UNDERSTANDING SOLAR ELECTRICITY

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Energy from the sun for thousands of years has been harnessed for several purposes. However it is vital that we see this energy in three forms and properly understands the separate applications.

• Solar energy as passive heat: This we receive from the sun naturally and is taken into account in the design of buildings so that less additional heating is required.
• Solar thermal energy: Where the sun's heat provideshot water for homes or swimming pools.
• Photovoltaics (PV): where energy from the sun is employed to createelectricity which runs appliances and lighting.
  

NOTE! PV requires only daylight - not direct sunlight - to generate electricity.

MODE OF OPERATION
Photovoltaic systems through cells convert solar radiation intoelectricity. The PV cell consists of one or two layers of a semiconductingmaterial, usually silicon. When light shines on the
cell an electric field is formed across the layers, hence electricity flows. The flow of electricity is detemined by the light intensity
There are three main types of solar cells viz
• Monocrystalline: made from thin slices cut from a single crystal of silicon. This has a typical efficiency of
15 per cent.
• Polycrystalline: made from thin slices cut from a block of silicon crystals. This has a typical efficiency of around12 per cent.
• Thin Film: made from a very thin layer of semiconductor atoms deposited on a glass or metal base. This has a typical efficiency of 7 per cent.

The PV cells are connected together to form a module. Modules are then linked and sized to meet a particular load (electrical energy demand). The result is a PV array which supplies power to the building it is fitted on. If the building has mains electricity, any excess electricity can be exported to the national grid (as is the case in the US and some parts of Europe).
Alternatively, when demand is high, extra electricity can be purchased from the national grid through the utility companies in addition to the PV electricity. In the event of a mains power failure, PV arrays can be
used to charge batteries.
PV arrays are in a variety of shapes and colours,ranging from grey 'solar tiles' that look like roof tiles, to
panels and transparent cells that you can use onconservatories and glass to provide shading as well as
generating electricity.