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Solar energy is energy from the sun. This energy drives 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 over 99.9 percent of the available flow of renewable energy.
Solar energy also describes technologies that utilize sunshine to produce other forms of energy. These technologies date from the time of the early Greeks, Native Americans and Chinese, who warmed their buildings simply by orienting them toward the sun. Modern solar technologies continue to harness the sun, but in more innovative ways, to provide heating, lighting, electricity and even flight.
The terms solar power and solar energy are often used synonymously but solar power usually refers to photovoltaic (PV) and concentrating solar thermal technologies that convert sunlight into electricity. In the case of solar PV, the process is direct, via silicon-based cells; in the case of solar concentrating thermal, the process involves heating a transfer fluid to produce steam to run a generator.
There are many technologies for harnessing solar energy within these broad classifications: active, passive, direct and indirect.

  • Active solar systems use electrical and mechanical components such as tracking mechanisms, pumps and fans to capture sunlight and process it into usable outputs such as heating, lighting or electricity.
  • Passive solar systems use non-mechanical techniques to control the capture of sunlight and distribute this energy into usable outputs such as heating, lighting, cooling or ventilation. These techniques include selecting materials with favorable thermal properties to absorb and retain energy, designing spaces that naturally circulate air to transfer energy and referencing the position of a building to the sun to enhance energy capture.
  • Direct solar generally refers to technologies or effects that involve a single-step conversion of sunlight that results in a usable form of energy.
  • Indirect solar generally refers to technologies or effects that involve multiple-step transformations of sunlight that result in a usable form of energy.

There is a good prospect of harnessing solar power in Bangladesh. In a recent study conducted by Renewable Energy Research Centre, it is found that average solar radiation varies between 4 to 6.5 kWhm-2day-1. Maximum amounts of radiation are available in the month of March-April and minimum in December-January. Following map has illustrated prospect of solar radiation in Bangladesh.