UK Solar Panel Savings Calculator

With electricity prices remaining a significant household cost, many homeowners are weighing up whether solar panels are worth the upfront investment. This calculator estimates your annual bill savings, export income and payback period for a home solar PV system, based on your system size, typical UK generation levels and your own electricity prices.

How to use the solar panel savings calculator

Enter your planned system size in kWp (kilowatt-peak) and the estimated upfront cost. Typical UK generation and self-consumption figures are pre-filled as editable defaults, but you can adjust the annual generation per kWp if you have a more specific estimate for your roof, and adjust self-consumption if you have a battery or particular usage pattern. Enter your electricity unit rate and your expected Smart Export Guarantee (SEG) export rate to see your estimated annual savings, export income and payback period.

How the calculation works

Annual generation is estimated as your system size multiplied by the typical generation per kWp for a UK installation. This generation is then split between self-consumed electricity, which saves you the full electricity unit rate, and exported electricity, which earns the lower SEG export rate instead. Adding the bill savings and export income together gives your total annual benefit, and dividing your system cost by this figure gives an estimated payback period in years.

Worked example

A 4kWp system costing £7,000, generating 950 kWh per kWp a year, would produce around 3,800 kWh annually. With 40% self-consumption, that is 1,520 kWh used directly, saving around £390.64 a year at a 25.7p unit rate, plus 2,280 kWh exported at 15p, earning around £342 a year. That is a total annual benefit of around £732.64, giving an estimated payback period of roughly 9.6 years. Over a typical 25-year panel lifespan, that could add up to around £18,316 in combined savings and income, before accounting for any changes in electricity prices or panel output over time.

Common mistakes to avoid

A common mistake is assuming all generated electricity is used in the home. Without a battery, a significant share is often exported, particularly for households out at work during the sunniest hours, so realistic self-consumption assumptions matter for an accurate estimate. It is also easy to overestimate generation for a north-facing, heavily shaded, or poorly angled roof, where actual output can fall well below the typical figures used as defaults here.

Another mistake is accepting the first SEG export rate offered without comparing others, since rates can vary considerably between suppliers. It is also worth getting quotes from more than one accredited installer, since system cost has a direct effect on payback period for the same expected savings.

Related calculators

Check your current usage and costs with our energy bill calculator before sizing a system, and see whether loft insulation could reduce your overall energy use first. If you drive an electric car, our electric car running cost calculator shows how home solar and EV charging can work together. If you are saving up for the upfront cost, our savings goal calculator can help you plan. Our guide to reducing UK energy bills covers other ways to cut costs alongside solar.