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Battery Retrofit of storage battery to existing Solar PV (worried about affect on FIT)

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I currently have a 3Kwh solar PV system which was installed over 12 years ago and getting a very good FIT payment and I don't want to lose it! I'm thinking about having a 10Kw battery installed, the idea being that I can divert excess generation to the battery and also have the facility to top up the battery from the grid (cheap-rate) during winter months.

I'm minded to go for the DC Coupled Solaredge 10Kw battery but my limited understanding tells me there are complications as far as the metering is concerned and topping up the battery from the grid i.e to account for any charging of the battery from the grid and avoid supply from the battery to the home being shown as generation. I currently have a separate generation meter only and submit readings for my FIT on a monthly basis.

My proposed installer said that he could fit a bi-directional meter which will measure consumed and exported electricity and net which will meet the rules as far as FIT is concerned. Is this actually the case?

I did briefly consider an AC-Coupled battery but it will be a lot more expensive. I currently have a Solaredge SE3000H inverter (this replaced a defective Sunny Boy inverter about 18 months ago). The proposed installer said AC coupled battery will require a replacement inverter or additional one fitted which will be more expensive.

If it helps, I have a smart meter and on the Octopus Go tariff. I have a PHEV which I connect to a Zappi for charging. Diverting excess generation to the car is problematic as the Zappi will only charge the car from solar when there is an excess of 1.4kWp which doesn't happen that often.

Another related question, solar pv will charge the battery but how is this measured? For example, if I generate 20kWp and 10Kwp is taken by the battery, will my generation figure be 20 or 10kWp for FIT puposes?

Welcome you thoughts/advice please
I'd like to know the answers to this too. As this was posted a year ago with no responses, I think it needs a bump.

I'm in a very similar situation - 2.7KW PV installed 13 years ago, 3kw inverter which is getting quite noisy so probably could do with replacing soon.

I'd like to add a 15KW battery system from Fogstar or Pylontech. I assume the draw will be restricted by the capacity of the inverter? So with my current inverter I can only use up to 3KW of energy, which is not an issue as I can only produce 2.7KW. But with batteries in theory the limit is whatever appliances in the house require. While we very rarely use more than 6KW at any time, we have an 10KW electric shower which is used maybe 15 minutes a week. Do we need an inverter that can cope with this, e.g. Growatt MIN 10000 TL-X or if we had a smaller inverter, e.g. Growatt SPH6000, would the extra 4KW required come from the grid, or would our shower just not work, or trip a fuse, etc?

As well as charging the batteries from the PV, I would like to top them up overnight using a cheap EV tariff. I guess I would need some form of controller for this (and also presumably for similar charging of an EV overnight - which we don't have at the moment but will in the future, along with more PV once I have had batteries for a while and worked out the cost benefit).

Thanks to anyone who can share some basic battery/PV info - a simple schematic of how all the components fit together would also be great.
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