Solar ROI Calculator

What changes solar ROI most?

Four assumptions move the answer far more than the rest, and they are not the ones most quotes emphasise.

1. The electricity price you avoid. Solar does not earn money; it stops you spending it. Every kWh is worth exactly what you would otherwise pay, so the same system pays back roughly twice as fast at $0.30/kWh as at $0.15/kWh. This is the single biggest driver, and it is the one input you can read straight off your own bill.
2. What you assume about future prices. Over 25 years, escalation compounds — the table below shows what that assumption alone is worth on the worked example. It is also the assumption you can least verify, which is why it belongs in a sensitivity table rather than buried in a default.
3. Production, not panel count. A system is worth what it generates where it is installed. Orientation, tilt, shading and local sunlight can move output by a third between two identical systems, so a per-kW yield taken from a national figure is the weakest number in any solar estimate.
4. Whether you consume what you generate. If you generate more than you use, the surplus is only worth what your utility pays for it — which may be the retail rate, may be a wholesale rate, and may be nothing. This calculator values surplus at zero when you supply your usage, because guessing an export rate would flatter the result.

The federal credit, as of now

The federal tax credit input on this page defaults to zero, which is not what most solar calculators do. The IRS states that the Residential Clean Energy Credit equals 30% of qualifying costs for property installed from 2022 through December 31, 2025, and that the credit is not available for any property placed in service after December 31, 2025.

So a calculator that silently applies 30% to a system you are planning now overstates its return by roughly a third of the installed cost. The field is editable rather than removed, because it is still the right input for modelling a system placed in service inside the eligible window, or for standing in for a state or utility incentive expressed as a percentage.

What this page does not do is tell you whether you qualify. Eligibility depends on your tax situation, and a nonrefundable credit is only worth what you have tax liability to offset. Confirm the current rule with the IRS source linked at the foot of this page before you rely on any figure here.

Why output falls every year

Panels lose a little output annually. The calculator compounds that loss: production in year N is year-1 production times (1 − degradation) raised to the power N−1, so year 1 is undegraded by definition and the decline accelerates in absolute terms as the system ages.

On the worked example below, output falls from 10,000 kWh in year 1 to 8,867 kWh in year 25. Bill savings still rise across the same period — from $1,900 to $3,047 — because the assumed electricity price climbs faster than the panels decay. That tension between the two curves is most of what determines a solar return, and it is why a single-year saving figure tells you very little.

Limitations worth reading before you decide

• The production estimate is the weak link. This calculator has no solar resource data and does not model your roof. Get a location-specific estimate — the Department of Energy points homeowners at NREL’s PVWatts for exactly this — and enter it here rather than relying on the placeholder yield.
• Surplus generation may be worth less than you think. Enter your annual usage and any excess is valued at zero, which is deliberately conservative. Your actual export credit depends on a tariff this site does not know.
• Simple payback ignores the cost of money. Cash spent today could have earned something elsewhere; a payback period does not account for that, and neither does simple ROI.
• Escalation is a guess, always. Use the sensitivity table rather than one number.
• Nothing here is tax advice, and no figure on this page is published by any agency. The government sources listed below support specific inputs and rules, not the results.

If you are financing the system

Price the loan and the project separately. The amortization calculator gives the monthly payment and total interest on any fixed-rate loan; if the quote carries an origination fee, the personal loan calculator also shows the cash you actually receive once the fee is withheld. Compare that total interest against the lifetime net savings above: if the interest exceeds the savings, the project pays back but the financed version does not.