Solar Panel Payback Calculator

Calculate how long it takes your solar panels to pay for themselves. Enter system size, cost, your electricity rate and SEG export tariff to see your payback period and 25-year return.

Last updated: April 2026

Solar panel details
Typical UK home: 3–5 kWp
2025 avg: ~£1,500–£1,800/kWp
Your energy usage
Rate paid for electricity exported to grid. Shop around - rates vary by supplier.
Typical without battery: 30–50%. With battery storage: 60–80%.
Solar panel payback
Payback period
-
-
Annual generation (est.) -
Annual bill saving -
Annual SEG export earnings -
Total annual benefit -
25-year return on investment -

How solar panel payback is calculated

A solar PV system generates electricity from sunlight. The financial benefit comes from two sources: electricity you use directly (saving you from buying it at the unit rate), and electricity you do not use which you export to the grid and sell via the Smart Export Guarantee (SEG). The payback period is the installation cost divided by the annual financial benefit from both sources.

Annual generation estimate

A south-facing solar panel in the UK generates approximately 850–950 kWh per kWp installed per year. This calculator uses 900 kWh/kWp as a baseline for south-facing panels, adjusted by an orientation factor for other directions. A 4 kWp south-facing system therefore generates around 3,600 kWh per year - roughly equivalent to the average UK household's annual electricity consumption.

The Smart Export Guarantee

The Smart Export Guarantee (SEG) replaced the Feed-in Tariff in January 2020. It requires energy suppliers with over 150,000 customers to offer a tariff for exported electricity, but the rate is set by the supplier and varies significantly - from around 4p/kWh to over 20p/kWh depending on the supplier and tariff. Shopping around for the best SEG rate can meaningfully improve the financial return on a solar installation. Octopus Energy and some others offer rates at the higher end of this range.

Battery storage

Adding a battery (typically £2,500–£5,000 for a 5–10 kWh system) allows you to store surplus daytime generation and use it in the evening, increasing your self-consumption rate from around 30–50% to 60–80%. This increases the proportion of generation you benefit from at the higher unit rate rather than the lower SEG export rate. Whether a battery is financially justified depends on your tariff, usage pattern, and battery cost - payback on the battery alone is typically 8–12 years.

Frequently asked questions

Most residential solar panel installations in England are permitted development and do not require planning permission, provided the panels do not protrude more than 200mm from the roof surface and the property is not a listed building or in a designated area (National Park, Area of Outstanding Natural Beauty, World Heritage Site). In Scotland and Wales, similar permitted development rules apply. Always check with your local planning authority if you are unsure, and consult your installer.
Most quality solar panels are warrantied for 25 years and carry a performance guarantee of 80–90% of original output at year 25. In practice, panels can last 30+ years. The inverter (which converts DC power from panels to AC for use in your home) typically lasts 10–15 years and costs £800–£1,500 to replace - this should be factored into long-term financial projections. Panel degradation is typically 0.3–0.5% per year, meaning output at year 25 is around 88–93% of year one output.
There is no bad time to install solar panels in the UK - the panels work year round and generate meaningful electricity even on overcast days (though less than on sunny days). However, many installers are busier in spring and summer, so autumn and winter installations may be scheduled more quickly. The financial return begins from day one of installation regardless of season, so acting sooner rather than waiting for summer is generally the right approach.

Related calculators

Appliance Energy CostEnergy & Utilities Heating CostEnergy & Utilities Water Usage CostEnergy & Utilities Savings GoalSavings & Investment