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There is no single right battery size. The best size for a home follows from when it uses electricity, how much spare solar it has in each season, the power its appliances need at once, and whether it wants backup.
This page explains a method for thinking about size, why a bigger battery is not automatically better, and why shifting usage into solar hours comes first.
Five things matter most. Each points to a different size, and a good design balances them.
Using solar directly is more efficient than storing it, because a battery loses some energy each time it charges and discharges. Before sizing a battery, move flexible use into solar hours where you can.
Once you have shifted what you can, the evening use that remains is what a battery would actually cover — often less than it first appears.
Extra capacity only adds value when it is regularly charged and used. In winter there may not be enough spare solar to fill a large battery, and in summer a modest battery may already cover the evening.
A battery that rarely fills, or rarely empties, adds cost without adding much value. A size that fills on most days and is mostly used each evening is usually better matched.
You can estimate a sensible range with your own data rather than a rule of thumb.
Usable capacity. It is the energy you can actually draw, and is usually less than the nominal figure.
Some batteries are modular and can be expanded, often only with the same model and within a time limit. Ask before you buy.
An incentive can change the price, but the size should still suit your usage. Check program rules on minimum or maximum capacity on the official program page.
Not yet reviewed by a person. Programs, products and rules change — check the official source before you decide.
General information only. PlaceNest's energy guides, and any estimates or incentive lists, are general information and estimates — not personalised financial advice, and not a quote. Programs, prices and rules change: check the official sources, and get written quotes from accredited installers before you decide.
PlaceNest guides are general information, not financial advice. Whether solar, a battery or an EV charger pays off depends on your home, usage and prices.
Any incentive or finance details PlaceNest shows come from a reviewed list, each with its official source and the date it was checked; eligibility is decided by each program. See how incentives work and paying for an upgrade.