKING ECONOMIC ASSUMPTIONS

1986 START OF OPERATION

GENERAL INFLATION RATE

MORTGAGE RATE

TAX BRACKET

ADDITIONAL PROPERTY TAXES

INSURANCE

OPERATION & MAINTENANCE

ENERGY PRICE ESCALATION RATE

SELLBACK-TO-BUY RATIO

SYSTEM LIFE

BATTERY LIFE

ARRAY COST

BATTERY COST

BALANCE-OF-PV PLANT COSTS:

WITH STORAGE

VARIABLE $26. 20/m 2

FIXED $3832

= 5%

= 10%

= 30%

= 0

0. 5% OF CAPITAL COST

$50/YR

= 2%, 4%, 6% ABOVE INFLATION

0.5

= 20 YRS

= 10 YRS

$500/kWP (FOB) ($660/kWp@ SITE)

$25/kWh OF NAMEPLATE RATING

WITHOUT STORAGE

$34. 20/m 2

$1047

THERMAL SYSTEM-TO-PV SYSTEM COST RATIO = 2:1

COMBINED SYSTEM COST SAME AS THERMAL-ONLY SYSTEM COST

F ~

r, ~

' C r' ~

~ ~

C ~ ~

r, ~

r, ~

~ ~

C ·Ci,::::,:

x:,··

C .

C

I

bJ

COST DATA

A key system trade-off was the PV-only system with battery storage versus that system with utility sellback. As indicated on the previous page, a sellback rate of 50% of the buy rate was assumed. The assumed balance-of-plant cost comparison for these two options is further outlined below in terms of fixed and variable costs. The costs include a 15% markup for the distributor and 15%. mark-up for the contractor who would install the system.

ELECTRICAL BALANCE-OF-PLANT COSTS FOR RESIDENTIAL PV SYSTEM

Energy Storage Option Cost Element With Without

Array Material & Installation $10.20/m2 $10.20/m2

(Based on PV Shingles)

DC/ AC Inverter ( $ 190/kVA) $16.00/m2 $24.00/m2

Total Variables Cost $26.20/m2 $34.20/m2

------------ -------·-- ----Battery Shelter $1660/System ---Shunt Charge Regulator $ 590/System ---

Lightning Protection $ 674/System $ 67 4/System

Electrical Equip & Installation $ 908/System $ 373/System

Total Fixed Cost $ 3832/System $1047/System

27

28

12.SUBSYSTEM PERFORMANCE

PV COLLECTORS

The PV solar array design was nominally based on the PV shingle concept developed by General Electric in the PV Conceptual Design Studies (AL0-3686-01). Each shingle, as shown below, contains 19 solar cells wired in series having a total cell area of 419. 2 cm2• The exposed portion of the shingle is hexagonal in shape with an area of 507 cm2 yielding a packing factor of O. 827. The module uses silicon solar cells with an unencapsulated air­mass- one efficiency of 13. 4% at 28°C. The module efficiency at 28°C is 14. 3% with the increase due to internal reflected energy from intercell regions, ("Zero- Depth Concen-trator11 effect). I

BATTERY

23991 . 47( l;.,t77tG 1 SEA, NO, •SH•31

2 3 4 6

GEN ERAL . ELECTRIC'

•

The battery charge and discharge voltage was modeled as a function of battery state of charge and instantaneous charge or discharge rate according to specific characteristic curves supplied by C&D Batteries Division of the Eltra Company. The average round trip efficiency of the battery, therefore, varied as function of battery capacity and collector area in the range of 75-88%. For the nominal condition of a 95 m2 array and 40 k¥lh bat­tery capacity, the average round trip efficiency was 83%.

Fl I

rr I '

bJ

SUBSYSTEM PERFORMANCE

THERMAL COLLECTORS

In side-by-side collector systems, the GE vacuum tube solar therm.al collector was used. This design provides high performance as shown in the figure below to allow maximum benefit to the thermal collectors. This figure also shows the combined PV /thermal collector per­formance used in the study. This collector was modeled as a tube and sheet-type collector with the solar cells mounted directly on the absorber plate.

80 1-ffi 70

~ 60 I.LI a. 50 l

G 40 z ~ 30 u -1.1.. 20 1.1.. I.LI

10

0

INVERTER

• T AMB = 4;5oc

FLAT -PLATE COMBINED COLLECTOR • WIND = 4.5 m/S SINGLE LEXAN COVER

- O. 75 ABSORBER EMMISSIVITY • 0° INCIDENT SUN ANGLE

• I = INSOLATION: WATT/m2

GE EVCUATED TUBE COLLECTOR

50 100 150 200 250 300 350 400

COLLECTOR FLUID INLET TEMPERATURE (°C)

The type of inverter used in the analysis varied for the several power conditioning options studied For the utility feedback system, a line-commutated inverter was used with the utility line providing the synchronization signal. Since different types of inverters were used in ·dif­ferent system options and limited performance data was available tor the inverter sizes con­sidered in the study, a constant 87% efficiency was assumed for the analyses.

29

30

13. SUMMARY OF ECO­NOMIC VIABILITY

Detailed performance analyses were completed on the systems identified previously. The annual performance results were utilized in the economic model with the economic assump­tions described to provide the cost-to-benefit ratios for the systems and regions as shown in the table on the opposite page. The table can be used for identifying the economic vi­ability ( cost-to-benefit ratio less than one) of systems in the twelve regions and can be used for relative ranking of systems for a given region. For example, all the systems in Phoenix show economic viability in the 1986 time frame except the combined systems, under the economic assumptions.

In general, the PV-only systems with utility feedback show better economic potential than systems with battery storage for all the regions and, in fact, they show the best viability of all systems in most cases. Several of the side-by-side PV/thermal systems show slightly lower cost-to-benefit ratios with small therm.al collector areas and these systems would become more attractive as the thermal system costs are reduced. The combined systems showed the poorest economic viability primarily because of the assumed thermal system costs and the poorer combined collector performance.

The results noted by parentheses in the table were calculated based on correlations de­veloped from the numerous parametric results. These correlations are discussed on later pages. The ratios in the table which were based on a 4% fuel escalation rate and a 20 year system life can easily be adjusted for different assumptions by employing the multipliers listed in the table below.

ECONOMIC CONVERSION FACTORS

Fuel Escalation System

Rate Lifetime** Factor

2% 20 yr 1.47

2% 30 yr 1.10

4% 30 yr 0.75

6% 20 yr 0.68

6% 30 yr 0.51

** Factors assume one battery replacement over system lifetime

F ~

r, ~

r, ~

f) ~

Fl lmJ

~ ~

r1 te&J

~ ~

~ ~

~ fu:lJ

fWl ~

Fl ~

F ~

C '

RELATIVE RANKING OF RESIDENTIAL SYSTEM PERFORMANCE AND ECONOMICS THROUGH COST-TO-BENEFIT RATIO

. -~!a,

:?'e"'

~I

PV-ONLY SYSTEMS ~ CONCENTRA TOR-,I SHINGLE ,---- SIDE-BY-SIDE SYSTEMS--,

l(a) I(a)' l(b) l(c) I(d) I(e) I(() Il(a) II(b) ll(c) U(d) ELEC'ltU\; ~~l)U., RANKlNt; ABSORP·.nuN

~ DIR.CHG. NIGHTTIME FOSSIL ALL MAX. TRACK ALL FOSSIL SOLAR SOLAR ELECTRIC FOSSIL Q'1'0DAflE CHARGE HEAT ELECTRIC STORAGE ELECTRIC HEAT HEAT HEAT R.Ar.K UP BACK UP

RE 95 m2 95 m2 95 m2 95m2 95 m2 32 m~ 32 m2 95 m2 95 m2 95 m2 95 m2

1. BOSTON 1.13 1.00 0.96 o. 87 1.64 1.82 o. 87 0.96 o. 85 9.95 (0%)* (0%) (7%) (131,)

2. WASHINGTON, D. C. (1. 59) (1.37) 1.20 2.49 2.75

3. CHARLESTON (1. 43) (1.24) 1.00 2.17 2.41

4. MIAMI (1. 34) (1.16) o. 96 2.10 2.33 o. 91 (5%)

5. BISMARCK (1. 59) 1.36 1.15 1. 95 2.16 1.15 1.36 (0%) (0%)

6. MADISON (1. 65) (1.42) 1. 24 2.37 2.64

7. OMAHA (1. 69) (1.46) 1. 26 2.16 2.40

8. FORT WORTH _1. 90 1.67 1. 53 2. 73 3.03 1.48 1.63 (3%) (191,)

9. NASHVILLE (2.10) 1. 85 1.62 3.12 3.46 1. 56 1.85 (6%) (0%)

10. PHOENIX 0.83 0.82 0.69 0.64 o. 83 o. 88 o. 97 0.61 0.69 0.63 0.76 (4%) (0%) (5%) (4%)

IL ALBUQUERQUE (1.11) 1.00 o. 89 1.20 1.34 0.85 1.00 0.84 (6%) {0%) (7%)

12. SEATTLE (6.78) (5. 86) 5.40 10. 58 11.76

13. SANTA MARIA (1.44) (1.24) 1.14 1. 82 2.02

NOTES: TABLE BASED ON 20-YR. LIFE AND4% ESCALATION RATE *OPTIMUM PERCENT THERMAL COLLECTOR AREA **ADJUSTMENT FACTOR ASSUMES ONE BATTERY REPLACEMENT OVER SYSTEM LIFETIME () RESULTS BASED ON CORRELATION DISCUSSED IN SECTION 12, VOLUME II

.-COMBINED SYSTEMS-, III(a) III(b)

t;Lt:l:.LJ:\l\; ~~u..,

SOLAR SOLAR HEA\ 26m

HEA~-26m

1.65 1. 99

3. 72 3,06

2. 86 4.06

1.20 1.76

n 0

n~ o• s:-1 -a9 ,-m :II m -2 cnm o-n z=i

14. COMPARISON OF PV SYSTEM PERFORMANCE

32

PV-ONLY SYSTEMS WITH STORAGE

Monthly performance of the PV-only system with storage is illustrated on the upper plot on the opposite page for site locations in Phoenix and Boston which represent extreme climatic conditions. The loads for this system at both sites were based on an all-electrical residence including heating and cooling. The peak for the Phoenix house corresponds to the summer cooling load, while the peak with the Boston residence corresponds to the winter heating load. Since the Phoenix maximum demand is in phase with the months of peak generation, the PV system is quite effective in supplying a high percentage of the total annual usage, as indicated by the near coincidence of curves for output and load on the Phoenix plot. The reverse is true for Boston since the peak heating demand is out of phase with the months of peak PV generation.

For both the Phoenix and Boston locations, the 95 m2 system exhibits a significant amount of excess generation that must be therm.ally discarded. As one would expect, the excess output occurs during the seasons of lowest load demand.

For the Phoenix location, both the maximum power tracker and the direct charge system were carefully modeled and analyzed using the identical weather data for both systems. Comparison of performance for the two systems in the upper plot on the opposite page indicated no appreciable difference between the two approaches.

PV-ONLY SYSTEMS WITHOUT ENERGY STORAGE

The solar array considered for this system is identical to that used for the system with storage. The instantaneous array output will be greater or smaller than the residence demand so the modes of operation were to "sellback" the excess output to the local utility, or to receive "makeup" power from the utility. These modes of operation are illustrated on a monthly basis on the lower plot on the opposite page for the Phoenix and Boston locations. The net energy to and from the utility is the algebraic difference of the sell­back and makeup energy that occurs each day, with sellback occurring during daylight hours (assuming sufficient illumination) and makeup being required at night. Because of the different cost value attached to makeup and sellback energy, it is necessary to keep a careful accounting of these energy components in determining the economic worth of this type of system. The total system output can exceed the demand on an annual basis since no energy is lost. Correlations for the system performance for all the regions are shown on the succeeding pages.

f'9 ~

C C ~ ~

~ ~

f821

~

~ ~

~ ~

C .

~ ~

C FJ ~

F7! ~

C

Fl ~

C '

F) ~

F1 w

I

>­(!) a:: w ~ 1 >-..J :::c 1-

5 :E

0

COMPARISON OF PV SYSTEM PERFORMANCE

MONTHLY PERFORMANCE OF PV-ONLY SYSTEM WITH STORAGE

IPl:IOENIX

• BATTERY CAPACITY: 40 kWh • ARRAY AREA: 95 m2

LOAD OUTPUT DIRECT CHARGE SYSTEM - l(a)

2

0

I BOSTON I • BATTERY CAPACITY: 40 kWh

• ARRAY AREA: 95 m2

OUTPUT -SYSTEM - I(•)

JFMAMJJASOND JFMAMJJASOND

2 .r: 3: :E

I

> (!) a: LL.I z 1 LL.I

> ..I ::c I-

a ii

0 J

MONTHLY PERFORMANCE OF PV-ONLY SYSTEM WITHOUT STORAGE

NET TO UTILITY

NET FROM UTILITY 2

PV SYSTEM .r: NET TO UTILITY OUTPUT 3:

~ I

> (!) a: LL.I ffi 1

> ..J LOAD

LOAD J: PV OUTPUT I PHOENIX I I- I BOSTON I SYSTEM a :E

0 F MA M J J A S ON D J F MA M J J A S 0 N D

33

15. CORRELATION OF PV­ONL Y SYSTEM OUTPUT

34

The annual PV system output was correlated as a function of cell efficiency, packing factor, heating and cooling degree days and annual total horizontal insolation. The cor­relations with and without storage based on the hour-by-hour system performance anal­yses are illustrated below. The annual energy output function, E0 , is seen to vary linearly with annual total horizontal insolation. The function 'E0 is related to the actual PV system output, E~, through the correlation expression

E = 0

.E' 0

11* PF* PF (1 + O. 006~) (in kWh/m2)

where T/ and PF are the cell efficiency and module packing factor with the (*) superscript indicating the reference study values of 13. 3% and O. 827 respectively. ¢ is a corresponding factor related to cooling degree days (CDD) and heating degree-days (HDD) by the expression

¢= CDD-HDD 365

For a specified cell efficiency and packing factor, these correlations provide an estimate of annual PV system output for any region or site once insolation and degree-day data are retrieved for that region.

250

N' 200

I 0 0

II.LI

..: ::::> a. ~ 0

~ 0:: I.LI

~ .J <( ::::> z z <

150

100

so

CORRECTED TO REFERENCE TEMPERATURE WITHOUT STORAGE

84 1 BOSTON

s-,f / 2 WASH. D.C. 3 CHARLESTON

9 10 4 MIAMI /

AWITH STORAGE

5 BISMARCK 1\ 6 MADISON

7 OMAHA 8 FT.WORTH 9 NASHVILLE

10 PHOENIX 11 ALBUQUERQUE 12 SEATTLE 13 SANTA MARIA

0----------------"----------' 1000 2000 3000

ANNUAL TOTAL HORIZONTAL INSOLATION.. i H' (kWh/m2)

C ~ ~

C '

'

F} ~

rl ~

fWl w ~ ~

~ ~

r} ~

~ ~

Fl ~

~ bd

~ ~

Fl ~

I

bJ

F w

CORRELATION OF ENERGY SELLBACK SYSTEM

OUTPUT

Systems without storage require the determination of both sellback energy to the utility (Es) and that portion of the total load that can be served by the PV system ref erred to as "direct energy" (E'n), for economic analysis. For this reason, sellback and direct energy were cor­related as a function of array area and annual total horizontal insolation. The results for a 95 m2 array are shown below for an all-electric system. The linear fit of the actual per­formance data for the regions shown represents the best estimates for both Es and En which sum up to E0 • The correlation can be adjusted for different array areas by the following ex­pression:

Es i

0

= ~ (~) .6 3 95

where A is the array area in m2.

250

200

cG' a } 150 0

~ 0:: bl

ffi ..J 100 ,c( :, z z ,c(

50

CORRECTED TO REFERENCE TEMPERATURE

• 95 m2 ARRAY AREA

- 2 -~Se! 3 EO

- ·1 -EDE! 3 EO

1000 2000

ANNUAL TOTAL HORIZONTAL INSOLATION, iH'(kWh/m2)

1 BOSTON 2 WASH. D.C. 3 CHARLESTON 4 MIAMI 5 BISMARCK 6 MADISON 7 OMAHA 8 FT. WORTH 9 NASHVILLE

10 PHOENIX 11 ALBUQUERQUE 12 SEATTLE 13 SANTA MARIA

3000

35

116. SIDE-BY-SIDE SYSTEMS I

36

Side-by-side systems are designed so that different sections of the residence roof pro­duce different forms of solar conversion. One section produces electricity by PV con­version, and the second section collects either low-temperature thermal energy for space beating and domestic hot water production or high-temperature output for use in heat engines or absorption chillers. The four different side-by-side configurations analyzed during the study are diagrammed below. Only the utility feedback case was considered since it shows better economic viability than the system with battery storage from pre­vious study results.

II (a) AU.. ELECTRIC. SOLAR SUPPLEMENTED HEAT

BACK UP

PV ARRAY

THERMAL ARRAY TES

DC/AC INVERT.

GENERAL LOADS

HEAT PUMP

Har WATER

II (c) AU- ELECTRIC, SOLAR DRIVEN COOLING

PV ARRAY

THERMAL ARRAY TES

DC/AC INVERT.

RANKINE ENGINE

BACK UP

GENERAL LOADS

HEAT PUMP

HaT WATER

PV ARRAY

THERMAL ARRAY TES FURNACE

FOSSIL FUEL

DC/AC INVERT.

BACK UP

GENERAL LOADS

HEAT PUMP

(COOLING)

HEATING

Har WATER

II (d) ELECTRIC/FOSSIL, SOIJ.R ABSORPTION COOLING

PV ARRAY

THERMAL ARRAY

BACK UP

~----------11 ~C/AC I t l~ENER INVERT. H LOADS

TES FURNACE

FOSSIL FUEL

ABSORP, CHILLER

HEATING

HOT WATER

Fl 6iliJ

~ ~

~ ~

~ I '

Cl ,

.

f9 ~

rrri ~

~ ~

~ ~

Cl ~ ~

~ ~

~ w

Fl ~

Ft ~

~ ~

r u

0 .

A w

SIDE-BY-SIDE SYSTEM PERFORMANCE

Performance analysis of these systems produced the annual outputs shown below for the Boston and Phoenix locations as a function of the percentage of the roof area devoted to the PV and therm.al collectors. Evacuated tube collectors were used as the thermal collectors. The PV output is proportional to the PV area since the sellback mode allows full utilization of the collected energy. The therm.al output which is defined as the useful solar energy con­tributed to the residence needs, on the other hand, is a strong function of energy demand on the system. The curves show a diminishing rate of solar utilization with larger collector areas resulting principally from tbe mismatch of generation and demand and the consequent need to discard large amounts of energy. This trend is particularly true for space and do­mestic hot water heating systems II(a) and Il(b) (on the opposite page) in the Phoenix location where the extreme low thermal requirements could be satisfied by thermal collectors cover­ing only about 10% of the roof area. The annual energy outputs for space heating, cooling and domestic hot water systems, II(c) and Il(d), are higher than that of the Il(a, b) systems as the otherwise discarded energy collected during summer months can be utilized for cooling. The increase in output also reflects the relative magnitude of heating and cooling loads in a given location. The Phoenix residence ha~ significantly l_arger cooJing load than heati~g load, while in the Boston residence, the cooling load is relatively small. The cooling system employing an absorption chiller, (ll(d)) yields better system performance th.an the one using a Rankine­driven heat pump configuration (Il(c)) as indicated by the higher annual output curves for II(d) system. This is due to the fact that the absorption chiller requires a lower solar tempera­ture than the Rankine system, and thus, the collector can operate at a higher efficiency and consequently, higher energy output.

2

! 5 IL

§ ~ ~ lD .J < :::> z z <

25

20

15

10

5

0

0 I

100

• TOTALCOLLECTORAREA 95 m2

• LIQUID THERMAL COLLECTORS

BOSTON 25 PHOENIX

20 ,... .c

II (d) ;:

11 (c) ~

5 15 IL I-

B ~

10 In > lD

PV SYSTEM .J II (a,b,c,d) < :::> z 5 z

c(

THERMAL 0 THERMAL 20 40 60 80 100 0 20 40 60 SO 100 I I I I I PV I -------1 __...__._1__.____.1___......__.1 PV

80 60 40 20 0 100 80 60 40 20 0

PERCENT COLLECTOR AREA PERCENT COLLECTOR AREA

37

38

17. COMBINED PV / THERMAL SYSTEMS

In these systems, the solar collectors are designed to both generate electricity and capture thermal energy. This is accomplished by placing solar cells in the optical path through the collector and providing a means for conducting away the thermal energy not converted to electricity. Both air and liquid means of removing the thermal energy are under development. Since the thermal energy must be at a somewhat elevated temperature to be of use, there is usually a corresponding sacrifice in PV output because of the solar cell's negative output dependency with temperature. Two system variations are illustrated below.

Configuration ill(a) uses the captured thermal energy to supplement space heating and hot water production. Since highly elevated temperatures would significantly sacrifice PV out­put, no cooling applications of this concept were considered.

For this reason, the regions for which this system was analyzed generally involve cooler climates. Configuration ill(b) is identical to fil(a) except that fossil energy provides heat­ing and hot water with solar thermal supplementation.

Utility feedback is used in both configurations.

lll(a) ALL ELECTRIC, SOLAR SUPPLEMENTED lll(b) ELECTRIC/FOSSIL, SOLAR SUPPLEMENTED

PV DC/AC GENERA PV DC/AC GENERA ARRAY INVERT. LOADS ARRAY INVERT. LOADS

HERMAL ARRAY HEAT ARRAY HEAT

PUMP PUMP (COOL)

HOT

HEATING

TES TES FURNACE

HOT WATER

FOSSIL FUEL

r kd

C I

Fl ~

F ~

~ ~

F1 ~

rt ~

rm ~

ri ~

~ ~

I C

r ~

F" . kw>

C r'1l ~

~ ~

F1 ~

F1 kJ

I

bl

COMBINED PV /THERMAL SYSTEM PERFORMANCE

The electrical and thermal outputs of the systems as a function of collector area in four climate locations are shown below o The PV output is proportional to the collector area since the electricity sellback mode allows full utilization of the collected energy. For a given col­lector array size, the electrical output is proportional to the available solar insolation as evidenced by the highest annual system output in Phoenix and lowest annual output in Boston and Nashville.

The therm.al output, which is defined as the useful solar energy contributed to the residence needs, is a strong function of energy demand on the system. The system produces the high­est energy output in Bismarck where the thermal demand is the greatest. On the other hand, a system with only 30 m2 of collector area can fully satisfy the extremely low therm.al re­quirements of a Phoenix single family residence.

Comparing the performance of the side-by-side system utilizing the evacuated tube thermal collector with the combined PV /therm.al system in Phoenix, the evacuated tube collector can perform three times better than the combined collector as evidenced by the 3 to 1 ratio in collector area required to meet all the thermal requirements in the two cases.

10

8 -:a 3: 6 I-[ 6

!5 0 ..I

~ 4 z z <

2

PV OUTPUT Ill (a,b)

10

BISMARCK

8 2 3: 6 I-[ 6

!; 0 ..I

~ 4 z z <

2

THERMAL OUTPUT Ill (a·, b)

BISMARCK

Ill (b)

0 '-----'------''------'------

0 ....__ __ i-.__ ____ ____.. ________ _

40 60 100 80 0 20 40 60 80 100 0 20

COLLECTOR AREA (m2) COLLECTOR AREA (m2)

39

I 18. ECONOMIC PARA­METRIC VARIATIONS

40

PV-ONLY SYSTEMS

An economic nomograph for PV-only systems without storage is illustrated below. The levelized annual system costs and benefits are plotted parametrically as a function of array cost, balance-of-plant cost, price of electricity and "utilized" annual PV system output for several electricity price escalation rates. The term "LAB*" refers to the levelized annual benefit at zero relative escalation rate; i.e. , when the electricity price escalates at the same rate as inflation. LAB* is the product of the electricity price, the system output and the ''utilization'' factor, U, which, in tum, is a function of the array area and sellback-to-buy ratio (pS/pE). The utilization factor is defined by

U = 1-f-::):: An example of how to use this nomograph is illustrated by the dotted lines for a utilized annual system output (E' U) of 150 kWh/m2 and BOP costs of $45/m2. For a 1975 elec­tricity price of 3. 5¢/kv!Ji escalating at a rate of 2% above inflation with a 1986 start would require an array cost of about $65/m2 just to break even economically.

Similar curves were developed for systems with battery storage and are included in Volume II of this report.

ELECTRICITY PRICE ESCALATION RATE ABOVE INFLATION

50 __..,. 6

40

0 o~-----:1~0---2~0-----.130

LAB• (f{m2)

CONSTANT 1975 $

LEVEUZED ANNUAL COST & BENEFITS

($/m2)

•zERO RELATIVE ESCALATION RATE

50

40

30

• 5% INFLATION RATE • 10%MORTGAGE RATE • 30%TAX BRACKET • 20 YEAR LIFE • NO ADDITIONAL PROPERTY TAXES

UTILIZED ANNUAL PV SYSTEM OUTPUT, E' U ( kWh/ m 2)

• 0 • - - - - PRESENT ESTIMATE

BALANCE CF PLANT COSTS ~m2).

20 100 ~

50

0

100 150 200

1975 ELECTRICITY PRICE, p (¢/kWh) E

ARRAY COST ($/m2)

r' ~

C '

C F kw

F' ~

F' ~

~ ~

F1 ~

Fl ~

~ ~

r> ~

F­kJ

F1 ~

C

C

0 .

C .

ECONOMIC PARAMETRIC VARIATIONS

SIDE-BY-SIDE SYSTEMS

An economic analysis of the side-by-side PV/thermal systems shows that for a given ratio of the cost($ /m2) of the solar thermal system (CT) to that of the PV system (Cpv), there exists an optimum percentage area mix of PV and thermal collection which yields the best overall cost-to-benefit ratio for the system. Typical PV-to-thermal cost ratios, (CT/Cpv ), com­puted as a function of optimum area mix are shown on the upper plot below for the specific system, region, and ground rules listed. Using this cost ratio curve, the lower plot illustrates the resulting levelized annual cost variation for several values of PV system cost and thermal system cost for escalation rates of O, 2%, 4% and 6% above inflation. The dotted lines repre­sent the corresponding levelized annual benefits as a function of percent thermal collector area. The parametric curves provide an estimate of the optimum thermal collector area and the required electricity price escalation above inflation for the system to be economically viable. Similar curves for each of the systems and regions studied were developed and in-cluded in Volume II of this report.

PARAMETRIC DATA FOR SIDE-BY-SIDE PV/THERMAL SYSTEM WITH ABSORPTION COOLING

2

>

I BOSTON I ARRAY AREA:::: 95 m2

Ps/pE = 0.5

a. 1 ~ c.)

N'

o------------------0 00 ~ ~ 00 100 OPTIMUM PERCENT TfflE_RMAL COLLECTOR AREA

25

PV SYSTEM COST (fv'm2)

20 t 240

THERMAL SYSTEM COST ($/mZ)

240 ! --LAC

! 15

~ .J

3 m :5

10

5

10% MORTGAGE 30% TAX BRACKET

5% INFLATION 1986 START CONSTANT 1975$

0 ,..__ _ ___. __ __.&., __ __._ ______ __,

0 20 40 60 80 100

PERCENT THERMAL COLLECTOR AREA

' 41

19. EXTENSIONS OF PERFORMANCE AND ECONOMIC RESULTS

From the analysis conducted during this study, correlations were developed which can extend the results of the study to various microclimates. These correlations provide: (1) estimates of the electrical heating and cooling load demands of a residence based on the heating and cooling degree day characteristics of the sites to be evaluated; (2) esti­mates of the annual electrical output for PV systems with and without energy storage for PV systems with electrical or fossil fuel backup heating based on annual insolation; (3) estimates of the economic viability of the system for that site. The restrictions on the use of the correlations include: (1) the correlations for load requirement can be applied to all regions but are limited to heat pump heating or cooling or resistance heating; (2) PV-only system performance with or without storage has been correlated and these values can be extended to initial side-by-side system performance, (3) the economic correlations can only be applied to PV-only systems.

The principal factors which characterize the climate for a particular site relative to solar system performance are: annual insolation, heating degree-days, and cooling degree-days. Such data for particular locations are available from various sources such as Local Cli­matological Data issued by NOAA and the Climatic Atlas. The technique can be exercised by using these climate factors as input along with systems cost estimates for array, bat­tery and B-0-P costs. The table on the opposite page summarizes the steps in using the correlation curves. A detailed discussion of the procedure and all the correlation curves are presented in Section 12 of Volume II of this report.

42

~ ktj

~ ~

C C .

I

ft ~

~ ~

F1) ~

F1 w

f3\ ~

C '

r ~

F blliJ

~ ~

EXTENSION OF PERFORMANCE AND ECONOMIC RESULTS

PROCEDURE FOR ESTIMATING PV SYSTEM PERFORMANCE

Specify:

• • •

•

Selected Site/ Region/Weather Year

House Type (Northern or Southern)

Array Area/ Cell Efficiency /Packing Factor

Specify Sell-Back Rate for Systems Without Storage

Step (1) Obtain from Local Climatological Data or Climatic Atlas

• •

Heating and Cooling Degree Days

Annual Insolation

Step (2) Estimate Annual Residential Load Requirements

•

•

Thermal Loads from Correlation Curves as shown in Section 4 as a Function of Insolation Heating and Cooling Degree Days

Electrical Loads from Tables for Diversified, Cooking and Clothes Drying, and Domestic Hot Water as shown in Section 7.

Step (3) Estimate Annual PV System Output

• Annual Loads from Correlation Curves as shown in Section 15 as a Function of Insolation

Step (4) Estimate Economic Viability

• •

Project Array, Battery and B-0-P Costs

Estimate Cost of Electricity for Sites

• Calculate Utilization Factor for Systems Without Storage

•

•

Levelized Annual Cost and Benefits from Nomograph similar to Figure Presented in Section 18

Calculate Cost-To-Benefit Ratio

43

1

20. COMPARISON OF . WEATHER DATA

The selected year of hourly weather data utilized in the detailed performance analysis differed from the data used by Westinghouse in a parallel program and from the Typical Meteorological Year (TMY) data developed by Sandia Laboratories toward the end of the program. A comparison, therefore, was made of pertinent weather data for four sites common between the GE and Westinghouse studies: Phoenix, Boston, Nashville and Seattle. A comparison of the three years of weather data evaluated at the four cites is shown in the table below. The numbers in parenthesis indicate the percent deviation from the GE se­lected year. In general, the spread of data for the several weather years used was less than 10%. The notable exceptions were for heating degree days determined for the West­inghouse year at Seattle and for the Test Meteorological Year at Nashville. Percentage­wise, there was also a large variation in cooling degree days for Seattle, but this can be attributed to the unique climate of this city.

IUIAL PV ELECTRICAL SYSTEM

LO CATI ON WEATHER LOAD OUTPUT YEAR (kWh) (kWh}

1953 (GE) 14701(+0.5%)** 20305 (+2%) PHOENIX 1967 ( w) 14704~+2%~ 19970 (-0.5%~

THY 14945 +2% 20223 (+0.2%

1960 (GE) 15111(-0.1%) 13517(-1%) BOSTON 1965 (W) 15316(+1%) 13627(-2%)

THY 15117(+0. U) 12909(-U)

1968 (GE) . 13749(-1%) 14222 ( +1%) NASHVILLE 1966 (W) 13479(-0.1%) 13879(+2%)

THY 13262(+1%) 13924(+3%)

1966 (GE) 12882(+0.5%) 11341(+6%) SEATTLE 1962 (W) 12978(+7%) 11656(+3%)

TMY 13090(+1%) 11654(3%)

*BASED ON NOMINAL ~ET OF ECONOMIC GROUND RULES

**INDICATES PERCENTAGE DEVIATION OF CORRELATION RESULT

(GE) (W) ( TMY) -

44

GENERAL ELECTRIC SELECTED YEAR WESTINGHOUSE SELECTED YEAR TEST MET~OROLOGICAL YEAR

SELLBACK COST TO ENERGY BENEFIT (kWh)· RATIO*

12944 (+H) .9 (+U) 12718 1+4%) .92~+2%) 12834 +5%) .91 +2%)

8410 ( +6%) 1.23(+5%) 8436 (+6%) 1.22(+5%) 8015 (+6%) 1.29(+5%) . 9129 (+5%) 2 .24(+1%) 8866 (+7%) 2.35(-0.4%) 8974 (+6%) 2.35(-1%)

6988 (+15%) 7.64(-2%) 7 37 4 (+8%) 7.53(-0.1%) 7244 (+10%) 7.47(+1%)

M ~

rn ~

F ~

F8' ~

~ ~

r3\ ~

Fl ~

Fl ~

~ ~

Fl ~

C C ~ tJ

0

C .

F1 b

, C

SYSTEM OUTPUT SENSITIVITY TO

WEATHER DATA

A further comparison was made to determine the effects of utilizing various weather data on system performance. The three different hourly weather data years described on the previous page were used in the hour-by-hour analysis for the PV-only system with energy feedback to the utility for each of the four sites.

The results of performance calculations are compared in the table at the bottom of the page. Again, only relatively small variations in system performance can be identified in the table indicating the small effect upon performance of the weather for a particular year o The cor­relation procedures were then exercised for each of the three weather years and the four cities to demonstrate the validity of the correlations. Results of these comparisons are also shown in the table as percent differences (values in parenthesis) between the calculated values and the correlated values. The correlations derived from this study gave excellent estimates of system performance.

LOCATION WEATHER HEATING COOLING ANNUAL TOTAL YEAR DEGREE DEGREE HORIZONTAL

DAYS DAYS INSOLATION (oc) (oc) (kWh/m2)

1953 (GE) 832 1861 2196 PHOENIX 1967 (W) 795 (4%) 1 931 (4%) 2110 (4%)

TMY 767 (8%) 2026 (9%) 2155 (4%)

1960 (GE) 3172 396 1328 BOSTON 1965 (W) 3467 ( 9 %) 349 ( 1 % ) 1326 (0%)

TMY 3190 ( l % ) 389 (2%) 1266 (5%)

1968. (GE) 2347 806 1462 NASHVILLE 1966 (W) 2154 (81) 840 (4%) 1447 ( 1 % )

TMY 1980 ( 16%) 869 (8%) 1461 (0%)

1966 (GE) 2711 35 1 201 SEATTLE 1962 ( w) 3299 (21%) 0 1179 (2%)

TMY 2927 {8%) 59 1187 { 1 % )

(GE) - GENERAL ELECTRIC SELECTED YEAR

(W) - WESTINGHOUSE SELECTED YEAR

(TMY) - TEST METEOROLOGICAL YEAR

~ 45

21. HABITABLE HOUSE DESIGN

The designs for the habitable houses were the same designs as used in the performance analysis incorporating all of the energy conservation features discussed previously. The two designs are depicted in isometric views on the opposite page. Several flat-plate panels are shown on the northern house and PV shingles are shown on the southern house indicating the general appearance with collectors mounted on the roof. The houses have three moderately-sized bedrooms for a family of four with two full-sized bathrooms.

Testing of the habitable residences would be limited to normal living routines. The aim of this testing would be to determine energy savings that could be effected under actual use of the home by the residents. To this end, the instrumentation would be relatively limited and would be configured so that it could be stored locally or integrated by means of commercial telephone lines into a centralized data accumulation system.

Construction and inhabitance of these houses would provide experience in addressing several of the potential building code problems which may be encountered by installing roof-mounted PV arrays and in assessing institutional issues with respect to financing, insurance and utility interface.

46

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C

rm> ~

M ~

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HOU HABITABLE I SE DESIGN .

NORTHERN MODEL

~ 10· 15

SOUTHERN MODEL

0~ 10· 15 · 47

22. RESIDENTIAL TEST FACILITY

A flexible test facility as shown on the opposite page was designed to serve as a test bed and as a working showcase for solar energy systems. Technically, the facility provides an evaluation of functional PV or combined PV/therm.al system performance and addresses problems of installing and operating such systems on residential homes. The facility design was based on the Sunbelt house but with a greatly expanded garage area to provide space for a variety of systems to be installed and to accommodate working area for technicians. This design is applicable to all the regions, although a steeper pitched roof would be used in northern locations. The living area portion of the design serves as a reception and dis­play area for visitors while the expanded garage is the equipment and test area. The de-sign allows for incorporation of all of the prime subsystem configurations and rapid re­configuration to maximize the usefulness of the facility. The roof of the reception center portion of the structure was fitted with the modular metal framing (e.g., Unistruts®) to permit installation of any type of PV and thermal collectors.

48

C F ~

F1 kJ

F' ~

F1 ~

F w ~ w

fl w

Fi I

f"'l I

SIMULATED RESIDENTIAL AREA

RESIDENTIAL I TEST FACILITY

STAIRWELL DORMER TO EXTERIOR ACCESS WALK

EXCESS EQUIP­MENT STORAGE

49

23. PV AND THERMAL TEST SYSTEM DESIGN

General conceptual design of the electrical system has been configured to permit the im­plementation of an arrangement either with or without battery storage. A schematic of the electrical system showing the required equipment and location of instrumentation is shown at the bottom of the page. Not all the equipment would be installed at the same· time. The schematic for the thermal system is shown on the opposite page •. A forced air circulation arrangement was selected for the building. The instrumentation is located to provide data for system and subsystem performance evaluation. Again, the figure shows the capability for introducing the various types of equipment which may be evaluated.

The loads imposed on the test facility consist of both real and simulated elements with appropriate controls for simulating family living patterns. Real loads can be generated by the personnel working in the facility while simulated loads can be developed through auto­matic control of typical appliances and lighting fixtures.

In addition to the instrumentation noted on the opposite page, appropriate meteorological instrumentation would be included to determine energy input to the system.

50

V

r. T r T T

·T • T

SOLAR

PV

PANELS

ELECTRICAL SYSTEM SCHEMATIC AND INSTRUMENTATION

UTILITY

T

I V W

MAX. POWER

TRACKER

T I

INVERTER

TT : ace* ;. ____ ,. L • • r------,

V W VAR

w VAR

T -i--' ~- .... -~ RECTIFl!R ~- -t----. T I 0-. I !_ - !'= - - ~ . . •. ·W T I --- w I ---r---l---, -- •--VAR .._~~ ~---~----,

: ~!~~;';_'t_ ; -::-•. -T : ELECTRIC : I SHUNT I ALTERNATOR I : REG. I ·-, BATTERY L - - - - - - - _I

-------· .,. I

SENSOR LEGEND

I = CURRENT I/ = VOLTAGE

W = TRUE POWER VAR = REACTIVE POf1ER

T = TEMPE.RATURE

.. BCC: BATTERY CHARGE CONTROLLER ' DOTTED LINES ARE ALTERNATIVE SYSTEMS

DOMESTIC HOT WATER

w

(.Wl

jEL-EC-TR-IC. ----­L!ACE HEATE_~

IW

~~ES ··....---__,.

~~ING w

[SOLAR S~~TEM11--------1

PARASITICS ------····

•W

CJ I

I

F1} bJ

ri ~

C .

F, h£d

C

F' bi

f) ~

~ ~

r, ' i ~

r, w

- - Differential

Sensor Legend

->Q;peratura

erature Probe (Arrow Heads Indicate Paired Sensors)

- Alr Flow Heter

- Llquld Flow Meter

- Power

Hot or ColiL_

Freoi\,!SI

Heat Pump

(Located. Outside)

Liquid Colluctora (Evacuated Tube, Flat-Plate or Hybrid)

®

ln•Duct Re1l1tance

Heater

©

- - - - - - - - - - ·- - - -- , ------ --------.

©

I I I

I

I I

AB

PoHU­Plred

Hot Vater

Cenerator

®

Cold

Air Collecton (Plat Plate or

· Hybrid) .

i l i-----'. I r-·-J

I ©

i I ··-· I I

I l I

I i l I!~ lockBe4 ;~ .,,,_,

i i I I

I I •

.J r l r- ·1-1

Alr Return

From Ruidence

Alr Handler (B lover)

@

I~' I I

_T __ _____i ~----_J I __ ;_ ,Ci)

-------------Condltionod Alr -+­

Supply

--- - --- ---- --------

----------------

THERMAL SYSTEM SCHEMATIC AND INSTRUMENTATION

-------, • ____ _J 1-

•

I • I _____ ....J

IC~]

1

24. TEST PROGRAM . RANKING

The final system test program ranking and location was based on the results of the cost­to-benefit ratio ranking which included both solar system performance and cost effects, current population level and growth rate rankings, and energy cost and usage growth rate rankings. The immediate implementation of a test program developed around PV-only con­cepts, presently appears to promote the best development strategy for residential appli­cations. The test program to develop the residential PV market should include the use of both the habitable house designs and test facility design discussed on previous pages. The test facility should be included in the plan due to the flexibility in system configurations and evaluation this facility can provide. It should be initially implemented with simple PV -only systems with and without battery storage. This facility design also allows for possible in­stallation of solar thermal collectors which should receive consideration in the test program as costs are reduced.

Because of the relative simplicity of the PV -only approach, particularly without storage, consideration should be given to concurrently building several PV-only habitable residences along with the test facilities. These houses would be less costly than the test facility and have instrumentation sufficient to compare results with those obtained from the test facility. They would also provide early experience in addressing institutional issues and family acceptance.

The primary location for initial test facilities should be the Southwest represented by Phoenix and Albuquerque in the study results. The Northeast area of the country is recom­mended as the next area for testing. The Boston area has the highest current population and energy costs that make it a prime area for PV system implementation. The next at­tractive area is the Southeast. Miami has shown relatively high population levels and en­ergy costs with viable system performance and costs.

These three locations provide good test visibility with the geographical dispersion of the test facilities and provide different weather climates for initial PV test results comparisons. Both habitable houses and test facilities should be erected in each region; however, the test facility may be located in only the Southwest and the Northeast to provide contrasting loca­tions. With this approach, comparison of the data between the test facility and the habitable residences can be made in the same regions. The test program should be implemented im­mediately to achieve acceptance of PV residential systems.

If additional funds are available, the next regions for testing should include those represent­ed by Charleston, Santa Maria, Bismarck and Washington, D. C., based mainly on the cost­to-benefit ratio ranking in Section 13.

52

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C F kJ

Fl bi

Fl ~

r1 ~

F1 ~

r, ~

C

C ~ ~

0 .

TEST FACILITY COST ESTIMATES

Massdesign obtained construction cost estimates for both the Test-Bed Facility and the Habit­able Residence from professional cost estimators. The costs are in 1978 dollars and are ex­clusive of solar related equipment and instrumentation. They were developed for the Boston area and adjusted to other locations using the 1978 Dodge construction cost guide. The tables below summarize the cost estimates •

Costs of Residential Test Facility in Selected Cities

City 1978 $

Boston (Basic) $125,253 Albuquerque 123,237 Bismarck 130,548 Charleston 98,678 Ft. Worth - Dallas 121,306 Madison 114,212 Miami 106,762 Nashville 103,143 Omaha 128,104 Phoenix 130,226 Santa Maria (Used San Jose) 139,898 Seattle 137,163 Washington, D. C. 120,328

Costs of Habitable Test Residences in Selected Cities

City 1978 $

Northern Residences Boston (Baseline) $ 85,797 Washington, D. C. 82,263 Bismarck 89,027 Omaha 87,557 Nashville 70,251 Seattle 93,887 Madison 78,205

Sunbelt Residences Boston (Baseline) $ 76,169 Charleston 59,857 Miami 64,939 Ft. Worth-Dallas 73,684 Phoenix 79,123 Albuquerque 74,866 Santa Maria (Used San Jose) 85,097

53/54

GENERALfj ELECTRIC