Fig. 7. Per capita scales of solar panel area in space and materials volumes on groun environmental/intrusion factors and other aspects. It is a path that is currently perceived to require very large and premeditated (years in advance) strides to successfully accomplish. Unfortunately, while government-sponsored analyses tended to emphasize the truly major challenges of SPSs deployed from Earth, they did not clearly state the attractions of obtaining solar power via facilities off Earth. One attempt at condensing 30 M$ of SPS studies into a single image is shown in Fig. 7. Remember the small 10 ton pile of coal in Fig. 3? The solar panel section and associated transmission electronics (mass about 100 kg) shown to human scale in Fig. 7 could capture sufficient solar energy continuously off Earth to match the effective power flow from burning 10 tons of coal a year. This assumes reasonable 1980s technologies for energy conversion and transmission (5% overall space-to-ground-power conversion). This is likely an overestimate because in general electric power can be used 3 times more effectively than can power from burning of carbon (51). It is general practice to assume a power plant will have an operating life time the order of 30 years. The middle size pile of coal (300 tons, Fig. 3) depicts the carbon equivalent energy which could be delivered by the solar panel section in Fig. 7 over 30 years. Ultimately. 50-70% overall conversion seems possible (52,53; thermophotovoltaics). Thus, the collection area in space (Fig. 7) could eventually provide the power equivalent of
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