What is the battery sizing calculator?
How our free tool helps you find the right home battery capacity based on your solar system, electricity usage and whether you plan to use a time-of-use tariff.
How to use the calculator
A step-by-step guide to entering your solar system size, daily usage, export data and tariff to get a personalised battery recommendation.
How we recommend battery size
How we calculate the optimal kWh capacity based on your overnight usage, daytime solar surplus and the diminishing returns of oversizing.
Cost estimates & payback
How we estimate battery installation costs, calculate payback from increased self-consumption and tariff arbitrage, and model the 25-year financial case.
With solar vs without solar
How the calculator adjusts recommendations for homes with solar panels versus homes using a battery purely for tariff arbitrage on time-of-use rates.
Tariff arbitrage modelling
How we model savings from charging on cheap overnight rates and discharging during peak hours, using real Octopus Agile, Go and Intelligent pricing data.
Battery degradation assumptions
How we account for battery capacity degradation over time, typical rates for lithium iron phosphate cells and how this affects long-term payback.
Interpreting your results
How to read the calculator output, what the numbers mean, how to compare different battery sizes and when a larger or smaller system makes more sense.
Limitations & next steps
What the calculator cannot model, including specific inverter compatibility, electrical panel capacity and three-phase supply considerations.
Frequently asked questions
Common questions about the battery calculator, including whether it works without solar, how we handle different tariff structures and data accuracy.