Photovoltaic (PV) cells convert radiation from the sun into electricity. A typical PV cell consists of a wafer of semi-conducting material, usually silicon, manufactured with two electrically different layers. When sunlight hits the cell it excites the electrons within the silicon, creating an electric field across the layers and causing a flow of electricity.
An optimally orientated, un-shaded 1kWp array will, each year, generate approx. 850kWh (units) of electricity.
PV systems are modular, allowing a great degree of flexibility in design and specification. In practice, the size of a system is often determined by the available roof space or the energy requirement of the property. A standard 1kWp PV array will occupy at least 8m² of roof.
PV arrays can be mounted in a range of locations but the roof of a building usually provides the best and simplest site. Flat roofs are not ideal as it is hard to make them water tight once the bolts to secure the panels are drilled in. However, ground solutions are available if your roof is unsuitable using ballasts or specially designed mounting frames.
Most importantly, Solar PV panels should be located in a south-facing, unshaded location.
Any shade, such as from trees or neighbouring buildings, can have a large impact on the performance of a PV system. Because modules are constructed from a number of PV cells interconnected together, if one cell is shaded it has a knock-on effect that prohibits the whole module from generating electricity. To work effectively, we recommend that whole PV array needs to be free from shade for the majority of the day.
There are several types of PV cell. Monocrystalline cells are made from a single large crystal of silicon – they seen as more efficient and slightly better in low light conditions but they can be more expensive. Polycrystalline cells are made from cast blocks of silicon that contain many small crystals and are slightly less efficient than Monocrystalline cells. In practice, for a typical residential property, there is little difference in the performance of these different products.
All of the Solar PV solutions on our website are designed to be mounted on top of an existing or new roof. Although Solar PV systems are not normally heavy enough to cause structural problems, if your roof is in poor condition we would recommend that you undertake a structural survey before proceeding with your installation. If your roof is in need of repair or replacement we would recommend combining this work with your PV installation as this will help to reduce cost.
The cost of the installation may be increased for slate or clay tiled roofs, as the PV systems are secured to the roof using stainless steel “roof hooks”. These hooks provide a very robust means of attachment and don’t compromise the weather proofing of the existing roof. Fixing these hooks to concrete tiled roofs is a relatively straightforward process. However, due to the way slate and clay tiles are laid, many more need to be removed to fit the hook, and layers of flashing are needed for weatherproofing – hence these installations are slower and more costly in terms of labour.
The reason why the installers need access to the loft is because this is usually where the Inverter is installed. The inverter generates a lot of heat whilst in operation so the loft is the perfect place to put it as it offers sufficient ventilation to distribute the heat. Inverters should not be kept in a cupboard or enclosed space as this creates a fire risk. If you do not have access to your loft, you will need to think about where else within your property this inverter can be placed that is close to the roof and in a well ventilated area.