Solar ROI & Payback Calculator - Payback, NPV, IRR & LCOE Prompts

How It Works

1. Enter Cost and Manual Incentive Prompts

   Input the gross installed system cost and only enter federal, state, utility, rebate, or SREC values that have been verified for the project. Current IRS public guidance says the residential Section 25D credit is not available after December 31, 2025, so the app defaults the federal credit prompt to 0 percent and treats any entered credit as a manual tax assumption.

2. Set Production and Degradation

   Enter first-year production directly from a current PV model, installer proposal, utility record, or monitoring data, or use the simple kW x peak-sun-hours prompt. The simple formula is not PVWatts, NSRDB, SAM, shading, azimuth, tilt, snow, soiling, or hourly weather modeling. The degradation field is a user prompt, not a module warranty.

3. Enter Utility Rate and Export Value

   Use the actual bill or tariff for the utility rate and verify current net-metering or net-billing rules. Full-retail, reduced-export, and no-net-metering modes are screening assumptions only; they do not model time-of-use periods, demand charges, fixed charges, taxes, monthly true-ups, or pending policy changes.

4. Configure Financing

   Select cash, loan, or lease mode and enter the visible terms. The loan mode models annual payments and a year-one tax-credit inflow if entered, but does not include dealer fees, points, prepayment, refinancing, tax-basis changes, lease escalators, buyouts, PPA kWh rates, or contract clauses.

5. Review the Source-Aware Output

   The output shows payback, NPV, IRR, LCOE, ROI, lifetime production, lifetime savings, and year-by-year cash flow. Treat the result as a comparison worksheet, then verify tax eligibility, tariff value, production, contract terms, maintenance, and financing assumptions with qualified review.

Built For

• Homeowners comparing installer proposals with consistent source-aware assumptions
• Installers documenting where customer-entered tax, tariff, production, and financing assumptions still need review
• Analysts screening NPV, IRR, LCOE, and payback before building a full financial model
• Tax and finance reviewers identifying manual incentive assumptions that require current eligibility checks
• Utility or policy reviewers stress-testing export-credit and rate-escalation assumptions
• Owners deciding what project data to collect before requesting bids or contract review

Features & Capabilities

Multi-Metric Financial Prompt

Calculates payback, NPV, IRR, LCOE, ROI, lifetime savings, lifetime production, and year-by-year cash flow from the entered assumptions. It does not decide whether the investment is suitable or compare every available financial alternative.

Current-Law Tax-Credit Warning

Defaults the federal credit prompt to 0 percent because current IRS public guidance says the residential Section 25D credit is not available after December 31, 2025. Commercial 48E and other credits have separate qualification rules outside this app.

Tariff and Export-Value Modes

Supports full-retail, reduced-export, and no-net-metering screening modes. The result still requires current utility tariff, fixed-charge, demand-charge, TOU, export-credit, and grandfathering review.

Production and Degradation Prompts

Allows direct annual kWh input or a simple kW x sun-hours production prompt, then compounds annual degradation. Product warranties, PVWatts/SAM/NSRDB modeling, shading, azimuth, tilt, snow, soiling, and measured performance remain outside the app.

Cash, Loan, and Lease Modes

Models cash cost, loan payments, or a flat lease payment as screening cash flows. Dealer fees, lease escalators, PPAs, buyouts, tax-basis adjustments, recapture, and contract terms must be reviewed separately.

Exportable Source-Gap Report

The PDF and CSV report includes source warnings, assumptions, residual gaps, and source pointers so a reviewer can see exactly what the local model does and does not cover.

Assumptions

• Federal credit is a user-entered prompt and defaults to 0 percent under current residential 25D warnings.
• Utility rate escalation uses a fixed annual percentage over the entered analysis period.
• Production uses direct annual kWh or the local kW x peak-sun-hours prompt.
• Panel degradation compounds annually from the entered percentage.
• Discount rate for NPV is a user-entered opportunity-cost prompt.

Limitations

• Does not determine tax-credit eligibility, tax liability, basis adjustment, recapture, or qualified expenses.
• Does not model TOU periods, demand charges, fixed charges, taxes, riders, or hourly export value.
• Does not include MACRS, SREC/REC income, inverter replacement, insurance, property value, roof work, or contract clauses.
• Does not call PVWatts, NSRDB, SAM, or any installer production model.
• Does not account for future tariff, tax-law, incentive, financing, or maintenance changes unless the user enters them manually.

References

• IRS Residential Clean Energy Credit and OBBB termination FAQ source pointers.
• IRS Clean Electricity Investment Credit 48E source pointer.
• EIA Electricity Monthly Update source pointer for residential average revenue per kWh.
• PVWatts and PVWatts V8 API source pointers for production-model context.
• NLR/NREL PV Lifetime Project and PV degradation compendium source pointers.

Frequently Asked Questions