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How do Solar Photovoltaic Systems Work

A solar photo voltaic (PV) system provides power by converting the sun’s energy into DC (Direct Current) electricity, which passes through an inverter to create AC (Alternating Current) electricity at 230V.

How is solar electricity generated?

PV systems use solar panels made up of individual PV cells to turn daylight into electricity.

A PV cell is made up of one or two layers of a semi-conducting material. When light shines on the cell, it creates an electric field across the layers and causes electricity to flow.  The more light the cell receives, the more electricity it can generate.

There are three main types of PV cells:

• Monocrystalline – made from thin slices of silicon, cut from a single crystal.

• Polycrystalline – made from thin slices of silicon, cut from a block of crystals.

• Thin Film – made from a very thin layer of silicon atoms on a glass or metal base.

These three kinds of PV cells vary in efficiency, suitability and cost.

PV cells are made from crystals made out of silicon. Normally pure silicon is a poor conductor of electricity. However, the addition of certain impurities, such as Phosphorus, creates a semi-conductor. The semi-conductors allow the silicon to conduct electricity by forcing electrons in the crystal to move around freely when exposed to light instead of just jiggling in place; thus, light absorption can flow around producing an electrical current as opposed to heat.

Several individual cells wired together create a module. Usually modules consists of an aluminum framed sheet of durable, low reflective, tempered glass that has individual solar cells adhered to the inner glass surface creating a panel. However, there are now some flexible modules available, using thin-film cell technologies. Individual PV cells are connected together to form a module. These cells are wired in specific series strings to increase the module’s voltage and electrical current.

Modules are then linked together to make up a PV array: the solar panel system that will supply electricity to your property.

Arrays can be roof mounted on flat roofs or pitched roofs, on the main house or outbuildings, on commercial, industrial or farm buildings, or ground mounted – both small scale and large scale.

 

Meeting your electricity needs:

You’re most likely to use a PV system to complement and feed into your mains supply, reducing the amount of grid electricity that you use and pay for. Such systems are known as ‘Grid tied’ and use a device called an inverter to ‘feed in’ the electricity generated by the solar array.

When your PV system is generating more electricity than you are using at property, the excess will flow back automatically to the national grid. When the system is generating less than you need, you can use your traditional mains supply to supplement your PV generation.

If your property is not connected to the electricity grid, you can install a ‘stand alone’ PV system, using batteries to store electricity that will help to power your appliances and lights.

 

Feed-in Tariff

Once installed, we register you on the central FIT (Feed-in Tariff) database and you will receive a certificate confirming FIT compliance. We will advise you how to inform your energy supplier that you are eligible to receive the FIT.  Your energy supplier will cross reference your installation with the central FIT database and payments will then be made at intervals to be decided between you and you and them. You will usually be required to provide meter readings to your energy supplier every 3 months.  More about the feed-in tariff can be found HERE.

 

Considerations:

  • Does your property have a south-facing roof or garden? For a PV system to give the best output you need an unobstructed surface that faces either to the south, south-east or south-west. Installations facing West or East will still work but the energy generated will be slightly less.
  • Is the area un-shadowed by other buildings or large trees? The output of PV system will be greatly affected by shading, even partial shading can reduce the output considerably.
  • Is the roof suitable for mounting a PV system on it, some roofs such as thatch can be very difficult to install onto.
  • Is the property’s electrical system suitable for solar PV to be connected?

 

Regulations and safety:

  • The system needs to be installed in lines with building regulations. This includes undertaking a structural roof assessment and calculations before undertaking roof works to ensure the structure is adequate and registering the system under the Part P Electrical certification scheme to cover the electrical parts of the system.
  • Planning permission may be required. A solar PV system is usually classed within permitted development rights, except when the property is listed, is within an area of outstanding natural beauty, is thatched, is in a national park or is in a site of special scientific interest.
  • To achieve the highest possible rate of feed-in-Tariff, the property needs to have an Energy Performance Certificate (EPC) rating of D or above.  We can undertake the EPC on your behalf and let you know if the efficiency of the property needs upgrading.

For larger PV systems, we have to apply to the electricity network operator for permission to feed into the grid.  This may be refused if the lines feeding your property are already close to capacity.