Photovoltaics

Photovoltaics (PV) consist of semi-conductor cells that convert sunlight into electricity. They produce electricity even in cloudy conditions, but power output increases with the intensity of the sun. They can be connected to buildings via batteries or via an inverter to the mains supply so that excess electricity produced can be sold to the national grid. Once installed, PV generates no CO₂ emissions and has no moving parts.

Types

• Various types with different efficiencies
• Panels, tiles or thin-film laminate

Other components

1. An inverter to convert DC output to AC for grid connections
2. Electricity meter that allows electricity export to grid
3. Battery if not grid-connected

Typical saving

Zero carbon renewable energy source. Generally a 6 to 8m² 1kWp PV system in the UK can generate 700-850kWh/yr (DTI). A modern gas-heated 2 bed flat uses approximately 1,500kWh/year electricity for lights and appliances, so this would provide approximately 45% of the dwelling’s electricity needs

Indicative cost

Relatively high cost. £5,000 to £8,000/kW peak output (~£1,000/m²) for a roof mounted system, £10,000 to 5,000/kW for façade/atrium systems. Long payback unless they are replacing a major building element such as solar shading

Main issues affecting feasibility

• Electricity demand: Ideally daytime electricity demand, especially in summer.
• Location: PV should ideally be mounted on a south-facing roof or façade,  but south-east/south-west will also function successfully.
• Shading: must be avoided where possible, it significantly reduces output.
• Visual impact: may need careful design for use in conservation areas.

Further information London Renewable Energy Toolkit

www.london.gov.uk/mayor/environment/energy/renew_resources.jsp