How home battery size is estimated
What this calculator does with daily kWh, cover hours, and reserve percentage — and what it does not try to do.
Read guideIntro
Step 1 of 6
Find the right home battery size in under 5 minutes.
How it works
We use your electricity bills, solar details, and a few questions about your home appliances to estimate the battery capacity you need to cover your usage outside of solar production hours.
What you'll need
Your average electricity usage in kWh — you can find this on your electricity bill under Have separate winter and summer figures available.
Solar Battery Calculator estimates how many kilowatt-hours of home battery capacity you may need from seasonal bill averages, your solar window, and optional major appliance loads. Daily energy is scaled by the hours you want the battery to cover, then uplifted for a reserve (minimum state of charge). It is a planning aid, not a substitute for an accredited system design.
Because electricity bills for solar homes already reflect grid imports after self-consumption, the results can reintroduce estimated solar self-use (generation minus export) so the capacity range is easier to compare with total household energy.
The tool is aimed at Australian households comparing storage options before talking to an installer. Work through winter and summer bill averages, solar generation and export, then optionally add EV, pool, air conditioning, or oven loads. You get a capacity range in minutes, with plain-language guides if you want to understand each input first.
How is home battery size calculated?
We average winter and summer bill daily kWh, optionally add appliance loads, then scale by cover hours and uplift for reserve (minimum state of charge). The result is a planning range, not a certified design.
Where do I find daily kWh on my bill?
Most Australian retailers show average daily usage on the bill summary. If you only have period totals, divide billed kWh by the number of days in the period and use separate winter and summer figures when you can.
Does solar export affect battery sizing?
Yes. Generation minus export estimates self-consumption. Bills for solar homes are usually already net of that self-use, so the calculator can show solar offset separately for a clearer capacity comparison.
Should I include EV charging?
Include home charging when you enable load details and your bill averages do not already reflect typical weekly kilometres charged at home. Skip it if charging is mostly away from home or already in the bill figures.
What this calculator does with daily kWh, cover hours, and reserve percentage — and what it does not try to do.
Read guideWhere average daily usage appears on typical Australian bills, and why winter and summer figures both matter.
Read guideHow generation and grid export relate to self-consumption, and why bills are already “net” of solar.
Read guideHow EV kilometres per week translate to daily kWh, and when to include charging in your storage estimate.
Read guideCommon residential capacities (5–15 kWh), what households they suit, and why nameplate kWh is not the whole story.
Read guideAnonymous examples from other calculator runs — battery size plus typical load and solar inputs. Similar kWh can appear when the underlying usage differs.
© 2026 Solar Battery Calculator. Estimates only — not financial advice.