Solar
Solar payback calculator
Have a quotation in hand? Put the installed cost next to an estimated yearly benefit and see how long the system would take to repay itself — with every assumption on show.
The calculator is free, needs no account, and keeps your figures in your own browser.
Open the solar calculatorEnter the quoted installed cost to see a simple payback period alongside the yearly figures.
Payback in one line
Installed cost divided by yearly benefit. The hard part is the yearly benefit, because it depends on generation, on how much of it you use at home and on the two prices that sit either side of your meter — what you pay for a unit and what you are paid for one.
Test the quote, not just the headline
A quotation usually shows one optimistic case. It is worth re-running the numbers with lower generation and a lower export rate to see whether the decision still holds. A free Decision Pack collects those cases, the assumptions and a list of questions for your installer into one downloadable record.
Where the estimate can be wrong
Shading, an unusual roof shape, an older consumer unit or scaffolding costs are not modelled. Treat the result as a planning estimate and let the installer's survey and your supplier's bill be the definitive figures.
Common questions
- How is solar payback worked out?
- Simple payback divides the installed cost you were quoted by the estimated yearly benefit. If the yearly benefit is zero or negative, there is no payback period, and the calculator says so rather than showing a misleading number.
- What is a realistic payback period for solar in the UK?
- There is no single answer: it depends on the quoted price, the size and direction of the array, how much generation you use at home and your unit and export rates. Change any of those and the answer moves, which is why the calculator lets you test each one.
- Should payback include finance, maintenance or an inverter replacement?
- Simple payback does not. If you are financing the system or expect a replacement inverter, add those amounts to the installed cost you enter so the comparison reflects what you will really pay.
- Do rising electricity prices shorten payback?
- They tend to, because self-used solar avoids buying units at whatever the price then is. The calculator uses the prices you enter rather than forecasting future prices, so you can test a higher and a lower price yourself.
- Does payback change if I add a battery?
- Adding a battery adds cost and adds saving, and the two rarely move by the same amount. Judge the battery on its own incremental cost and incremental saving rather than folding it into the solar figure.