Small scale solar electric energy
Small scale solar electric (Photovoltaics)
Solar electric panels (or photovoltaics) convert the sun’s energy into electrical energy. The amount of electrical energy produced will depend on how much sunlight that falls on the panel, what type of panel you use and its size. Solar panels are normally mounted on the roofs of buildings, either as a panel or as a series of individual tiles.
Q. How do Solar Photovoltaic panels work?
A. A photovoltaic (PV) cell is a device that converts sunlight into electrical energy. The PV cell consists of one or two layers of a semi-conducting material, usually silicon. When light shines on the cell it creates an electric field across the layers, which causes electricity to flow. The greater the intensity of light, the greater will be the flow of electricity. PVs will only produce electricity whilst there is daylight. The energy must therefore be consumed as it is being generated, stored for later use or exported to the national grid.
Q. How much energy can a typical domestic roof- top PV system provide?
A. This will depend how much power you need, the type of PV cell used, roof space available and your budget.
The maximum power generated by a PV cell under ideal conditions in full sun is expressed as its kilowatt peak (kWp). The kWp will vary according to the time of day, month, year as well as the cell’s location. It is advisable to find out from the manufacturer what the estimated annual yield would be. This is given in kilowatt-hours per year (kWh/yr) and can be compared with the current household electricity bill (also measured in kWh) to allow the savings to be calculated.
A 1.5 to 2.5 kWp system should generate enough electricity to provide nearly half of the average family’s annual requirement (assuming roof area of between 10 – 40 m2 ). In the UK the annual average yield of a domestic PV array on an unshaded south-facing inclined plane, would be 750 kWh per kWp. For a 2 kWp installation you can therefore expect to generate 1500 kWh of electricity compared with the average household consumption of 4000 KWh of electricity per year.
Q. Is it difficult to install photovoltaics on an older roof?
A. The weight of the PV array will be borne by the roof rafters which must be capable of supporting the panel. The supplier or installer will have information as to the weight in order that a roof survey can be undertaken to see whether it is suitable.
However careful the installer, it is inevitable that tiles or slates may get broken during installation, so it is advisable to have replacements readily available. For roofs with stone or old handmade tiles, replacements can be expensive and difficult to find so it is advisable to investigate what type of roof covering you have and how to get replacements before undertaking any work.
Q. Are all houses suitable for solar photovoltaics?
A. Typical domestic PV installations need a roof surface of 10 – 40 m2, depending on the type of PV that is used. The roof should be south- facing, free from shading and with an angle 30° to 50° above horizontal. PVs can still be effective on east and west faces, but the annual yield will be lower.
Consent for an installation on some types of buildings may be a problem.
see ‘What approvals do I need?’
Q. What grants are available for micro- generation technologies for householders?
A. The Department of Energy and Climate Change (DECC) run a Low Carbon Buildings Programme that provides grants for micro-generation technologies for householders www.lowcarbonbuildings.org.uk .
Q. How can you find an Installer?
A. Recipients of Low Carbon Buildings Programme grants must use accredited installers and materials. The list of accredited installers is a useful resource even if you are not applying for a grant for all types of renewable technologies.
Q. How much does Solar PV cost?
A. Domestic systems costs £4,000 to £9,000 per kWp installed, with the average installation usually having a capacity of between 1.5 and 2 kWp.
Q. What is the difference between a grid- connected and a standalone system?
A. Where no mains electricity is available, a PV system can be used to replace or supplement the existing local electricity supply (a diesel generator, for example). Batteries can also be used to store energy generated by the turbine for later use.
If a house is already linked to the national grid a PV system can also be used to supplement the mains electricity. When the array is not generating enough energy, mains electricity is used. If more electricity is generated by the array than is needed, the excess can be exported to the national grid by agreement with the regional electricity company.
Q. Is planning permission needed to install photovoltaic panels on a house?
Small scale solar electric energy
This guidance looks at the issues to be considered when planning an installation on a traditional building
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