Every number on this site traces back to one of the public datasets listed below. This page records the source, the licensing terms, and the date of the snapshot we are currently displaying. For the live mechanism behind those snapshots, see the data status page.
The EIA, an independent statistical agency within the U.S. Department of Energy, is the source of our residential electricity rates by state. We reference Table 5.6.A of the Electric Power Monthly ("Average Price of Electricity to Ultimate Customers by End-Use Sector, by State"), updated monthly by EIA with a two-month lag.
NREL, operated by the Alliance for Sustainable Energy under U.S. Department of Energy contract, publishes the National Solar Radiation Database. We derive state-level peak-sun-hour averages from NSRDB grid cells, weighted toward population centres. NREL also operates PVWatts, which we recommend for site-specific (roof orientation and tilt) modelling.
The 30% Residential Clean Energy Credit is codified at 26 U.S.C. § 25D and described in plain language on the IRS's Residential Clean Energy Credit page. The current 30% / 26% / 22% step-down schedule was set by §13302 of the Inflation Reduction Act of 2022 (P.L. 117-169).
DSIRE is operated by the N.C. Clean Energy Technology Center at North Carolina State University and is the most comprehensive single source of state, local, utility, and federal renewable-energy incentives in the United States. The state pages on this site render DSIRE programs filtered to residential solar; the authoritative current list is DSIRE itself.
scripts/dsire_import.php. Same data,
monthly cadence — sufficient for residential-solar reference use.
scripts/dsire_import.php) and Windows/Linux wrappers (scripts/refresh_dsire.*) are included; see scripts/README.md for Task Scheduler / cron setup.EnergySage publishes a semi-annual Solar Marketplace Report with median cash-purchase cost per watt for residential systems quoted through its installer-bidding platform. We use this as one of three reference points for our $2.90/W default cost. See energysage.com/data.
A quarterly market-tracking report published jointly by Wood Mackenzie and the Solar Energy Industries Association. We cite the executive-summary statistics, which SEIA releases publicly. See seia.org/us-solar-market-insight.
NREL's annual bottom-up modelled cost benchmark, derived from labour surveys, equipment pricing, and contractor margins. The most rigorous publicly-available reference for "should cost" in residential solar, cited here as a third anchor for our cost-per-watt assumption.
The 0.5%/yr panel degradation rate is the median value from the warranty datasheets of LG (NeON 2), Q-Cells (Q.PEAK DUO), REC (Alpha Pure), and SunPower (Maxeon) monocrystalline modules across the 2020–2024 product generations. Manufacturer warranties bound degradation by the worse of (a) the cited annual rate or (b) a 25-year end-of-life output floor (typically 84–92% of nameplate).
The 0.80 performance ratio is the long-standing NREL PVWatts default for well-designed residential rooftop systems.
Where we present content derived from DSIRE, the derivative content (our state-incentive summaries) inherits the CC BY-SA 4.0 license. All other original content on this site — methodology pages, guides, glossary, and the calculator's source code — is published under the same license. You may reuse it with attribution, including commercially, provided you license derivatives under the same terms.
EIA, NREL, IRS, DSIRE, SEIA, EnergySage, Wood Mackenzie, and equipment-manufacturer names referenced on this site are the property of their respective owners. References are nominative — used to identify the source of the data we cite — and do not imply affiliation, endorsement, or sponsorship.
If you find an out-of-date figure or a citation that fails to support the claim it references, please flag it via our contact form. Data corrections are treated as priority.
Four inputs. Sixty seconds. Every number traceable to a public source.