Solar energy is the most extensive renewable energy resource available. It is the only renewable resource that could, by itself, replace all of our current fossil fuel energy consumption. This chapter considers the properties of solar radiation and the ways in which it can be used to contribute to our energy use. Solar energy may be used as a source of thermal energy or as a source of electrical energy. Thermal solar energy can be used for space heating and water heating for individual residential properties or for industrial, business or community use. Solar electricity can be obtained from solar thermal energy by the use of a heat engine or directly through the use of photovoltaics. In either case, systems can be grid connected to replace existing thermal generation from burning fossil fuels.