20kW Solar Battery Price in Australia
A 20 kWh battery is roughly double what an average household needs, which makes it either an excellent decision or an expensive mistake depending on your situation. This guide covers what it costs, who genuinely benefits from that capacity, and when two smaller units make more sense than one large one.
A 20 kWh battery suits households using 35 kWh or more a day, properties with three phase supply, homes charging an electric vehicle overnight, or anyone wanting extended blackout coverage. Below roughly 30 kWh of daily use, the extra capacity sits idle most nights and the payback stretches out accordingly.
Who a 20 kWh battery actually suits
Capacity only earns its keep if it gets cycled. A battery that never drops below 60% charge is carrying weight it isn't paid for, so the question isn't whether bigger is better but whether you'll use it.
Five or more people, multiple bathrooms and consistently high evening load. Daily consumption above 35 kWh is the usual trigger.
A single overnight charge can draw 20 to 40 kWh on its own, which changes the sizing conversation entirely.
Properties in areas with frequent or extended outages, where running longer on essential circuits matters more than payback.
Workshops, home offices with server equipment, or any setup running significant load outside daylight hours.
Fully electrified homes with heat pumps and reverse cycle carry far more load than gas-connected properties.
A 13 kW or larger array generates more surplus than a 10 kWh battery can absorb, so capacity matches generation.
When 20 kWh is the wrong answer
Households using under 30 kWh a day rarely cycle the full capacity, which means paying for storage that sits idle. In those cases a 13.5 kWh unit covers the evening load and comes in considerably cheaper, with the option of adding modules later if usage grows.
What a 20 kWh battery costs installed
Indicative figures before any state incentives. Switchboard upgrades, structural mounting and outdoor enclosures are priced separately where required.
The cost per kilowatt hour drops at this size
Installation labour, grid connection paperwork and inverter work barely change between a 10 kWh and a 20 kWh system. Spread across double the capacity, the rate per kilowatt hour comes in noticeably lower, which is the main financial argument for going larger if you'll use it.
One large battery or two smaller ones?
Twenty kilowatt hours can be delivered as a single unit or as stacked modules, and the choice affects more than price.
Modular stacking
Most tier-one brands build 20 kWh from stackable modules on a single inverter. That keeps installation simpler, uses one warranty, and lets you start at 13.5 kWh and expand later. For the vast majority of homes this is the sensible route.
Two separate systems
Occasionally worth considering where the property has three phase supply and you want redundancy, or where physical space forces the units apart. It costs more overall, since you're duplicating inverter and connection work, though it does mean a single failure doesn't take out all your storage.
Distributors cap how much you can export to the grid, and in some networks that limit is low enough to change what system size makes sense. A large battery paired with a large array can hit those limits sooner than expected.
We check your distributor's current limits as part of the assessment, because designing a system that can't legally export its surplus wastes capacity you paid for.
How long 20 kWh actually runs
After depth of discharge, a 20 kWh battery gives roughly 18 kWh usable. What that covers depends entirely on what you're running.
Runtimes assume steady draw. Real consumption fluctuates, and inverter output limits may cap how fast the battery can discharge regardless of capacity.
Our calculator shows how much of your evening load it would cover, plus runtime and blackout backup time.
Open the calculatorOutput matters as much as capacity
A large battery on an undersized inverter is a bottleneck. Capacity determines how long you run; output determines what you can run simultaneously.
Why this bites on larger systems
Households buying 20 kWh usually have the load to match, which means aircon, oven and hot water potentially running together. If the inverter caps at 5 kW output, the battery can't supply more than that regardless of how much it holds, and the shortfall comes from the grid. Check the continuous output rating, not just the storage figure.
What should be in the quote
- Battery modules, mounting and any required enclosure
- Hybrid inverter sized for both capacity and output
- Continuous and peak output ratings stated clearly
- All cabling, isolation and circuit protection
- Switchboard assessment with upgrade costs disclosed
- Backup circuit wiring and which circuits are covered
- Distributor approval and export limit confirmation
- Commissioning, testing and monitoring setup
Frequently asked questions
Sizing, pricing, runtime and whether bigger is worth it.
How much does a 20kW solar battery cost?
Installed cost depends mainly on whether your existing inverter can handle both the capacity and the output, and whether the switchboard needs work. The rate per kilowatt hour comes in lower than a 10 kWh system since the labour and connection costs are spread across double the storage. A fixed quote follows the site assessment.
Do I need 20kWh of storage?
Only if you'll cycle it. Households using 35 kWh or more a day, charging an EV at home, or running fully electric heating and hot water will use the capacity. Below around 30 kWh daily, a 13.5 kWh battery usually covers the evening load at considerably less cost.
How long will a 20kWh battery run my house?
Around 18 kWh is usable after depth of discharge. At a typical evening draw of 1.5 kW that lasts roughly twelve hours, comfortably covering from sunset to morning. On essential circuits only during a blackout, it stretches past two days.
Can I start smaller and expand to 20kWh later?
With modular systems, yes. Most tier-one brands stack modules on a single inverter, so starting at 13.5 kWh and adding capacity later is straightforward. Fixed-capacity units can't be expanded, which is worth confirming before committing if your usage is likely to grow.
Will a 20kWh battery charge my EV?
Partially. A 7 kW home charger draws down 18 kWh of usable storage in about two and a half hours, which covers a typical daily commute but not a full charge from empty. Most EV owners charge from solar during the day and use the battery for household load instead.
Send us your address and usage, and we'll confirm whether the capacity suits your load before quoting.
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