When most people think about solar power the first thought that comes into their heads is of photovoltaic solar panels. It was not until the 1970s, during the oil crisis, that people started thinking seriously about the use of solar energy. The first commercial plants were established in the 1980s. As of May 2011, there are more than 800 photovoltaic power plants around the world, the largest being Canada's Sarnia Photovoltaic Power Plant, which has an output of 97 megawatts. (This compares with the average output of a nuclear power station of 850 megawatts.) More and more use is being made of photovoltaics on a small scale for the individual homeowner, and the Obama administration is planning to place solar panels on the White House once more.
There are far more thermal solar power stations than there are photovoltaic, one of the reasons being that they are cheaper to produce. There are two main ways of harnessing the sun's radiant heat --- the parabolic trough and the solar power tower. The former concentrates the sun's heat onto a pipe, heating the oil contained in it to 400 degrees Celsius. A heat exchanger makes steam, which drives a turbine to make electricity. The power tower uses the same principle, except that the heat is reflected to a heat exchanger located at the top of a high tower. As of May 2011, the world's largest thermal solar power station is being built in the Mojave Desert, with an output of 370 Megawatts. Domestically, radiant heat is used in many hot water systems.
Wind farms are becoming a more and more common sight. They're the modern version of an idea that has been used for centuries. The old fashioned windmill, which converted the wind's power into the energy source for rotating a large millstone, has been replaced by the wind turbine generator. All of the world's winds are caused directly by the sun, from the afternoon's gentle sea breeze to the largest of hurricanes, so making use of the wind is yet another way of harnessing the sun's energy. Wind farms can be found both onshore and offshore, and on a smaller scale wind turbines can be used in remote areas such as farms for generating electricity and for pumping water. Yachts also use the wind, and hence the sun, as a source of power.
The sun's energy can be harnessed from hydroelectric power stations set into dam walls. Rivers and dams are all part of the hydrologic cycle. The sun heats up the sea, the sea evaporates and water vapor rises, eventually forming clouds, which in turn deposit rain and snow over the land. These eventually find their way back into rivers and dams and back to the sea. In the past the sun's energy was harnessed from rivers by means of water wheels, usually to rotate a millstone for grinding grain.
There is plenty of research going on into new ways of harnessing the sun's energy in the future. Many of these make use of nanotechnology. Solar panels produced by Nanosolar reduce the cost of photovoltaic electricity production from $3 a watt to 30 cents a watt, a tenfold saving. Research is also being conducted into the production of hydrogen from water using nanotubes in a way that mimics photosynthesis.