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Moving FIT array onto a Tesla Powerwall 3 possible?

Solar Photovoltaic (PV)

Last Post by Judith 1 month ago

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AdamK

(@adamk)

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Joined: 9 months ago

Posts: 176

Topic starter 27/09/2025 9:46 pm

I currently have a 3.68kw inverter hooked up to 4kwp of solar on a 2014 FIT. I had planned to leave it alone until the FIT runs out in 9 years but I’m considering making my setup far cleaner and just have the 4kwp going to the PW3. I’ve not looked at the wiring diagrams yet but I’m wondering if it’s possible to separate the solar inverter output from the battery output, so my generation meter can sit between the grid and inverter.

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AgentGeorge

(@agentgeorge)

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28/09/2025 1:12 am

We had a solar array to start, hooked direct into the main CU.

we added a battery pack soon after when we realised we could time shift the cheap tariff during the peak period in the winter; summer time we have plenty of PV at 5-6pm.

we added a battery charger/inverter and fed the PV output into this, and the output of this inverter goes to the CU.

it was simpler to add a new inverter than replace the PV inverter with a combined unit.

Also means if the battery inverter has problems, the PV will still power the house

Downside is the Machine Room has another big black box and big red power switch; but the wiring is all neat as I insisted on it looking tidy

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Judith

(@judith)

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28/09/2025 6:42 am

We have a 4kW FIT array, and have added a battery with no problems. The key is using an AC inverter to the battery. Hybrid ones charge the battery at DC and so are more efficient. The Tesla installer must have met this situation before and of course your FIT tariff is precious.

2kW + Growatt & 4kW +Sunnyboy PV on south-facing roof Solar thermal. 9.5kWh Givenergy battery with AC3. MVHR. Vaillant 7kW ASHP (very pleased with it) open system operating on WC

👍

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AgentGeorge

(@agentgeorge)

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28/09/2025 9:04 am

@judith

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AgentGeorge

(@agentgeorge)

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Joined: 9 months ago

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28/09/2025 9:31 am

Batteries are all charged at DC wether from a Solar Inverter or a Hybrid.

The Hybrid has all 3 functions built into one module, so when it fails, you loose everything. Having a separate solar inverter allows batteries to be isolated should a fault occur on their charger/inverter.

PV output is 48V, batteries are 52V

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AdamK

(@adamk)

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Topic starter 28/09/2025 12:01 pm

What I’m trying to say is I want the solar inverter on the pw3 to just export not charge the batteries or for the batteries to affect the FIT meter, as I need the FIT to only pay for solar units not any battery units that might have been charged on a cheap rate.

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Judith

(@judith)

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28/09/2025 2:37 pm

Posted by: @agentgeorge

↑

Batteries are all charged at DC wether from a Solar Inverter or a Hybrid.

The Hybrid has all 3 functions built into one module, so when it fails, you loose everything. Having a separate solar inverter allows batteries to be isolated should a fault occur on their charger/inverter.

PV output is 48V, batteries are 52V

I know batteries and PV are DC! (& I have a Physics degree.) My point was possibly badly worded. An AC inverter for a battery takes the power from the AC mains interface. PV panels have their inverter which goes from DC to mains. A hybrid Battery PV inverter goes from the PV DC to battery DC without going to mains, and hence is more efficient. But there is no AC measurement of the generated power.

The FIT tariff measures the AC power that is generated by the panels and could be sent to the mains. It is based on generation, and since back in 2014 there were few smart meters they ‘deemed’ usage of the household is 50% of generation. It is particularly valuable to the homeowner in total.

So in buying a battery the owner needs an AC inverter to the battery to leave the FIT payment power links untouched. I don’t know if the Tesla powerwall has such an option.

2kW + Growatt & 4kW +Sunnyboy PV on south-facing roof Solar thermal. 9.5kWh Givenergy battery with AC3. MVHR. Vaillant 7kW ASHP (very pleased with it) open system operating on WC

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Toodles

(@toodles)

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Joined: 3 years ago

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29/09/2025 12:46 pm

@judith The PW3 can accept AC or DC inputs. Regards, Toodles.

Toodles, heats his home with cold draughts and cooks food with magnets.

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Judith

(@judith)

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30/09/2025 8:07 pm

@toodles that’s good news for @adamk

2kW + Growatt & 4kW +Sunnyboy PV on south-facing roof Solar thermal. 9.5kWh Givenergy battery with AC3. MVHR. Vaillant 7kW ASHP (very pleased with it) open system operating on WC

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