How to Size a Home Battery in Adelaide
Size a battery to your overnight use, not your whole bill. Most Adelaide homes use 8 to 16 kWh between sunset and sunrise, which is why 10 to 14 kWh of usable storage is the most common fit. Then check two limits: how much your solar can refill each day, and the 14 kWh point where the federal battery rebate starts tapering.
The Quick Formula
A battery earns its keep by covering the power you’d otherwise buy after the sun goes down. So the number that matters is your overnight use: everything from about 5pm until your panels pick up again the next morning.
Usable battery size (kWh) ≈ your overnight use (kWh)
Then check it against your solar: about 1.5 kWh of battery per kW of panels.
If you only know your daily total, overnight use is usually 50 to 70 percent of it for households that are out during the day, and closer to 40 percent for those at home. Here’s how that plays out:
| Overnight use | Usable battery | Solar to keep it full | Rebate rate |
|---|---|---|---|
| 5–8 kWh | 5–8 kWh | 5–6.6kW | Full |
| 8–12 kWh | 10 kWh | 6.6kW+ | Full |
| 12–16 kWh | 13–14 kWh | 8.8kW+ | Full |
| 16 kWh+ | 14 kWh, or more with care | 13kW+, often three-phase | 60% above 14 kWh |
Rebate rates are the Cheaper Home Batteries tiers in place since 1 May 2026. Solar figures assume a well-placed Adelaide roof averaging 4.2 kWh per kW per day. See our guide on how to size a solar system for where that figure comes from.
Not Sure What You Use at Night?
Our solar calculator estimates your usage from your bill and suggests a solar and battery combination to match. For an exact figure, ask your retailer for your smart meter interval data, which shows your use every 30 minutes.
Sizing Your Battery in Five Steps
This is the process our designers follow before recommending a battery. Use it to check any battery quote you receive.
1. Find your overnight use
Smart meter data is the best source. Most retailers show half-hourly usage in their app or can email it on request. Add up what you use from roughly 5pm to 8am on a typical weekday, and check a winter week as well as a summer one. Heating on winter evenings often pushes overnight use up by a third or more.
No interval data? Take your daily use from your bill (total kWh divided by days) and multiply by 0.6 if the house is mostly empty during the day, or 0.4 if someone is usually home.
2. Check your solar can fill it
A battery only saves money on energy it actually stores, and it can only store your surplus: what the panels make after the house has taken what it needs. In winter, Adelaide systems produce far less, so a battery sized to summer surplus can sit half-empty from May to August.
A practical check is about 1.5 kWh of usable battery per kW of panels. A 6.6kW system suits a battery of around 10 kWh. If your solar is smaller than that, consider adding panels at the same time, because more solar usually lifts savings more than more battery.
3. Work within the rebate tiers
The federal Cheaper Home Batteries rebate is paid as small-scale technology certificates (STCs) based on usable capacity. Since 1 May 2026 it pays:
- Full rate on the first 14 kWh
- 60 percent of the rate from 14 to 28 kWh
- 15 percent from 28 to 50 kWh
The rate itself also steps down every six months until 2030. And only one battery system per property can claim it, so you can’t top up later with another rebate. For most homes that makes 13 to 14 kWh usable the best value. Read more on our battery rebate page.
4. Check the power rating, not just the capacity
Capacity (kWh) is how much energy the battery holds. Power (kW) is how fast it can deliver it. A 13 kWh battery that only outputs 3kW will still leave you buying from the grid when the oven, kettle and air conditioner run together at 6pm.
Look for at least 5kW of continuous output for a typical family home. On single-phase power, SA Power Networks allows 10kW of inverter capacity in total, and the battery inverter counts toward it. That’s why a hybrid inverter, which runs both panels and battery, is usually the most efficient choice.
5. Decide on backup and VPPs
Backup. A battery doesn’t automatically keep your lights on in a blackout. It needs a backup-capable inverter or gateway and circuits wired for it. Most backup setups cover essentials like the fridge, lights, internet and a few power points. If backup matters to you, keep 20 to 30 percent of the battery in reserve.
Virtual power plants. Your battery must be VPP-capable to get the rebate, but joining is optional. If you join, the operator may discharge part of your battery to the grid at peak times. That’s worth factoring in if your evenings already use most of your capacity.
Three Adelaide Homes, Three Battery Sizes
The same logic gives different answers depending on usage, solar size and connection.
Working couple, Marion
Existing 6.6kW solar. About 16 kWh a day, with roughly 11 kWh used after 5pm.
Recommendation: a 10 kWh usable battery.
It covers most weeknights and matches what 6.6kW of panels can refill. A 14 kWh battery would rarely fill in winter, so the extra capacity would mostly sit idle.
Family of five, Golden Grove
13.2kW solar on single-phase. About 40 kWh a day, with roughly 22 kWh used overnight in winter.
Recommendation: a battery of 13 to 14 kWh usable, plus running the pool pump and dishwasher in the middle of the day.
Going to 22 kWh would earn only 60 percent of the rebate rate on the extra 8 kWh, and single-phase limits leave little room for a bigger inverter.
Three-phase home with an EV, Mawson Lakes
15.8kW solar on three-phase. About 44 kWh a day, including the EV. Roughly 18 kWh used overnight.
Recommendation: a 14 kWh usable battery, with the EV charged from solar during the day wherever possible.
Charging the car from a home battery at night means storing energy twice. Charging it straight from the panels is cheaper and saves the battery for the house.
Battery Sizing Mistakes We See
Comparing nominal capacity. Two batteries sold as “13 kWh” can differ by more than 1 kWh of usable storage. Ask for the usable figure in writing.
Buying more battery than solar. A large battery on a small solar system spends much of the year partly empty. Upgrading panels often gives a better return.
Chasing the biggest rebate. A bigger battery gets a bigger rebate cheque, but above 14 kWh each extra kWh gets far less support. Size to your nights, not the rebate.
Assuming blackout backup. Backup is an option that has to be designed in, not a default feature.
Forgetting the free midday window. Since 1 July 2026 SA retailers must offer a Solar Sharer plan with free power from 12pm to 3pm, capped at 24 kWh a day. On that plan, a battery can top up from the grid at no cost on cloudy days. Ask us whether it suits your setup.
Adding a Battery to Existing Solar
Most batteries we install in Adelaide go onto a system that’s already on the roof. That works well, with a few checks first:
Your inverter. The inverter your battery connects to must be VPP-capable and on the approved list for the rebate. Older solar inverters can stay and run alongside a separate battery inverter, as long as the total stays within SAPN’s limits.
Your solar size. A 3 to 5kW system from the 2010s often can’t fill a modern battery in winter. Adding panels at the same time usually makes the battery pay back faster.
Your switchboard. Older boards sometimes need an upgrade to meet the battery installation standard. We check this during the site assessment so there are no surprises in the quote.
Frequently Asked Questions
What size battery do I need for my home in Adelaide?
Start with how much electricity you use between sunset and sunrise, then pick a battery with about that much usable capacity. Most Adelaide homes use 8 to 16 kWh overnight, so batteries of 10 to 14 kWh usable are the most common fit.
Is a 10 kWh battery enough?
A 10 kWh usable battery covers the evening and overnight use of a typical Adelaide household using 18 to 22 kWh a day. If you run ducted air conditioning at night, charge an EV in the evening or use more than about 12 kWh after dark, a battery closer to 13 or 14 kWh usually suits better.
What is the difference between usable and nominal battery capacity?
Nominal capacity is the total energy the cells can hold. Usable capacity is what the battery lets you draw before it stops to protect itself, typically 90 to 100 percent of nominal. Always size and compare batteries on usable capacity, because that is what runs your home.
How big should my battery be compared with my solar system?
A battery only helps if your panels can fill it. As a rough check, allow about 1.5 kWh of usable battery for every kW of solar panels. A 6.6kW system comfortably fills a battery of about 10 kWh on most days, while a 13.2kW system can support a battery around 14 kWh or more.
What battery size gets the best federal rebate?
Since 1 May 2026 the Cheaper Home Batteries Program pays the full rate on the first 14 kWh of usable capacity, 60 percent of the rate from 14 to 28 kWh and 15 percent from 28 to 50 kWh. For most homes the best value per kWh is a battery at or just under 14 kWh usable.
Can I add more battery capacity later and still get the rebate?
Usually not. Only one battery system per property can claim the federal rebate, and extra capacity added to a battery that has already claimed it is not eligible. That makes it worth choosing the right size the first time.
Will a battery keep my power on in a blackout?
Only if it is installed with backup. Many batteries can run the home during an outage, but it needs a backup-capable inverter or gateway and the right wiring. Backup usually covers selected essential circuits such as the fridge, lights and internet, not ducted air conditioning or an oven.
Do I have to join a virtual power plant to get the rebate?
No. The battery must be VPP-capable to qualify for the rebate, but joining a VPP is optional. If you do join one, keep a reserve in the battery for your own evening use when deciding on size.
Get a Battery Sized to Your Nights, Not a Guess
Send us a recent bill, or your smart meter data if you have it. We’ll work out your overnight use, check what your solar can refill and recommend a size that makes the most of the rebate. No obligation.
