1. A Conceptual Cost Model Although no study has yet attempted a comprehensive formal cost model, several references address the need for such a model and one (A16) suggests a plan for its development. Based largely on the methodology, presented in the ECON study (All), a tentative conceptual cost model has been formulated as a framework within which to summarize the available literature. This conceptual cost model is presented in word-equation form in Exhibit 22. The equations presented in Exhibit 22 are intended to show the general interrelationships of capital costs, DDT&E costs, and recurring costs to finally determine unit energy costs expressed in mills/kWh. The balance of this section provides summaries of the key findings in selected references presented in a topical sequence that parallels the sequence of equations in the Conceptual Cost Model. These summaries are followed by a brief discussion of projected competitive terrestrial energy generation costs. The discussion deals exclusively with four versions of the SPS concept, three of which involve solar energy, and excludes any further treatment of the PRS concept. The Power Relay Satellite (PRS) concept is dealt with relatively clearly in the ECON report, which strongly suggests that it offers no significant economic advantages for domestic power transmission (under 3500 miles or 5630 km). In addition, the study points out that in addition to the same uncertainties and problems which characterize the economic analysis of the SPS concept, any analysis of the PRS is further complicated by the absence of any present or readily projectable comparable terrestrial system costs. A final and perhaps decisive problem is posed by the potential environmental hazards of high concentration radiation in transmission from earth. Of the numerous SPS concepts that have been at least briefly examined, the four considered here are: the solar-photovoltaic, the solarthermal (Brayton cycle), the solar-thermal (thermionic), and the nuclear (Brayton cycle). Most of the emphasis is on the solar-photovoltaic since it is currently the best documented and, perhaps for that reason, the most apparently promising.
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