Solar energy is one of the world’s most abundant energy sources. The sun’s energy is the source of nearly all renewable energy resources, including biomass (stored solar energy), wind energy (uneven solar heating), and hydroelectric (evaporation and gravity). Humans can also use solar energy by harnessing the sun’s rays directly. There are four main types of solar energy: concentrating solar power, solar electric (photovoltaics), solar thermal water and space heating, and passive solar design.