Fast read
Getting the right size for your home battery is all about understanding how much electricity you use, especially in the evenings, and what you want your battery to do. Whether you're looking to slash energy bills, protect against blackouts, or maximise your solar self-use, battery sizing needs to match both your goals and your energy profile.
Most Australian homes choose batteries between 5 kWh and 15 kWh. As a rough guide, aim for storage that covers your evening usage or about 25– 50% of your daily consumption. But for the best results, look at your energy bills, solar generation, and future needs—or talk to an accredited installer for tailored advice.
How to work out what size home battery you need?
Choosing the right battery size is crucial. Go too small and you’ll run out of stored energy when you need it most. Go too large and you could spend thousands on unused capacity. Sizing is especially important if you want to:
- Maximise the use of solar power
- Reduce electricity bills
- Protect against blackouts
- Or eventually go off-grid
Step 1: Understand your household energy use
The first step in battery sizing is working out how much energy you actually use—and when you use it.
Look at your bills
Your electricity bill usually shows your average daily consumption in kilowatt-hours (kWh). A typical Australian home uses 16–20 kWh/day, but this can vary:
- Single-person homes: 8–12 kWh/day
- Families with children: 17–25 kWh/day
- Larger homes with pools or EVs: 30–60+ kWh/day
For more accuracy, check your usage across seasons—winter heating and summer cooling can cause large swings.
Focus on evening and night-time usage
If you’re pairing your battery with solar panels, the key metric is how much electricity you use after the sun goes down. This is when your panels aren’t producing power and your battery kicks in. Many households use 5–10 kWh in the evening, which can be a good starting point for battery sizing.
Plan for the future
Think ahead. If you’re planning to buy an electric vehicle, install ducted air conditioning, or add extra appliances, your future energy needs will grow. Allow extra battery capacity or choose a modular system that can expand later.
Step 2: Define your goals for having a battery
Your energy goals will shape the battery size that’s right for you.
Maximise solar self-consumption
If your aim is to use more of your own solar energy instead of exporting it to the grid (at low feed-in tariff rates), size your battery to absorb most of your daytime solar surplus. For example, if your 6.6 kW solar system typically exports 10 kWh/day, a battery around that size would capture most of it.
Save on electricity bills
Batteries can help reduce peak-time grid usage by storing cheap solar or off-peak electricity for later use. Even if you don’t have solar, some systems let you charge the battery using off-peak tariffs, then use that energy during expensive peak periods.
Provide blackout protection
For homes in areas prone to outages, battery backup is a key priority. You’ll need to size your battery based on how long you want to run essential appliances, like fridges, lights, or medical equipment, and add a buffer (typically 2–3 kWh). Not all batteries offer backup by default, so check this feature when comparing products.
Go off-grid
If you’re aiming to go completely off the grid, battery sizing becomes more complex. You’ll need storage capacity for multiple days of use, plus redundancy for cloudy weather. Systems over 20– 30 kWh are common for full off-grid setups, and you’ll likely need generator backup too.
Step 3: Match your battery to your solar PV system
Your solar system’s capacity limits how much energy is available to charge your battery each day.
Don’t oversize your battery
If your solar system generates 25 kWh/day and you use 15 kWh during the day, only 10 kWh is available for charging. Installing a 15 kWh battery in that scenario means some of it will sit empty.
A useful rule of thumb
Many installers suggest pairing 1kW of solar with about 1.5kWh of battery capacity. So a 6.6kW solar system might match well with a 10kWh battery—but your night-time usage and export levels will ultimately guide the best fit.
Step 4: Know your battery’s usable capacity
Batteries aren’t all equal in terms of how much stored energy you can actually use.
Depth of Discharge (DoD)
DoD is the percentage of a battery’s capacity that can be used before it needs recharging. Most modern lithium-ion batteries—like those from Tesla, Sungrow or Sigenergy—offer 80–100% DoD.
For example, a 10 kWh battery with 90% DoD gives you 9 kWh of usable energy.
Using 100% DoD frequently can shorten battery life, so some manufacturers recommend operating within a more conservative range (e.g., 20–80%).
Step 5: Consider other practical and financial factors
Off-peak charging
If you’re on a time-of-use tariff, you might benefit from charging your battery during cheaper off-peak hours. This can be especially useful if your solar generation is limited in winter.
Expandable (modular) systems
Some brands—like Sonnen or Redback—offer modular batteries, allowing you to start small and add more later as your needs change.
Minimum sizing for value
A common recommendation is to start with at least 25% of your daily energy use, plus a few kWh for backup. So, if your home uses 20 kWh/day, a 7–10 kWh battery is a good starting point.
Don’t chase 100% grid independence—unless you’re going off-grid
Completely offsetting your power bills with a large battery can be extremely costly. Often, a smaller battery that covers your evening peak gives the best return on investment.
Get expert help for the best results
While online calculators can offer a starting point, your battery sizing decision should be based on a detailed load analysis. CEC-accredited installers can:
- Analyse your electricity usage and solar exports
- Use smart meter data to profile your consumption
- Factor in your roof size, orientation, and shading
- Recommend systems with the right battery chemistry, warranty, and inverter compatibility
In conclusion
The best battery size for your home depends on your energy habits, solar system size, and personal goals. For most Australians, this lands between 7–15 kWh—but your ideal setup may differ. Remember to focus on usable capacity, future energy needs, and financial return.
If you want a tailored recommendation, Your Energy Answers can connect you with trusted, accredited professionals who’ll design a system to meet your needs, now and in the future.
