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What size solar battery do I need?

The right battery size depends on how much power you use after the sun goes down, how much spare solar you have to charge it, and whether you want backup during blackouts. This guide explains how our accredited battery installers size home batteries for Newcastle, Lake Macquarie and Hunter homes, drawing on around 5,000 battery installations since 2014.

The quick answer

Size your battery’s usable capacity to match the electricity you use between late afternoon and the next morning, when your solar isn’t producing.

For example, a home that uses 12 kWh overnight suits a battery with around 12 to 14 kWh of usable capacity.

Most Hunter homes end up with a battery between 10 kWh and 20 kWh, paired with enough solar to fill it, even in winter.

How to size a home battery in 5 steps

1. Find out how much power you use overnight

A battery’s job is to cover the hours your solar panels can’t. So the most important number isn’t your total daily use, it’s how much you use from roughly 4 pm until 7 am the next morning.

If you have a smart meter, your retailer’s app or online account shows your usage in 30-minute intervals. Add up the evening and overnight periods over a few typical days, including some in winter, to get an accurate figure.

If you don’t have interval data, a rough guide is that households who are out during the day use around 60 to 70% of their power outside solar hours. Households who are home during the day use closer to 40 to 50%.

2. Check you have enough solar to charge it

A battery is only useful if it fills up. It charges from the solar your home doesn’t use during the day, so you need a genuine surplus on top of your daytime use.

In the Newcastle and Hunter region, each 1 kW of solar produces around 4 kWh a day on average, but only around 2.5 to 3 kWh on short winter days. To reliably fill a 10 to 13.5 kWh battery, most homes need around 3 to 4 kW of solar above what their daytime use requires.

Many older systems, especially 3 to 5 kW installations, don’t produce enough surplus to fill a modern battery. In that case, adding panels at the same time as the battery usually gives a better result. Our solar system sizing guide explains how to work out the right solar size.

Sigenergy home battery installed by Hunter Solar Solutions in the Hunter region

3. Understand usable capacity and power output

Battery specifications can be confusing. These are the three numbers that matter most.

Usable capacity (kWh). This is how much energy you can actually draw from the battery. It’s usually a little lower than the “nominal” or total capacity on the box, because batteries keep a small reserve to protect their lifespan. Always size on usable capacity.

Power output (kW). This is how much the battery can supply at once. A battery with plenty of stored energy but a low power rating may not be able to run your oven, air conditioner and kettle together, so some of that load will come from the grid. Families with high evening loads should look for a higher continuous output.

Round-trip efficiency. Some energy is lost charging and discharging. Modern lithium batteries are typically around 90% efficient, so allow a little extra solar to cover it.

Homeowner checking solar battery performance on a monitoring app in Newcastle NSW

4. Decide if you want blackout backup

Not every battery keeps the lights on during a power outage. Backup needs a compatible inverter and backup gateway or switchover equipment, and it’s worth deciding on this before you choose a system.

  • No backup. The battery stores solar for evening use only and switches off during a blackout, like your solar panels do.
  • Essential circuits backup. Selected circuits, such as the fridge, lights, Wi-Fi and some power points, stay on during an outage.
  • Whole-home backup. Your entire home runs from the battery during an outage. This needs a battery with a higher power output and usually more storage.

If you’re on acreage in the Hunter Valley or Upper Hunter, or on a part of the network that sees more outages, backup is often worth prioritising.

5. Plan for the future and the rebate

Electric vehicles. Charging an EV straight from your solar during the day is usually far better value than charging it from your battery overnight. If you’re planning an EV, think about adding panels and a smart EV charger alongside your battery, rather than simply buying a much bigger battery.

Going all-electric. Replacing gas heating, cooking or hot water with electric appliances will increase your evening use, so allow for it now.

Expandable batteries. Many modern batteries are modular, so you can start with a smaller size and add modules later. Check that the system you choose can be expanded if your needs are likely to grow.

The federal battery discount. The Cheaper Home Batteries Program reduces the upfront cost of an eligible home battery. Changes that took effect on 1 May 2026 mean the discount now reduces every six months, and the full per-kWh discount applies to the first portion of a battery’s capacity, with lower support for larger batteries. In practice, that makes sizing your battery to your actual needs more important than ever. We apply the discount directly to your quote and handle the paperwork.

Network export pricing. Ausgrid, which covers most of Newcastle, Lake Macquarie and the Central Coast, has moved to two-way network pricing for solar exports. Depending on your retailer’s plan, energy exported in the middle of the day can be worth very little. Storing that energy in a battery and using it in the evening makes more of every kWh your panels produce.

Battery sizes for common Hunter households

Use this table as a starting point. Your actual size depends on your usage data, your solar system and whether you want backup.

Household Typical evening and overnight use Suggested usable battery size Solar needed to fill it
1 to 2 people 6 to 9 kWh 8 to 10 kWh 6.6 to 8 kW
Family of 3 to 4 10 to 14 kWh 12 to 16 kWh 8 to 10 kW
Family of 5 or more 15 to 20 kWh 16 to 24 kWh 10 to 13.2 kW
All-electric home or acreage 20 kWh+ 24 kWh+ 13.2 kW+ (often three-phase)

Figures are general guides for the Newcastle and Hunter region. Winter solar output is lower, so a battery that fills every day in summer may only partly fill on cloudy winter days.

Two real-world battery sizing examples

A retired couple in Cardiff

Usage: 18 kWh a day, with around 8 kWh used in the evening and overnight. They’re home most days.

Existing solar: a 6.6 kW system that exports a lot of power in the middle of the day.

Our recommendation: a battery with around 10 kWh of usable capacity. Their existing system has enough surplus to fill it on most days, and the battery covers nearly all of their evening use. See more about our solar and battery installations in Cardiff.

Backup: essential circuits backup for the fridge, lights and internet.

A young family in Thornton

Usage: 30 kWh a day, with around 17 kWh used in the evening and overnight thanks to cooking, heating and cooling after school and work.

Existing solar: an older 5 kW system that barely covers their daytime use.

Our recommendation: upgrading to a 13.2 kW solar system with a battery of around 18 to 20 kWh usable capacity. Without the extra panels, the battery would rarely fill. See more about our solar and battery installations in Thornton.

Future-proofing: a modular battery lets them add capacity later if they electrify their hot water or buy an EV.

Common battery sizing mistakes to avoid

Sizing on total daily use. Your battery only needs to cover the hours your solar can’t. Sizing it to your full daily use usually means paying for capacity you’ll never fill.

Buying a battery your solar can’t fill. A large battery on a small solar system will sit partly empty most of the year. Check your surplus first, especially in winter.

Confusing kW and kWh. kWh is how much energy the battery stores. kW is how fast it can deliver it. You need enough of both.

Assuming every battery provides backup. Blackout protection needs the right equipment. Ask for it specifically if it matters to you.

Ignoring compatibility. Some existing inverters work with some batteries and not others. An accredited installer should check your current system before recommending a battery. Our team holds dedicated battery storage accreditation for exactly this reason.

Let us size your battery for you

Send us a recent power bill and details of any existing solar system, and we’ll recommend the right battery size for your home. Free, no obligation and no high-pressure sales, from a local team rated 5 stars across 348 Google reviews.

Battery sizing FAQs

Answers to the questions Hunter homeowners ask us most about choosing a battery size.

What size battery do I need for my home?

Size your battery’s usable capacity to match the electricity you use from late afternoon until the next morning. Most Hunter homes use between 8 and 20 kWh in that window, so most end up with a battery between 10 kWh and 20 kWh. Make sure your solar system produces enough surplus to fill it.

A 10 kWh battery suits many smaller households and couples who use around 8 to 10 kWh in the evening and overnight. Larger families, homes with ducted air conditioning or all-electric homes usually need more.

Your solar needs to produce enough surplus above your daytime use to fill the battery. In the Hunter, each 1 kW of solar produces around 4 kWh a day on average, so filling a 10 to 13.5 kWh battery usually needs around 3 to 4 kW of solar on top of what your home uses during the day. Read our solar system sizing guide for more.

In most cases, yes. Depending on your current inverter, the battery may connect through a new hybrid inverter or its own battery inverter. If your existing system is small or older, adding panels at the same time often makes the battery much more effective.

Only if it’s installed with backup capability. Some systems back up essential circuits like the fridge, lights and internet, while others can run the whole home. Let us know if backup matters to you and we’ll design the system around it.

Nominal capacity is the total energy a battery can hold. Usable capacity is the amount you can actually draw from it, after the reserve that protects the battery’s lifespan. Always compare batteries on usable capacity.

Yes. The federal Cheaper Home Batteries Program provides an upfront discount on eligible home batteries. Since 1 May 2026, the discount reduces every six months and is lower for the larger portion of bigger batteries, so it pays to size your battery to your real needs. We apply the discount to your quote and handle the paperwork.

Usually not. Charging an EV directly from solar during the day is generally better value than charging it from a battery overnight. Adding panels and a smart EV charger is often a better investment than a much larger battery.