Solar energy is the least polluting and most inexaustable of all known energy sources. Even the other "renewables" have some significant drawbacks. Today we are just beginning to tap its potential. While solar energy has been available to mankind since prehistoric times, we have not been able to use it as effectively as other sources. Creating a system which provides a reliable energy supply from solar energy can be a very technical and difficult task. However, not all solar energy systems are difficult to create or use.
Several, very practical solar energy systems are in use today. The two most common are passive solar heated homes (or small buildings), and small stand-alone photovoltaic (solar electric) systems. These two applications of solar energy have proven themselves popular over a decade of use. They also illustrate the two basic methods of harnessing solar energy: solar thermal systems, and solar electric systems. The solar thermal systems convert the radiant energy of the sun into heat, and then use that heat energy as desired. The solar electric systems convert the radiant energy of the sun directly into electrical energy, which can then be used as most electrical energy is used today.