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 calculator
- Enter the system's total installed cost and size in kWp.
- Set the expected annual generation per kWp — this depends heavily on your region and roof orientation; the default is a rough UK-wide average.
- Enter your electricity price and how much of the generated power you expect to use yourself (rather than export).
- Read the estimated annual saving and payback period.
Assumptions
- The default 850 kWh/kWp/year is a rough UK-wide average — actual generation varies significantly by region, roof orientation, pitch and shading. Get a proper site survey for an accurate figure.
- Only self-consumed generation is valued at the full electricity price; exported electricity (via a smart export tariff) is typically paid at a different, usually lower, rate and is not included in this estimate.
- 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.
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 — varies significantly with UK region (sunnier south vs. cloudier north), roof orientation and shading. The default is a rough national average; a solar installer's site survey will give you a far more accurate figure.
- 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 to the grid. Exported electricity is typically paid at a lower rate than the electricity price you avoid buying — this estimator only values self-consumed generation.
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: systemCostGbp=5000, systemSizeKw=3.5, annualGenerationKwhPerKw=850, electricityPricePerKwh=0.28, selfConsumptionPercent=50
Result: 2,975 kWh/year generation, £417/year saving, 12.0 year payback
Practical guidance
- A battery storage system can increase self-consumption significantly — re-run this with a higher self-consumption percentage to see the effect.
- Get a proper site survey from an installer for an accurate generation estimate specific to your roof — the default figure is a rough national average only.
Common mistakes
- Using a generic national-average generation figure instead of a site-specific survey result.
- Valuing exported electricity at the same rate as self-consumed electricity, which overstates savings — export rates are usually lower.
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.