Solar payback estimator (with explicit assumptions)
Estimate roughly how many years a home solar PV system might take to pay for itself in avoided electricity costs, using your own generation, self-consumption and price assumptions.
Result
Estimated payback period
Estimated annual saving
Estimated annual generation
How to use this tool
- Enter the system's total installed cost and size in kWp.
- Set expected annual generation per kWp from a location-specific PV yield estimate or an installer's site survey; the prefilled 850 is only an example scenario, not a UK-wide average.
- Enter your electricity price and the share of generated power you expect to use yourself; export income is excluded, so check your own SEG tariff separately if you want to assess it.
- Read the estimated annual saving and payback period.
Assumptions
- The prefilled 850 kWh/kWp/year is an illustrative scenario, not a sourced UK-wide average. Actual generation depends on location, roof orientation, pitch, horizon and shading; use a location-specific PVGIS estimate or site survey.
- The prefilled 50% self-consumption value is also an illustrative scenario, not a typical household benchmark. Your usage pattern and any battery affect the share you consume.
- Only self-consumed generation is valued at the entered electricity price. Export payments vary by tariff and are not included.
- Assumes constant electricity prices and constant generation/self-consumption every year — real prices and household usage patterns change over time.
- Does not account for panel degradation over the system's lifetime, inverter replacement costs, or maintenance.
Sources & reference data
Technical details: what the fields mean
- System cost
systemCostGbp - Total installed cost of the solar PV system, after any grants/incentives.
- System size
systemSizeKw - System size in kWp (kilowatt-peak) — stated on the quote/spec.
- Annual generation per kWp (check your region)
annualGenerationKwhPerKw - Expected annual generation per kWp installed. Use a site-specific PVGIS result or installer's survey; 850 is an illustrative input, not a national benchmark.
- Electricity price
electricityPricePerKwh - Your electricity price per kWh, used to value the generation you consume yourself.
- Self-consumption
selfConsumptionPercent - Percentage of generated electricity you use in the home rather than export. The calculator values self-consumption only; export payments depend on your own Smart Export Guarantee tariff and are excluded.
Methodology
Annual generation = system size × generation per kWp. Annual saving = annual generation × self-consumption% × electricity price. Payback period = system cost ÷ annual saving.
Worked example
£5,000 system, 3.5kWp, 850 kWh/kWp/year, 28p/kWh, 50% self-consumption
Inputs: System cost: £5000, System size: 3.5 kWp, Annual generation per kWp (check your region): 850 kWh/kWp, Electricity price: £0.28/kWh, Self-consumption: 50%
Result: 2,975 kWh/year generation, £417/year saving, 12.0 year payback
Practical guidance
- If comparing a battery scenario, use a self-consumption assumption supported by your installer or measured usage; check your own SEG tariff separately for export income, which is not included. Battery purchase and replacement costs are also outside this calculation.
- PVGIS can estimate generation for a location, system size, slope and orientation; an installer's site survey can account for roof-specific shading.
Common mistakes
- Treating the prefilled generation or self-consumption values as a national average rather than replacing them with site/usage-specific values.
- Assuming exported electricity earns the same value as energy consumed at home; this estimate does not calculate export income.
FAQs
How long does a solar panel system take to pay for itself?
It varies enormously by system cost, your region's sunlight, roof orientation and how much of the generated power you use yourself — use your own figures above rather than a generic answer.
Is this financial advice?
No — this is a rough energy-cost payback estimate based on the assumptions you enter, not financial, investment or tax advice. It does not account for financing costs, grants eligibility, or property value effects.
Last reviewed: 2026-10-11
A rough estimate based on the assumptions you enter — not a substitute for a professional site survey or financial advice. Does not model panel degradation, maintenance, financing costs or changing electricity prices over time.
This tool provides an indicative estimate, based on the assumptions stated above.
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