. 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 not an export meter. If your levels of generation are high and annual daytime consumption is low then an export meter will worthwhile, and you will need to arrange this through your electricity company.
However, as a good alternative to fitting an export meter, most supply companies offer 'deeming' of 50%, where they assume that you are exporting 50% of the power you generate. This obviously suits people well when they are using the majority of the generated power in the house, and exporting less than 50%. If you find you are exporting more than 50%, you should find out what fee (if any) your supplier will charge for installing an export meter, and if the 3p / kWh paid for exported power makes this worth it.
Our advice for new domestic installations is to go with the 50% deeming, and see how you feel after a year of getting used to the PV system. It helps to change your patterns of use where possible, so that you use generated power as it comes off the roof - eg set timers so the dishwasher comes on at 10am, and the washing machine at 12. This way you will save a higher proportion of expensive imported power (at say 16p), and decrease the proportion of power being exported (for 3p).
You may find this doesn't work for you, but it will be easier to arrange installation of an export meter after a year than to fit it straight away and then have it removed.
Commercial buildings often use much more daytime power than the PV’s will generate so an export meter is definitely not required. In such a case, all generated power is used on-site and the owners will benefit from the FiT and the saving on import bills.
OLD METERS Old meters – Modern digital import meters will slow down and stop when PV’s are supplying more power to the building than is being consumed. Old meters (with the spinning wheel) will actually reverse under these conditions and so any exported power becomes worth 3p + the 16p saved from the bill. However, using an old meter under these circumstances could be considered fraudulent.
The introduction of ‘smart