Question about DNO approvals and inverters

[Beelbeebub]

I see that you can fit up to a 3.6kw inverter without approval, just notify.

 

I have space for a considerably larger array. Which would be useful as my house seems to be high demand (15-20kwh a day) so a big battery and an array to fill it would be useful.

 

Is it possible to have a larger inverter fitted but have it limited to 3.6kw outgoing?

[RobLe]

Yes.  

 

eg a sunsynk 3.6kW Ecco, will allow 2 strings of 425V*13A max.  It can charge a 16cell LiFePo4 batt at 90A while sending 3.6kW to grid.

 

Or get an even bigger unit that is g100 certified, and get the overall grid export limited to 3.6kW.

[Dillsue]

2 hours ago, Beelbeebub said:

Is it possible to have a larger inverter fitted but have it limited to 3.6kw outgoing?

Yes via a G99 and G100 application using an inverter certified for export limitation.

 

Do you know how big an array you can fit in? I'm sure other manufacturers do it but I believe the the current solaredge range of inverters can have double the inverters kw rating in DC input from panels. A 3.68kw inverter can have around 7.3kw of panels hooked up to it, even more if they aren't all facing the same way so not all generating at max at the same time. As the inverter is limited to 3.68kw its G98 compliant so notify only. Not the most efficient use of the panels in the summer but you'd be using the bulk of the panels output outside of summer. Youd avoid a G99 application/cost 

[Mattg4321]

The other thing to consider with a 3.68kW inverter and DC battery storage is that 3.68kW will be the most it will be able to supply to the house with any balance made up from the grid. 
 

So it wouldn’t be able to run a double oven with both oven elements heating for example. 

[ProDave]

22 minutes ago, Mattg4321 said:

The other thing to consider with a 3.68kW inverter and DC battery storage is that 3.68kW will be the most it will be able to supply to the house with any balance made up from the grid. 
 

So it wouldn’t be able to run a double oven with both oven elements heating for example. 

This is what bugs me with this whole battery storage and DNO restrictions nonsense.

 

It would be simple to design a system that just used a CT on the mains feed to ensure it never exported more than 3.68kW but could deliver a lot more than that from the batteries when the house was using it.

 

[RobLe]

While I agree you can draw over 3.6kW in a home, in practice I believe it’s sufficient for most people.  We have 2+2 people here, and don’t make any attempt to limit our combined appliance useage - kettle/cooker/washing/gshp(v small) whatever.  Cars charge and dhw heats at night on the cheap rate.  Our 3.6kW sunsynk +15kWh Seplos batt system charges at night in the winter, and gives us 97.3% cheap rate elec useage.  The most significant aspect I found for improving the cheap rate useage has been getting the CT coil noise related offset working well.

pic below ignoring export:

[MikeSharp01]

You don't necessarily have to stick with the 3.68 kW, do a G99 application and ask for more. We did that and asked for 6kW export limit on single phase with 7kW of panels connected and it was granted. You may be unlucky and live in an area where everybody has solar and the local infrastructure can't cope - they have to allow 3.68kW of export but after that it is down to the DNO - so very little is lost just asking.

[Nickfromwales]

7 minutes ago, MikeSharp01 said:

You don't necessarily have to stick with the 3.68 kW, do a G99 application and ask for more. We did that and asked for 6kW export limit on single phase with 7kW of panels connected and it was granted. You may be unlucky and live in an area where everybody has solar and the local infrastructure can't cope - they have to allow 3.68kW of export but after that it is down to the DNO - so very little is lost just asking.

Defo the right advice. 
We’ve done loads of PV installs where we’ve simply asked up front for 5.5kW and above (highest 1ph we got granted was about 8.2kW), and got it. Depends, as said, if you’re on a good bit of the network or the last 2 bits of straggly copper in the woods, but asking is ‘free’, and if you don’t ask you won’t get.

Limiting yourself to the lowest is ok if you’ve calculated that you’ll never need more, but with the markets now making forced export very attractive I doubt you’d want to be stuck with that constraint long term. 
For new build this needs ‘massaging’ as you’ll be making a DNO application for everything at one point, so needs considering case by case. 

[Mattg4321]

Exactly what I did. My array won’t generate enough to need going above a 3.68kW inverter, but I’ve gone for 5.5kW at almost no extra cost and a bit of G99 aggro

[Beelbeebub]

Thanks for the responses!

 

So is it possible to have a large inverter (say 10kw)somehow set, maybe with some hardware, so it can never export. More than 3.6kw and thus be a g98 job. If at some point in the future I can export more I coukd ask, get permission and the outgoing limit be reset to a higher number?

 

Basically I have room for a lot of panels, potentially 14kwpeak or more but pretty west facing.

 

I honestly can't be arsed with the faff of applications etc especially if the price I get for the exported energy isn't great.

 

Say I manage 8kw export for an average of 5h a day, over the summer  that's 40kwh. At 5pkw that's only £2 a day for 180 days. £360. OK not nothing but is it worth the faff?

 

Could I just get a10kw inverter that has no export facility at all and not bother with g98/99/100

 

 

[Dillsue]

21 hours ago, Beelbeebub said:

So is it possible to have a large inverter (say 10kw)somehow set, maybe with some hardware, so it can never export. More than 3.6kw and thus be a g98 job.

 

Could I just get a10kw inverter that has no export facility at all and not bother with g98/99/100

 

 

No and no!

 

Under G98 the inverter must be limited to 3.6kw and never produce more than 3.6kw so you cant have a 10kw inverter. If you want a 10kw inverter that can pump 10kw to your house but only 3.68 or less to the grid, then you need export limitation which is done via G99 with a G100 supplement to cover the setup of the export limitation.

 

If you've got a grid connection you can't avoid G98/99/100 if you're connecting a PV inverter. The Gxx processes are there to help the DNO manage the grid for everyone's benefit so take whichever route is applicable

 

Personally if you've potentially got 14kw of panels I would go for G99 and see what the max export they'll allow is...you might be surprised. We got 7.3kw without any dramas and we've got that for "ever". Capacity allocation seems to be done on a first come first served basis so if you went for a 3.68kw system and all your neighbours did the same you might not get any extra export allowance in the future as all your neighbours have used up all the spare capacity in the local grid. If you got consent now for 5/6/7/8kw then you've likely got that for life:)

[Dillsue]

22 hours ago, Beelbeebub said:

I honestly can't be arsed with the faff of applications etc especially if the price I get for the exported energy isn't great.

 

Say I manage 8kw export for an average of 5h a day, over the summer  that's 40kwh. At 5pkw that's only £2 a day for 180 days. £360. OK not nothing but is it worth the faff?

 

Octopus Outgoing pays 15p/kwh so seemingly triple what youre getting now. Worth the faff for over a grand a year??

[Beelbeebub]

2 hours ago, Dillsue said:

Octopus Outgoing pays 15p/kwh so seemingly triple what youre getting now. Worth the faff for over a grand a year??

15p/kwh is attractive.

 

I think I'll enquire about a g99 route.

 

I noticed some inverters have a current loop to check if any is being exported.

 

Presumably it could be set to limit the export even though the inverter was more powerful.

 

If I was limited to (say) 6kw, a 6kw inverter might be too small for my needs. So would I have to chose between a bigger inverter or exporting? Seems mad there is no way of simply limiting the amount that can be exported even with a bigger inverter.

[Dillsue]

40 minutes ago, Beelbeebub said:

I noticed some inverters have a current loop to check if any is being exported.

 

Presumably it could be set to limit the export even though the inverter was more powerful.

 

If I was limited to (say) 6kw, a 6kw inverter might be too small for my needs. So would I have to chose between a bigger inverter or exporting? Seems mad there is no way of simply limiting the amount that can be exported even with a bigger inverter.

Any inverter thats supports export limitation will have an energy meter/CT clamp  to monitor how much is going to the grid and throttle output if there's too much being exported.

 

You can have whatever size inverter you want so long as it is certified to G100 for export limitation.... that's what G100 is for.