Sunday 28 August 2011

4kW or not 4kW? That is the system..

Many of you guys may have already encountered the newly enforced grid connected inverter G83/1 requirements recently. In simple terms, all the District Network Operators (DNO's) have finally got together and are now insisting that all installations should completely comply with G83/1 requirements. Click here for ENA guideline document

For the purposes of changes that affect us, this means you can no longer have a Grid connected renewable power system that can export more than 16Amps without special permission. In principle, this has always been the case, however when we first started installing PV some years back the DNO's were quite happy to bend the rules a little to accomodate a possible maximum of 17.4Amps. Now due to the heavier installation rates of PV, and possibly upsetting the balance of local electricity networks, the DNO's have laid out simple rules:

1) If the output of the system will never be more than 16A, install as normal with normal notification when the work is complete.
2) If the output of the system may exceed 16A, then a G83/1 Stage 2 application will need to be carried out. The DNO will carry out a network study to ensure the local network will take this extra power, possibly charging you up to £250 for costs, and will advise if you can indeed install this system. Do not install and connect the system first, or you may be issued with a disconnection notice.

This all sounds pretty harsh, but in practice its not so bad if you can adjust your thinking. One of the main problems until recently has been availability of a good range of 3.6kW inverters to match the UK G83/1 standard. These are now coming on board by all the manufacturers quite quickly. SMA (Sunny Boy) for example are simply de-rating their 4kW range and certifying for the UK.. Easy!

On the other side of the coin, in the UK for the most part a 4kWp system will hardly ever generate 4kW. There will be occasions on a south facing roof in midsummer, when the module temperature will be low enough to maintain efficiency, you will see the meter clock over the 4kW mark, otherwise it will lurk around 3.5kW, in bright sun, obviously less as brightness reduces.
Thus, carry on installing those arrays of 3.98kWp, etc and connect a 3.6kW inverter. That way, you'll still be generating just about the same annually as you would by fitting a 4kW inverter.

While I could ramble on about ideal inverter sizing for a given size of array, the above info kind of covers this in itself, plus re assuring you the new DNO requirements are really not a problem, simply adjust your thinking.

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