If you’re thinking about adding battery storage to your solar system, you’ve probably asked yourself:
“What size solar battery do I need?”
It’s one of the most common questions Australian households face—and an important one. A battery that’s too small won’t give you the night-time coverage you expect. Too large, and you could spend thousands more than necessary without seeing the return.
This guide walks you through how to choose the right size solar battery for your home. By the end, you’ll know what to consider, how to calculate your needs, and which mistakes to avoid.
Why Battery Size Matters
The right solar battery size is the balance point between performance and cost. Getting it right means you’ll:
- Maximise self-consumption of your solar power
- Reduce reliance on the grid
- Lower your electricity bills
- Improve your return on investment
- Have reliable backup power when you need it
Key Factors That Influence Battery Size
Before calculating the ideal solar battery size, keep these factors in mind:
- Daily electricity usage – Check your bills for your average daily kWh.
- When you use electricity – Night-time demand requires more storage.
- Excess solar after daytime loads – The most important factor. If your panels only just cover your daytime usage, there won’t be enough left over to charge a battery.
- Solar system size and production – Larger arrays produce more excess energy to store.
- Desired level of backup – Do you want partial coverage or full independence?
- Budget and payback period – A bigger battery isn’t always better if you can’t fully use it.
- Battery type and compatibility – Ensure your battery works with your inverter and solar setup.
How to Calculate What Size Solar Battery You Need
Here’s a simple step-by-step approach:
- Work out your night-time usage
Example: 10 kWh between sunset and sunrise. - Check how much excess solar you have available
Look at your system’s daily production and subtract your daytime usage.
If your system produces 25 kWh/day and you use 15 kWh during the day, you’ll have ~10 kWh left to charge a battery.
If your excess is less than your night-time demand, a bigger battery won’t help.
- Decide what percentage of your night-time load you want to cover
For example, 80% of a 10 kWh load = 8 kWh. - Match the battery size to the lower number
**Your usable battery size should be whichever is smaller:
The excess solar available, or
The night-time usage you want to cover.**
👉 Example:
- Night-time usage = 10 kWh
- Excess solar = 9 kWh
- Target coverage = 8 kWh
Result: You’d need a ~9–10 kWh battery, but since you only have 9 kWh of excess solar, a 9 kWh battery makes the most sense.
Try Our Solar Battery Calculator
Want to check the numbers for your own home? Use our interactive tool below:
Disclaimer: The information and calculations provided in this blog are general in nature and intended as a guide only. Actual solar and battery requirements can vary depending on your household’s unique energy usage, property layout, and lifestyle. We recommend speaking with one of our experienced system designers at Stag Electrical to ensure your solar battery size is correctly matched to your needs.
Typical Battery Sizes & What They Suit
Top 3 Solar Battery Brands Worth Considering
When picking a battery, you don’t just want size - you want reliability, good support, and features that match your needs. Here are three brands doing well in Australia right now:
Choosing the right solar battery size doesn’t have to be complicated. The key is balancing your night-time demand with your excess solar production. Get that match right, and you’ll maximise savings, boost energy independence, and ensure long-term value.
