Can a Tesla Powerwall 3 Run a Whole House?

"Will it run the whole house?" is the first question we get about the Tesla Powerwall 3, and the honest answer is: yes, but for a length of time that depends entirely on what you switch on. Here is how to work that out for your own home rather than trusting a number from a brochure.

What "whole-home backup" actually means

A Powerwall 3 is set up for whole-home backup. When the grid drops, the system disconnects from the network and runs the house from the battery, switching over fast enough that most households barely notice. That is different from a battery that only backs up a few chosen circuits. What it does not mean is unlimited power: you are running on 13.5kWh of usable storage until the sun or the grid comes back.

The arithmetic that matters

Work in kilowatt-hours. A fridge-freezer uses roughly 1 to 1.5kWh a day. Lights, a router, a TV and phone charging together add a few kWh. Those loads are small, and a full Powerwall will carry them for the best part of a day. The heavy loads are the ones that change the answer: an electric shower, an oven, an immersion heater, a kettle used repeatedly, and above all an EV charging at 7kW — that last one can empty a full battery in about two hours on its own.

So the practical answer is: for lights, fridge, internet and a few sockets, a Powerwall 3 will hold a typical home up for many hours and often overnight. For a house running electric heating or charging a car, it is measured in hours. Neither is a criticism of the battery; it is what 13.5kWh means.

When one battery is not enough

If you have an EV, a heat pump, or a household that uses a lot of electricity in the evening, one 13.5kWh battery may be full by teatime and empty by bedtime for most of the year. That is where the expansion unit comes in: it takes usable storage to 27kWh. As a battery-only install that is £13,950 from, against £7,450 from for the 13.5kWh unit on its own — both subject to a free survey.

Don't count the same kilowatt-hours twice

Savings estimates often add two things together that cannot both happen: storing your own solar for the evening, and charging cheaply overnight to sell into the peak export window. On 25 September 2026 Octopus Flux paid 29.79p per kWh for exports between 4pm and 7pm in the South Eastern region and 29.00p in the Southern region, against a flat 12p on Outgoing Octopus — attractive, but a 13.5kWh battery can only move about 13.5kWh a day in total. Pick the job you want it to do, then size it.

What we do before quoting one

We look at your actual usage — the annual kWh on your bill and, where you have one, the half-hourly data from a smart meter — and model the battery against your own evening curve. Then we tell you whether the Powerwall is the right answer, whether a smaller battery does the same job for less, or whether the money is better spent on panels. Solar with a Fox ESS 5.76kWh battery starts at £6,995; solar with a Powerwall 3 starts at £12,920.

Whatever you choose, the install goes through a G99 application to your network operator, approved before we fit anything. If you want the full picture on the hardware, read our Tesla Powerwall 3 review, or see what a battery-only retrofit involves on our page for home battery storage without solar. For sizing beyond the Powerwall, see what size solar battery do I need.