Calculator
Solar ROI Calculator — UK
Estimate UK solar payback from your region, monthly bill, and project year
Going solar is a financial decision as much as an environmental one. This calculator starts with inputs most UK homeowners know: region, monthly electric bill, and project year. RenewableCalc then applies Ofgem price-cap electricity rates, MCS-certified installer cost-per-watt benchmarks, PVGIS-SARAH2 production estimates, and SEG/0% VAT incentive defaults while keeping advanced inputs editable. The result is a planning estimate for payback, net upfront cost, 25-year savings, bill offset, and a solar quote checklist for reviewing MCS installer assumptions.
All estimates use £ / UK local data: electricity rates, solar costs, and incentives.
Quick estimate State Monthly bill Project year
Enter Your Details
Start with the required inputs. Open advanced assumptions when you have a quote or utility details.
Fill in the form and click Calculate to see results.
Before You Sign
Check for these red flags in any solar quote before committing to a contract.
- System size significantly larger than your annual usage
- Estimated annual production seems too optimistic
- Battery storage bundled without clear need analysis
- Warranty or production guarantee is vague or missing
- Price per watt above $3.50 without justification
- "Free solar" or "no cost" language (usually a lease/PPA with hidden costs)
- APR on loan exceeds 7–8% without explanation
0% VAT on energy-saving materials expires 31 March 2027. SEG export rates vary by supplier — check your tariff. Read the policy details
Policy status
UK solar and battery incentive policy status
UK incentive assumptions depend on the project year and your eligibility. RenewableCalc applies 0% VAT on energy-saving materials (until 31 March 2027) and Smart Export Guarantee (SEG) export rates. ECO4, Boiler Upgrade Scheme (BUS), and Home Energy Scotland grants are available for eligible households — verify current eligibility on gov.uk before treating any estimate as final.
Policy last reviewed: 2026-06-09 · Source: Ofgem SEG guidance, HMRC Energy Saving Materials Relief, and MCS installer standards.
Data Sources
Assumptions behind this calculator
Electricity rates
Ofgem
Uses the Ofgem price cap for England, Scotland and Wales. Updated quarterly. Current cap: 24.5p/kWh (April–June 2026).
Solar production
PVGIS-SARAH2
Uses UK regional solar irradiance data (850–1,100 kWh/kWp/year depending on region). South coast highest, Scotland lowest.
Installation costs
MCS Installer Database
England average £1,591/kW for MCS-certified installers (March 2026). London premium 10–30% above national average.
Export tariff
Smart Export Guarantee (SEG)
Suppliers pay 1–27p/kWh for exported solar. Octopus Energy Intelligent Flux pays the highest at 25–27p/kWh peak. All major suppliers required to offer SEG.
VAT relief
HMRC Energy Saving Materials Relief
0% VAT on solar panel installations for residential properties until 31 March 2027. Automatically applied by MCS-certified installers.
Overview
Going solar is a financial decision as much as an environmental one. This calculator starts with inputs most UK homeowners know: region, monthly electric bill, and project year. RenewableCalc then applies Ofgem price-cap electricity rates, MCS-certified installer cost-per-watt benchmarks, PVGIS-SARAH2 production estimates, and SEG/0% VAT incentive defaults while keeping advanced inputs editable. The result is a planning estimate for payback, net upfront cost, 25-year savings, bill offset, and a solar quote checklist for reviewing MCS installer assumptions.
Use this result
Use the calculator inputs first, then compare the result against local rates, incentives, roof conditions, and utility export rules.
Method, assumptions, and sourcesOpen this section when you want to audit the calculation behind the estimate.ShowHide
Calculation Method
ROI = (lifetime savings - net system cost) / net system cost
Key Assumptions
- State, monthly electric bill, and project year are the minimum inputs for a planning estimate.
- Federal residential credit assumptions depend on project year; 2026+ projects default to no federal residential credit.
- 25-year system life
- 0.5% annual panel degradation
Data Sources
Electricity rates
Ofgem
Uses the Ofgem price cap for England, Scotland and Wales. Updated quarterly. Current cap: 24.5p/kWh (April–June 2026).
Solar production
PVGIS-SARAH2
Uses UK regional solar irradiance data (850–1,100 kWh/kWp/year depending on region). South coast highest, Scotland lowest.
Installation costs
MCS Installer Database
England average £1,591/kW for MCS-certified installers (March 2026). London premium 10–30% above national average.
Export tariff
Smart Export Guarantee (SEG)
Suppliers pay 1–27p/kWh for exported solar. Octopus Energy Intelligent Flux pays the highest at 25–27p/kWh peak. All major suppliers required to offer SEG.
VAT relief
HMRC Energy Saving Materials Relief
0% VAT on solar panel installations for residential properties until 31 March 2027. Automatically applied by MCS-certified installers.
Result Summary
Strong fit
Payback under 8 years
Good fit: usually worth deeper quote comparison, especially with high local electricity rates.
Borderline
Payback 8-12 years
Needs review: check roof condition, financing, battery needs, and utility export rules before committing.
Weak fit
Payback over 12 years
Weak financial case: solar may still help resilience or emissions goals, but the financial case needs scrutiny.
Assumptions Data Sources Related Links
How to Use This Calculator
Select your UK region, enter your average monthly electricity bill, and set the project year. Leave system size, installation cost, electricity rate, and incentives blank if you want RenewableCalc to use regional UK defaults. Edit advanced fields when you have a real MCS installer quote, smart-meter tariff, SEG export rate, or grant assumption. The result shows payback period, net upfront cost, 25-year net savings, estimated system size, bill offset, assumptions used, next-step actions, and a quote-review checklist covering installed cost per watt, production, SEG export value, 0% VAT treatment, battery scope, financing, and roof work.
Formula & Methodology
ROI is calculated using a discounted cash flow model: NPV = Σ (Annual Savings / (1 + Discount Rate)^Year) - Net Investment. Payback period = Net Investment / Annual Savings. UK defaults use Ofgem electricity-rate references, MCS installed-cost benchmarks, PVGIS-SARAH2 production estimates, Smart Export Guarantee export assumptions, 25-year system life, and 0.5% annual panel degradation. The 0% VAT treatment for residential solar is treated as installer-pricing context rather than a separate cash rebate, and grant assumptions remain editable when a household has confirmed eligibility.