Solar Electricity Generation (Photovoltaics)

What are Photovoltaics?

Solar panels
Solar panels
Photovoltaic means electricity from light. Photovoltaic, or PV systems, use daylight to power ordinary electrical equipment, for example household appliances, computers and lighting. The solar photovoltaic (PV) process uses cells to convert the sun's energy directly into electricity.

A PV cell consists of two or more thin layers of semi-conducting material, most commonly silicon. When the silicon is exposed to light, electrical charges are generated and this can be conducted away by metal contacts as direct current (DC). The electrical output from a single cell is small, so multiple cells are connected together and encapsulated (normally behind glass) to form a module, or panel. The PV panel is the principle building block of a PV system and any number of panels can be connected together to form an array, to give the desired electrical output.

Does Solar PV provide hot water or heating?
PV systems provide electricity, which can then be used for a variety of purposes, including powering electric boilers or water heaters. Solar PV technology does not however directly generate hot water - this is solar thermal technology, or Solar Hot Water, which works differently.

Why install a PV system?
Installing your own PV system means that you can generate your own electricity using a non-polluting, free and inexhaustible energy source - the sun. A PV system never needs refuelling, has no moving parts, emits no pollution, is silent, and requires minimal maintenance.

Can a PV system be installed on my building?
Photovoltaic panels can be placed on almost any building surface which receives daylight for most of the day. Roofs are the usual location for PV systems on houses, but panels can also be placed on facades, conservatory or atrium roofs, sun shades, etc.

The surface on which the PV array is mounted should receive as much light as possible as the more light received, the more electricity will be generated. The three issues which affect how much light a surface receives are:
Orientation: Due south is the best possible orientation. Systems should be preferably within 45 degrees of south facing.
Tilt: A tilted array will receive more light than a vertical array. Tilts should be between 0 and 60 degrees of horizontal.
Shadowing: for example from tall trees or neighbouring buildings, can reduce system performance considerably.
In addition, the area needed for a PV array depends on the output electricity desired and the type of module used.

Will I require planning permission?
Planning permission is not normally required. However, exceptions may apply for systems on listed buildings or in areas of outstanding natural beauty. In all cases it is best to check with your local council planning department.

Is PV expensive? How much will it cost to install?
Over the last 20 years, the price of PV modules have fallen dramatically. AT the moment, a typical price for a grid connected PV system is between £6,000 and £7,000 per kWp, which means that a 2kWp system for a typical domestic property would cost around £15,000 - £2,000. per kWp, which means that a typical 3-4kWp system for a typical domestic property (12-16 individual panels, depending on roof size) would cost around £6,000 - £7,000.

There are also schemes to help with the cost of PV. The Governments Feed-in Tariff pays a price to the equipment owner for each kWh of electricity generated, which means that as well as receiving free electricity you receive a quarterly Feed-in Tariff payment for the electricity that you have generated. In most cases, a proportion of the electricity generated will be deemed to be fed back into the national grid, and a small payment will also be made for this element.

If you do not want to invest your own money on installing PV, but would like the free electricity, some companies will fit your PV installation for free and in return they take the Feed-in Tariff. These are sometimes called Rent-a-Roof schemes. For these schemes, the electricity generated by the PV system for your home will generally be free but you should always check the terms and conditions of the agreement before signing up.

How much will I need to power my home?
A typical domestic system of 3-4kWp in the UK would produce around half of the annual electricity demand of an average family household. The more energy efficient your home, the more value you stand to gain from your PV system. Solar PV systems produce electricity during daylight hours - any electricity produced and not used through the day can be sold back to the electricity grid.

Does PV technology need bright sunshine to work properly?
The electrical output of a PV cell is dependent upon the intensity of the light to which it is exposed. So PV cells will tend to generate more electricity on bright days than when skies are overcast. However, photovoltaics do not need to be in direct sunlight to work, so even on overcast days a PV cell will be generating electricity.

Information provided by the Energy Savings Trust.
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