TABLE 2.3-1 MASS ANALYSIS OF 9 GW TPV SYSTEM A parametric model of the thermophotovoltaic conversion system has been developed (section 2.3.3). The model includes the solar concentrator and the cooling system. Output includes the total mass and the earth mass for each major subsystem and for the total TPV converter. Assumptions used in the model are described below. 2.3.2 TPV Design Description The most massive subsystem is the cooling system. Heat pipe radiators and liquid droplet radiators were considered. For LDR, the heat rejection temperature (less than 400 K) would require silicone oil as the working fluid, so the non-lunar mass of the LDR was unacceptably high. Heat pipe radiators at this temperature can use water in the main coolant loop and as heat pipe working fluid. Heat pipe radiators were selected for the TPV design because of their more advanced development and lower non-lunar mass requirement. The second most massive system is the concentrator. An all-aluminura concentrator like that described in section 2.7 was selected, so no non- lunar materials are required. The TPV model assumes the concentrator’s specific mass does not change for different concentration ratios (CRs). This assumption is overly simplistic, but should not cause significant errors in this application (CR < 400). Silicon solar cells were assumed because they can be nearly 100Z lunar in composition and they can be manufactured in large quantities. Conventional cells are not optimum for TPV converters. TPV-optimized cells should be highly transparent to long-wavelength radiation and should have different spectral response than conventional cells. TPV cells should be thin for better cooling and for better long-wave reflection. They should be designed to operate at high radiant intensity. The design assumes cells which are designed for TPV conversion, but which are not close to the achievable limit. Note that cells used in a TPV converter do not require periodic annealing because the body of the converter completely surrounds the cells, protecting them from harmful radiation.
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