The next consideration concerns the effects of these new blanket cost projections on the solar collector costs. The baseline concentrator structure is of a flat-plate channel design with a concentration ratio of N = 2.06. At this concentration ratio, the power (delivered in space after 5 years of life) from the blanket corresponds to 38 W/cm2 (Figure 3.5-20, Ref. 63) or an area-to- power ratio of 26.3 cm2 per watt (Figure 3.5-23, Ref. 63). The reflector or concentrator surface area required to achieve a concentration ratio of N = 2.06 for the new channel design is 2.12 times the blanket area. Therefore, multiplying the new blanket area per watt figure of 26.3 cm2 per watt by 2.12 results in a reflector area per watt figure of 55.7 cm2 per watt (generated in space after 5 years). Based on the analysis of the effects of cell layout and interconnection pattern on bussing weight, a substantial decrease in the array bus weight and, consequently costs, can be projected. The layout utilizing the blanket as the bus for the complete length of the array results in a bus weight of 4 x 107 grams for the 8 x 109 watt (in space) solar collector array or a weight-power ratio of 5 x 10~3 gm/W. Using the updated costs, the solar collector costs can be summarized and compared to the original SSPS cost projections (Table 3.8-1, Ref. 63). Since these new cost projections are based on ribbon cell technology and a flat-plate, channel-type concentrating mirror design, the cost comparisons were made with the web-type solar cells using the low-cost projections for such cells and the N = 3 petal-type concentrating mirrors. These cost comparisons are shown in Table 32. The cost projection of 0.352 cent per watt of power generated on Earth is substantially lower than the 0.672 cost per watt figure used in the 1971 projection. Therefore, the cost projection of $352 per kilowatt is assumed for the solar collector array cost. Cost projections based on actual experience in the production of single-crystal silicon solar cells are presented in Figure 91. The 2x2 cm cells are widely used on unmanned spacecraft. The 2x6 cm cells were produced for the Apollo telescope mount portion of the “Skylab” spacecraft. The 2-inch diameter cell represents the costs of solar cells for terrestrial applications produced from 2-inch diameter wafers of single-crystal silicon boules. This perspective on experience for solar cells can be used to test the reasonableness of the solar cell cost projections. The 1971 low cost projection corresponding to 1.5 cents per cm2 fits on a 75% slope line while the 1973 cost projection of 0.7 cents per cm2 fits on a 72% slope line. Both of these cost projections are reasonable slopes, since experience indicates that typical cost reduction curves follow about a 70% slope. Therefore, this test of reasonableness for the solar cell costs indicates that these projections follow past industry experience (66). The concept that solar arrays can be manufactured inexpensively in the future was emphasized by Paul A. Berman (67): “.. .it seems almost inconceivable that such a simple thing as a solar array jbstrate with printed circuit interconnections and wiring upon which cells are mounted in some
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