2.2 POWER CONVERSION The power conversion system consists of the solar cells and blankets, reflectors, slip rings, and the electrical power distribution network. GaAlAs was selected as the reference solar cell laid on a thin-film Kapton substrate. Since the SPS operates in GEO and must be capable of delivering 5 GWe to the utility interface on the ground, the size of each of the four modules that make up the solar array was determined to be 0.5 km wide by 12.6 km long. Each of the modules would consist of 21 bays of solar cells and each bay is 0.5 km by 0.6 km based on an array concentration ratio of 2. 2.2.1 SPS Efficiency The overall system efficiency used to size the SPS is 7.5-percent; the efficiency chain is shown in Figure 2.2-1. The overall efficiency of the microwave antenna, distribution, rectenna, and power interface with the utility company is 63.7 percent. The orientation of the SPS is for the longitudinal axis to be perpendicular to the orbital plane. A ±1° pointing tolerance was used in the analysis. The combined effects were assumed to produce a sun incident angle on the array of ± 24-1/2°. The maximum sun angle will only occur during the summer and winter solstice. Figure 2.2-1. SPS Efficiency
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