Solar energy has been used by humans for thousands of years. For example, ancient cultures used energy from the sun to keep warm by starting fires with it. They also kept their homes warm through passive solar energy designs. But isn't solar energy expensive to maintain? In fact, An economic breakthrough occurred in the 1970's when Dr. Elliot Berman was able to design a less expensive solar cell bringing the price down from $100 per watt to $20 per watt. This huge cost savings opened up a large number of applications that were not considered before because of high costs. These applications included railroads, lighthouses, off-shore oil rigs, buoys, and remote homes. For some countries and many applications, solar energy is now considered a primary energy source, not an alternative.Solar energy is one of the only sources known to man to be able to last all day and all night. Because although the sun only stays out for a portion of the day, the panels absorb the sun's energy and stores it so that it may used when the panel itself isn't. Researchers have developed cells with more than 20% efficiencies. 20% efficient means that out of the total energy that hits the surface of a solar cell, about 20% is converted into usable electricity.
http://www.youtube.com/watch?v=EsiFzFDI54Q
http://www.makeitsolar.com/solar-energy-information/01-solar-history.htm
