Energy from the sun has been harnessed for thousands of years. We utilise this energy in three main ways and when talking about solar energy it is important to distinguish between these three types:

• Passive heat: This is the heat that we receive from the sun naturally. This can be taken into account in the design of buildings so that less additional heating is required.

• Solar thermal: Where we use the sun’s heat to provide hot water for homes or swimming pools.

• Photovoltaic (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 PV technology 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 450kg of carbon dioxide per year for each kilowatt peak installed (Kilowatt Peak(kWp) - PV cells are referred to in terms of the amount of energy they generate in full sun light).

Domestic installations

The size of a PV array required to provide electricity for a typical home varies, depending on a number of issues; load requirements (what you want it to power), the type of cell used, roof space available and budget. Typical systems are generally around 1.5-2kWp, enough to provide almost half of the average family’s annual supply (assuming gas is used for heating requirements and there are no energy efficiency savings). This array would typically cover 10-15m2 of roof area.

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.

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 occasionally by a qualified technician. For stand-alone systems, i.e. those not connected to the grid, further maintenance is required on other system components, such as batteries.