Sensitivity tool · move the assumptions
Solar payback calculator — assumptions exposed.
A 7-year payback figure on a proposal is a 25-year forecast resting on four assumptions: rate escalator, production, degradation, and compensation model. This calculator runs the year-by-year math with each input editable and the headline year visible across conservative / moderate / aggressive escalator scenarios.
Updated May 22, 2026. EIA escalator data1 + PVWatts production methodology2 re-verified the same day.
The forecast test
The payback year is not the answer by itself. The useful answer is whether it survives a lower utility-rate escalator and a realistic export credit. If the result moves by more than two years, the proposal is selling a forecast, not a fact.
Your numbers — type them in
Payback + sensitivity
Within the plausible 7-15 year window for most US residential systems. Still worth running low/mid/high escalator scenarios — if the year shifts by more than two between conservative and aggressive assumptions, the headline number is fragile.
View 25-year savings table →
| Year | kWh | Rate | Savings | Cumulative |
|---|---|---|---|---|
| 1 | 10,900 | $0.1883 | $2,052 | $2,052 |
| 2 | 10,845.5 | $0.1958 | $2,124 | $4,176 |
| 3 | 10,791.3 | $0.2037 | $2,198 | $6,374 |
| 4 | 10,737.3 | $0.2118 | $2,274 | $8,648 |
| 5 | 10,683.6 | $0.2203 | $2,353 | $11,002 |
| 6 | 10,630.2 | $0.2291 | $2,435 | $13,437 |
| 7 | 10,577.1 | $0.2383 | $2,520 | $15,957 |
| 8 | 10,524.2 | $0.2478 | $2,608 | $18,565 |
| 9 | 10,471.6 | $0.2577 | $2,699 | $21,264 |
| 10 | 10,419.2 | $0.2680 | $2,792 | $24,056 |
| 11 | 10,367.1 | $0.2787 | $2,890 | $26,946 |
| 12 | 10,315.3 | $0.2899 | $2,990 | $29,936 |
| 13 | 10,263.7 | $0.3015 | $3,094 | $33,030 |
| 14 | 10,212.4 | $0.3135 | $3,202 | $36,232 |
| 15 | 10,161.3 | $0.3261 | $3,313 | $39,545 |
| 16 | 10,110.5 | $0.3391 | $3,429 | $42,974 |
| 17 | 10,059.9 | $0.3527 | $3,548 | $46,522 |
| 18 | 10,009.6 | $0.3668 | $3,671 | $50,193 |
| 19 | 9,959.6 | $0.3815 | $3,799 | $53,993 |
| 20 | 9,909.8 | $0.3967 | $3,931 | $57,924 |
| 21 | 9,860.3 | $0.4126 | $4,068 | $61,992 |
| 22 | 9,811 | $0.4291 | $4,210 | $66,202 |
| 23 | 9,761.9 | $0.4463 | $4,356 | $70,558 |
| 24 | 9,713.1 | $0.4641 | $4,508 | $75,066 |
| 25 | 9,664.5 | $0.4827 | $4,665 | $79,731 |
What this payback can't see
Time-of-use rate design (peak vs off-peak pricing). Inverter replacement around year 12-15 ($1,500-$3,000 for string inverters; microinverters are usually warrantied longer but not free). Roof re-shingle if needed mid-life. Property-tax assessment changes (some states exempt; others assess). Fixed monthly utility charges that survive the solar offset. For the bill-floor framing see the bill-not-zero guide.
Escalator reality check
What EIA actually reported.
Most solar proposals model a 3–4% utility-rate escalator compounded for 25 years. The math the salesperson didn't show you is what residential prices have actually done. Each EIA Electric Power Monthly release appends a row here — never overwrites the prior one.
| Month | Residential ¢/kWh | YoY change | EIA released | Note |
|---|---|---|---|---|
| March 2026 | 18.83¢ | +10.2% | 2026-05-21 | April CPI/PPI energy shock now visible in residential pricing — biggest YoY since the 2022-23 spike. |
| February 2026 | 17.65¢ | +7.4% | 2026-04-23 | |
| March 2025 | 17.09¢ | — | 2025-05-23 | Anchor — pulled as YoY comparison for March 2026 from the EIA Table 5.6.A grapher. |
| February 2025 | 16.43¢ | — | 2025-04-22 | Anchor — pulled as YoY comparison for February 2026. |
Source: EIA Electric Power Monthly, Table 5.6.A. Next release: June 24, 2026. Rows marked “—” are prior-year anchors used as YoY denominators for the more recent rows above. The 10-year residential-rate trend has been ~2–3% per year; recent year-over-year prints exceed that.
History grows each month after the EIA release — appended, not overwritten, so the audit trail stays public.
What this calculator owns.
Inputs
net cost, year-1 production, current bill rate, escalation, degradation, export value
Output
the first year cumulative savings cross the net project cost
Use it for
rerunning a proposal's headline payback with your own assumptions
Do not use it for
a full explanation of why proposals inflate payback assumptions
This page now owns the payback assumption audit. For the export credit part of that audit, use the net metering vs net billing guide.
- 1. EIA Electric Power Monthly, Table 5.6.A — Average Price of Electricity to Ultimate Customers by End-Use Sector. March 2026 residential average: 18.83 ¢/kWh, +10.2% year over year. 10-year residential rate trend: ~2–3% per year. Released 2026-05-21. Verified 2026-05-22. eia.gov/electricity/monthly ↩
- 2. NREL PVWatts (v8) — annual production estimator using NSRDB irradiance data with default 14% total system losses (soiling, shading, snow, mismatch, wiring, connections, light-induced degradation, nameplate rating, age, availability). Typical US residential output: 1,000–1,600 kWh/kW annually. Verified 2026-05-16. pvwatts.nrel.gov · API docs ↩
Next: Net metering vs net billing — the export-credit assumption that can move the payback year by years.