As with most of our earthly energy sources, the origin of solar power lies in constantly occuring nuclear reactions in the Sun. Energy from these reactions is radiated in the form of light, and some of this makes it to Earth. While some is reflected back by the atmosphere, clouds and pollution, most of it reaches lower levels where we can make use of it.

Unsurprisingly, some regions do recieve more energy in this way than others: Over a year, the UK recieves considerably less solar energy per square metre than the Sahara desert. This is due not just to the increased number of clouds to reflect sunlight in the UK, but also because the angle of incidence with the Sun's rays is greater. However, there is enough energy to be useful almost everywhere.

Once where we can get at it, sunlight can be collected by photovoltaic panels (also referred to as modules). These consist of a number of of silicon cells that, when exposed to certain frequencies of light, experience a voltage potential from one side to the other. The cells in each panel are connected together such that when the cables from the panel are formed into a circuit, a electrical current can flow.

In order to be connected to the grid (see When should I have a grid-connected system?) the 'constant' electrical (DC) current needs to be converted to a wavelike current (AC). This can be acheived by connecting an inverter into the circuit, which takes in DC power from one circuit and sends out AC power onto another. Inverters often have additional tasks to perform, such as optimising the PV cells' performance and protecting the equipment from electrical faults on the electricity network. When the system is not connected to the grid, an inverter may also be required to extract energy from batteries.

The AC 'side' of the inverter will in most systems then be connected to the main distribution board of the building. From here, the power generated by the PV system can be used just like (and alongside) 'normal' electricity, providing power for lighting, computers, electical appliances and even machinery. When more energy is being generated than is being used on site, the excess will be exported onto the grid to be used elsewhere or stored in the backup batteries (off-grid systems only).

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