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Tesla Powerwall 3: should you install one?
Updated
Powerwall 3 is sold as an integrated home battery and solar inverter. On a retrofit that often means the existing string inverter comes off the wall rather than sitting beside a second box.
Where this kit fits
Larger all-electric houses that want a single cabinet, a high discharge rate and backup, and can pay a premium over a modular rack. It is a weak buy when small evening loads, leasehold flats with nowhere legal to put a heavy cabinet, and budgets that only work if the pack is half this size.
Small evening loads, leasehold flats with nowhere legal to put a heavy cabinet, and budgets that only work if the pack is half this size.
A September 2026 sketch for Tesla Powerwall 3
Take a 13.5 kWh pack, cycled about 340 times, at 90% round trip. Charge at 11.0p, and value what comes back at 30.8p. Export given up is priced at 12.0p. About 1943 kWh a year of the charge is treated as spare solar from 4 kWp that might otherwise have been exported. Delivered energy is about 3060 kWh. After charging cost and lost export, the sketch saves about £596 a year. Set that against £6,880 fitted, which is a September 2026 illustration at the temporary 0% residential rate, not a quote. That is a simple payback of about 11.5 years on these assumptions. Nudge the night rate up by 4p and see if you still like it.
In most single-phase houses in Britain, 3.6 kW is in the band where G98 connect-and-notify is often enough. Export can still be capped. Agree that before the inverter is ordered. The sketch uses 13.5 kWh and 4 kWp, which is enough to tell two quotes apart if they assumed something else.
At a steady 600 W evening load, 13.5 kWh lasts about 22.5 hours. A 3 kW kettle only works if the inverter can deliver it. Capacity on the badge does not answer that.
VAT, paperwork, refusal
Where the job is a qualifying install in a home, the 0% rate runs to 31 March 2027 and is due to become 5% after that. This sketch prices the work at £6,880 on that basis. It does not apply to a shop, and it does not apply to a battery you buy and fit yourself.
I would not treat backup as included on a 13.5 kWh quote unless the circuits are listed.
Ask the installer for the last Tesla Powerwall 3 they commissioned: postcode area, inverter size, and whether G99 was required. A first-ever install of this range is a risk you can choose not to fund.
Questions worth asking out loud
Is the price on this page a quote?
No. £6,880 is a September 2026 illustration for a 13.5 kWh example at the temporary 0% residential rate. Your survey replaces it.
Will it stay on in a power cut?
Only if a gateway or essential-load board was designed and paid for. A standard grid-tied battery turns off with the grid. On this 13.5 kWh sketch the inverter is 3.6 kW, and backup is still a separate line.
What paperwork should I keep?
Keep the MCS certificate where the job is certified, the electrical certificate, the DNO record, the schematic, the warranty registration and a photo of the schedule. For an illustrated £6,880 job, that folder is part of what you bought.
What if the cheap rate is not 7p?
Then the sketch changes. This page used 11.0p as a charge rate and 30.8p as the rate avoided. A smaller gap means a worse payback. Read the live tariff.