These consist of two or more thin layers of semi-conducting materials that when exposed to light generate electrical charges. These can then be conducted away by metal contacts as direct current into your electricity supply.
Top of the range are monocrystalline panels, which are cut from single silicon crystals and harness 15% of the sun' energy. Five square meters of top-grade monocrystalline panel, costing around £5000 and positioned on a south-facing roof can generate around 600 kW hours over a year - about 20% of an average family's needs.
Multicrystalline panels, made from melted down silicon cut into wafers, are slightly cheaper and are still 13% efficient. PVs are suitable for any wall or roof that faces within 90 degrees of the sun (as long as they are strong enough to carry the extra weight) and require little maintenance.
Grants are available through the DTI's funded Low Carbon Buildings Programme (0800 915 0990: www.lowcarbonbuildings.org.uk). For more detailed information on PVs, contact The British Photovoltaic Association (www.greenenergy.org.uk/pvuk2/index.html