Solar ROI and Payback Calculator
Enter the quote you received, any subsidy and your tariff to calculate payback and long-term benefit with transparent assumptions.
Confirm eligibility on the official portal.
Average rate on your bill.
Assumptions and formulas
You supply the quote, subsidy and tariff, so no prices come from SaveBill. Yearly savings = generation x tariff x (1 + escalation)^year, minus yearly maintenance (% of quote). Generation uses 4 peak sun hours/day, 80% system efficiency, 550 W panels, 10 m² per kW (flat roof) or 8 m² per kW (sloped roof), 0.5% yearly output decline. Monthly generation = kW x 30 x 4 x 0.8. Payback is when cumulative savings reach net investment.
Disclaimer: results are illustrative estimates based on the assumptions above, not a quotation or guarantee. Actual generation depends on your site, shading, season and equipment.
Why you enter the numbers
Prices and tariffs differ by supplier and consumer category, so this tool uses your inputs instead of ours.
What it includes
- Yearly output decline for panel ageing
- A tariff rise assumption you can change
- Maintenance as a percentage of the quote
Frequently asked questions
Are these results a quotation?
No. They are illustrative estimates from the stated assumptions.
Is the payback guaranteed?
No. It depends on actual generation, tariff changes and your usage.