The right battery size is the one that covers most of your evening and overnight power use, the hours your solar cannot. Go too small and you still buy peak power, go too big and the extra capacity sits idle. For most family homes that lands at 10kWh to 13.5kWh.
A simple way to size it
| Household | Typical evening use | Battery size |
|---|---|---|
| Small (1 to 2 people) | Lower evening use | 5 to 8 kWh |
| Family home | Cooking, aircon, devices | 10 to 13.5 kWh |
| Large or high-use | EV, pool, electric heating | 13.5 to 16 kWh+ |
| Wants backup | Whole-home through outages | 13.5 kWh+ with backup |
What pushes the size up
- High evening use, like cooking, air-conditioning and electric heating after dark.
- An EV you charge at home overnight.
- Backup, if you want to run the whole house through a blackout.
- Big solar, a large array makes more surplus to store.
The easy way: model it
Rather than guess, put your power bill into the savings calculator and try a few sizes to see how the saving and payback change. Then your matched installer confirms the right size from your actual usage. For pricing by size, see how much a solar battery costs.