Solar Payback & Savings Calculator
Last reviewed August 2, 2026. The model excludes financing and tax advice; verify current tariffs, incentives, production, and replacement assumptions.
Direct answer: This tool separates simple payback, cumulative nominal cash flow, discounted operating cash flow, and NPV over an explicit analysis period. It is a cash-purchase model; loan, lease, and PPA financing are excluded.
Inputs
Financing: excluded. Enter the cash price and only incentives you have verified. Do not enter loan payments as maintenance.
Financial results
Results appear here after you click Calculate. Enter your values, then compare the result with the interpretation notes below.
Interpretation
- Simple payback is the first modeled year when cumulative nominal cash flow recovers net upfront cost.
- Cumulative nominal cash flow sums undiscounted annual savings and replacement costs.
- Discounted operating cash flow converts modeled annual cash flows to present value.
- NPV equals discounted operating cash flow minus net upfront cost.
These outputs are scenario comparisons, not tax, investment, or financing advice.
Formula or method
Each year’s production applies degradation; self-consumed and exported portions use separately escalated rates. Maintenance and selected replacement costs are subtracted in their modeled years. Simple payback uses cumulative nominal cash flow. Discounted cash flow divides each year’s nominal cash flow by (1 + discount rate)year; NPV subtracts net upfront cost.
Assumptions and limitations
- Cash purchase only; financing, leases, PPAs, taxes, depreciation, insurance, property value, fixed charges, and demand charges are excluded.
- Incentives must be independently verified; eligibility and tax value are not calculated.
- Rate escalation inputs are scenarios, not forecasts.
- Replacement timing and cost are user assumptions; enter zero when not applicable.
Worked example
The defaults model 25 years, separate retail and export values, 0.5% annual production degradation, annual maintenance, and an inverter replacement in year 15. Change one assumption at a time to compare base and conservative cases.
Sources
- U.S. EIA electricity data: a starting point for historical electricity-rate context; use the current tariff for the actual project.
- U.S. Department of Energy home solar guide: supports evaluating production, use, rates, export compensation, costs, and financing before purchase.