Solar
Solar Payback Calculator
Simple solar payback is reached when accumulated modeled bill offsets equal visible net installed cost. The production estimate remains independent of rates and policy data.
Estimate solar production independently, then calculate simple payback from visible installed cost, energy use, rate, escalation, and degradation.
Calculated result
Solar production estimate
Calculating…
Calculated locally in your browser
Planning math only. Verify equipment specifications and installation requirements separately.
Layer B · economics
Economics estimate
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State averages are editable prefills, not utility tariffs. This section is not tax, financial, or investment advice.
Data provenance: NLR PVWatts v8 grid awaiting its first private-key refresh; the visible peak-sun-hours fallback is active. EIA residential state averages updated 2026-08-13. ZIP centroids use the 2025 Census Gazetteer. No ZIP or calculator input is sent to those sources. Read the solar data provenance and limitations.
What this calculator returns
Simple payback is not discounted cash flow and does not predict resale value, financing, taxes, maintenance, or tariff changes.
Use payback to locate the break-even year
This page answers when cumulative modeled bill offsets first equal the entered net installed cost. It emphasizes the crossing point, not the percentage return after that point.
- Break-even test
- Each modeled year adds that year's bill offset until the running total reaches the entered net cost.
- No discounted cash flow
- Simple payback gives equal weight to dollars in different years and therefore does not calculate net present value or financing cost.
- No crossing within 25 years
- When cumulative offsets remain below cost, the page reports that outcome instead of inventing a payback date beyond the modeled period.
Formula and variables
The calculation runs entirely in your browser. Static formulas, definitions, examples, and tables remain readable without JavaScript.
Simple payback is the point when accumulated modeled bill offsets equal the visible net installed cost; annual offsets use adjusted production, usage, and rate.
- tpayback
- First modeled year in which cumulative simple bill offsets equal or exceed entered net cost.
- Cnet
- The visible net installed cost that the cumulative offset must recover.
- St
- Modeled bill offset in year t after the entered rate-change and degradation assumptions.
- ΣSt
- Running total of annual modeled offsets used to test for the break-even crossing.
- T
- The 25-year limit of this scenario; the calculator does not extrapolate beyond it.
Layer A annual kWh is always calculated first. Layer B can be disabled without changing that production result.
Worked example
| Input | Value |
|---|---|
| Solar array size | 8 kW DC |
| Monthly energy use | 900 kWh |
| ZIP Code | 80202 |
| Peak sun hours fallback | 4.5 h/day |
For an 8 kW array, the page first reports annual production, then accumulates the visible annual bill-offset scenario until it equals the entered $18,000 cost.
Reference table
| Payback driver | Effect on the crossing point | Evidence to use |
|---|---|---|
| Net installed cost | A higher cost takes more cumulative offsets to recover | Final installed quote and verified adjustments |
| Annual production | More eligible energy can increase each year's offset | Site-specific production model |
| Electricity value | A higher eligible rate can shorten simple payback | Current tariff and export terms |
| Degradation and rate change | Alter the sequence of future annual offsets | Module data and user-selected scenarios |
Frequently asked questions
What does a payback beyond 25 years mean?
The modeled annual offsets did not recover the entered net cost within the calculator's 25-year comparison period.
Does simple payback include financing interest?
No. Use the Solar Loan Calculator for an amortization comparison and enter the appropriate net cost here.
Are incentives included?
No incentive is automatically applied. The visible net installed cost should already reflect only amounts you have independently verified.
Assumptions and limitations
- Not tax, financial, or investment advice.
- EIA values are state averages, not utility tariffs.
- A result beyond 25 years is reported without extrapolating indefinitely.
- Obtain a licensed installer site assessment.
Method and sources
Review the solar data sources, calculation methodology, and electrical formulas for the references most relevant to this calculation. The broader technical sources index records source scope and verification. Last reviewed .