DNO G98 restrictions with battery storage

[yebaws]

Currently have 3.65 Kw solar PV installed, with 3.68Kw inverter. DNO notified with G98 and that's all fine...

 

Now looking to install 6.4KWh battery storage with 3.6Kw hybrid inverter / charge control unit.

 

Solar PV is on the roof of an outbuilding about 100m away from house and feeds back to house CU through SWA cable. As the charge controller needs a CT clamp connection to the supply coming into the house CU in order to detect export, it wasn't practical to have the batteries up by the panels, so they will be in the house near the consumer unit and connected to the AC supply. This also means that we can charge the batteries at night with off-peak electricity as well as excess solar.

 

Once installed, I will need to submit a separate G98 form to DNO. What are the rules about this? Could they refuse / request a G99 application, saying that I will have more than 3.68Kw exporting capacity? In practice, we would never be exporting from both the PV inverter and the battery inverter at the same time (the whole point of the battery storage is to reduce the amount of electricity we're exporting for free), but the battery inverter does have a "force discharge" option, so it would be possible to do it.

 

Help much appreciated.

 

 

[SteamyTea]

46 minutes ago, yebaws said:

What are the rules about this? Could they refuse / request a G99 application, saying that I will have more than 3.68Kw exporting capacity? In practice, we would never be exporting from both the PV inverter and the battery inverter at the same time

It matters not two hoots how you use the system.

All that matters is if it is capable of exporting more that the 16A per phase.

So either redesign so it can't, or apply for G99 before you start.

[joth]

You maybe able to do this with G100 export limitation instead, so the batter inverter is commissioned to ensure no more than 3.68kW is ever exported net. (in practice as you say you'd set it to never export from battery to grid)

I've no experience but I understand G100 is easier/cheaper than doing G99 application.

 

[Dillsue]

G100 is in addition to G99 so you apply for G99 and if you or your DNO want to limit export you have a G100 application as a supplement to the G99. That's the way that our DNO does things which I beleive is the same across the UK.

 

Certainly for us, G100 means you must use a professional installer who can set up the limitation with factory/engineer passwords to prevent the user altering the settings. It also means your DNO will want to witness the limitation at a cost of several hundred pounds. Not really DIYable with G100.

 

If you want to add AC coupled batteries best speaking to your DNO to see if theyll accept 2 x 3.68kw.  If not maybe replace your existing inverter with the hybrid unit so the inverter limits total export from batteties and PV to 3.68kw

 

If your SWA is the right size/spec you can move the the inverter to wherever the batteries are and bring the DC from the PV through the SWA. 

Edited March 6, 2023 by Dillsue

[Marvin]

As I understand it some DNO's have previously permitted the equipment being "limited", however, whether this is still so or not I don't know.

 

In my understanding, as a basic principle if the battery supply is controlled through the approved inverter and then to the mains then ok. If the battery supply avoids the approved inverter or goes through another inverter and is connected to the mains, then need to apply to DNO.

[Dillsue]

2 hours ago, Marvin said:

As I understand it some DNO's have previously permitted the equipment being "limited", however, whether this is still so or not I don't know.

Yes. I'm sure theres folk on here that have said their DNO has given permission for 5kw export without batting an eyelid??

[ProDave]

26 minutes ago, Dillsue said:

Yes. I'm sure theres folk on here that have said their DNO has given permission for 5kw export without batting an eyelid??

Some do but ours made it pretty clear there would be a charge for 1W above 3.68kW

 

Wait until after April when the rules change, after then, it should be unusual for domestic installs to be charged a network upgrade fee.  The cynic lurking in me suspects things they previously wanted to charge you to upgrade, they might decide don't actually need upgraded if they can no longer charge you.

[yebaws]

15 minutes ago, ProDave said:

Some do but ours made it pretty clear there would be a charge for 1W above 3.68kW

 

Wait until after April when the rules change, after then, it should be unusual for domestic installs to be charged a network upgrade fee.  The cynic lurking in me suspects things they previously wanted to charge you to upgrade, they might decide don't actually need upgraded if they can no longer charge you.

That's interesting to hear. I might just wait and see. Any link to more info on this?

 

Failing that, G99 might be the easiest way to go. What are peoples experience of doing this? How long is it likely to take? What are the fees likely to be? What are the chances in my case that they might say I have to pay for an upgrade? SSE North is my DNO. Rural single phase supply. Anybody had any success in getting informal advice from SSE pre application?

 

Also, I find it strange that a lot of sites (https://www.deegesolar.co.uk/dno_for_solar_panels/ for example) say that you only need to notify DNO if your battery storage has EPS / UPS.

[yebaws]

4 hours ago, Dillsue said:

If your SWA is the right size/spec you can move the the inverter to wherever the batteries are and bring the DC from the PV through the SWA. 

Cable is 6mm2 I think from memory. But it is about 100m long. Did think about this at the time, but I think there was some issue with DC voltage drop.

 

Thinking about this now, and remembering what we paid to connect the house up initially, it might be cheapest just to ask SSE for a separate supply to the workshop, so then we get 2 x 3.68 with no issues (and it all goes to the same transformer and into the same lines without SSE upgrading anything - what a farce)

[Dillsue]

You'll not know for sure if any grid upgrades are required, paid for or not, until you ask. Our DNO gave informal approval within a few days of contacting them with a G99 to formalise things. New transformer goes in on Thursday not far off a year after first contact!! I'm not paying so hard to complain.

 

We're at the end of a few miles of 33kv overhead lines and it was our puny transformer that was the problem, not the cabled supply to it so being rural doesnt necessarily mean problems

[joth]

1 hour ago, yebaws said:

Also, I find it strange that a lot of sites (https://www.deegesolar.co.uk/dno_for_solar_panels/ for example) say that you only need to notify DNO if your battery storage has EPS / UPS.

Yeah that's misleading, it's saying *additional* DNO notification is then needed, besides the G98/99.

 

Page 34 of this guide is useful:

https://www.energynetworks.org/assets/images/Resource library/G99 Type A Full Guide.pdf

"G99 Form A1-2" apparently is your friend.

Edit: actually probably not, reading that form it only applies to hybrid (integrated) PV + storage inverters

 

Edited March 6, 2023 by joth

[Dillsue]

50 minutes ago, yebaws said:

Thinking about this now, and remembering what we paid to connect the house up initially, it might be cheapest just to ask SSE for a separate supply to the workshop, so then we get 2 x 3.68 with no issues (and it all goes to the same transformer and into the same lines without SSE upgrading anything - what a farce)

A couple of years standing charge would cover the cost of a beefier SWA so a second supply might not be that economic??

Edited March 6, 2023 by Dillsue