affect the ranking only if two circumstances applied. The first circumstance is that a shift in energy sources, e.g., from oil to coal, would be accompanied by a change in energy efficiencies for the same manufacturing or operating processes required for a particular power plant. If such changes occurred uniformly for all different types of power plant manufacture, they still would not change the rank order. The second circumstance which would be required to change the relative position would be that the changes in energy efficiencies associated with changes in energy mix would be specifically selective of the types of processes and materials needed for the SSPS. Based on the limited available information considered for this study, there is no basis for assuming that either of these two conditions would apply. Also shown in Exhibit 44 are the annual operating energies required. 12 These add up to approximately 7.97 x 10 Btu per year. Approximately 25% of this total will be drawn from coal, with almost 65% from crude oil and gas, and less than 10% from hydroelectric and nuclear powered sources. Within the overall capital energies, the two most important energy components are the solar array and the flight component of the overall transportation cost. Transportation costs, including both the vehicles and the flights, account for approximately 35% of the total. 12 Most of this is in the flight cost which accounts for over 100 x 10 Btu. In estimating solar array costs, the energy requirements developed by ECON were used rather than the input-output coefficients developed by DSI. While present energy costs are something in excess of 400 watt hours per square centimeter of solar cell material, the projected goal is 82 watt hours per square centimeter of solar cell material. This projected goal has been used and converted appropriately for its cost and 12 Btu equivalent to derive the estimated 120 x 10 Btu required for solar array manufacture. Even assuming these substantially greater efficiencies, the solar array represents over 27% of the total capital energy requirement. Although the external energy subsidy required for the SSPS could be significantly affected if target energy cost reductions in solar cell production are not achieved, any comparative or parametric treatment of this subject is outside the scope of this preliminary energy balance
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