7-5. A Space-based Combined Thermophotovoltaic Electric Generator and Gas Laser Solar Energy Conversion System OKTAY YESIL Summary This paper deals with methods of efficiently converting solar energy into electricity and into gas laser radiation. A space-based system, consisting of a thermophotovoltaic (TPV) electric generator and a gas laser, is proposed. The system utilizes an intermediate blackbody cavity, heated to a temperature of 2000-2400 K by concentrated solar radiation, as a power source for the conversion into both electricity and laser radiation. In the proposed solar-electric TPV system, a Cassegrainian optical device concentrates solar radiation to heat the blackbody cavity. A double-layer solar cell of gallium arsenide (GaAs) and silicon (Si) forms a cylindrical surface concentric to this blackbody cavity, receiving the blackbody radiation and converting it into electricity. Cell conversion efficiencies of 50% or more are possible with this type of TPV electrical generating system. It is further proposed that this blackbody cavity encloses a laser medium, so that the blackbody radiation is also used to pump a lasing gas simultaneously. The concept of solar-powered gas lasers via an intermediate blackbody cavity has been demonstrated in which solar pumping was simulated by an electrically-heated oven. A lasing gas mixture of CO2 and He was exposed to 1500 K thermal radiation for brief periods of time. A peak gain coefficient of 2.8X1O~3 cm ' was measured at 10.6 m wavelength and 1 Torr of pressure. A simple analytical model is used to describe the rate of change of energy distribution of the vibrational modes of CO2 and to predict the gain. Good agreement is found between predictions and the experimental data. The experimental results suggest that the maximum overall efficiency of the blackbody-pumped CO2 laser system is about 12%. 1. General Introduction The world's fuel reserves will eventually reach near-depletion with recovery of the remainder at ever-increasing cost and potential ecological risk. Therefore, future long- range energy programs must be aimed at the development of energy resources such as solar, fusion, geothermal, ocean temperature gradients and wind energy. In this direction, solar energy is already being considered for industrial applications, ranging from central solar power stations to solar chemical processing plants. Oktay Yesil, The Boeing Company, Seattle, Washington 98124, USA. Paper number IAF-ICOSP89-
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