Earth receives about 174 petawatts of solar radiation (known as insolation, which is defined as the rate of solar radiation received per unit area) at the upper atmosphere at any given time. When it meets the atmosphere, approximately 6 percent of the insolation is reflected and approximately 16 percent is absorbed. Average atmospheric conditions further reduce insolation traveling through the atmosphere by about 20 percent due to reflection and another 3 percent via absorption. These atmospheric conditions not only reduce the quantity of energy reaching the earth’s surface, but also diffuse approximately 20 percent of the incoming light and filter portions of its spectrum. After passing through the atmosphere, approximately half the insolation is visible light with the other half mostly in the form of heat.

The absorption of solar energy by atmospheric convection and evaporation and condensation of water vapor affects the winds and the water cycle. Upon reaching the surface, sunlight is absorbed by the oceans, land masses and plants. The energy captured in the oceans drives the thermal conveyor belt that drives our planets weather. Solar energy is ultimately responsible for temperature-driven ocean currents known as the thermohaline cycle and wind-driven currents such as the Gulf Stream. The energy absorbed by the earth, in conjunction with that recycled by the Greenhouse effect, warms the surface to an average temperature of approximately 14 °C. The small portion of solar energy captured by plants and other phototropic organisms is converted to chemical energy via photosynthesis. All the food we eat, wood we build with, and fossil fuels we use are products of photosynthesis. The flows and stores of solar energy in the environment are vast in comparison to human energy needs.

·         The total solar energy available to the earth is approximately 3850 zettajoules (ZJ) per year.

·         Oceans absorb approximately 2850 ZJ of solar energy per year.

·         Winds can theoretically supply 6 ZJ of energy per year.

·         Biomass captures approximately 1.8 ZJ of solar energy per year.

Solar energy is energy derived directly from the Sun. This energy drives the climate and weather and supports virtually all life on Earth. Heat and light from the sun, along with solar-based resources such as wind and wave power, hydroelectricity and biomass, account for most of the available flow of renewable energy.

Solar energy technologies harness the sun’s energy. These technologies date from the time of the early Greeks, Native Americans and Chinese, who warmed their buildings by orienting them toward the sun. Modern solar technologies provide heating, lighting, electricity and even flight.

The terms Solar Power and Solar Energy are used interchangeably to refer to the conversion of sunlight into electricity. This can be done either through the photovoltaic (PV) effect or by heating a transfer fluid to produce steam to run a generator.