Calculator · Batteries
What size battery could work for you?
Find a starting size and see how much a larger battery might add. Use your own numbers, then take a clearer brief to an installer.
See what is doing the work
What limits the saving?
Three daily limits, on the same scale. The smallest determines how much energy the battery can deliver.
The model delivers 10.5 kWh per day with the 15 kWh option. More storage helps only when spare solar and later use can fill the extra capacity.
What changes with a different size?
The same home and rates. Three capacities to compare.
First-year, average-day estimates. Capacity, output and backup capability still need to be checked for your home.
Keep a copy of your results.
We’ll email you what you entered and what it came to. We won’t use your address for anything else unless you ask us to.
How this tool works
The sizing starting point is the smaller of your later electricity use and spare solar after round-trip losses. We then allow for the capacity you hold in reserve.
For each comparison battery, the model limits daily delivery by available capacity, spare solar after losses and your later use. Annual savings subtract the export credit you give up from the electricity usage charge avoided.
The example uses 90% round-trip efficiency, a 20% reserve, a 35 c/kWh usage rate and a 5 c/kWh feed-in tariff. You can change them. This is a first-year, average-day solar-storage model. It does not simulate interval data or seasonal operation.
It excludes installation prices, finance, degradation, fixed supply charges, VPP payments and grid-charging strategies. It does not determine output power or backup compatibility. Use it to frame a quote discussion, and ask an installer to model your interval data and the complete system.
Sources
During solar hours your home uses solar first. Surplus can be stored in a home battery within system limits. After solar hours the battery supplies later use, and the grid covers any shortfall.
Solar now. Stored energy later.
During solar hours
Your solar
Home uses solar first
Surplus to store
Home battery
Within system limits
After solar hours
Later use
Grid covers any shortfall
The opportunity depends on the home, rates and equipment.
