Solar Energy

Solar energy is the radiant light and heat from the sun that has been harnessed by humans since ancient times using a range of ever-evolving technologies. Solar radiation along with secondary solar resources account for most of the available renewable energy on earth.

However, only a minuscule fraction of the available solar energy can be used to:
Generate Electricity
Heating and Cooling
Cooking
Water Desalination


Solar Radiation at the Earth's Surface

While the solar radiation incident on the earth's atmosphere is relatively constant, the radiation at the earth's surface varies widely due to:
Atmospheric effects, including absorption and scattering; Local variations in the atmosphere, such as water vapour, clouds, and pollution; Latitude of the location; Season of the year and the time of day.

The above effects have several impacts on the solar radiation received at the earth's surface. These changes include variations in the overall power received, the spectral content of the light and the angle from which light is incident on a surface. In addition, a key change is that the variability of the solar radiation at a particular location increases dramatically. The variability is due to both local effects such as clouds and seasonal variations, as well as other effects such as the length of the day at a particular latitude. Desert regions tend to have lower variations due to local atmospheric phenomena such as clouds. Equatorial regions have low variability between seasons.


Solar Technologies and Techniques

Solar energy technologies refer primarily to the use of solar radiation for practical ends. All other renewable energies other than geothermal derive their energy from energy received from the sun.

Solar technologies are broadly characterized as either passive solar or active solar depending on the way they capture, convert and distribute sunlight. Active solar techniques include the use of photovoltaic modules (also called photovoltaic panels) and solar thermal collectors (with electrical or mechanical equipment) to convert sunlight into useful outputs. Passive solar techniques include orienting a building to the Sun, selecting materials with favorable thermal mass or light dispersing properties, and designing spaces that naturally circulate air.

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.

Solar Thermal Technologies
 

Solar thermal technologies are harnessing solar energy for thermal energy (heat). Solar thermal technologies comprise flat collectors for low- and medium temperatures and high temperature collectors concentrating sunlight using mirrors and lenses.

Solar Electric Technologies

Sunlight can be directly converted into electricity using photovoltaics (PV) and various experimental technologies.