3.2.2 Central-Station Terrestrial Photovoltaic System The reference terrestrial photovoltaic (TPV) alternative is a 200-MW system in which silicon cells are mounted in fixed-tilt, flat-plate arrays, in eight 25-MW modular components. The reference system, which does not include storage, is based primarily on designs published in a 1978 EPRI study.9 That study defined the cost and performance goals for utility photovoltaic conversion devices and assessed the effects of photovoltaic generation on electric utility systems. The reference TPV system is assumed to have a silicon-cell efficiency equal to that of the SPS silicon cell, or 19%. (A cell efficiency of 12% was assumed in the EPRI study.) This modified assumption alters the EPRI design, in that it reduces by approximately 37% the number of solar cells required to generate 200 MW. Figure 3.4 shows the energy efficiency chain for this system. Eight 25-MW modules of photovoltaic arrays are connected radially to a 34.5-kV switchyard, which, in turn, supplies the transmission grid through a step-up transformer. Each module contains 48.9 x 10$ cells measuring 6 cm x 6 cm. Each module is composed of the solar array field and its connecting DC cables and main bus, the DC-to-AC converter station, and the AC medium-voltage connection to the 34.5-kV switchyard. Within each module, the photovoltaic cells are connected in series and parallel to provide as high a voltage as Fig. 3.4 Efficiency Chain of the Central-Station Photovoltaic System
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