The Short Answer
In our view, buy a Powerwall 3 for what it does, not to save money. On a standard tariff it earns about £179 a year with a 4kW array in a typical home on our model. Even at the Energy Saving Trust's £5,000 to £8,000 for a battery, payback runs to 28 to 45 years, against a 10-year warranty.
A time-of-use export tariff changes the sum: on Octopus Flux's rates filling it overnight and exporting it all in the evening peak could be worth about £567 a year on our assumptions, before charging losses. Tesla publishes no UK price, so put your quote into the estimator below.
What It Is
| Powerwall 3 (Tesla UK) | |
|---|---|
| Capacity | 13.5 kWh |
| Output | Up to 11.04 kW, depending on local conditions |
| Inverter | Solar inverter built in; 97.5% solar-to-grid efficiency |
| Warranty | 10 years |
| UK price | Not published by Tesla: on quote |
The 97.5% is Tesla's inverter figure, solar to grid, not a round-trip efficiency for the battery. Ask your installer for the warranty document and read what it says about capacity at the end of the term and any cycle limit.
Will It Pay for Itself?
Powerwall 3 payback estimator
How long a Powerwall 3 takes to pay for itself, from your solar size, electricity use, tariff and quote. Prices are the price cap (1 October to 31 December 2026) and Octopus's published rates.
Extra solar used at home
1,251 kWh
per year
Annual saving
£179
Payback period
45 years
against a 10-year warranty
Show the working
Standard tariff: panels make 950 kWh a year per kW (our central England figure). The share of that solar used at home, with and without the Powerwall's 13.5 kWh, comes from the government's SAP 10.2 self-use formula for your array and yearly use (BRE fitted it to batteries up to 6.4 kWh and extended it to 15 kWh, so at this size it's an extrapolation). Each extra kWh used saves buying it at 26.32p but loses 12p of export, a gain of 14.32p.
Octopus Flux: the battery's 13.5 kWh filled at 16p off-peak and exported at 30p in the 4pm to 7pm peak on 300 days a year (our assumption), at Octopus's average rates on 24 October 2026, before charging losses, so treat it as a rough guide. It doesn't count the solar, and Octopus says Flux is designed only for homes with solar and a battery. Real results depend on your usage and the weather.
The Money
On a standard tariff a battery only earns the gap between import and export on the extra solar it lets you use. It moves solar you'd have exported (earning 12p on Octopus's Outgoing tariff) into the evening, where it saves buying at 26.32p. On the government's SAP 10.2 self-use formula, a 4kW array in Ofgem's typical home using 2,500 kWh a year goes from 26% used at home to 59% with a 13.5 kWh Powerwall. That's about 1,251 kWh a year more, worth about £179. A home with an electric car or a heat pump can use more of it.
On Octopus Flux (cheap 16p imports overnight, 30p for exports from 4pm to 7pm, at Octopus's average rates on 24 October 2026), a battery can be filled cheaply and emptied at the peak. If it did that with the Powerwall's full 13.5 kWh on 300 days a year (our assumption), that's about £567 before charging losses. Treat that as a rough guide, not a promise: real results depend on your usage and the weather, and using some of it at home instead of buying at the 37p peak rate is worth more per kWh (21p rather than 14p), if your home uses that much in those three hours. Our battery guide covers both cases for batteries generally.
Grants and VAT
- No Boiler Upgrade Scheme money for a battery in England and Wales: the scheme is for heat pumps and biomass.
- 0% VAT on batteries installed in homes, including on their own, until 31 March 2027, then 5%.
- Scotland: Home Energy Scotland doesn't fund battery storage.
Who Should Buy One
- You want backup in a power cut and a battery set up for it, in a home where outages happen or matter.
- You're fitting solar at the same time, so the built-in inverter saves a second box.
- You'll use a time-of-use export tariff, where the arbitrage, not the solar, does the work.
What You Don't Need
- A Powerwall as an investment on a standard tariff, in our view: it won't pay back inside its warranty.
- More capacity than you'll cycle. Size it to what you use in the evening.
Get several quotes from installers who fit Powerwalls, and ask each for the warranty document. If you have GivEnergy kit, see what GivEnergy's administration means for owners.
Frequently Asked Questions
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