Fig. 3-1. Solar Thermionic Direct Radiation Cooled System Fig. 3-3. Solar Brayton Cycle System Fig. 3-2. Solar Thermionic, Liquid-Cooled System Fig. 3-4. Cascaded Solar Thermionic/Brayton Cycle System converter is used to provide the DC necessary to energize the transmitter. The solar thermionic, actively-cooled system is shown in Figure 3-2. 3.4 SOLAR CLOSED BRAYTON CYCLE (CONCEPT 3) The Brayton cycle turbomachine provides a rotating shaft output which drives the generators. Thermal energy is added to the helium working fluid in heat exchanger tubing located within the cavity absorber. The hot gas is expanded through the turbine, providing power to turn both the compressor and generator. The recuperator exchanges energy across the loop to increase the system efficiency. Waste heat is rejected through a gas-to-liquid heat exchanger to a liquid metal cooling loop; the liquid metal pumps use power drawn from the generators. The 50,000 volt AC output of the generators is stepped-up to 382,000 volts in transformers; this high voltage facilitates on-board distribution. Stepdown occurs in the rotary transformers. An AC to DC converter is used to provide the DC required to energize the transmitter. The solar Brayton cycle system is shown in Figure 3-3. 3.5 SOLAR THERMIONIC/BRAYTON CYCLE CASCADE (CONCEPT 4) This "cascaded" system offers potentially high efficiency. All waste heat from the thermionic diodes is available to the Brayton cycle; the diodes are cooled by the helium flow in the Brayton loop. The Brayton loop is cooled by a liquid metal radiator. The DC output of the diodes is stepped-up to 50,000 volts AC in the rotary converters/trans- formers; the turbomachine generators produce 50,000 volts AC which is combined with the output of the rotary converters/transformers. An AC to DC converter is used to provide the DC required to energize the transmitter. The cascaded solar thermionic/Brayton cycle system is shown in Figure 3-4. 3.6 SILICON PHOTOVOLTAIC (CONCEPT 5) A photovoltaic, or solar, cell directly converts solar energy to electric power. Performance may be augmented, within certain limits, by concentrating
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