Solar photovoltaic (PV) technology is a semi-conductor based technology that converts the energy in sunlight into electricity. A PV system comprises the PV panel (generator) and the wiring and electronics.

If the energy in the daylight is sufficient, it causes a flow of electrons across the junction of the semi-conductor: electricity is generated. A solar panel is made up of cells, which are connected together in different configurations to give different voltage and current outputs.

The PV panel should be oriented between southeast and southwest (optimally south). The optimal tilt angle (inclination of panel from horizontal) should be calculated to ensure the best possible output of the system during the year. (Sun tracking systems are available but they are expensive and, by introducing a mechanical element, can sometimes be less reliable.) In the UK, the angle of most residential roofs is suitable for mounting PV panels. Panels can also be mounted on A-frames on flat-roofed buildings.

PV technology comes in a range of forms: PV panels that can be retrofitted to the roof of an existing building or equally, sunk to fit flush with the roof line; PV roofing tiles, which can replace traditional roof tiles; PV cells that are 'laminated' between sheets of glass to provide shading in a glazed area, and PV cladding.

Due to its high capital cost, PV technology is particularly suited to areas that are not grid-connected. PV systems are low maintenance as they have no moving parts and panels generally have 25-year warranties, although the life-time of the panel can be expected to be beyond this time. Payback times for this technology are reducing year on year as the technology matures and are set to reduce further as fuel prices increase. The cost can be further off-set by integrating PV into a building and replacing other building materials.

The PV systems should be unshaded. Shading caused by other buildings, greenery and roof 'furniture' such as chimneys or satellite dished, even over a small area of the panel, can significantly reducing performance. Excess energy can be exported to the grid. Although the feed-in tariffs are generally not great, exporters can negotiate with their utility company.

Although PV is one of the more expensive renewable energy technologies, its cost is set to reduce significantly in the future as the PV market expands. Current domestic prices are around £6000 for an installed 1kWp system and grants for just under 50% of this cost are currently available. A system of this size would be expected to generate 750kWh of electricity per year. The cost of larger systems would benefit from 'economies of scale'.

Please email or call CEN on 020 8683 6694 for further information or advice.