Homeowner
Solar Payback Calculator
Nobody knows their annual kilowatt-hours off the top of their head, but everybody knows what the power bill was last month. Put in the system price and the bill, and this tells you how long until the system has paid for itself — in years and months, not a percentage.
What it asks for
- Installed system cost ($) — The total contract price, before any credit.
- Tax credit or rebate (%) — Enter 0 if you are not sure you qualify. Confirm with a tax professional.
- What do you know?
- Average monthly electric bill ($) — Add up twelve months and divide by twelve. One summer bill will mislead you.
- Fixed monthly charges ($) — Meter, service, and connection fees. Solar does not remove these — you stay connected to the grid.
- Share of usage the system covers (%) — A system sized to your whole bill is 100%. Shading or a small roof means less.
- Year-one production (kWh) — From the proposal, or from the array sizing calculator.
- Utility rate ($/kWh) — Divide a bill by its kWh. Do not use the advertised rate.
- Annual utility rate increase (%) — What the power company raises rates by each year. The US long-run average is roughly 2-4%.
- Annual panel degradation (%) — Modern modules lose about 0.4-0.55% of output per year.
Assumes cash purchase. Financing interest, maintenance, inverter replacement, and net-metering rules are not modeled. Savings grow with the utility rate and shrink with panel degradation.