What size solar and battery do I need in Perth?

Last updated: 22 October 2026

The short answer

Size the panels to your daytime use and the loads you plan to add, and size the battery to what you use from late afternoon to morning. The two do different jobs, so they are worked out together from your own Synergy bill rather than picked from a standard package.

Why are solar size and battery size worked out together?

Panels make cheap daytime power and a battery stores it for the evening. Too much solar for the battery and the surplus is exported for as little as 2c/kWh. Too little and the battery is still part empty when the evening peak starts. The right pair covers the day and fills the battery.

Midday export
2¢/kWh
what Synergy's buyback (DEBS) pays outside the peak window
Peak export
10¢/kWh
DEBS rate for exports from 3pm to 9pm
Midday Saver peak
55.33¢/kWh
what that plan charges from 3pm to 9pm, as at 1 July 2026
WA rebate cap
10 kWh
the most capacity the WA rebate pays on; a ceiling, not a size

What size solar system suits a Perth home?

There is no one right size. 6.6 kW is where our sizing starts, the entry level for a small household, not the answer for most homes. The array is sized up from your two-month bill and the loads you plan to add, such as an EV, a heat pump or a pool, because undersizing is the costlier mistake.

The 6.6 kW and 10 kW pages show what each size makes and saves on a typical Perth day, so you can see where your own use sits between them.

What size battery do I need?

Size it to your evening and overnight use, not your whole day. The battery's job is to carry the house from the 3pm to 9pm peak through to morning on stored solar. Beyond that, extra capacity mainly serves an EV charged at night or longer blackout cover, so size up for those on purpose.

Prices are ranges, for two sizes

Our price guide covers two sizes: about $7,000–$9,000 for 10 kWh and $10,000–$15,000 for 20 kWh before rebates (estimate, Oct 2026). The rebates you qualify for come off that. Any other size needs a quote. The battery sizing guide works through the evening load step by step.

Should I buy more solar or more battery?

It depends which one is short. If your panels already cover the day with surplus left over, more battery captures that surplus for the evening. If the battery is still part empty at 3pm on a normal day, the panels are the constraint, and more solar comes first.

Our suggested starting point

For most family homes: make the solar generous enough to run the day and fill the battery, then size the battery to the evening peak. An installer working from your bill can tell you which of the two is the limit in your case.

Should I buy solar and a battery together, or add the battery later?

Buying both at once means one design, one installation and one Western Power application. Adding the battery later lets you size it from real usage once the solar is running, but it can mean a new inverter and a second application. Either works if the solar is planned with a battery in mind.

The solar and battery packages guide sets out what changes each way, line by line.

Can I add a battery to the solar I already have?

Usually, yes. If your inverter is a hybrid that can run a battery, the battery connects to it directly. If it runs solar only, the battery needs its own inverter beside it, or the old inverter is replaced with a hybrid. Either way, an installer checks the model on your wall before quoting.

In WA, adding a battery to an existing solar system counts as an alteration and can trigger whole-of-site compliance, so compare an AC-coupled retrofit against replacing your inverter with a hybrid. For many existing systems the sound path is replacing toward a DC-coupled / hybrid-inverter setup rather than expanding an AC-coupled one, avoiding future compliance limitations. Bring the inverter brand, model, install year and array size to the quote, so the battery is sized as an addition to what you have.

What do I need for an accurate sizing?

A recent two-month Synergy bill, ideally two, because the usage and the tariff on it are what the sizing reads. Add your roof type and any shading, a photo of your switchboard and meter if you can, and what is coming next: an EV, a pool, a heat pump or the end of your gas connection.

Adding a load later changes the answer. See hot water on your solar and charging an EV from your solar.

Get a system sized for your home

Tell us about your home and an installer from our network that covers your area gives you a free, no-obligation quote. Have a recent Synergy bill ready for them.

Get a free solar and battery quoteExplore your options

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