Terrestrial solar power.- A brief design and evaluation study was performed to determine the relative cost of electricity for alternate terrestrial solar power concepts. Figure XI-4 illustrates a generalized energy flow diagram for a terrestrial solar power system. As two example cases, a photovoltaic and a thermal cycle (steam Rankine) were analyzed to determine the cost of electricity for these systems. The systems were sized to 5 GW to be comparable with a 5-GW SPS rectenna. In both cases, it was assumed that the plants were located in the southwestern region of the United States, where plant factors of as high as 0.16 to 0.25 may be obtainable. Figures XI-5 and XI-6 show the energy flow diagrams for hydro pumped storage and fuel cell/water electrolysis cell (hydrogen) storage terrestrial solar power systems. In the solar thermal case, a hybrid system consisting of a combination solar plant and coal-burning steam powerplant was analyzed. Figures XI-7 and XI-8 show the estimated COE for these cases as a function of storage time. It was assumed that with no storage the plant factor varied from 0.16 to 0.25, which is optimistic for such systems. The terrestrial photovoltaic system was costed based on $300/kW solar cells operating at 11-percent efficiency. Note on figure XI-8 that the nominal SPS cost (50 to 60 mills/ kWh) is lower than the solar thermal terrestrial system by a substantial margin. The hybrid solar - coal plant has about half the cost of electricity of the SPS, but it saves only 13 percent in thermal energy (coal), whereas the SPS is a 100-percent substitution for the coal. Figure XI-9 shows the estimated land requirements for the two cases mentioned above together with SPS land requirement. The terrestrial photovoltaic system requires about three times the land area of the solar thermal system because of its lower conversion efficiency.
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