Our Earth receives 174 petawatts (PW) of solar radiations at the upper atmosphere, out of which almost 30% is reflected back to space whereas the rest is absorbed by clouds, oceans and land masses.
The Earth’s land surface, oceans and atmosphere that absorb solar radiation, raises their temperature. This causes warm air that contains evaporated water from the oceans to rise, causing atmospheric circulation or convection.
The water cycle gets completed when the air reaches a high altitude, where low temperature prevails, and the water vapor condenses into clouds, which rain onto the Earth’s surface.
The energy from the sun which is absorbed by the oceans and land masses helps to keep the surface temperature at an average of 14 °C. This energy is used by green plants to carry out photosynthesis, which produces food, wood and the biomass from which fossil fuels are derived.
Solar energy has been consumed by humans since ancient times using a number of ever-changing technologies. Together with other secondary solar resources such as wind and wave power, hydroelectricity and biomass, these energy account for most of the available renewable energy on Earth. However, currently, only a minute fraction of the available solar energy is used.
Solar power technologies provide electric energy by means of heat engines or photovoltaics. Some of the commonly used solar applications include space heating and cooling through solar architecture, potable water via distillation and disinfection, daylighting, hot water, thermal energy for cooking, and high temperature process heat for industrial purposes.
It is possible to characterize solar technologies as either passive or active, depending on the way they capture, convert and distribute sunlight. Active solar techniques include use of photovoltaic panels, pumps, and fans to convert sunlight into useful outputs, whereas 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.
The total solar energy absorbed by Earth’s atmosphere in a year by the oceans and land masses is around 3,850,000 exajoules (EJ). Out of this, photosynthesis captures about 3,000 EJ per year in biomass.
The total amount of solar energy that reaches the earth’s surface is so enormous that in one year, it accumulates about twice as much as the amount that will ever be obtained from all of the Earth’s non-renewable resources combined of coal, oil, natural gas, and mined uranium combined.
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