For most Australian homes, the right size solar battery is between 10 and 13 kWh of usable capacity. That range covers the typical overnight electricity use of a family home with a 6.6 kW solar system and sits in the sweet spot for payback period under the 2025 federal rebate. Smaller homes with two occupants and modest evening usage often do fine with 6 to 8 kWh. Larger households running pool pumps, ducted air conditioning, electric hot water, or an electric vehicle usually need 15 to 20 kWh.
The quick rule is useful, but the right answer for your home depends on four specific numbers: how much power you use between sunset and sunrise, how much surplus solar you export each day, what you want the battery to do, and what changes you expect in the next five years. Get any of those wrong and you either oversize and waste money, or undersize and leave savings on the table.
This guide walks through how to work out the right kWh capacity for your home without guessing.
The quick sizing rule for most homes
As a starting point, you can match battery capacity to daily household electricity usage as follows:
- Small household, 10 to 15 kWh/day total usage: 5 to 8 kWh battery
- Average family home, 15 to 25 kWh/day usage: 10 to 13 kWh battery
- Large household or high usage, 25 to 40 kWh/day: 15 to 20 kWh battery
- Very large or all-electric home with EV: 20 kWh or more
These are usable capacity figures, not nameplate capacity. There is a meaningful difference between the two, which we will cover next.
Remember that a battery is sized to cover overnight load, not total daily load. The solar panels handle daytime usage directly. You only need stored energy for the hours the sun is down, which is usually 40 to 60 percent of daily consumption for a typical Australian home. The energy.gov.au solar and battery guide outlines average household usage profiles if you want a reference point.
What kWh actually means on a battery
Battery manufacturers list two numbers: nameplate (or total) capacity, and usable capacity. These are not the same. A 13.5 kWh nameplate Tesla Powerwall has 13.5 kWh of usable capacity because Tesla rates it that way. Some brands list the larger nameplate number but only let you discharge 85 to 90 percent of it to protect the cells. Always size based on usable capacity.
Depth of discharge (DoD) is the percentage of the battery you can actually use. Most modern lithium iron phosphate (LFP) batteries allow 90 to 100 percent DoD. Older lithium nickel manganese cobalt (NMC) chemistry was often capped at 80 to 90 percent.
A second number to check is the continuous power rating in kilowatts (kW), which is separate from capacity in kilowatt hours (kWh). Power is how fast the battery can discharge; capacity is how much it can store. A 10 kWh battery with a 5 kW continuous rating can run 5 kW of load for two hours, or 2 kW of load for five hours. If you want the battery to run heavy loads like air conditioning during a blackout, the power rating matters as much as capacity.
Step by step: work out your battery size
Step 1: Find your overnight usage
Pull up your last few electricity bills or log into your retailer portal. Most smart meter portals show hourly or half-hourly consumption. Look specifically at usage between roughly 4pm and 9am in summer, or 3pm and 8am in winter. That is the window a battery would cover.
If you cannot get hourly data, a reasonable estimate is that 50 percent of your total daily usage happens outside solar hours for homes without pool pumps or ducted AC, and 60 to 65 percent for homes with both. A house using 25 kWh/day total would therefore need the battery to cover 12.5 to 16 kWh overnight.
Step 2: Check your solar generation
A battery can only store what your solar system produces in excess of daytime load. A 6.6 kW solar system in southeast Queensland generates around 26 to 30 kWh on a sunny day, less in winter or cloudy weather. If your daytime load is 10 kWh, you have 16 to 20 kWh of surplus available for the battery, assuming you export nothing. The Australian PV Institute live map shows real-time solar output by region if you want to sanity check your own numbers.
In winter, or across multiple cloudy days, a battery may not fully charge. This is why a slightly larger solar array often pairs better with a battery than a larger battery paired with an undersized array. Many homes are upgrading 5 kW systems to 10 kW when they add a battery, which transforms the economics. If your current solar system is more than seven or eight years old, this is the right moment to look at both together.
Step 3: Decide what you want the battery to do
A battery can serve three different jobs, and each influences sizing:
- Daily cycling (most common): store surplus solar by day, discharge through the evening. Sized to cover overnight load.
- Blackout backup: keep essential circuits running during grid outages. Usually sized for 24 to 48 hours of essentials like fridge, lights, internet, and a few power points. Essential-load-only backup needs less capacity than whole-home backup.
- Time-of-use arbitrage: charge from the grid at off-peak rates and discharge at peak. Not relevant for most solar-paired batteries.
If backup is a priority, make sure you choose a battery and inverter combination with backup capability. Not all setups include it by default. For homes in storm-prone parts of southeast Queensland, this is worth paying for, and worth having an emergency electrician on call for anything outside the battery’s scope.
Step 4: Factor in the next five years
Your energy demand is probably going to rise, not fall. An electric vehicle adds 3,000 to 5,000 kWh per year of charging demand. Replacing gas with electric cooking and a heat pump hot water system adds 2,000 to 3,000 kWh. Going fully electric in a typical home can easily double your electricity consumption.
If any of those changes are on the horizon, size the battery for where you will be in three to five years, not where you are now. Undersizing is easier to regret than oversizing, because you cannot always stack a second battery without further inverter and electrical work.
Matching battery size to solar system size
Battery and solar should be matched so the battery can charge fully on an average solar day and discharge fully overnight. A useful ratio is roughly 1 to 1.5 between battery kWh and solar system kW.
- 6.6 kW solar: 10 kWh battery
- 10 kW solar: 13 kWh battery
- 13 kW solar: 15 to 20 kWh battery
If your battery is larger than your solar can reliably charge, you will end up pulling grid power to top it up, which kills the savings. If your battery is smaller than your solar surplus, you will export a lot of excess energy for very little feed-in return. The Clean Energy Council battery consumer guide covers sizing and pairing principles in more detail.
If you are unsure whether your existing solar array is enough, this is the point to have an installer pull generation data from your inverter rather than guess.
Worked examples for common Australian homes
Example 1: Young couple, no kids, no pool, 6.6 kW solar. Daily usage 14 kWh, evening usage around 7 kWh. Plan to stay long term and may buy an EV in three years. Recommended size: 10 kWh usable battery. Leaves room for growth without needing to expand.
Example 2: Family of four, ducted AC, pool, 10 kW solar. Daily usage 32 kWh, evening usage around 18 kWh. Planning to replace gas stove with induction next year. Recommended size: 15 to 20 kWh. A 13 kWh battery would cover most evenings but fall short on AC-heavy summer nights.
Example 3: Retired couple, single-storey home, 5 kW solar. Daily usage 11 kWh, evening usage around 5 kWh. No plans to add EV or change major appliances. Recommended size: 6 to 8 kWh. A larger battery would not meaningfully improve savings and would extend payback unnecessarily.
Example 4: Work-from-home family with EV, 13 kW solar. Daily usage 40 kWh including EV charging. Recommended size: 20 kWh battery, or a 13 kWh battery paired with smart EV charging set to daylight hours. In most cases the second approach is cheaper than oversizing the battery. The economics of each route are covered in our guide on how much solar batteries cost in 2026.
Common sizing mistakes that cost money
Sizing on total daily usage instead of overnight usage. Leads to batteries that are 40 to 60 percent oversized. The extra capacity never gets used, but you paid for it.
Ignoring solar output on cloudy days. Sunny-day averages overestimate how often the battery fills up. Check winter averages too, not just summer peaks.
Forgetting switchboard compliance. An older switchboard may not safely connect to a large battery. This adds cost to the project but is sometimes overlooked at the sizing stage. If yours has fuses instead of circuit breakers or looks 20 years old, a switchboard upgrade may be required alongside the battery install.
Assuming every kWh of battery saves you the full import price. Roundtrip efficiency losses are typically 5 to 10 percent on modern batteries. A 10 kWh discharge actually required 10.5 to 11 kWh of solar to store. Small, but it matters when running precise payback numbers. If you want the underlying financial case first, our post on whether solar batteries are worth it covers that side in detail.
Chasing blackout backup without checking the inverter. Backup capability depends on the inverter, not just the battery. A battery without a backup-rated inverter cannot keep your home running through an outage, regardless of capacity.
Related questions
What size solar battery for a 6.6 kW solar system?
For a standard 6.6 kW solar array on an average family home, a 10 kWh usable battery is the most common and best-matched size. It captures most of the daily surplus and covers typical overnight load.
What size solar battery for a 10 kW solar system?
A 10 kW solar system pairs well with a 13 to 15 kWh battery for most households. If you have an EV, pool, or all-electric appliances, bump that to 15 to 20 kWh.
Can a solar battery be too big?
Yes. Oversizing happens when the battery cannot be filled by your solar array on an average day, or cannot be discharged before the next solar charging window. Both leave capacity sitting unused while you continue to pay for it.
Do I need a bigger battery if I have an electric vehicle?
Usually yes, but not always. A smarter approach is to schedule EV charging for daylight hours when solar is generating, which reduces the need for evening battery discharge into the car. Most modern EVs and home chargers support time-based charging natively.
How many kWh does an average Australian home use per day?
Around 16 to 20 kWh/day for a standard home, 25 to 35 kWh/day for larger families or all-electric homes, and 40 kWh or more for homes with EVs or pools. Check your actual bill for a real figure before sizing a battery.
Can I add more battery capacity later?
Some systems allow stacking additional battery modules with the same inverter. Others require a full separate inverter for a second battery, which adds significant cost. Ask about expandability at the sizing stage if you are uncertain about future needs.
The short answer
If you want a single number to start with, most Queensland family homes land at a 10 to 13 kWh usable capacity battery paired with a 6.6 to 10 kW solar system. That combination covers evening load, fits the 2026 federal rebate structure well, and has the best payback profile for average Australian usage patterns.
Before you commit, check your actual overnight usage from your bill or smart meter portal, confirm your solar system is large enough to charge the battery on average days, and think about how your electricity demand will change in the next few years.
If you want this mapped specifically to your home rather than averages, Essence Electrical runs a battery sizing assessment based on actual usage data, existing solar output, and future plans before quoting. Get in touch if you want that done properly.