Characteristics of various photovoltaic systems were studied to select a solar cell technology suitable for the SPS. The rapid progress in this technology makes assessment of practical performance goals difficult. The work reported here has assumed the availability and utilization of high efficiency low cost silicon solar cells, although competing technologies show promise. The rationale for this choice is the availability of user experience, the broad industrial basis for semiconductor silicon, and the known availability of silicon. Table 7-1 summarizes candidate photovoltaic device progress up to mid-1976. The design and application of low mass solar arrays has been a continuous problem in spacecraft design. The most common solutions have been the mounting of solar cells on the spacecraft or on special rigid panels, and these represent methods that are probably not feasible for the SPS. Recent requirements for large lightweight solar arrays for space station and the solar electric propulsion stage (SEPS) have resulted in a substantial body of useful lightweight array engineering data. The use of plastic film materials has received a great deal of effort, and products of this technology have been flown in small solar arrays. The largest, highest performance array presently under construction is that for the SEPS, rated at 25 kW, which is the latest power collection technology from which to evolve the SPS. The construction of the SEPS array has been used extensively to derive the SPS design reported herein. The potential for increasing the output of solar cells by sunlight concentration is subject to solar cell performance constraints, e.g., the loss of conversion efficiency at elevated temperatures and illumination levels. The aspects of maintaining reasonable cell temperatures at low levels with moderate concentration (less than 10 Sims) were investigated. The literature concerning photovoltaic devices under increased illumination was reviewed, and it was concluded that silicon technology was satisfactory for the less than 10 Sun level. Several concepts for cooling the solar cells were studied, and one of the more promising concepts is depicted in Figure 7-3. This concept may be capable of a savings of 34 percent in mass and 22 percent in planform area, and a 40°C temperature reduction at the solar cell as compared to the original configuration utilized in the SPS study. These types of configuration changes will be factored into the next phase of study activity. The integrated reflector/radiator concentrates sunlight on the thin narrow solar cell assembly, which is thermally coupled to the reflector/radiator. 7.1. 2 SOLAR ARRAY SUBSYSTEM The SPS solar cell blanket/reflector concept used for this study is illustrated in Figure 7-4(a) and considers the structure as an integrated part of
RkJQdWJsaXNoZXIy MTU5NjU0Mg==