Choosing the right solar battery size is one of the most important parts of getting good value from your solar and battery system. Too small, and you may run out of stored solar power early in the evening. Too large, and you may pay for storage capacity your home rarely uses.

For many Brisbane, Redlands, Logan, Ipswich and Bayside homes, the most common battery sizes customers ask about are 10kWh, 20kWh, 32kWh and 40kWh. The right choice depends on your night-time power usage, solar system size, backup power expectations and whether your home is likely to add higher loads such as electric vehicle charging in the future.

Start with how much power you use at night

Solar batteries are mainly used to store excess solar power from the day so you can use it later in the afternoon, evening and overnight. That means the best battery size is not just based on your total daily usage. It is based on how much power your home uses when your solar panels are no longer producing enough to cover the load.

A home that uses most of its power during the day may not need a very large battery. A home that runs air conditioning, cooking appliances, pool equipment, entertainment systems or EV charging in the evening may benefit from more storage.

10kWh, 20kWh, 32kWh and 40kWh solar batteries compared

The table below is a general guide for Brisbane and Redlands homeowners comparing the most common battery sizes people ask us about.

Is a 10kWh battery enough?

A 10kWh battery can be a good option for smaller homes, couples, retirees or households with moderate evening power use. It may help cover basic night-time loads such as lighting, refrigeration, Wi-Fi, television and some general power usage.

Where a 10kWh battery can fall short is in homes with heavy air conditioning use, pool equipment running late in the day, larger families, electric cooking or customers wanting more backup power during outages.

Is a 20kWh battery a good size?

A 20kWh battery is often a strong option for larger family homes because it provides more usable storage without jumping straight into a very large battery system. This size may suit homes that regularly use power in the evening and want to capture more of their daytime solar production.

For many Brisbane and Redlands homes with a suitable solar system, 20kWh can be a practical balance between storage capacity, cost and everyday usefulness.

When does a 32kWh battery make sense?

A 32kWh battery is generally suited to high-usage households, larger homes, properties with bigger solar systems, or customers wanting more backup flexibility. It may also suit homes planning for EV charging or future electrification.

The important point is that a 32kWh battery needs to be designed properly. If the solar system is too small, heavily shaded or already using most of its production during the day, the battery may not charge as expected.

Who should consider a 40kWh battery?

A 40kWh battery is usually for homes with very high power usage, larger families, bigger solar systems, EV charging, or customers wanting a premium backup power setup. It can also suit properties where future energy use is expected to increase.

With a battery this size, design matters. The installer should check your solar production, inverter limits, switchboard condition, available space, backup requirements and usage pattern before recommending a 40kWh system.

Do not choose a battery size based only on the rebate

Battery rebates can make larger batteries more attractive, but the best battery is still the one that suits your home. A bigger battery is only useful if your solar system can charge it and your household can actually use the stored energy.

Before deciding on a system size, it is worth comparing your estimated rebate across different battery capacities. You can use our Solar Battery Rebate Calculator for Brisbane and Redlands to get a quick estimate.

We have also written a separate update explaining the battery rebate changes from 1 May if you want to understand how rebate timing may affect your installation.

Backup power can change the right battery size

If your main goal is to reduce your power bill, your ideal battery size may be different from someone who wants backup power during blackouts. Backup power should be designed around what you want to keep running, such as lights, fridge circuits, Wi-Fi, selected power points, garage doors or essential appliances.

Not every battery installation automatically backs up the whole home. In many cases, selected backup circuits are wired separately. Your switchboard condition, available space, existing circuits and compliance requirements can all affect the final design.

If your home has an older switchboard or you are planning a larger battery system, it may be worth checking whether a switchboard upgrade is needed as part of the installation.

Make sure your solar system can charge the battery

One of the biggest mistakes is installing a large battery without checking whether the solar system can charge it properly. If your solar system is too small or your home already uses most of the solar power during the day, there may not be enough excess solar to fill a larger battery.

The bigger the battery, the more important it becomes to review solar panel capacity, inverter setup, roof space, shade, export limits and household usage data.

So, what size solar battery do you need?

As a general guide, a 10kWh battery may suit smaller or lower-usage homes. A 20kWh battery may suit many larger family homes wanting more stored solar available overnight. A 32kWh battery can suit higher-usage homes, EV charging or stronger backup needs. A 40kWh battery is usually best for very high-consumption homes or premium backup power setups.

The right answer depends on your actual power usage, solar production, backup expectations and the condition of your existing electrical setup. That is why battery sizing should be done as part of a proper system design, not just by choosing the biggest battery available.

Solair Electrical installs solar battery systems across Brisbane, Redlands, Logan, Ipswich, the Gold Coast and Sunshine Coast. You can learn more about our solar battery installation services in Brisbane and Redlands or use our calculator to compare estimated rebate values by battery size.