Home Battery Size Calculator

How we size your battery

A battery's job is to store solar you'd otherwise export cheaply and use it in the evening instead of buying from the grid. So the useful size is the smaller of two things: how much you use after sunset, and how much spare solar you have to fill it. If you want blackout backup, we make sure the battery covers your essential load for the hours you choose. The result is rounded up to a common battery size.

What we assume

• About 90% round-trip efficiency, typical of modern lithium (LFP) home batteries.
• Each kWh shifted saves your electricity price minus the feed-in rate you'd have earned for exporting it.
• Capacities shown are usable kWh. Check the usable figure on any spec sheet, not the total.
• Savings from virtual power plant (VPP) programs or time-of-use tariffs aren't included and can shorten payback.

Does a battery pay for itself?

It depends on the gap between what you pay for power and what you're paid to export it, and on battery prices after rebates. If the payback comes out longer than the warranty (often 10 years), a battery is more about backup and independence than savings.

These results are estimates for general information only, not financial advice. Get quotes from accredited installers and check current rebates before deciding.