IV-B-l-c ALTERNATE ENERGY CONVERSION CONCEPTS William E. Simon/EP5 IV-B-l-c-1.0 Introduction The reference JSC SPS design concept uses silicon solar cells for solar energy collection and conversion to electricity. There are, however, several other energy conversion system candidates that are potentially attractive for SPS application. One of the more promising alternate concepts, advanced by The Boeing Company, utilizes a solar concentrator- closed Brayton cycle system for power generation. To gain additional perspective into energy conversion alternatives, a study was conducted to define and evaluate candidate concepts. In the following text, a discussion of "thermal engine" power conversion systems and other thermal system concepts is presented, with emphasis on the closed Brayton or Joule cycle. This is followed by an evaluation of the proposed Boeing closed Brayton cycle design concept. IV-B-l-c-2.0 Alternate Power Conversion Systems 2.1 Introduction This section consists of a survey of available thermal engine (dynamic) system concepts, and it includes an evaluation of the Boeing (Brayton cycle) system. 2.2 Background and Related Work 1 * An alternative concept to the Glaser photovoltaic system is a thermal engine system consisting essentially of solar reflectors, energy absorbers, dynamic converters, and a heat rejection subsystem (radiators). This alternative to photovoltaics is being pursued primarily due to the inherently higher conversion efficiency of the heat engine system (as high as 40%), which results in reduced area required for the solar reflector, and also because the generation of a.c. power in large quantities reduces conductor weight significantly. There are other advantages and disadvantages of this system which will be discussed in more detail in the text of this report. Early comparison studies of nuclear turboelectric power plants operating on both the Brayton and Rankine cycle principles resulted in more favorable acceptance of the Rankine cycle system due to its smaller radiator area and lighter weight at peak cycle temperatures (at that time 1150- 1250°F). Several Rankine-cycle space power systems received major development emphasis, among them the solar Sunflower and ASTEC systems, and the nuclear SNAP systems (e.g., SNAP-2, SNAP-8, and SNAP-50).2 For the short- duration missions (compared to SPS) being considered for early missions, ♦Superscripted numbers refer to similarly numbered references at the end of this report.
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