"The Pentagon issued a report indicating that space-based solar power 'has the potential to help the United States stave off climate change and avoid future conflicts over oil by harnessing the Sun's power to provide an essentially inexhaustible supply of clean energy.' The report, from the Pentagon's National Security Space Office, calls for funding the development of space-based solar power culminating in 'a platform in geosynchronous orbit bigger than the international space station and capable of beaming 5-10 megawatts of power to a receiving station on the ground.' The Pentagon's interest in such an effort stems from the need to acquire energy on the battlefield, which today often comes at a painful premium."NASA and DOE have collectively spent $80M over the last three decades in sporadic efforts studying this concept (by comparison, the U.S. Government has spent approximately $21B over the last 50 years continuously pursuing nuclear fusion). The first major effort occurred in the 1970's where scientific feasibility of the concept was established and a reference 5 GW design was proposed. Unfortunately 1970's architecture and technology levels could not support an economic case for development relative to other lower-cost energy alternatives on the market. In 1995-1997 NASA initiated a "Fresh Look" Study to re-examine the concept relative to modern technological capabilities. The report (validated by the National Research Council) indicated that technology vectors to satisfy SBSP development were converging quickly and provided recommended development focus areas, but for various reasons that again included the relatively lower cost of other energies, policy makers elected not to pursue a development effort.
Read full here: http://www.nss.org/settlement/ssp/library/nsso.htm