How it works
Photovoltaic systems use cells to convert solar radiation into 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.
PV systems generate no greenhouse gases, saving approximately 325kg of carbon dioxide emissions per year - adding up to about 8 tonnes over a system's
lifetime - for each kilowatt peak (kWp - PV cells are referred to in terms of the amount of energy they generate in full sun light).
PV arrays 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. As well as enabling you to generate free electricity they can provide an interesting
alternative to conventional roof tiles!

Solar PV and your home
You can use 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. If the
roof surface is in shadow for parts of the day, the output of the system decreases.
Solar panels are not light and the roof must be strong enough to take their weight, especially if the panel is placed on top of existing tiles.
Solar PV installations should always be carried out by a trained and experienced installer.

Cost and maintenance
Prices for PV systems vary, depending on the size of the system to be installed, type of PV cell used and the nature of the actual building on which the PV is
mounted. The size of the system is dictated by the amount of electricity required.
For the average domestic system, costs can be around £4,000- £9,000 per kWp installed, with most domestic systems usually between 1.5 and 2 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, generally limited to ensuring that the panels are kept relatively clean and that shade from trees has not
become a problem. The wiring and components of the system should however be checked regularly by a qualified technician.
Stand-alone systems, i.e. those not connected to the grid, need maintenance on other system components, such as batteries.

Planning considerations
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. Obtaining retrospective planning permission can be difficult and costly.

Source of information is: The Energy Saving Trust January 2007.

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