Solar energy involves capturing and harnessing the sun’s energy. There are three main ways of doing this:

• Passive solar design
• Active solar water heating
• Solar photovoltaics

How it works

Passive solar design

Passive solar design involves the application of design principles (such as south-facing windows) to make sure that excess heat loss is avoided and solar radiation is captured, in order to minimize the need for heating and lighting. The reverse is also true, so that minimizing the capture of solar radiation, coupled with the use of natural ventilation, helps to reduce dependency on mechanical systems such as air conditioning.

Active solar water heating

Active solar water heating uses collectors, usually on the roof of a building, to capture and store the sun’s heat via water storage systems. The collectors provide heat to a fluid that circulates to a water tank. The heat is primarily used for heating water in domestic dwellings, industrial facilities and commercial buildings. This includes the growing market for solar swimming pool heaters.

Solar photovoltaics

Solar photovoltaics (PVs) convert energy from daylight into electricity using a semiconductor material such as silicon. When light hits the semiconductor, the energy in the light is absorbed, ‘exciting’ the electrons in the semiconductor so that they break free from their atoms. This allows the electrons to flow through the semiconductor material (in a similar manner to a normal electrical circuit) producing electricity.

There are a number of PV technologies, including polycrystalline, monocrystalline and thin-film. Solar PV cells can be arranged in panels on a building’s roof or walls, and can often directly feed electricity into the building. With the latest PV technology, cells can also be integrated into the roof tiles themselves.

Groups of solar PV cells can be added together to provide increasing levels of power. This can range from small, kilowatt-sized solar panels for use in domestic households, to larger arrays, which function as separate solar power plants feeding power directly into the electricity grid.

Solar PV cells can be used in both stand-alone and grid-connected systems.

Solar energy is only produced during the day and also varies in output due to cloud cover. In the case of small-scale solar PV systems, batteries or other forms of electricity storage can be used to store the electricity for periods when the output is low but the demand is high. For solar thermal systems, the hot water can be stored for a limited period of time in well-insulated water tanks.

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