The right battery size comes from your power bills, not a package. Here is how we work it out.

Too small and you are still buying power every night. Too big and you have paid for capacity that never gets used, or that your solar can never fill. We size every battery from how your household actually uses power.

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kWh and kW, in plain words

kWh (kilowatt-hours) is how much energy a battery stores, like the size of a water tank. kW (kilowatts) is how fast it can deliver power, like the width of the tap. You need enough of both: enough kWh to get through the evening and night, and enough kW to run what you switch on at the same time.

Look for usable capacity. That’s what you can actually draw, and it’s what the federal rebate is based on.

What we read from your bills

• Daily average use. How much power your home uses in a typical day, and how it changes between summer and winter.
• When you use it. If you are on a time-of-use tariff, the peak, shoulder and off-peak split shows how much falls after dark.
• Your export. If you already have solar, how much you send to the grid shows what’s spare to charge a battery.
• Interval data, if you have it. Half-hourly data from your retailer or smart meter shows exactly when you use power. It helps, but one or two bills are enough to start.

How we size it

1. Cover the evening and night. The battery should comfortably cover what you use from late afternoon until the sun is back.

2. Make sure your solar can fill it. Including in winter, when days are shorter. If it can’t, we design extra panels. See adding a battery to existing solar.

3. Plan for blackouts. Our typical install backs up the whole home. If backup matters to you, we allow for it. See blackout backup.

4. Think about what’s coming. An EV, a pool, working from home or a growing family all change the answer. Modular batteries such as Sigenergy and the GoodWe ESA (8 kWh modules) can be added to later.

Bigger isn’t always better

The federal rebate applies in full to the first 14 kWh of usable capacity, then at a reduced rate from 14 to 28 kWh, and at a much lower rate from 28 to 50 kWh. Every extra kWh costs about the same to buy but gets less rebate. A battery that never fully empties overnight is also capacity you are not using. We show you where the sensible size sits for your home. See battery rebate step-down.

A real example

Some households need a big system. Ross and Holly in Bilambil Heights have 19 kW of solar and a battery since expanded to 33 kWh: “Our $600 quarterly bills are gone.” Their size suited their usage. Yours might be quite different, which is why we start with your bills.

Next: how to choose a battery brand, the NSW 0% loan, or solar and battery installation across the Northern Rivers.

Why locals trust our sizing

• Sized from your real usage, not a generic package.
• Our own in-house team designs every system and does every install. 25 years in solar and large commercial electrical work.
• A face-to-face site visit before every install: compliant battery position, switchboard and RCBO check, no surprises on the day.
• Honest about size: we will tell you when a smaller battery does the job.

Battery sizing FAQs

What size battery do I need?

It depends on how much power you use in the evening and overnight, whether your solar can fill the battery, and whether you want blackout backup. We work it out from one or two recent power bills.

What does kWh mean on a battery?

Kilowatt-hours: how much energy the battery stores. Look for usable capacity, which is what you can actually draw and what the federal rebate is based on.

Can you size a battery from one bill?

Yes, though two bills from different seasons help. If you have half-hourly interval data from your retailer, that is even better.

Should I get a bigger battery to get more rebate?

Usually not. The rebate tapers above 14 kWh and again above 28 kWh, so each extra kWh gets less. We size to your usage, not to the rebate.

Can I add more battery later?

With modular systems such as Sigenergy and the GoodWe ESA, yes. We can design with room to grow.

Does an electric car change the battery size?

It can. Charging an EV from a home battery overnight uses a lot of stored energy, so we plan EV charging into the design. See our home EV charger page.

Send us your bills and we will size it properly

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