Single phase, 2 separate battery systems?

[Christiano]

Hi all,

 

We have ~10kWp of Solar generation and an 8kW Powervault battery. We are thinking of adding 4kW to the Powervault which is £3k and at current Octopus Go rate (40p/7.5p) based on the last year I calculate that would pay back in 4.1 years although I suppose prices will probably go down within that time.

 

The battery is in an outbuilding with a small east/west facing roof and I had thought about putting 2-3 panels facing west because our generation from the south-facing array drops off when the sun goes around.

 

So I had this crazy thought that if I put a new system - panels/inverter/battery - it would all be at zero rated VAT so maybe, for not much more than the cost of upgrading the Powervault I could add both without affecting my FiT.

 

I know I’d have to do something to control discharge so maybe only discharge from the second battery when the Powervault is empty. On the charge side maybe the new battery would only charge from the panels?

 

Stupid idea?

[RobLe]

Givenergy say that battery systems should be wired as below - each batt system has it’s own CT current sensor.  The critical thing is that the power connections are separated, so that the two CTs can measure different things, otherwise you can get power slopping back and forth between batts, being wasted.  I think it will be difficult to do this with two systems at the end of a single long cable.

 The one marked ‘hybrid inv’ measures load+hybrid inv, while the ‘existed inv’ will have a ct (unmarked) near the supply meter.

https://midsummerwholesale.co.uk/pdfs/giv-ct-manual.pdf

 

The snip below is from it, which considers a pre-existing install of an inverter:

 

Above pic modified to include ct location for ‘existed inv’:
 

 

[Christiano]

That’s interesting, thanks.