Photovoltaics

Solar photovoltaic (PV) converts sunlight directly into electricity to run appliances and lighting.

The electrical output from a single cell is small, so multiple cells are connected together to form a module. Any number of modules can be connected together to give the desired electrical output.

The main types of PV are:

Monocrystalline is the most efficient of the PV technologies. It consists of thin slices cut from a single crystal of silicon. This has a typical efficiency of 15 per cent and they are more expensive than other technologies.

Polycrystalline cells are made from cells cut from an ingot of melted and recrystallised silicon. They are cheaper to produce than monocrystalline ones, however they are slightly less efficient, with typical efficiency of around 12 per cent.

Amorphous silicon, also known as “thin film" PV technology, absorbs light more effectively than crystalline silicon, so the cells can be thinner.

They are made from a very thin layer of semiconductor atoms deposited on a glass or metal base. They are cheaper to produce and are suited for applications where high efficiency is not required and low cost is important. This has a typical efficiency of 7 per cent.

Other Thin Films - A number of other promising materials are now being used for PV modules. They can be manufactured by relatively inexpensive industrial processes, yet they typically offer higher module efficiencies than amorphous silicon.

Since the PV system will be producing DC electricity a piece of equipment called an inverter will be needed to change the DC into AC, the kind of power that is in the utility grid and flows out of the wall sockets in a normal home.

PV arrays are typically mounted on a roof facing south and angled at 30o with the horizontal for optimum performance in the UK. A typical system for a house will measure between 10 and 40 m2 and will generate between 1,000 and 3,000 kWh per year.

At a smaller scale, PV panels can be used in caravans and also in boats to power nautical equipment and other devices.

Batteries should also be considered for the system so it can provide power when the weather is poor, or at night.

PV systems can be connected to the Grid or as stand-alone applications. Systems can be connected to the local electricity network, allowing any excess solar electricity produced to be sold to the utility. Electricity is then taken back from the network outside daylight hours.

Grid Support are those systems connected to the local electricity network and a back-up battery. Any excess solar electricity produced after the battery has been charged is then sold to the network.

Stand-alone photovoltaic systems are completely independent of the grid, as the solar system is directly connected to a battery, which stores the electricity generated and acts as the main power supply.

Prices for PV systems vary, depending on the size of the system to be installed, type of PV cell used, the building on which the PV is mounted and installation considerations. It is usually cheaper to integrate PV into a new building than installing it on an existing property.

Larger systems benefit from economies of scale and are generally cheaper per kWp than smaller systems.

Some local authorities require planning permission before you can install a PV system, especially in conservation areas or on listed buildings. Always check with your local authority before you have a system installed.

PV equipment has no moving parts and emits no noise during operation. It generates electricity without producing greenhouse or any other gases, saving approximately 325kg of carbon dioxide emissions per year.

Harnessing the sun’s energy and converting it into electricity will reduce your fuel bills and at the same time reduce your daily impact on the environment.

Grants are available for up to 50% of the costs for domestic installations from the Low Carbon Buildings Programme.

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