The right battery is sized for your evening and overnight use, not the biggest unit on the shelf. Go too small and you keep buying peak-rate power. Go too big and you pay for storage your solar can’t fill, while the federal rebate pays less on every kWh above 14. Here’s how to find your number before you ask for a quote.
How big a battery do most Victorian homes need?
Most homes land between about 10 and 14 kWh of usable capacity. That covers the evening and overnight for a household using 15 to 20 kWh a day, which is the typical Australian range according to CHOICE.
It’s also the band where the federal rebate pays in full. The first 14 kWh of usable capacity gets 100% of the certificate factor, so a battery up to that size is the simplest to price.
Victorian battery buyers also skew towards heavier electricity users. In Solar Victoria’s study of more than 4,400 sites, homes with batteries used about 30% more electricity than other Solar Homes Program sites, so don’t assume your household is average.
Your own number can sit well outside it. A couple who are out all day may need far less. A large home with ducted heating, an EV or a pool may need more. The next sections show how to work it out.
One trap first: size on usable capacity, not the headline number. Nominal capacity is the battery’s total physical size. Usable capacity is what you can actually draw. A battery sold as 10 kWh might offer 9 kWh. The rebate is calculated on usable capacity too, so ask for that figure in writing.
How do you work out the right size for your home?
Start with how much power you use after the sun goes down. That’s the energy the battery has to supply each night, and it’s the number that decides your size.
Find your daily use. Your bill shows an average daily kWh figure. Check 12 months of bills, not one, because Victorian homes use more in winter.
Estimate your night share. SolarQuotes founder Finn Peacock, speaking to CHOICE, says a household out from nine to five uses roughly 70% of its power at night. If someone is home all day, your share will be lower.
Multiply. Daily use x night share = the kWh your battery would need to cover the whole night.
Check it against real data. A smart meter records your use in intervals. Your distributor can supply the file (called a NEM12 file), which shows exactly what you use after sunset.
Working example: a home using 18 kWh a day, with everyone out during the day, uses about 12.6 kWh at night (18 x 0.7). A battery with 12 to 13.5 kWh of usable capacity would cover most of the night.
You don’t have to cover all of it. A slightly smaller battery that handles the expensive evening peak, with the grid topping up late at night, can be better value than chasing a zero-power bill. Add your future plans to the sums: an EV, a heat pump hot water system or a growing family all push the number up. Our 5 signs your home is ready for a battery guide helps you check the fit first.
What size suits what kind of household?
Match the size to your daily use, then adjust for who is home and what you plan to add. These starting points assume 50% to 70% of your daily use happens after dark. They are a guide for the conversation with your installer, not a quote.
About 10 kWh a day (a couple who are out most days): you’ll use roughly 5 to 7 kWh at night, so start with a 5 to 7 kWh battery.
About 15 kWh a day (a small family, or a couple working from home): night-time use is roughly 7.5 to 10.5 kWh, so start with 8 to 10 kWh.
About 20 kWh a day (a family of four): night-time use is roughly 10 to 14 kWh, so start with 10 to 13.5 kWh.
30 kWh a day or more (a large home with ducted heating or cooling, an EV or a pool): night-time use is 15 kWh or more, so size it quote by quote.
The top row is the one people over-buy. A battery you can’t empty each night earns less than you expect. The bottom row is where a real usage assessment matters most, because the rebate steps down above 14 kWh and your solar may not be able to refill a larger battery. The next two sections cover both.
How do the rebate tiers change the best-value size?
The rebate pays in full up to 14 kWh, then drops sharply. Under the federal Cheaper Home Batteries Program, the Clean Energy Regulator applies the certificate factor in bands of usable capacity:
the first 14 kWh gets 100% of the rebate
14 to 28 kWh gets 60% of the rebate
28 to 50 kWh gets 15% of the rebate
nothing is paid above 50 kWh
Will your solar system fill the battery?
Only if it produces more than your home uses during the day. A battery fills from your surplus, so the useful number is your daily export, not your panel size.
Victorian data shows how much surplus there is to work with. In Solar Victoria’s study, solar-only households used about 29% of the solar they generated and exported the rest. Homes with a battery used about 57%. Battery homes also had bigger systems, averaging 8.06 kW of panels against 6.51 kW for solar-only homes.
Check your monitoring app or bills for your average daily export across the whole year. Summer flatters the numbers. CHOICE warns against sizing on summer data and then being caught out in winter. Victorian households also use more electricity in winter than in summer, just when solar output is lowest, so check your winter export before you settle on a size.
If your export is smaller than the battery you want, you have three options: choose a smaller battery, add panels (our solar cost guide shows how system sizes are priced), or top up from the grid. Some retail plans offer free or cheap midday power, which can charge a battery on dull days. See our Midday Power Saver guide for how that works in Victoria.
Shifting appliances such as the dishwasher and washing machine into solar hours also changes how much storage you need. Our solar usage optimisation guide covers it.
Is a bigger battery always better?
No. Unused capacity is money spent for nothing. SolarQuotes puts installed battery costs at roughly $500 to $800 per kWh after the rebate, as reported by CHOICE, so every kWh that never gets used adds up fast. Our battery ROI guide shows how payback changes with size.
Going too small has a cost as well. If the battery is empty by 9pm, you’re buying evening peak power again, which is the very thing you installed it to avoid.
Capacity isn’t the only number. The inverter’s power rating (in kW) controls how fast the battery can charge or discharge. CHOICE gives the example of a 20 kWh battery with a 5 kW inverter, which can only supply 5 kW at a time. If your home draws more at that moment, the rest comes from the grid. Ask for both figures.
Can you start small and add more later? It depends on the system. Modular batteries let you add modules, while single units don’t. The rebate allows one battery per premises, and stackable systems can claim certificates only on the new modules. Ask your installer how both rules apply before you decide.
Does joining a VPP change the size? It can. CHOICE notes that trading power takes more capacity than your own home uses, which costs more now that the rebate pays less above 14 kWh. A virtual power plant also shares control of your battery and cycles it harder. Size for your home first, then decide whether VPP income justifies any extra. CHOICE’s VPP pros and cons guide is a good independent read.
How Sunrise Sizes a Battery
We start with your usage, not a product list. Our team looks at your bills or smart meter data, your night-time load, your solar export and what you plan to add, then prices more than one size so you can see the trade-off. Sunrise is CEC-accredited and Solar Accreditation Australia (SAA) accredited with a battery endorsement, which the rebate requires.
Two recent designs show the scale we pair with solar. A Clyde North home has 6.65 kW of panels with a 15 kWh battery, and a Highett home has about 10 kW of panels with a 15 kWh battery. Both include the ZeroHero VPP program in their design. Whether a 15 kWh battery sits inside the 14 kWh full-rebate band depends on its usable capacity, which is why we quote usable figures. The Highett design projects an 88% cut in electricity costs. These are design projections from our project files, not measured results.
We recommend systems from Tesla, Sigenergy and AlphaESS, compared in our best solar and battery systems guide, and you can see what we install on our products page. Batteries carry a 10-year warranty, and after installation we deliver the Certificate of Electrical Safety within 10 business days and monitor performance daily for the first three months.
Sunrise Innovations Verdict: For most Victorian homes, the best-value battery is the one that covers your evening peak and fits inside the first 14 kWh, where the rebate pays in full. Go larger only if your night-time use, your solar export and your plans (an EV, a heat pump, a bigger household) justify paying more of the cost yourself. If you’re installing before 1 January, the rebate factor is 6.8. After that it falls to 5.7.
What should you check before you buy?
Your average daily use across 12 months of bills, or your smart meter data
How much of it happens after dark
Your daily solar export, including winter
The battery’s usable capacity and inverter kW rating, in writing
The rebate value and installation date assumed in your quote
Any plans that will change your use, such as an EV or heat pump hot water
Quick Answers
Q: Is a 10 kWh battery enough? A: Often, if your night-time use is around 10 kWh or less and your solar can refill it. Check your own data rather than the average.
Q: Does the rebate use nominal or usable capacity? A: Usable capacity. Ask your installer for that figure and for the certificate value in your quote.
Q: Does a bigger battery get a bigger rebate? A: Yes, but each kWh above 14 earns only 60% of the factor, and above 28 kWh only 15%.
Q: Should I add extra capacity for blackout backup? A: Maybe. Backup needs the right equipment and wiring, and a reserve of stored power. Decide it with your installer before you settle on a size.
Get a Battery Sizing Check for Your Home
We’ll look at your usage, solar export and plans, show you more than one size, and give you a realistic installation date. Request a battery quote, try the energy savings calculator, or read what past customers say. Already have solar? See how to add a battery to existing solar.