Solar Electricty: Photovoltaics (PV)
Turn your home into a power station! The Earth receives more energy from the Sun in just one hour than is used by humans worldwide in a whole year. Why not use it? This energy comes to us for free, and is now readily accessible. Photovoltaic cells convert daylight into electricity, reducing the need to exploit fossil fuels and thereby reducing the impact we have on the environment.
What is a Photovoltaic system?
A photovoltaic system comprises:
- Modules (panels) -usually on your roof - to convert solar energy into electricity
- A wiring system to connect to your electric system
A module consists of a number of photovoltaic cells made from semi-conducting material, usually silicon. These cells convert the Sun’s rays into electricity using the Photovoltaic Effect. The Photovoltaic Effect has been known since the 19th century and was developed for use in space technology and again during the oil crises of the 1970s. The silicon technology has also benefited from developments in semi-conductors for the computer industry.
This page covers the use of PV to generate electricity for use in the home. Smaller systems, such as PV powered lights and fountains can be bought at large DIY stores or on the Internet.
Why install a photovoltaic system?
- You will be at the forefront of renewable energy developments.
- You will help alleviate global warming because a home system reduces carbon dioxide emissions by up to ¾ of a tonne per year.
- A small home system can typically provide 25% of your electricity needs, and in certain cases a lot more, particularly if you are more careful with your energy use. Some properties can generate 100% of their energy needs.
- A solar system will increase the value of your home.
- The systems are expected to last 30 years or more, need very little maintenance and are very reliable.
- Solar systems help safeguard against future rises in fuel prices, providing-inflation proof electricity for 30 years and more.
Installation
Home systems for generating electricity can be fitted by professional installers in as little as one day. For a list of installers accredited with the DTI grants scheme see here.
The fuel (daylight) is free but the cost of the system can vary quite considerably. A typical fully installed family system can cost over £10,000. However there is a government grant available to pay for 50% of the cost of the system, see below for details. In addition, if integrated into roof tiles or cladding then the cost of other building materials is also saved.
Is my home suitable?
You will need:
- A roof area that is not shaded by other buildings or trees.
- A suitable area of at least 10m2.
- The most effective roofs face between south-east and south-west.
- Solar panels do not usually need planning permission if they are not on the roadside of the house, do not project beyond the roofline and are not in a conservation area or on a listed building. It is advisable to check with your local authority.
Different Systems
Building Integrated or Bolt-On?
If you are improving your house you could consider a system designed into the building such as roof tiles. These systems will have shorter payback periods as you effectively only pay the difference between conventional roof tiles and solar ones. If you are not re-doing your roof, then modules mounted on the existing surface are probably the most cost effective option.
On-Grid or Off-Grid?
Most homes get their electricity from the National Grid, the national network for electricity distribution. Stand-alone or off-grid systems are suitable for those homes that are not connected to the Grid. These systems have a battery and an inverter and may have a wind turbine or diesel generator to satisfy peak demand. They can work out to be highly cost effective as grid connection can be very expensive.
Grid-connected modules, mounted on the roof, provide electricity for the home and for selling to the Grid. No battery is needed, as the electricity is sold back to the supplier when you are not using it via an inverter which synchronises it with the mains supply.
Grid connection needs an agreement with the electricity supplier and can be arranged through accredited installers. It is possible to get a net metering deal where you get paid as much for the electricity you sell/export as you pay for the electricity you buy/import. However, with some electricity companies you may find you lose out financially due to the price difference between imported and exported electricity.
Crystalline or thin film cells?
The most important part of a PV system is the cell. This is the part that turns the sunlight into electricity. There are two different types of cells that can be used to make up the solar panel, thin film and crystalline cells.
- Thin film cells perform better in low light conditions but more surface area is needed compared to crystalline modules for the same output.
- Crystalline cells which require a smaller surface area and make up 85% of the market.
Costs for modules made from these different technologies are comparable.
Renewable Energy Technologies: Solar Water Heating
A great way to make your house more environmentally friendly
The earth receives more energy from the sun in just one hour than is used by humans in a whole year. Why not use it? This energy comes to us for free, and the technology to capture is is now readily available. Daylight can be used to heat your home’s hot water, reducing the need to exploit fossil fuels and thereby reduce the impact you have on the environment.
What is Solar Water Heating?
Solar water heating uses heat from the sun to warm up liquid pumped through a panel on your roof. In the most common kind of system, this liquid then goes through a coil in a hot water cylinder where the heat is transferred to water that comes out of your hot tap. Most systems have a small pump that moves water around the system.
Solar water heating should not be confused with photovoltaic systems which make electricity - see the separate section for information on this topic.
Why go Solar?
- You will be at the forefront of renewable energy developments.
- You help to alleviate global warming as a home system could reduce Carbon Dioxide emissions by as much as ½ of a tonne per year.
- It is a reliable technology already used by over 42,000 homes in Britain.
- Produce 50-70% of your hot water from renewable energy and help protect yourself against future gas price rises.
- Increase the value of your home.
- Solar water heating works even on cloudy days.
Different Systems
A solar water heating system is made up of three main components, solar panels, a plumbing system and a hot water cylinder.
- Solar panels are fitted to your roof and contain collectors. These collectors absorb and retain heat from the sun’s rays and transfer this heat to a fluid.
- The plumbing system is made up of simple piping and sometimes a pump, which moves the heated fluid around the system and through the hot water cylinder.
- A hot water cylinder is used to store the hot water that is heated by the fluid being pumped around the system.
Flat plate or evacuated tube collector panels?
Solar panels are made up of either flat plates or evacuated tube collectors to absorb and retain heat from the sun’s rays.
- Flat plates are most common and tend to be cheaper but need more surface area than evacuated tube collectors. They use dark absorber plates to retain the heat most effectively. These plates are situated under clear covers.
- Evacuated tube collectors have glass tubes which have air evacuated around the pipes containing the fluid to be heated. This makes evacuated tube collectors more efficient as heat loss by convection is almost totally eliminated. Evacuated tube collectors tend to need less area, but can be more expensive.
Active or Passive?
The fluid in the system can either be moved by a pump or be allowed to flow naturally. In a passive system the water moves by natural convective flows. In an active system the heated fluid is transferred to the hot water cylinder by a pump. Active systems are usually easier to fit but they may be more expensive.
Open or Closed Loop?
The collector panels can either directly heat the water that goes to your taps or they can heat an intermediary fluid, which then transfers heat to the water.
- Open systems heat the hot water directly.
- Closed systems use an intermediary fluid and a heat exchange system. These are most suitable for areas that have periods of freezing weather, as the liquid in the external part of the system contains anti-freeze.
Installation
You can choose to have the solar heater installed by a professional, which will take less than a day. This option benefits from a 5% VAT rate as well as our discount and interest-free loan schemes. See details of our installation programme here. The scheme we run ensures you get a hassle-free service from trained installers. The systems come with a 10-year warranty and require very little maintenance.
Alternatively you can fit the system yourself. This option is charged VAT at 17.5%. It can still work out cheaper (around £500 -£1,500) but will take longer and requires a certain level of skills. You can get training and support from your local solar club.