Wattcrunch is a free, independent set of solar tools for US homeowners. We exist to answer the questions every household asks before going solar - how big a system do I need, what will it cost, how much will I save, and how long until it pays for itself - with numbers you can actually trust, and without a sales pitch attached.
Why we built it
Solar planning depends on production, installation costs, financing and utility settlement rules. Wattcrunch makes those assumptions visible so homeowners can compare scenarios before requesting an installation quote. The federal residential Section 25D credit ended for expenditures after December 31, 2025; confirm the applicable tax treatment with official guidance rather than assuming a credit applies to a new installation.
How our numbers are calculated
Calculator results use documented formulas and automated tests. Editable defaults and worked examples are planning assumptions, not measured customer outcomes or verified prices. Production estimates use the National Renewable Energy Laboratory's PVWatts model, the same engine professional installers rely on, tied to your exact latitude and longitude. Financial projections account for module degradation, utility rate escalation, net-metering policy, and the current federal and state tax landscape. Our incentive database is curated from DSIRE and public utility tariffs, and every record shows when it was last verified.
Our commitment to accuracy
Tax and incentive policy changes, and we change with it. The 2026 expiration of the Section 25D homeowner credit is reflected throughout our calculators by default, while still letting you model systems placed in service in 2025 or earlier. When the rules shift again, our tools will too. We would rather show you a smaller, honest number than a flattering, wrong one.
What we don't do
We are a planning resource, not an installer, lender, or tax advisor. We never sell your personal information, and our calculators work without an email address. For a binding quote, confirm your numbers with a licensed local installer; for tax questions, consult a professional.
Who writes and maintains Wattcrunch
The Marcus Vance leads the research, calculation, testing, and review of every guide and tool. We publish our formulas, assumptions, primary sources, limitations, and update process on our methodology and editorial policy page. Production estimates are grounded in the National Renewable Energy Laboratory's PVWatts® model, and incentive data is sourced from the DSIRE database and public utility tariff filings.
Ready to run your own numbers? Start with the System Size Calculator, estimate your savings with the Solar Savings Calculator, or find what you qualify for in the Incentive Finder. Questions? Contact us.