Humans have harnessed the power of the sun for millennium. In the fifth century B.C., the Greeks took advantage of passive solar energy by designing their homes to capture the sun’s heat during the winter. Later, the Romans improved on solar architecture by covering south-facing windows with clear materials such as mica or glass, preventing the escape of solar heat captured during the day.
In the 1760s, Horace de Saussure built an insulated rectangular box with a glass cover that became the prototype for solar collectors used to heat water. The first commercial solar water heaters were sold in the U.S. in the late 1890s, and such devices continue to be used for pool and other water heating.
In the late 19th century, inventors and entrepreneurs in Europe and the U.S. developed solar energy technology that would form the basis of modern designs. Among the best known of these inventors are August Mouchet and William Adams. Mouchet constructed the first solar-powered steam engine. William Adams used mirrors and the sun to power a steam engine, a technology now used in solar power towers. He also discovered that the element selenium produces electricity when exposed to light.
In 1954, three scientists at Bell Labs developed the first commercial photovoltaic (PV) cells, panels of which were capable of converting sunlight into enough energy to power electrical equipment. PV cells powered satellites and space capsules in the 1960s, and continue to be used for space projects.
In the 1970s, advances in solar cell design brought prices down and led to their use in domestic and industrial applications. PV cells began to power lighthouses, railroad crossings and off shore gas and oil rigs. In 1977, solar energy received another boost when the U.S. Department of Energy created the Solar Energy Research Institute. It was subsequently renamed as the National Renewable Energy Laboratory (NREL), and its scope expanded to include research on other renewable energy sources. NREL continues to research and develop solar energy technology.
In the last 20 years, solar energy has made further in roads and now is used extensively in off -grid and remote power applications such as data monitoring and communications, well pumping and rural power supply, and in small-scale applications such as calculators and wristwatches. But solar power has not yet achieved its potential to become a major contributor to world electrical grids.
Private and government research and development in solar energy technologies have led to continuing innovation over the last 30 years. The conversion efficiency of PV cells — that is, the percentage of sunlight hitting the surface of the cell that is converted to electricity — continues to improve.
Commercially available cells now on the market have efficiencies approaching 20 percent.
Cell efficiencies achieved in research laboratories recent surpassed 40 percent. The worldwide PV market has grown by an average of 30 percent annually for the past 15 years, an increase that has improved economies of scale for manufacturers.
As a result, the cost of electricity generated from PV modules has fallen significantly, from more than 45 cents per kilowatt hour (kWh) in 1990 to about 23 cents per kWh in 2006.
In 2006 and 2007, a shortage of silicon (a primary component of crystalline silicon PV systems) temporarily increased PV module costs, but prices are expected to decline once again between 2008 and 2011, when silicon plants currently under construction are completed.