Solar photovoltaic (PV)

PV uses energy from the sun to create electricity to run appliances and lighting. PV requires only daylight - not direct sunlight - to generate electricity.

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, a typical domestic system can save approximately 1.2 tonnes of carbon dioxide emissions per year - adding up to almost 30 tonnes over a system's lifetime.

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 £5,000- £7,500 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.

A 2.5kWp array can provide enough electricity to meet around half a households electricity needs, this means a saving of around £250 a year.

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

In England, changes to permitted development rights for domestic microgeneration technologies introduced on 6th April 2008 have lifted the requirements for planning permission for most solar PV installations. Roof mounted and stand-alone systems can now be installed in most dwellings, as long as they respect certain size criteria. (See page on Planning Permission for further details). Exceptions apply for Listed Buildings, and buildings in Conservation Areas and World Heritage Sites.

In Wales, Scotland and Northern Ireland, the devolved governments are currently all considering changes to their legislation on permitted developments, to facilitate installations of microgeneration technologies, including solar PV. Legislation is expected in all three countries later this year (2008).

Until then, householders in Wales, Scotland and Northern Ireland must consult with their local authority regarding planning permission.

Modern wind turbines use the wind's lift forces to turn aerodynamic blades that turn a rotor which creates electricity.