A solar battery can transform how much value you get from your panels, but only if it is the right size. Too small and you still rely on expensive evening power. Too large and you pay for storage you rarely use. At Steadfast Solar, we design battery systems around the way South Australian homes actually use energy. This guide explains how to choose wisely.
Key Takeaways
- Size your battery around your evening and overnight energy use.
- Your solar system must be large enough to charge it.
- Most homes suit a 13 kWh to 14 kWh battery.
- Bigger batteries cost more and may take longer to pay back.
- Backup power and plans can change the ideal size.
Why Battery Size Matters
Home batteries are booming across Australia. ChannelNews reported that 85,000 home batteries were sold in the first half of 2025, nearly three times the level of a year earlier.
However, more households buying batteries does not mean everyone is buying the right size. An analysis republished by Startup Daily found that the average battery installed under the federal program was more than 22 kWh, while the government considers 4 to 14 kWh typical for a regular household.
An oversized battery ties up money in capacity you may never use. An undersized one leaves you buying grid power every evening. Getting the balance right is what delivers the best return.
Step 1: Measure Your Evening and Overnight Usage
Your battery's main job is to power your home after the sun goes down. So the most useful number is how much electricity you use between late afternoon and the next morning.
To estimate this:
- Check your power bill for your average daily usage in kWh.
- Log in to your retailer's online portal to view hourly or half hourly data.
- Add up usage from around 5 pm to 7 am.
- Consider seasonal changes, as heating and cooling can increase evening use.
Usage patterns have a big impact on returns. The Australian Energy Market Commission analysed real hourly data from 1,000 households and found that evening peak and high usage households see the fastest battery payback.
Step 2: Match the Battery to Your Solar System
A battery is only useful if your panels can fill it. Your solar system needs to cover your daytime usage and still have enough surplus to charge the battery.
As a general guide:
- 13 kW to 15 kW Solar: Often suits a battery of around 13 to 15 kWh
- 15 kW and Above: May support a larger battery of 15 kWh or more
Winter is the real test. Shorter days mean less solar, so a very large battery may not fully charge for several months of the year.
Low export payments also make storage more attractive. Using your own solar matters more than ever.
Common Battery Sizes and Who They Suit
Solar battery capacity varies depending on household size, electricity consumption and backup requirements. Understanding common battery sizes can help you choose storage that suits your energy needs without paying for unused capacity.
- 13 to 14 kWh: Typical families with moderate evening use
- 15 to 20 kWh: Larger homes, high evening use or ducted air conditioning
- 20 kWh and Above: All electric homes, EV owners or those wanting extended backup
Step 3: Think About the Economics
A larger battery usually costs more upfront, and the extra capacity does not always pay for itself.
Research has explored this trade off for many years. A study of Australian households, presented at an IEEE conference and listed by Analysis and Policy Observatory, found that the maximum battery cost at which storage makes financial sense falls as battery capacity rises. It also highlighted how deep discharge cycles affect battery life.
The solar and battery rebate structure also matters. The federal discount is now tiered, with smaller batteries receiving the full rate and larger capacities receiving less.
Step 4: Decide Whether You Need Backup Power
Many people buy a battery to keep the lights on during outages. However, not every battery system provides backup automatically.
As Open Forum explains, a battery needs an inverter that supports backup operation and an automatic transfer switch to power a home during a blackout. The article also cites an average home battery size of 17 kWh.
If backup is important to you, consider:
- Which essential circuits you want to keep running
- How long outages typically last in your area
- Whether you need power for medical equipment or a home business
- How much reserve capacity to hold for emergencies
Step 5: Consider Virtual Power Plants
South Australia has a long history of linking home batteries together. Utility Magazine reported on one of the first virtual power plant rollouts in Adelaide homes back in 2016. The model has grown since then.
Virtual power plants connect participating home batteries to coordinate energy storage and supply. Depending on the programme, households may receive financial incentives for allowing their stored electricity to support the wider grid. Before joining, check participation requirements, battery control arrangements and potential benefits to ensure the programme suits your household’s energy needs.
Step 6: Plan for the Future
Think about how your energy use may change over the next 10 years:
- Switching from gas to electric heating or cooking
- Installing a heat pump hot water system
- Buying an electric vehicle
- Growing family or working from home
- Adding a pool or air conditioning
Modular batteries can be a smart option, allowing you to start with a smaller capacity and add more later.
Signs Your Battery Is the Wrong Size
- Too Small: The battery runs flat before midnight most days.
- Too Large: The battery rarely charges past 60 or 70 per cent.
- Poorly Matched: You still export lots of solar while buying evening power.
Get a Tailored Recommendation
The best way to choose a battery is to review your actual usage data, solar output and plans. A tailored design avoids paying for capacity you do not need.
At Steadfast Solar, ANYTIME Solar and Battery Plan offers $0 deposit, no upfront installation, so you can start saving before you start paying.
Conclusion
The right solar battery size depends on your evening usage, solar system and plans. For many South Australian homes, a 13–14 kWh battery may be suitable, though some households need more. Choosing carefully can help improve payback and reduce electricity bills. Contact us today for a battery recommendation tailored to your home.
FAQs:
1. What size solar battery do I need for my home?
Most homes may suit a 13–14 kWh battery, depending on evening and overnight electricity usage and the size of their solar system.
2. Is a 13–14 kWh battery enough for a house?
A 13–14 kWh battery can suit many typical families, covering a significant portion of their evening and overnight electricity usage.
3. How long will a 13–14 kWh battery last overnight?
It depends on household usage, but a 13–14 kWh battery can often run essential appliances for most of the night.
4. Can I add more battery capacity later?
Many modular batteries allow expansion, but you should confirm compatibility with your installer before purchasing.
5. Does a solar battery work during a blackout?
Only if the system includes backup capability, such as a compatible inverter and an automatic transfer switch.
6. Is a bigger battery always better?
No. An oversized battery costs more and may rarely charge fully, which can slow your payback period. The right capacity should match your household's energy consumption.
