Renewable technologies

How do photovoltaic (PV) cells work?

PV cells are panels you can attach to your roof or walls. Each cell is made from one or two layers of semiconducting material, usually silicon. When light shines on the cell it creates an electric field across the layers. The stronger the sunshine, the more electricity is produced.

The strength of a PV cell is measured in kilowatt peak (kWp). That's the amount of energy the cell generates in full sunlight.

Is solar electricity suitable for my home?

To tell if solar electricity is right for you, there are a few key questions to consider:

• Do you have a sunny place to put the panels? You'll need a roof or wall that faces within 90 degrees of south and isn't overshadowed by trees or buildings. If the surface is in shadow for parts of the day, your system will generate less energy.
• Is your roof strong enough? 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. If in doubt, ask a construction expert or an installer.
• Do you need planning permission? In England, Wales, Scotland and Northern Ireland, you don't need planning permission for most home solar electricity systems, as long as they're below a certain size - but you should check with your local planning officer, especially if your home is a listed building, or is in a conservation area or World Heritage Site.

Information courtesy of the Energy Saving Trust.

How do wind turbines work?

Wind turbines use large blades to catch the wind. When the wind blows the blades are forced round, driving a turbine which generates electricity. The stronger the wind, the more electricity produced.

There are two types of domestic-sized wind turbine:

• Mast mounted: these are free standing and are erected in a suitably exposed position. Often these are around 2.5kW to 6kW.
• Roof mounted: these are smaller than mast mounted systems and can be installed on the roof of a home where there is a suitable wind resource. Often these are around 1kW to 2kW in size.

Savings can be considerable - around 1 tonne of CO₂ a year. A 2.2 kWp system can generate around 40% of a household's yearly electricity needs. If the system is eligible to receive the Feed-In-Tariff it could generate savings and income of around £900 per year.

Is wind electricity suitable for my home?

To tell if a small scale domestic wind turbine is right for you, there are a few key questions to consider:

• Is your home is a windy area? To be effective you need an average wind speed of no less than 5m/s.
• Are there any large obstacles like buildings, trees or hills near your home? Small domestic wind turbines work best in exposed locations, without turbulence caused by these types of obstacles.
• Do you need planning permission? Small domestic wind systems normally do require permission from your local authority, so check before you install a system.

Information courtesy of the Energy Saving Trust.

How does a ground source heat pump work?

A ground source heat pump circulates a mixture of water and antifreeze around a loop of pipe - called a ground loop - which is buried in the garden. Heat from the ground is absorbed into this fluid and is pumped through a heat exchanger in the heat pump. Low grade heat passes through the heat pump compressor and is concentrated into a higher temperature useful heat capable of heating water for the heating and hot water circuits of the house.

The length of the ground loop depends on the size of your home and the amount of heat you need - longer loops can draw more heat from the ground, but need more space to be buried in.

Heat pumps have some impact on the environment as they need electricity to run, but the heat they extract from the ground, air, or water is constantly being renewed naturally.

Unlike gas or oil boilers, heat pumps deliver heat at lower temperatures over much longer periods. This means that during the winter they may need to be left on 24/7 to heat your home efficiently.

Is a ground source heat pump suitable for my home?

To tell if a ground source heat pump is right for you, there are a few key questions to consider:

• Is your garden suitable for a ground loop? It doesn't have to be particularly large, but the ground needs to be suitable for digging a trench or a borehole and accessible to digging machinery.
• Is your home well insulated? Since ground source heat pumps produce a lower temperature heat than traditional boilers, it's essential that your home is insulated and draught proofed well for the heating system to be effective. It could also make the system cheaper and smaller.
• What fuel will you be replacing? If you're replacing an electric, or coal heating system, a ground source heating system will save you more on your heating bills. Heat pumps are not recommended for homes on the gas network.
• What type of heating system will you use? Under-floor heating systems, larger radiators or low temperature fan convectors (warm air heating) require lower water temperatures and so tend perform better than standard radiator-based systems.
• Is the system intended for a new development? Combining the installation with other building work can reduce the cost of installing the system.

For information on air and water source heat pumps see below.

Information courtesy of the Energy Saving Trust.

These systems use similar principles to ground source heat pumps to extract heat from air or water instead of the ground.

Air source heat pumps can be fitted outside a house and generally perform better at slightly warmer air temperatures. Water source heat pumps can be used to provide heating in homes near to rivers, streams and lakes.

Information courtesy of the Energy Saving Trust.

What is micro CHP?

'Micro-CHP' stands for micro combined heat and power. This refers to a heating technology which generates heat and electricity simultaneously, from the same energy source, in individual homes or buildings.

The main output of a micro-CHP system is heat with some electricity generation, at a typical ratio of about 6:1 for domestic appliances.

Any electricity generated and not used in the home can be exported back to the grid.

A typical domestic system is expected to have the potential to generate up to 1kW of electricity per hour once warmed up. This would be enough to power the lighting and appliances in a typical home. The amount of electricity generated ultimately depends on how long the system is running.

Most domestic micro-CHP systems today use mains gas or liquefied petroleum gas (LPG) as a heating fuel, although they can also be powered by oil or bio fuels. The technology is considered to be a 'low carbon technology' because it is more efficient than just burning the fossil fuel for heat and getting electricity from the national grid.

Micro-CHP systems are comparable in size and shape to an ordinary, modern, domestic boiler and can be wall hung like most boilers, or floor standing. Servicing costs and maintenance are estimated to be similar to a standard boiler – although a specialist will be required.

The only difference to a standard boiler is that they are able to generate electricity while they are heating water.

Information courtesy of the Energy Saving Trust.

Financial support for micro CHP

Under the new Feed-in Tariff scheme, set up by the government, it is possible to receive 10 pence per unit of electricity generated, and an additional 3 pence per unit for each unit exported.

Costs: Typical installation costs are from £5,500.

For information about wood fuelled systems see below.

How do wood fuelled heating systems work?

There are two main ways of using wood to heat your home:

• A standalone stove burning logs or pellets to heat a single room. Some can also be fitted with a back boiler to provide water heating as well.
• A boiler burning pellets, logs or chips connected to a central heating and hot water system.

Log burning stoves and boilers have to be filled with wood by hand. Some pellet and chip burners use automatic fuel feeders which refill them at regular intervals from fuel storage units called hoppers.

Is a wood fuelled heating system suitable for my home?

To tell if wood fuelled heating is right for you, there are a few key questions to consider:

• Do you have enough space? You'll need a large dry area close to the boiler to store your wood. Ideally this should be close to where the wood is delivered to your home to minimise the distance you have to carry it.
• Do you have a suitable flue? You need a vent which is specifically designed for wood fuel appliances, with sufficient air movement for proper operation of the stove. Your existing chimney can be fitted with a lined flue, which is relatively inexpensive.
• Can you comply with safety and building regulations? If you live in an old or unusual home this may be an issue. For more information, see Part L of the Building Regulations, England, Northern Ireland and Section 3 of the Technical Handbooks, Scotland.
• Do you live in a smokeless zone? If so then wood can only be burnt in certain exempted appliances (www.uksmokecontrolareas.co.uk/locations.php).
• Do you need planning permission? You need to talk to your local authority if your flue will extend 1m or more above the height of your roof, or your home is in a Conservation Area or World Heritage Site and you plan to install a flue on the principal elevation visible from a road.

Information courtesy of the Energy Saving Trust.

How do solar water heating systems work?

Solar water heating systems use solar panels fitted to your roof to collect heat from the sun and use it to warm water stored in a hot water cylinder.

A boiler or immersion heater can be used as a back up to heat the water further to reach the temperature set by the cylinder's thermostat when the solar water heating system does not reach that temperature. The cylinder thermostat should be set at 60 degrees centigrade.

Larger solar panels can also provide energy to heat your home as well - though usually only in the summer months when home heating is unnecessary.

Is a solar water heating system suitable for my home?

There are a few key questions to consider before opting for a solar water heating system:

• Do you have a suitable sunny place to put solar panels? You'll need around 5 square metres of roof space which faces south, south-east or south-west and receives direct sunlight for the main part of the day. The panels don't always have to be mounted on a roof; they can also be fixed to a frame on flat roofs.
• Do you have space for a larger, or an extra, hot water cylinder? If a dedicated solar cylinder is not already installed then you will need to replace the existing cylinder, or add a dedicated cylinder with a solar heating coil.
• Is your current boiler compatible with solar water heating? Most conventional boiler and hot water cylinder systems are compatible with solar water heating. If your boiler is a combination boiler (combi) and you don't currently have a hot water tank then a solar hot water system may not be compatible.
• Do you need planning permission? In England most solar water heating systems don't need planning permission, but it is always best to consult your local planning office if you live in a Listed Building, or a building in Conservation Area or World Heritage Site. If you live in Wales, Scotland or Northern Ireland you will need to consult your local authority.

Information courtesy of the Energy Saving Trust.