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Battery with existing PV - regulations

JamesPa · 2025-11-25T17:08:23Z

Im now looking again at batteries because recent changes in tarifs (which are no surprise and I suspect are the direction of travel) have altered the equation. I have grid tied solar and I am looking at grid tied AC coupled batteries. Ideally I would want islanding to be possible to cover power cuts and 3.6kW output maybe a bit more At this stage I am trying to get my mind around the regs. As I understand it a) even if the battery inverter is set so that it does not discharge when this would lead to export, I still need G99, which will need to specify both inverters, because the DNO assumes it might export. This might limit the max output of the battery inverter even though its not intended to export b) If the inverter does support islanding, there must be a suitable cut out device |(presbetween the supply and any part of the internal wiring that will be energised during a power cut, to ensure that nothing is fed back to the grid in this circumstance Have I got this correct? Im not trying to 'design' the system, just understand so I am an informed customer! Also, has anyone looked seriously at sodium ion batteries. They seem to be obtainable and are, at least prima facie (but who knows what happens under the hood), more ethical in production and lower fire risk. Sorry to ask simple questions, Im starting on a new learning curve here!

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Last Post by antonical 3 months ago

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antonical

(@antonical)

Eminent Member Member

Joined: 3 months ago

Posts: 18

24/01/2026 6:33 pm

@jamespa Thanks for the links. Yeah, the DNO just doesn't seem to care or even want to listen to the fact we are using Fully type certified ENA compliant G99/G100 devices. Its just an arbitrary discussion with them. Forget that the inverters for their ENA certifications have G99/G100 modes in the firmware. Once selected the correct UK grid parameters are automatically set. Voltage, freq, full harmonics etc. etc. etc. And of course export limitation thresholds. In our case zero (technically approved for 10kW). If we were pushing energy out to the grid I can understand it raising local votages etc. But we would be happy with Zero export and 16kw Inverter!

Seems a total lottery with little room for negotiation or accommodation for the client needs. The Gov is on a massive warm homes push to renewables with regs made for the 70's!

We will keep the fight going.

Cheers

6.5kWp of Solar G98 3.6kW inverter 32kWh battery. Samsung Gen 7 16kW Integrated Unit Newark Cylinders 'Heat Geek' Custom SuperTank and 50Ltr Volumiser Tank.

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Batpred

(@batpred)

Prominent Member Member

Joined: 1 year ago

Posts: 767

24/01/2026 6:46 pm

Posted by: @antonical

↑

Now we need to scale up but are limited to a 10KW inverter. We requested a 16kW inverter with G100 enabled at whatever the level the DNO wanted. Their answer was to ignore all of the technology and simply limit the inverter to 10KW with 10KW export.

Welcome, you have a very interesting setup and I am hoping it is about how to approach the DNO.

I am with UKPN and when I contacted them about the inverter and G98, they were not interested as I was not planning to export. Then they offered 5kw, asked me to fill the details on the first G99 form "as if G98" (my inverter is also type tested). When I submitted the G99 commissioning form, the discussion had moved to 8kw and they approved and issued the export MPAN. Hope you manage to get something similar!

But much of it will depend on your DNO and even your specific location.

The power ratings that you are mentioning made me think whether a three phase inverter with a suitable upgrade of the DNO service would be a better solution... Transparent posted in this forum about how to get the service upgraded on safety grounds but I cannot find where..

Having said that, I agree with @jamespa : that thread does cover much of it, except the three phase considerations. For that, this discussion on a three phase inverter setup may help

This post was modified 3 months ago 2 times by Batpred

8kW Solis S6-EH1P8K-L-PLUS hybrid inverter; G99: 8kw export; 16kWh Seplos Fogstar battery; Ohme Home Pro EV charger; 100Amp head, HA lab on mini PC

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antonical

(@antonical)

Eminent Member Member

Joined: 3 months ago

Posts: 18

25/01/2026 1:16 am

Many thanks. The 3 phase is a non starter. Starting price 65K as they will have to upgrade the entire piece of string to put one in. Thats after we pay then 1K for a study they already know the answer to! It is a complete lottery. Very happy for you that your DNO is so easy to work with. The G98 no one cared about. Only the G99 is when the issues arose.

Cheers

6.5kWp of Solar G98 3.6kW inverter 32kWh battery. Samsung Gen 7 16kW Integrated Unit Newark Cylinders 'Heat Geek' Custom SuperTank and 50Ltr Volumiser Tank.

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