Doubling up battery

[Alexphd1]

I already have solar and batteries (3.68kw inverter and 12kwh batteries) but was thinking of adding another inverter and another set of batteries, do I need dno approval for the 2nd inverter even though there is no solar going on it?

 

[Nickfromwales]

2 hours ago, Alexphd1 said:

I already have solar and batteries (3.68kw inverter and 12kwh batteries) but was thinking of adding another inverter and another set of batteries, do I need dno approval for the 2nd inverter even though there is no solar going on it?

 

It’s still classed as AC coupled micro-generation, so is notifiable afaik.

[JohnMo]

If you add the same make of inverter and they can operate as master and slave, so the master inverter has all control you should retain G98 certification. But this will be dependent on makes and models etc. The master is what allow stuff to to flow to the grid, slave just does as it's told.

[MikeGrahamT21]

I suspect you’ll probably need a G100 compliant export power manager style device, to limit your export to agreed limits

[Nickfromwales]

2 hours ago, MikeGrahamT21 said:

I suspect you’ll probably need a G100 compliant export power manager style device, to limit your export to agreed limits

They may say it’s fine to have them both at full capacity, it’s down to the DNO, so best to simply ask first, panic afterwards. 

[Dillsue]

On 20/11/2025 at 18:09, Alexphd1 said:

I already have solar and batteries (3.68kw inverter and 12kwh batteries) but was thinking of adding another inverter and another set of batteries, do I need dno approval for the 2nd inverter even though there is no solar going on it?

 

Yep, G99 for the second one if it's AC coupled and capable of exporting regardless of where the exported power is coming from. Worth speaking to your DNO before you commit to anything

[Alexphd1]

Yeah I will go and have a look at the paperwork. When the out buildings get built we can add more solar so the the proposed 2nd battery system so will get everything cleared 1st from DNO.

I have came across a company called g59 projects who will take care of the paperwork side for £250, maybe the easy route for applying for a bigger system.

[Dillsue]

Try and speak to them if you can before you do all the paperwork and pay the application fee. Our DNO was very approachable and we had a verbal agreement within a couple of days. That was formalised with a G99 application.

 

If you've already got one PV system then you should already have submitted a G98 notifcation, or earlier version, for that system. There's not alot of extra work involved between a G98 and G99 application and the single line drawing that you should already have.