Payback period is the simplest honest measure of whether solar makes sense for your house: how many years of electricity savings it takes to recover what you spent. Since the 30% federal credit ended, every payback figure published before 2026 is optimistic by several years, so it is worth recalculating rather than trusting an older estimate.
The formula
Payback years = net system cost ÷ annual electricity savings
Where annual savings = annual kWh produced × your effective rate per kWh. Two subtleties matter: net cost now means the full cost minus any state or utility incentive, with no federal credit to subtract; and effective rate is a blend of your retail rate for self-consumed power and your export rate for surplus, not simply your retail rate.
The four inputs, in order of how much they move the answer
- Net system cost. DIY versus professional is a 2-3x difference — the largest single lever, and entirely within your control.
- Your effective rate per kWh. Set by your utility. The gap between retail net metering and a poor export rate can add 3-6 years on its own.
- Annual production. Driven by peak sun hours and array size. A Seattle array produces roughly half what the same array does in Phoenix.
- State and utility incentives. Now the only incentives left, and worth checking properly before assuming zero.
Worked examples: an 8 kW system, 11,000 kWh a year
| Scenario | Net cost | Effective rate | Annual saving | Payback |
|---|---|---|---|---|
| DIY, retail net metering | $10,000 | $0.17 | $1,870 | 5.3 years |
| DIY, poor export rate | $10,000 | $0.135 | $1,485 | 6.7 years |
| Professional, retail net metering | $24,000 | $0.17 | $1,870 | 12.8 years |
| Professional, poor export rate | $24,000 | $0.135 | $1,485 | 16.2 years |
| Professional in NY, with 25% state credit | $19,000 | $0.17 | $1,870 | 10.2 years |
| Professional, 2025 with 30% federal credit | $16,800 | $0.17 | $1,870 | 9.0 years |
That last row is the comparison worth sitting with: the same professional installation that paid back in 9 years in 2025 takes 12.8 years in 2026. Nothing about the hardware changed. For DIY the shift is from 3.7 to 5.3 years — real, but far less damaging, which is the whole argument for DIY now.
Two adjustments that pull in opposite directions
Panel degradation reduces output by roughly 0.4-0.5% a year, so year-20 production is about 90% of year-one. This lengthens payback slightly.
Utility rate inflation has historically run a few percent a year, which means the electricity you avoid buying gets more valuable over time. This shortens payback, usually by more than degradation lengthens it.
For a first-pass estimate the two roughly cancel and can be left out. If you want to model them, apply degradation to production and an escalation rate to your utility rate, then find the year where cumulative savings cross net cost — but be honest that you are forecasting utility rates two decades out, which nobody does reliably.
What payback period does not tell you
- What happens after payback. A system paying back in 6 years with a 25-year warranty delivers roughly 19 years of near-free electricity — the return does not stop at break-even.
- Outage protection. Worth real money if you lose power regularly, and it does not appear anywhere in this calculation.
- Home value. Owned solar generally adds value at sale; leased solar has a mixed record.
- Roof timing. If the roof needs replacing in five years, add the cost of removing and reinstalling the array.
To fill in the inputs accurately, start with your real annual kWh, size the array in the full sizing walkthrough, and confirm your export rate using the net metering guide.