The second parameter that was investigated in the sensitivity analysis was the implementation rate for the satellite power system. The reference design scenario for the implementation of the SPS is to build 60 5,000 MW satellites over a 30-year period. As was pointed out in the scenario description of this report, this number of satellites may not be feasible if the demand for energy is not adequate (e.g., in the unconstrained intermediate or the constrained intermediate supply/demand scenarios). Table 4.15 shows the change in cost with different building schedules for both the silicon and the gallium aluminum arsenide reference systems. The table shows the total capital cost per unit as a function of three different schedules. The first schedule entails building 60 units over a 30-year period, and the other schedules are 30 and 20 units, respectively, over a 30-year period, a substantial reduction in the commitment to SPS. The increase in unit cost is less than 4% as the implementation rate decreases. However, this may be a result of the accounting system, rather than a real estimate, because the SPS base costs were derived under the assumption of a mature industry. The third cost parameter that was examined for sensitivity to comparative costs was the set of economic or financial assumptions that were made in order to calculate energy costs. The baseline economic assumptions were reported in Table 4.13. Figure 4.19 shows the relative technology cost ranges and percentages for bonds, stock, and preferred stock returns on investment for the baseline assumptions and two other sets of assumptions. As shown in the figure, the cost range of each of the technologies varies slightly with different assumptions, but the overall comparative cost position does not change at all. Table 4.15 Effect of Reduced SPS Implementation Rate on Costs: Nominal Average Unit Costs (10^6 1978 $)
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