r 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. Under G83 we can install a system and notify the DNO (District Network Operator) afterwards.
If we multiply 16A by 230volts you’ll see the maximum system size is 3.68kW. However, we can install up to 4kW under G83, which is the point at which the best economies of scale meet the highest Feed in Tariff, by under-sizing the inverter i.e. installing an inverter that limits the maximum a.c. output to <3.68kW. Under-sizing the inverter is normal practice anyway, and is explained further here.
If a building has a three-phase electrical supply then we have three times as much capacity under G83 regs, so we can install up to 11.04kW (perhaps 12kW with inverter under-sizing) without the need for an application to the DNO, as long as the system is divided so that it is <16A on each phase.
Tip: the easiest way of telling if you have single or three / phase electrics in your building is to check the number of wires connected at the bottom of the electricity meter. Single phase = 4 (1 live in, 1 live out, 1 neutral in and 1 neutral out). Three phase = 8 (3 lives in, 3 lives out, 1 neutral in and 1 neutral out).
G59: For systems above 16A / phase we need to apply for permission from the DNO. Most inverters have built in safety features that satisfy G59 regs, and so you don’t need a separate G59 safety relay, contrary to popular belief. However sometimes there may be a requirement for the DNO to upgrade the local transformer (and charge for it) prior to connection so that it can safely handle the amount of power being fed into grid. This depends on the size of the system and also the location, and becomes more of an issue in rural areas ‘at the end of the line’. We’ve seen a lot of flexibility from DNO’s with our applications, and have had 50kWp systems (73A / phase) accepted without the need for any additional work or charges. It’s always best to get that application in early during the design stage so everyone is certain about this.
Exporting Your Electricity
We install a generation meter as part of our installation, but no