Estimate the generation, savings and payback time of a home solar panel system.
Defaults are typical estimates: about 850 kWh per kWp a year and 15p per kWh SEG export. Real generation varies by location, roof direction, pitch and shading, and export rates vary by supplier.
Uses today's prices for all 25 years with no inflation, maintenance or inverter replacement. Net benefit is total savings and export income minus installed cost.
Thinking about solar panels but not sure they will pay for themselves? This solar panel calculator UK estimates how much electricity your system could generate, what it saves on your bills, what you earn from exporting the rest, and how long it takes to pay back. The Energy Saving Trust solar panel guide is a good place to check the basics before you get quotes.
What Is a Solar Panel Payback Calculation?
Solar panels earn their money in two ways. Electricity you use at home replaces power you would otherwise buy at your import price. Electricity you do not use is sent to the grid and paid for through a Smart Export Guarantee (SEG) tariff, which is usually a lower rate per kWh.
The calculator works out generation = system size × kWh per kWp, then savings = generation × self use × import price and export income = generation × (1 − self use) × export rate. Payback is the installed cost divided by the yearly benefit. You can also add 0.5% yearly panel degradation for a more cautious view.
How to Use the Solar Panel Calculator UK
Step 1: Enter Your System Size
Enter the size in kilowatts peak (kWp) from your quote. A 4 kWp system is common for a three bedroom home. Generation of about 850 kWh per kWp is a typical UK estimate, higher in the south and lower in the north.
Step 2: Set Your Self Use
This is the share of solar power you use at home. Around 50% is a reasonable estimate if someone is home in the day. Your yearly usage from the energy bill calculator helps you judge how much you could use, and a battery can raise it considerably.
Step 3: Add Prices and Installation Cost
Enter your electricity import price, your SEG export rate and the installed cost per kWp. The default import price is the Ofgem price cap rate for October to December 2026, and the kWh cost calculator can help you check your own unit rate if you are on a different tariff.
Step 4: Read Your Results
You will see yearly generation, bill savings, export income, total yearly benefit, payback time and the net benefit over 25 years after the installation cost.
Solar Panel Savings Examples
| System | Generation | Yearly benefit | Cost | Payback |
|---|---|---|---|---|
| 3 kWp | 2,550 kWh | £527 | £4,800 | 9.1 years |
| 4 kWp | 3,400 kWh | £702 | £6,400 | 9.1 years |
| 6 kWp | 5,100 kWh | £1,054 | £9,600 | 9.1 years |
Examples use the default settings: 850 kWh per kWp, 50% self use, 26.32p import, 15p export and £1,600 per kWp. To be paid for exported power you need a smart meter and an MCS certified installation, as explained in the Ofgem Smart Export Guarantee guide. These are typical estimates that vary by location, roof and supplier, so always compare a few installer quotes.
Frequently Asked Questions
How much do solar panels save in the UK?
A typical 4 kWp system could save around £450 a year on bills and earn around £250 from exports, based on 50% self use and current prices. Your result depends on your roof, location and usage.
How long do solar panels take to pay back?
Many UK systems pay back in roughly 8 to 12 years, depending on installation cost, how much power you use yourself and your export rate.
How much electricity does a 4 kWp system generate?
A rough UK estimate is about 850 kWh per kWp a year, so around 3,400 kWh for a 4 kWp system. South facing roofs in southern England generate more.
What is the Smart Export Guarantee?
It is a scheme that requires larger energy suppliers to pay you for electricity you export to the grid. Rates vary a lot between suppliers, so compare tariffs.
Do solar panels lose efficiency over time?
Yes, slowly. Many panels lose around 0.5% of output a year, which you can include in this calculator using the degradation option.
Does a battery make solar panels pay back faster?
A battery raises your self use, which increases bill savings, but it also adds cost. Whether it shortens payback depends on its price and your usage pattern.