Alternative solar cell materials being considered for the solar power satellite are described and price, production, and availability projections through the year 2000 are presented. The chief materials considered are silicon and gallium arsenide

Almgren, D. W.

Csigi, K. I.

Glaser, P. E.

English

NASA Technical Reports Server

N82 22721
EVALUATION OF SOLAR CELL MATERIALS FOR A SOLAR POWER SATELLITE I
Dr. Peter E. Glaser - Dr. David W. Almgren - Ms. Katinka I. Csigi
Arthur D. Little, Inc. - Cambridge, Massachusetts
As originally conceived, a solar power satellite (SPS) can utilize current
approaches to solar energy conversion, e.g., photovoltaic, thermal electric,
and others, which may be developed In the future. Among these conversion pro-
cesses, photovoltaic conversion represents a useful starting point because solar
cells already are in wide use in satellites. An added Incentive is the sub-
stantial progress being made In the development of low-cost reliable photovol-
talc systems for terrestrial applications, the increasing confidence in the
capabilities to achieve the required production volumes to sustain expanded
markets. Figure i projects the cost reduction of silicon solar ceils and the
necessary transition to thin-film solar cells which will have to be developed
to meet projected terrestrial photovoItaic system production and cost goals.
Several photovoltaic energy conversion systems applicable to the SPS con-
cept have been evaluated. Two alternative photovoltaic systems--one employing
single-crystal silicon, and the other, gallium arsenlde--have been selected for
the SPS reference system. The silic_n photovoItaic system utilized 50 pm thick,
single-crystal, silicon solar ceils sandwiched between layers of 75pm and 50 pm
thick borosilicate glass, while the alternative design utilizes 5 pm thick,
single-crystal heteroface gallium arsenide solar cells formed by a chemical
vapor-deposition process on a 20 pm layer of sapphire as the substrate/cover
glass for the solar cell. The array is then encapsulated with 13 pm of Teflon
bonding the solar cell to a 25 pm Kapton cover. The gallium arsenide solar
cells are Integrated with thin-film Kapton solar reflectors with a concentration
ratio of 2 to reduce the required solar cell area. The mass of the photovoltaic
systems represents 40_ of the mass of the SPS reference system.
The beginning of life (BOLl and end of life (EOL) conversion efficiencies
of the SPS solar cells has a Significant impact on the total size of an SPS and
the total mass that has to be carried to geosynchronous orbit.
The SPS system studies have been primarily concerned with such photovoltaic
factors as:
• Beginning of life solar cell efficiency;
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• Rate of degradation of output on
- orbit
- solar cell/array/system performance:
• Photovoltaic efficiency recovery techniques;
• Cell/array cost;
• Mass; and
• Availability of photovoltaic materials.
In addition to these parameters, consideration has to be given to the cell/array
manufacturing processes to meet SPS production requirements and cost goals.
Silicon is presently the only photovoltaic material that is being consid-
ered for mass production as part of the U. S. Department of Energy (DOE) Photo-
voltaic Program. 2 Single-crystal silicon solar cells could meet the projected
needs of the ground-based exploratory development and space technology verifi-
cation during the period 1980 to 1985, and is the most likely photovoltaic ma-
terial for use in SPS pilot and prototype systems. Gallium arsenide is a prom-
ising photovoltaic material, however, gallium arsenide solar cells in suitable
form, sufficient quantity, having reproducible characteristics and an accept-
able cost are unlikely to be available before 1985 unless there is a near-term
significant R&D program commitment. Furthermore, other advanced photovoltaic
materials, e.g., amorphous silicon, are being investigated as part of the DOE
Photovoltaic Program which may deserve consideration as candidates for SPS solar
cell arrays if they could be mass produced at low cost.
The industrial capability needed to manufacture the SPS solar cells and
arrays will require the development of large-volume production technology which
could serve both the SPS and terrestrial PV system requirements. Figure 2 pre-
sents a solar cell/array production scenario based on the deployment of one
10 GW on two 5 GW SPS's per year including inventory accumulation. This implies
that the selection of solar cell materials and array designs will be completed
by 1985, and that a long-term on-orbit solar cell array test program will pro-
vide data on the performance of candidate solar cell arrays in the space envi-
ronment prior to commitment to a pilot-plant program.
The scale of commitment of capital material and labor resources to con-
struct large-scale manufacturing facilities will require that the risks and un-
certainties in achieving required solar cell/array performance and cost goals
have been evaluated and that they are acceptably low. Funding commitments for
gallium arsenide, or other promising photovoltaic materials, would have to
approach the present level of funding for silicon solar cells in the next sev-
eral years so that they could be considered for an operational SPS in the 2000
time frame.
1Arthur D. Little, Inc., "Evaluation of Solar Cells and Arrays for Potential
Solar Power Satellite Applications." Final Report to NASA Lyndon B. John-
son Space Center, March 1978.
2U.S. Department of Energy, National Photovoltaic Program, Multi-Year Program
Plan, June 6, 1979. DOE/ET-O105-D.
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PHOTOVOLTAIC CELL/ARRAY PRICE GOALS AND HISTORY
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Figure 1.
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SOLAR CELL/ARRAY PRODUCTION SCENARIO FOR YEAR 2000 SPS DEPLOYMENT
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Evaluation of solar cell materials for a Solar Power Satellite

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