Technically speaking, solar energy is the only energy we have. Every other “energy” is a derivative of the sun's energy hitting the earth. Fossil fuels, wind power, biofuels, and even wood are all products of the sun. It is the most abundant and basic form of energy. Unfortunately, it is difficult to capture without some technology, though the simpler that technology is, the longer it will last.
Solar energy is most efficient if used directly as thermal energy for heating water, air, or a thermal appliance. Many systems are available for using the sun's heat, and by designing an appropriate system for your needs, a solar thermal system can assume a central role in your energy supply.
Combined Heat and Power uses the sun's energy to make electricity, while using the waste heat that it produces for other systems like heating water, refrigeration and heating a room.
A Solar Tower is a large energy producing system that converts sunlight into thermal or electrical energy. Solar towers can be constructed in a variety of ways, from an array of heliostats to a large greenhouse structure.