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Solar PV

The sunshine falling on your roof can be converted into electricity using solar photovoltaic panels, usually referred to as ‘solar PV’.


Using solar panels to produce your own electricity will save you money on your electricity bills and provide a source of un-taxed income through payments from the feed-in tariff. The electricity that your panels generate will power any appliances (or lights) in your house that happen to be on – washing machine, TV and so on. Any surplus electricity is exported to the grid.

A decent PV system like the ones you see on many homes, provides around half of the average household’s electricity needs and costs between £6,000 and £7,000.

Solar electricity systems are rated in kilowatts peak (kWp). This is the maximum rate at which the panels generate electricity. The kWp of a solar array depends on the size and number of solar panels, with a typical domestic system being around 2kWp. Note that this peak performance is only achievable around noon on a clear sunny day on panels that face due south. The rest of the time the output from the panels will be lower.

The electrical energy produced by solar panels is measured in kilowatt hours (kWh) – the same unit that is shown on your household electricity bill. The amount of electricity produced over the course of a year will be determined by the orientation of the system (i.e. which way the panels face), if there is any shading and how sunny the location is, and the size of the system in kWp. And it obviously varies a great deal from season to season.

For a more detailed introduction to solar technology, watch this video (which also covers solar hot water):

Before you invest in a solar electric system you need to check the following:

  • Is the roof more or less south facing? Solar panels need maximum exposure to the sun, and this means facing between south east and south west.
  • Will trees or buildings cast a shadow over the solar panels? If even a part of a panel is in the shade, the amount of electricity generated will be greatly reduced.
  • Is your roof structurally sound? It will need to take the extra weight of the solar panels plus the fixing frames. 

Income and savings

Once installed, you can register your solar PV system for the feed-in tariff. Under this scheme your fuel supplier will pay you for every kWh of electricity your system produces, regardless of whether you export it to the grid or use it yourself. For exported electricity you’ll be paid 4.5p for every kWh (as of 2012). But you’re better off using it yourself because the electricity you buy from your supplier costs you around 14p per kWh.

To be eligible for the feed-in tariff your solar panels and your installer must be registered with the Microgeneration Certification Scheme (www.microgenerationcertification.org). You should also check that your chosen installer is a member of the Renewable Energy Consumer Code which has a consumer code that members must adhere to.

Costs

A typical domestic solar PV system of 2kWp costs between £6,000 and £7,000, though this obviously depends on the size of the array, the type of cells you are using and how easy it is to install at a particular site.  Most systems require little or no maintenance although it is worth checking once a year that the panels are not too dirty as this can reduce performance. The inverter may need to be replaced after around 10 years at a cost of about £1,000.

Planning permission

Solar arrays are classed as ‘permitted developments’ which means they don’t need planning permission if they stick out 200 mm or less from your building and meet other basic requirements. However, it’s still worth checking with your local planning department, especially if you live in a listed building, a conservation area, an area of outstanding natural beauty or a world heritage site.

A decent PV system will provide around half of the average household’s electricity needs, but there are two things you can do to really make the most of your solar panels. The first is to buy energy efficient appliances which use less electricity. The second is to run appliances like washing machines and dishwashers during the day when the electricity is free, though you’ll probably need to stagger their use so they’re not all on at once. Your PV system should include a display that shows how much electricity is currently being produced, so if you know the energy demand of your appliances, you can judge which ones can be operated for free at that moment.

How PV panels work

Solar PV systems turn light into electrical energy by using thin layers of a semiconductor material like silicon encased in glass. This is known as a solar cell and they come in three basic types, which vary in efficiency and cost:

1) Monocrystalline: made of thin slices of silicon, cut from a single crystal

2) Polycrystalline: made from thin slices of silicon, cut from a block of crystals

3) Hybrid: combining crystalline cells with a thin layer of silicon on a glass or metal base. These tend to be the most efficient.

The electricity leaves the panel as direct current (DC) and passes through an inverter that converts it to 240V alternating current (AC) so that it can be used in your home.

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