Run your own conservative solar payback scenario.

How to read this estimate

This calculator is a screening tool for comparing assumptions. It does not inspect your roof, read a utility bill, select an installer, or predict the exact production of a specific address. The result is useful when the same inputs are tested across several quotes, because it makes optimistic assumptions easier to see before you spend time on a proposal.

The gross-cost screen starts with system size in kilowatts, converts that value to watts, and multiplies it by the installed cost per watt used by the selected scenario. The calculator then applies its displayed 30% federal-credit scenario to show a net-cost estimate. That scenario is not a finding that a household qualifies for a credit. Check current eligibility, timing, and tax guidance with the Internal Revenue Service and a qualified tax professional before relying on it.

Annual savings combine the system size, an annual production estimate, the retail electricity rate, and the export-credit factor. A factor of 1.0 represents a full-retail scenario in the model; a lower factor represents a more conservative value for exported production. This is why two homes with the same system size can have different results. Household usage, the timing of consumption, utility fixed charges, demand charges, battery dispatch, shade, roof orientation, equipment degradation, financing, and installer pricing can all change the real outcome.

Run at least three cases before treating a result as useful: a quote case using the installer's assumptions, a conservative case with higher cost and lower production, and a local-policy case with the export value you can actually verify. If the payback changes materially between those cases, the important next step is not a more precise decimal. It is to request the missing production, tariff, interconnection, and financing details from the installer or utility.

The 25-year net figure is a model output rather than a promise of savings. It is intended for side-by-side screening and should be read with the estimate disclaimer. Do not use it by itself to decide whether to borrow money, sign a contract, claim a tax benefit, or assume that a policy will remain unchanged. The methodology page explains the model boundaries, while the editorial policy explains how source dates and corrections are handled.

Public reference points

The site separates generation, rate, installed-cost, and policy inputs so readers can inspect the original public reference points. These links are starting points for verification, not endorsements of a quote or an installer.

• NREL PVWatts v8 — Solar generation modeling.
• U.S. Energy Information Administration — Residential electricity rates (2024).
• LBNL Tracking the Sun — Installed cost by state (2024).
• DSIRE — State incentive and net metering policy.

Public source values have review dates and may not match a current utility tariff or a current installer quote. Recheck the local source, ask what date a quote uses, and send corrections through the contact page when a source link, label, or calculation explanation needs attention.

For a reproducible comparison, save the date, unit, and value for every input beside the calculator result. Record whether the number came from a bill, a proposal, a public table, or a policy document. When an installer changes one assumption, change only that input first so the effect is visible. This simple record prevents a favorable output from being compared with a different quote basis and makes later source updates easier to audit.