Solar energy is heat and light from the sun. This energy resource powers the climate and weather and sustains life on Earth. Solar radiation along with secondary solar resources such as wind and wave power, hydroelectricity and biomass account for over 99.97% of the available flow of renewable energy on Earth.

Solar energy technologies can provide daylighting and thermal comfort in passive buildings; potable water via distillation and disinfection; water and space heating; space cooling by absorption or vapor-compression refrigeration; high temperature process heat for industrial purposes; and electrical generation by thermal or photovoltaic means.

Energy from the Sun

main: Solar radiation

The Earth receives 174 petawatts (PW) of incoming solar radiation (insolation) at the upper atmosphere.Smil (1991), p. 240 Approximately 30% is reflected back to space while the rest is absorbed by clouds, oceans and land masses. The spectrum of solar light at the Earth's surface is mostly spread across the visible and near-infrared ranges with a small part in the near-ultraviolet.

The absorbed solar light heats the land surface, oceans and atmosphere. The warm air containing evaporated water from the oceans rises, driving atmospheric circulation or convection. When this air reaches a high altitude, where the temperature is low, water vapor condenses into clouds, which rain onto the earth's surface, completing the water cycle. The latent heat of water condensation amplifies convection, producing atmospheric phenomena such as cyclones and anti-cyclones. Wind is a manifestation of the atmospheric circulation driven by solar energy. Sunlight absorbed by the oceans and land masses keeps the surface at an average temperature of 14 °C. The conversion of solar energy into chemical energy via photosynthesis produces food, wood and the biomass from which fossil fuels are derived.

Solar radiation along with secondary solar resources such as wind and wave power, hydroelectricity and biomass account for over 99.9% of the available flow of renewable energy on Earth. The total solar energy absorbed by Earth's atmosphere, oceans and land masses is approximately 3,850 zettajoules (ZJ) per year.

Applications of solar energy technology

Solar technologies are broadly characterized as either passive or active depending on the way they capture, convert and distribute sunlight. Active solar techniques use photovoltaic panels, pumps, and fans to convert sunlight into useful outputs. Passive solar techniques include selecting materials with favorable thermal properties, designing spaces that naturally circulate air, and referencing the position of a building to the Sun. Active solar technologies increase the supply of energy and are considered supply side technologies, while passive solar technologies reduce the need for alternate resources and are generally considered demand side technologies.