manufacturers, there is a high probability that low-cost, high-volume silicon single crystals of the desired thickness can be produced once there is a large enough market (62). Hand assembly techniques of solar cells, which are adequate to meet the present very small demand, will have to be replaced by automated methods similar to those that have been perfected for the production of other semiconductor devices. Since the preliminary cost projections for the SSPS solar photovoltaic array (63) were prepared in November 1971, there have been several developments which have led to new inputs to solar cell cost estimates. These new cost estimates will have an impact on the solar array costs that were used in the overall system cost analysis. In addition to these new cost projections, there have been design changes influencing the concentration ratios and leading to a decrease in the bussing requirements. Therefore, a re-evaluation has been made of the cost projections to point out areas and to update these projections. Cell efficiency, or power output, for a 50-gm (2-mil) thick cell was projected to be 19.7% and have a power output of 26.7 mW/cm2 (Figure 3.2-7, Ref. 63) at beginning of life and at 300°K. This is assumed to still be an accurate projection. Since a 50-gm thick cell is still being assumed, there is no change in the cell weight which was listed as 16.8 mg/cm2 (Figure 3.3-12, Ref. 63). The method of growing crystals of silicon and obtaining thin 50-pm thick material was assumed to be either hex rod or pulled web (Table 3.4-2, Ref. 63). Recent studies with edge- defined, film-fed growth (EFG) of silicon ribbons has provided new information for the SSPS cost analysis (64, 65). A comparison was made of the Reference 64 cost analysis of the ribbon, the cells fabricated from the ribbon and the SSPS report. The raw EFG ribbon cost was projected to be 0.25 cent per cm2, whiie the pulled web cost (Table 3.4-2, Ref. 63) was 0.20 cent per cm2. This shows very close agreement to the lowest costs projected, although the hex rod material costs were much higher. Therefore, it appears that the hex rod approach is too conservative and the ribbon cost of 0.25 cent per cm2 is more representative as a silicon crystal raw material cost. The cell fabrication cost used in Reference 63 was 1.0 cent per cm2 and, when added to the web material cost of 0.2 cent per cm2, amounted to a total solar cell cost of 1.2 cent per cm2 (Table 3.4-2, Ref. 63). The EFG ribbon cell cost analysis indicated that the total cell cost is estimated as 0.38 cent per cm2. This is a significantly lower cost and will be used in the updated analysis. The complete blanket cost was obtained (Table 3.4-2, Ref. 63) by adding 0.3 cent per cm2 for laminating the cover and printed circuit substrate to the total cell cost of 1.2 cent per cm2, thus resulting in a blanket cost of 1.5 cent per cm2. For the updated analysis, the lamination cost will remain at 0.3 cent per cm2, and this is added to the 0.38 cent per cm2 cost to total 0.68 cent per cm2 for the complete solar cell array blanket. Using the power output number.of 26.7 mW/cm2 (STC), this results in a blanket cost to power ratio of $255 per kilowatt compared to the $566 per kilowatt figure used in the preliminary SSPS cost analysis.
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