3-phase supply and PV

[mutleybones]

I've got a 3-phase supply coming into the house, if I were to have PV installed would I need a 3-phase inverter to balance the out-going power across the phases? Or at 3.9kWp is it not worth worrying about balancing and send all of the out-going out on one phase?

Would it make sense to have the generated power on its own phase, un-used by the rest of the house, so that it is all exported, we're in France where the export is currently €0.57 a unit vs €0.072 to purchase a daytime summer unit (+standing charge). Or wouldn't it make any odds as the overall net consumption/generation across the 3-phases will be combined by the meter (not sure if there would be a separate generation meter).

Steve.

[JohnS]

IIRC the French do not allow self use of generated electricity and require it all to be exported.  Hence the high FIT rate which combines export.

I may be wrong, can anyone confirm this?

John

[Kombi]

You are correct. No self consumption to benefit from higher rate of FIT.

[GavinA]

I had a look recently for a 3 phase inverter of that size, and the closest I got was a 2 phase 6kWp inverter, so I'd think sticking to single phase and picking whichever phase works best financially is the way to go.

no idea about the french regulations on connection though.

[knighty]

I don't know about smaller models... but the 3 phase GTIs I looked at were much much cheaper than single phase ones....
(I was looking at 15+kw tho)

:-)

[MarkB]

Without wanting to hijack the thread too much, I have some 3-phase questions.

I'm looking at installing a PV system of around 7kW pk on a new build. It's a new build, so the 4kW limit doesn't come into effect (in theory at least) but I save the 5% VAT on the install. Since it's over the 3.68kW limit, I either get lucky and the DNO allows me to connect to a single phase, or I'd have to go three phase.

I'm also keen to allow for 3-phase to make it quicker to charge an electric vehicle if such a thing ever makes sense in the UK energy mix, especially if I can use the power from my PV to charge it.

Anyway, I believe that the three phase supply is available on a telegraph pole at one end of the plot, so the theoretical cost of running a three-phase cable instead of a single-phase should not be too high although I guess I'd need a 3-phase or 3 single phase meters. However, do the electricity suppliers charge extra for a 3-phase supply vs a single phase, i.e. higher standing charge or unit costs?

Also, if I go for a 3-phase inverter then I understand that the generated load should be balanced between the phases (~2.5kW pk per phase) and that normally the house load is only connected to one phase. If this is the case then it would mean that I could only ever use 1/3rd of the generated power, unless I was actually using a three-phase load.

Is there a way of wiring this lot up so that I could minimise the imported electricity, while keeping the DNO happy and providing the opportunity of simple connection to 3-phase at some time in the future?

E.g. can you run half a house off one phase, and the other half off another, with the third going to the garage?

Alternatively, can an inverter be setup to monitor the actual export balancing between phases after the house load has been drawn?

What makes the most sense?

[BruceB]

I can answer some of that as I have domestic 3 phase for a large heat pump.

If you have 3 phase available then grab it.  But do not ask for too big a supply.  If you do you might get charged for network reinforcement.

You will get charged for its installation of course.  Some of the works are 'contestable' which means you or your builder can do trenching, which you might be doing anyway for water and telephone, so an opportunity to save money.

For me, EON charge the same standing charge and usage whether I am on single phase or 3 phase. 

If you have 3 phase then you should balance your load across the phases.  I recall that was in the small print. 

With 3 phase you still get the G83 16A per phase, so no need to talk to your DNO in advance about PV until you hit around 10kW.

If you want to see what the inverters will do then download a Sunny tripower installation manual.

Regards
Bruce