Solar Photovoltaic (PV) systems use cells to convert solar radiation into electricity. 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, causing electricity to flow. The greater the intensity of light, the greater the flow of electricity.

The four main types of solar cells are:

1. Amorphous silicon/thin film: this is made from a very thin layer of semi-conductor atoms deposited on a Glass or metal base. This has a typical efficiency of 7 to 10%.

2. Poly-crystalline: this is made from thin slices cut from a block of silicon crystals. This has a typical efficiency of about 12 to 13%.

3. Mono-crystalline: This is made from thin slices cut from a single crystal of silicon. This has a typical efficiency of 13 to 14%.

4. Hybrid: This is a combination of mono-crystalline and amorphous silicon producing a PV cell with exceptional performance in variable lighting conditions and an efficiency of about 18%.

Thin PV film which can be massed produced to reduce cost and which has been reported to achieve in excess of 30% efficiency is currently being developed and tested. It could however be some time before this is commercially available at a competitive cost.

Individual PV cells are connected together to form a module. These modules are then linked and sized to meet a particular load which is needed to suit a purpose. The result is a PV array which supplies power to the building it is fitted on. If the building already has mains electricity any excess electricity can be exported to the national grid. Alternatively, when demand is high, extra electricity can be purchased from the national grid through the utility companies.

Where a building has no mains electricity supply, PV arrays can be used to charge batteries.

Applications

There are many applications for PV ranging from calculators, solar torches and battery chargers to fully integrated systems for homes, offices, factories and public buildings. Ideally the PV collector array needs to be fitted on a sloping roof or wall which is facing within 90 degrees of south, as long as no other building or large trees overshadow it, otherwise the performance will be reduced.

Another consideration is that the roof needs to be strong enough to support the significant weight of the panels, especially if they are fitted on top of the existing tiles.

If you have solar photovoltaic panels fitted onto your house, apart from increasing the capital value and arguably the sales value of it, you will also benefit financially in three ways including the following Generation and Export Tariff rates available from April 1st 2010.

1. If you can use your electrical appliances during daylight hours when you are generating your own electricity you will save having to buy in some electricity thereby reducing your electricity bill.

2. The Generation Tariff of 41.3 pence will be paid for every kilowatt hour of electricity that your system generates, whether you use it or not.

3. The Export Tariff of 3 pence will be paid for every kilowatt hour of surplus electricity that you do not use and which is automatically exported out to the national grid for others to use.

These Feed-in Tariff payments are tax free, index linked and guaranteed for twenty five years.

The following diagram shows how a typical domestic installation might be specified.

In order to qualify for the Tariff payments the products will have to be certified and the installation will need to be completed and commissioned by an accredited installer under the Microgeneration Certification Scheme.

If you would like a more detailed fact sheet about PV systems and how they could work for you or if you would like a quotation of performance and cost for an accredited installation either contact us or complete our online home energy survey and we will report back to you as requested.

Either way, also check out the many local installations shown in our gallery.

Thank you for your interest in our Solar Industry.