The concept of space-based solar power has been studied for decades, and the first patent for such a system was issued in 1973. The basic technology is straightforward (a large photovoltaic array in Earth orbit, with power beamed to a receiving antenna in the form of microwaves or lasers), and a space-based collector would have several advantages over one on Earth's surface. Earth's atmosphere absorbs and reflects much of the sun's energy before it reaches the surface, so a space-based collector would receive more intense solar radiation. A collector in geosynchronous orbit would also experience nearly continuous sunlight, with the day/night cycle reduced to brief daily periods of shadow near the equinoxes (collectors in lower and less expensively achieved orbits would experience progressively more darkness as the orbital distance decreased). However, these advantages must be weighed against the cost of sending dozens of square kilometers of solar panels (plus the transmission antenna and associated hardware and support structures) into space as well as the construction of the ground-based receiving antennas. A 4-gigawatt solar power satellite would require 40-80 shuttle flights to lift the solar panels alone into low earth orbit (support structure and transmission antenna not included), at a current cost of tens to hundreds of billions of dollars. Once the power satellite is in orbit, it is subject to damage from such things as meteoroid impacts, and repairs would also be very expensive. Solar power satellites may become more economically viable in the future, especially if a space elevator is ever constructed, but at the present time the reduced efficiency of ground-based solar panels is outweighed by the enormously greater cost of sending them into orbit and building the needed space- and ground-based infrastructure.
Source(s):
http://en.wikipedia.org/wiki/Space_solar_power
http://ams.allenpress.com/perlserv/?request=get-abstract&doi=10.1175%2F...

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