Solar photovoltaic (PV) systems convert solar radiation into electricity and require only daylight - not direct sunlight - to generate that electricity. The PV cell consists of one or two layers of a semi conducting material, usually silicon. When light shines on the cell it creates an electric field across the layers, causing electricity to flow. The greater the intensity of the light, the greater the flow of electricity...

Arrays of solar PV cells now come 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 on conservatories and glass to provide shading as well as generating electricity.

You can use solar PV systems for a building with a roof or wall that faces within 90 degrees of south, as long as no other buildings or large trees overshadow it. Solar panels can be quite heavy and the roof must be strong enough to take their weight, especially if the panel is placed on top of existing tiles.

Prices for solar PV systems vary, depending on the size of the system to be installed, type of solar PV cell used and the nature of the actual building on which the solar PV cell is mounted. The size of the system is dictated by the amount of electricity required. Solar PV cells are referred to in terms of the amount of energy ( kilowatt peak - kWp) that they generate in full sun light.

For the average domestic system, costs can be around £5,000- £8,000 per kWp installed, with most domestic systems usually between 1.5 and 3 kWp. Solar tiles cost more than conventional panels, and panels that are integrated into a roof are more expensive than those that sit on top.

If you intend to have major roof repairs carried out it may be worth exploring PV tiles as they can offset the cost of roof tiles.

Grid connected systems require very little maintenance. A periodic check of the wiring and system components and, that the panels are clean and that shade from trees has not become a problem.

Stand-alone systems, i.e. those not connected to the national grid, need maintenance on other system components, such as batteries.

Some local authorities require planning permission to allow you to fit a PV system, especially in conservation areas or on listed buildings. Always check with your local authority about planning issues before you have a system installed.