e almost the same dimensions as 170Wp Sharp polycrystalline modules. Our design team tends to recommend the (proportionally more expensive) high efficiency modules for smaller roof areas or where a client really wants to maximise output, and less expensive polycrystalline modules for large roof areas.
Despite some manufacturers claims, we have found that hybrid, mono and polycrystalline all give the same kWh yield / kWp over the year. Quality and guarantee periods are similarly high with all the common brands available for use in the UK.
Daylight levels in the UK mean that PV will produce an average of 858 kWh of electricity per kWp system size, per year (South-facing & un-shaded). This figure is reached by Standard Assessment Procedure, and forms the basis of our predictions.
An average UK household uses around 3000 kWh per year (so a 1kWp system would supply a quarter of the yearly use). Simple energy efficiency measures in the building will increase the proportion of energy coming from the PV's.
The PV array will usually be mounted on a Southerly facing, pitched roof.
The "solar sundial" below shows that a fair bit of deviation in the positioning of the array will still yield a large percentage of the energy expected from an optimum orientation (a pitch of 30/40 degrees facing due South).
Whenever shading decreases the power output of any one module in an array, then the output of the whole array is similarly decreased. It is therefore very important to avoid shading (from trees, other buildings etc) when siting a PV array. However, if, for example, the shading only occurs late on winter afternoons then it will have less impact on the annual output of the array than shading that occurs every morning until 12:00.
For complicated shading situations, our designers can plot the PV array and the surrounding objects and run a PVSYST simulation to show predicted output throughout the year.
Roof Area Required
Allow approximately 8m2 of pitched roof area (16m2 of flat roof) for every 1kWp of PV. Obstructions like dormer windows and roof vents need to be considered when surveying the site.
Planning permission is not normally required unless it is a listed building or in a conservation area - please see the Town and Country Planning Amendment of April 2008. If in doubt, check with your local council, and if you do need to make a planning application we will advise you and supply all the drawings, photographs etc that you need for a successful outcome.
Where Does It Go?
There are two ways of storing the electrical energy produced by a photovoltaic array. One is by using batteries in a stand alone system (the remote house, boat, caravan etc); the other is by connecting to the national grid.
In a grid connect system, the grid works in effect as a battery. During the day the PV array might produce more energy than is required by the building it serves. This excess will be exported to the building next door or down the road via the mains. In the evening, or any other time of high use / low sun, electricity is drawn in the usual way from the grid, and supplemented by the PV system. This all happens automatically due to natural ebb and flow of electricity as it finds the shortest route to a load. Grid-connect PV is often referred to as 'fit and forget' because of the lack of user interaction or maintenance required.
If there is a power-cut the inverter will shut the system down, and there will be no generation. This is a safety mechanism to avoid 'islanding' - where workers on a supposedly dead grid might get a shock from PV systems in the area exporting power. Power cuts are thankfully few and far between in the UK at the moment, and the considerable problems associated with batteries (expense, maintenance, lifetime, storage, disposal etc) mean that grid / standalone systems are very rare. Advances have been made in the switching technology though - see http://www.sma.de/en/products/backup-systems.html.
G83 / G59 Regulations
G83 regulations deal with the export of power below a maximum of 16A per phase, and cover most domestic systems