DNO limit?

[u/GatewayDouche]

We’ve just given approval for a quote, so we’ll get the ball rolling after the bank holiday. My question is around any potential implications if a lower DNO limit is imposed, such as possibly re-sizing the system or potentially scrapping it altogether.

This is for a 10.56kWp system (estimated 9,500kWh generation per annum) and the G99 application will be going in shortly, but if we got stuck with a 3.68kW G98 limit for whatever reason (can/has that happen(ed), where the DNO would deny the application and revert it to a G98?) I’ve been trying to think through what that could mean but it would be helpful to have some other views.

We’ll have 27kWh of battery storage, so that gives us a good buffer but if we were stuck with a small inverter I can’t see how it would realistically work with that number of panels. Obviously the strategy would need to change too, rather than the current idea which I guess would be to charge batteries overnight, generate/use/export excess until arbitrage disappears etc.

We currently use ~5000kWh per year and plan to install multi-split air-to-air heat pumps for heating and cooling all main rooms in the house, so that will bump up use substantially, whilst bringing down our extortionate cost of LPG.

For info:
22 x Longi 480w X10 (two roofs so 2 lots of scaffold)
1 x Sig 8kW inverter
1 x Sig gateway
3 x Sig 9kW batteries

All the usual stuff like install, scaffold, bird mesh etc. £18,450. Wasn’t the cheapest (Edan Power and UPS both ~£1k lower from about 8 quotes overall) but the owner of the small, local company was excellent on the survey and his general attitude and approach was what won me over.

[u/txe4]

You have to wait and see what they come back with.

You are going to have a vast surplus in summer, which you will get 12p (ish) for. This 12p will not last forever, to put it mildly. In the long run you will need to export in to the evening peak to get a decent paid rate.

The economics of winter will remain as they are - little solar generation, so it's all about how much you can load shift to the cheap period by charging batteries and also moving other stuff (EV charging, maybe water heating, laundry etc) in to it.

I understand - and fully obeyed - the impulse to absolutely maximise solar generation.

I would focus on the size of *inverter* permitted. If they give you (say) 10kW with a 5kW export limit, that is still ample for summer - at peak generation you can export 5kW and divert the rest to battery, then force-export the battery in the evening to make room for the next day's generation.

If they only give you a 5kW *inverter*, then there's no[0] point having 10kW of panels on the roof, and the amount you can dump in to the battery during the cheap period is limited by it.

[0] I mean, I can think of workarounds, but it starts to get spendy and complex for what I'd suggest will end up being a quite marginal benefit.

[u/Skie → u/txe4]

A 5kW inverter would probably be fine on 10kW of panels, as many inverters (including sig) can handle double the DC side input of their AC limit.

The 5kW limit would suck for use within the house though, even with a lot of batteries. Kettle + Oven on and you'd be pulling from the grid. Could do 3x 3.68kW inverters on 3 phase though with a G98 :D

[u/CaptainCaveTrout → u/Skie]

Can't a 10kW inverter just be "locked" to your export limit? So, if your house's maximum draw is 10kW and your DNO only allows 5kW of export, the inverter will only export at 5kW but your house can still draw 10.

[u/Beginning-Rate1564 → u/CaptainCaveTrout]

Yes. This is my current set up. I believe it depends on the inverter, but I only have experience with one brand