Hourly battery model
Solar battery savings and payback calculator
Compare the same household with and without storage across a full year of hourly solar and electricity use. Estimate battery savings and payback with real capacity, power and energy losses rather than treating every export as recoverable.
Use your own annual figures
Annual generation from your inverter or export portal is a stronger starting point than the example. For electricity use, use a recent bill or annual statement. The calculator distributes those totals into hourly shapes; it does not send them to a server or save them.
If you are still planning a system, first use the property solar calculator to get an annual generation range. Run the battery model more than once with different capacities and realistic installer prices. A larger battery is not automatically a better financial fit because summer surplus and winter demand happen in different months.
For a simpler first-pass estimate of panel costs and savings, use the UK solar panel cost and payback calculator.
What to compare in an installer quote
Check whether quoted capacity is usable or nominal, the continuous charge and discharge power, warranty throughput or cycles, round-trip efficiency, expected degradation, backup capability and whether a separate inverter is included. The fields here use usable capacity and continuous power.
Questions about battery modelling
Does the calculator assume a battery stores all exported solar?
No. Each hourly period uses solar in the home first. The remaining solar can charge the battery only up to its usable capacity and charge-power limit. Anything left is exported. Demand beyond the battery discharge-power limit or remaining state of charge is imported.
What does round-trip efficiency mean?
It represents energy lost while charging, storing and discharging. At 90% round-trip efficiency, roughly 90% of energy put through a complete battery cycle reaches the home. The model applies the loss across charging and discharging rather than hiding it in the financial result.
Does it model cheap overnight grid charging?
Not yet. This version models solar-only charging at a flat import and export rate. Time-of-use tariff optimisation needs half-hourly tariff and household data, so adding it to a flat-rate result would overstate its precision.
Is the payback figure a quotation?
No. It is installed cost divided by the additional annual benefit in this model. It excludes finance, degradation, replacement, maintenance and future tariff changes. Use installer proposals and product warranties before making a purchase decision.
What size solar battery do I need?
There is no single size that suits every home. It depends on when you use electricity, when your panels generate, usable battery capacity and charge or discharge power. Compare several realistic sizes in the calculator and check the result against installer proposals.