Solar Battery Payback Calculator

How solar payback is calculated

Annual generation is estimated using the UK average yield of 900 kWh per kilowatt-peak (kWp) of installed capacity. This figure represents a south-facing roof at moderate tilt in an average UK location; actual output varies by orientation, pitch, shading, and local irradiance.

The self-consumption percentage determines the split between electricity used in the home and electricity exported to the grid. Self-consumed solar replaces grid imports at the import tariff rate. Exported electricity earns the Smart Export Guarantee (SEG) rate or any agreed feed-in rate.

Total annual benefit = (self-consumed kWh × import tariff) + (exported kWh × export tariff). Simple payback = installation cost ÷ total annual benefit.

Battery storage and self-consumption

Adding battery storage increases self-consumption by storing excess daytime generation for use in the evening. Without a battery, typical self-consumption for a household out during the day ranges from 20 to 35%. A well-sized battery can raise this to 60–80%, significantly increasing the value of each kWh generated.

Battery storage adds to the installation cost. The calculator lets you include a battery capacity figure and adjust self-consumption to reflect the improved self-use. The payback model will then show whether the extra storage cost is offset by higher self-consumption savings.

Tariff sensitivity and limitations

Energy tariffs change over time. The calculator shows payback under base, +15%, and −15% tariff scenarios to illustrate how sensitive the result is to future tariff movements. Higher tariffs improve payback; lower tariffs extend it.

This tool provides estimates only. It does not account for panel degradation (typically 0.5–0.8% per year), inverter replacement costs, VAT, scaffolding, or variations in household consumption. The 900 kWh/kWp yield is a national average — London and the south-east typically exceed this, while Scotland and northern England may fall short.