Chriso said:

My thoughts are that obviously each inverter should be on it's own circuit, there is also the issue of the new inverter and battery now being connected to the FIT export meter.  But for me the big one is if the battery is full and the PV is in optimum conditions you could have a overload situation.

The latest guidance on this is available in the 3rd Ed of the IET CoP for EESS.

According to BS 7671:2018+A2:2022, there is the current rating of CUs to consider, as well as circuits ... although the issues were also covered in a similar manner for 2nd Ed of the IET CoP (big change is the consideration of the calculation of minimum CSA, S).

How is the battery charged? If it can only be charged from the PV system, so battery inverter output is simply "delayed" PV output - then the metering arrangement might be acceptable. If the battery can be charged from mains (e.g. off peak), then it's a no-no, possibly to the point of being fraudulent.

Likewise is there any co-ordination between the PV inverter and battery inverter? e.g. if the battery is just making up for the lack of PV output at that point in time, there might be no possibility of overload (and logically the two items are behaving as a single appliance).

   - Andy.

Thanks for the responses, apologies for my delayed reply.

I take the point about the distribution board and the rating of the RCD main switch, but with the B16 MCB in place I guess that should limit the loading.

Battery has it's own independent inverter so I suspect it can charge from the grid as well as using any spare PV generation.  Being wired in with the initial solar installation I think you could in theory charge the battery from the grid and then resell at a later date running through the FIT generation meter, so I think there is potential for fraudulent use.

The inverters appear to be working independently of each other, that's what made me think there was the possibility of overload in the right circumstances.

It's obvious this hasn't been done diligently but I'm conscious of wording this appropriately on my report, I know the customer is going to challenge the company who installed the battery.  I think this company should have directed the customer to replacing the submain to the outbuilding and installing a new distribution board to allow for a new circuit for the battery.