PVWatts production · 20- and 25-year scenarios

Solar Panel Savings Calculator

Estimate solar energy production, electricity savings, financing costs and payback. Change the assumptions to compare scenarios for your home.

Home, roof and cost assumptions

Annual consumption overrides the bill estimate. If left blank, usage = (monthly bill minus fixed charges) × 12 / retail energy rate. Use the energy portion of your tariff; demand charges and time-of-use pricing are not modeled. Fixed utility charges remain after solar and are not treated as savings.

Self-use is the share of generated electricity used on site, capped at annual consumption. Remaining output is exported at your entered compensation rate, assumed payable without an annual credit cap. Enter 0 if surplus energy receives no compensation. This annual approximation does not model hourly loads, batteries or utility-specific net-metering rules.

Roof azimuth: north 0, east 90, south 180, west 270. Tilt is degrees from horizontal. Other losses exclude shading; combined loss = 1 − (1 − other loss) × (1 − shading loss). In manual mode, roof inputs are disabled: your annual estimate must already include them.

No automatic 30% federal credit. IRS guidance says the residential clean-energy credit is unavailable for expenditures after December 31, 2025. Incentive inputs default to zero. Enter only amounts you have confirmed; this calculator does not determine eligibility, tax liability or interactions between rebates and tax credits.

Upfront rebates reduce purchase cost before financing. Tax-credit cash is assumed received at the end of year 1 and is not automatically paid against the loan. Loan fees are paid upfront; maintenance and export rates stay constant in nominal dollars. All displayed starting values are editable assumptions.

PVWatts lookup sends only ZIP and roof/system parameters to this website, uses Zippopotam.us for approximate ZIP coordinates, and sends those coordinates and system parameters to NLR/NREL PVWatts. Financial inputs remain in your browser. No account balances or financial results are sent to those services. A ZIP centroid is not your roof location.

Model and assumptions

Automatic production uses PVWatts V8 with NSRDB typical-year weather near the ZIP centroid, standard roof-mounted modules, DC/AC ratio 1.2 and inverter efficiency 96%. Your roof angle, orientation, size and combined losses feed that model. This is a typical-weather estimate, not an inspection or a forecast of a particular year. Shading is a simplified loss assumption. Snow, roof obstructions, equipment selection and local conditions can change actual output. A failed API lookup produces an error; it never substitutes invented production.

Alternatively, enter a first-year AC estimate from your installer or PVWatts. Manual production is not independently verified or recalculated from the ZIP or roof fields. The illustrative example is a sample scenario, not a local production quote. Approximate panel count rounds system watts divided by panel watts upward; it does not check roof fit or size a system to your usage.

Year 1 uses the production estimate as supplied. Each later year multiplies it by (1 − degradation rate). Electricity consumed on site is valued at the retail rate, escalating at your entered annual change. Surplus electricity uses the fixed export rate. Installation cost, maintenance, loan interest and fees reduce net savings; incentives increase it. Loan amortization rounds monthly payments and interest to cents and clears the balance on the last payment. No battery, lease, PPA, tariff caps, equipment resale value, roof replacement, taxes on export income or discount rate is modeled.

Sources and review

Reviewed October 5, 2026. PVWatts V8 model and API documentation; Zippopotam.us ZIP coordinates; IRS residential clean-energy credit guidance. Confirm utility export rules and incentive eligibility before committing to a system.

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