Published on Apr 02, 2024
Solar Power from Space (SSP) promises clean and everlasting energy supply for the growth of the mankind. With the state-ofart technologies yet developed, SSP is feasible but not economic. Key issues regarding SSP are launch cost, efficiency of solar cells, wireless power transmission, heavy investment, maintenance etc.
Yet proposed models suggest to place space segment in GEO, LEO or at lunar surface, which are either economically infeasible due to huge launch cost or require long setup time.
Next major breakthrough required is efficiency of solar cells, to reduce launching weight and size for SSP to be economic. Yet stateof- art solar cells have efficiencies only about 15%. Author proposes Metal-Metal junction cavity structure solar cell, which theoretically promises to increase solarelectric conversion efficiency many folds. Rest of the paper discusses fetter's analysis about economic feasibility of SSP, issues regarding microwave power transmission and influences of SSP on environment and existing life.
The SSP concept arose because space has several major advantages over earth for the collection of solar power. Space is free from day-night cycle, atmosphere, clouds, dust, rain, fog and other climatic changes, so it would receive 30% more intense and at least eight times more sunlight than that of at ground constantly and continuously unaffected by the weather. In geosynchronous orbit it would receive sunlight almost 24 hours a day hence avoiding the expensive storage facilities necessary for earthbased solar power systems. Since earth's axis is tilted, it would be in earth's shadow only for 70 minutes maximum at late night when power demands are at their lowest, during 42 days near the equinoxes
Ground power receiving site uses a device called rectenna (rectifying antenna) to receive and rectify the microwave power beam. The rectenna system converts the microwave power back to DC power which is then converted to conventional AC (Alternating Current), and is connected to existing electric power networks.
Assuming typical values for efficiencies like 15% for solar panels to convert solar energy into DC, 70% conversion rate in the space segment from DC to microwave, 90% beam (power) collection efficiency, and 80% conversion rate for rectenna from microwave to DC in ground segment, the estimated over-all efficiency is approximately 7.5 %. With such efficiency a SSP space segment would be of size of about 50 km2 (5 km x 10 km) to generate 5 GW DC power on earth
Due to the huge size of the SSP space segment launching cost is the major factor affecting its economic feasibility. Consequently various ideas arouse due course of time about where to place it. The first concept is proposed to place it in GEO (Geostationary Earth Orbit, 36000 km) so that it would be always in sunlight and directly above earth station hence it would supply non-stop constant energy to the earth station without need of controlling microwave beam's direction
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