Solar calculator

Solar panel return calculator

Estimate the yearly value of a solar panel system from self-used electricity, export income, install cost, and maintenance. Results are a general guide, not a quote.

Inputs

Use the installed quote, expected annual generation, current import tariff, export tariff, and the share of solar electricity you expect to use at home.

Method

The calculator values self-used generation at the import price, exported generation at the export rate, then subtracts the yearly maintenance allowance.

Result

Payback is a simple estimate. It does not model tariff changes, battery effects, finance costs, tax, grants, shading, inverter replacement, or panel degradation.

Last reviewed: 16 June 2026Calculation type: simple solar payback estimate

How to use the solar return estimate

This calculator gives a simple annual-value and payback estimate for a solar panel installation. It is best used before or after getting quotes, when you want to test how system size, export rate, electricity price, and self-use change the result.

System sizeEnter the quoted system size in kW or kWp. A larger system can generate more electricity, but only the electricity you use or export has value in this calculation.
Annual yieldUse the installer estimate if you have one. Roof direction, pitch, shading, location, and inverter setup can make a large difference.
Self-use percentageThis is the share of generated electricity used in the property instead of exported. It is often higher if you can run appliances during daylight or use a battery.
Maintenance allowanceAdd an annual allowance for monitoring, small repairs, cleaning if needed, or future inverter replacement planning.

Worked example

A 4 kW system generating 850 kWh per kW produces about 3,400 kWh per year. If 45% is used at home at 28p per kWh, that self-used energy is worth about £428. Exporting the rest at 15p per kWh is worth about £281. After a £100 maintenance allowance, the net annual benefit is about £609.

What affects payback most

Simple payback divides the installed cost by the net yearly benefit. It is easy to understand, but it does not show all financial outcomes over the system life.

Generation estimateUse the figure from your installer quote, survey, or monitoring app if the system is already installed.
Import tariffUse your current electricity unit rate in pence per kWh, excluding the standing charge.
Export tariffUse the export rate offered by your supplier, and check whether the rate is fixed, variable, or tied to a specific import tariff.
Important limitationThe calculator does not model battery degradation, panel degradation, future tariff changes, borrowing costs, or property-specific shading.

Why does self-use matter so much?

Electricity used in the property usually replaces imported electricity at your import unit rate. Exported electricity is valued at the export rate, which may be lower, so the self-use percentage can strongly affect payback.

Does this include a home battery?

Not directly. A battery can increase self-use, but it also adds cost and has its own efficiency and lifespan. You can test the effect by changing the self-use percentage, but treat that as a simplified estimate.

Why is the 25-year estimate only a guide?

It assumes the same annual benefit every year. Real systems may have changing tariffs, component replacement, panel degradation, export rule changes, and different maintenance costs over time.