The right size battery for your home depends on your daily usage, and how much support you need during the evening when your solar isn't generating. If your battery is too small, you'll be pulling from the grid during the night, but if it's too big, you'll be paying too much for a capacity that you can't fill. Below we walk through exactly how to pick the right size for your home, based on usage and budget — including how the WA Residential Battery Scheme works in your favour.
Why Battery Size Matters More Than You'd Think
A battery is only as useful as the solar it can soak up during the day and the grid power it can replace at night. Oversize it and it sits half-empty — you've paid for capacity that never gets cycled. Undersize it and you're still buying power from Synergy at 32.37 c/kWh in the evening, even while your panels were dumping cheap energy to the grid at 2 c/kWh during the day (Synergy, 2025). You should also consider factors such as your bill size, the existing age and size of your system, and your usage patterns.
Bill size: If you have a larger bill, with high electricity usage, you'd likely benefit from a larger battery. But if you have a small power bill and opt for a large battery, it can potentially not fill — meaning you're not getting bang for your buck.
Existing age and size of system: When purchasing your battery, you should consider whether additional panels are needed to support optimal power savings. If you have high usage and are pulling from the grid more frequently, additional support may be needed for your home's electricity supply, which would also help fill your battery quicker during the day.
Usage patterns: It's important to consider how much electricity you're using, and when. This comes back to how much you're paying, because if you're constantly pulling from the grid during peak hours your bill will be high. By having a battery, your reliance on the grid is reduced, using your own power more consistently and ultimately reducing your bills. This could also come down to the energy tariff you're on — you should consider your usage and whether changing tariffs would help you save more money.
The sweet spot for a battery is one that covers your usage during peak hours and overnight, using that precious sunny energy to reduce your bills.
Step 1: Work Out Your Evening and Overnight Usage
Let's start with your previous Synergy bill. Typically, the average daily usage of energy in Australia is between 10-15kWh for a single-person household, or anywhere between 25-30kWh for a family of four. This can vary depending on the size of your home, and whether you have a pool, reverse-cycle air conditioning or other appliances that will ultimately increase your bill.
During the hours of 3pm-9pm electricity usage spikes, and the cost to use energy from the grid during peak times is higher. From the usage on your bill, and compared to other bills, we can determine the best battery size.
Step 2: Match the Battery to Your Solar System
Your battery can only store what your solar can produce. There's no point getting a battery and having to use the grid to fill it up because your panel generation isn't large enough to support the system. The most common battery size homeowners have is 10kWh-14kWh, meaning a 6.6kW-10kW solar system is required to support optimal power storage.
It's important to remember that this will differ for each home — some homes may need additional panels to support a specific battery size they've requested. If you're unable to match the battery to your solar system, you should consider how changing your energy tariff will benefit your savings.
Quick Sizing Guide by Household Type
The right number for your home depends on whether you want backup power during outages, whether you've got an EV, and how much of your daily load happens after dark. These factors will impact how large a battery you should acquire to reduce your bills as much as possible without paying too much for a capacity you can't fill.
This also comes down to your usage. You should consider how much energy you're using, and when you're using it. This will help determine the best size battery to suit your energy needs and energy independence.
Step 3: Factor in the WA Battery Rebate
The WA Residential Battery Rebate Scheme has been in place since July 1st 2025, offering a reduced price for homeowners acquiring a battery. This scheme includes the WA state rebate and the federal rebate. The state rebate offers Synergy customers $130 per kilowatt-hour of battery capacity up to 10kWh, reducing the cost by $1,300. For Horizon Power customers, the government is offering $380 per kilowatt-hour, reducing the cost by $3,800.
Recent changes to the federal rebate have been made. This price point will differ by a certain percentage based on battery size.
To be eligible, you must be a WA resident over the age of 18, a permanent resident and Synergy customer, and own the home. The battery must be installed by an SAA-accredited installer and use products from the Clean Energy Council Approved Battery list. To receive the state rebate you will need to be part of a Virtual Power Plant (VPP).
Please note: A home is not eligible for rebates twice.
Step 4: Think About the Future, Not Just Today
When applying and receiving quotes for your home battery, it's important to consider your home in the future. Will you get a pool? Are you interested in improved aircon for summer? Do you need a heat pump?
These are all questions you should be asking yourself when looking into a battery, because once you exhaust the rebate, you can't use it again. Meaning, if you need more electricity stored to support the future of your home, you'll be paying full price.
Frequently Asked Questions
Is a bigger battery always better?
Not necessarily. Your battery size comes down to how much energy you're using and how much you need supporting during the evening. Sometimes, it's best to have a little bit left in the tank for those cloudy mornings where solar generation is delayed, helping you reduce those bills as much as possible.
Can I add a battery to my existing solar system?
Yes, and it's very common. Most modern batteries are AC-coupled, meaning they can be retrofitted to any existing solar setup without replacing your inverter. Our team can assess your current system and recommend a compatible option.
What about backup power during blackouts?
If blackout protection is important to you (protecting your fridges, Wi-Fi and essential home needs), look for a battery that includes this. Some batteries require additional hardware for blackout protection and don't automatically come with it, so it's worth flagging during the quoting process. This way you can get the best possible battery to suit your needs.
How long do batteries last?
Modern lithium-ion solar batteries have a lifetime of 12-14 years. If mistreated, lifespan can reduce, but if treated with care and if the guidebook is followed, your solar battery will have a long life.
Not sure which size is right for your home? Send us a recent Synergy bill and we'll size a battery to your actual usage, your solar system and your goals — including the full WA and federal rebate breakdown. Free, no-obligation. Call 9300 9324 or request a quote online at solaireconnect.com.au/get-a-quote.
References
Government of Western Australia. (2025). WA Residential Battery Scheme — Information for Applicants. https://www.wa.gov.au/government/wa-residential-battery-scheme-information-applicants
Synergy. (2025). Standard Electricity Prices and Charges — South West Interconnected System. https://www.synergy.net.au
Australian Government. (2025). Cheaper Home Batteries Program.
SolarQuotes. (2025). Solar Batteries: Lifespan. https://www.solarquotes.com.au/blog/solar-batteries-lifespan/
Esteem Energy. (2025). Average Electricity Bill Perth. https://esteemenergy.com.au/average-electricity-bill-perth/