Data sources

We use public, official datasets. Each table and chart on the site names its source and the period covered.

U.S. Energy Information Administration (EIA)

What we use: Monthly and annual residential electricity price, sales and customers by state (electricity/retail-sales); residential natural gas prices (natural-gas/pri/sum) and heat content of delivered gas; weekly retail regular gasoline prices (petroleum/pri/gnd), latest week 2026-11-02; Residential Energy Consumption Survey (RECS) 2020 state tables for space heating (CE4.6.NG.ST, CE3.1.ST, State Square Footage).All via the EIA Open Data API v2 or EIA’s published tables.
Latest period on this site: Aug 2026 (retrieved November 5, 2026)
Update schedule: Checked monthly. EIA releases state data with a lag of about two months, and monthly figures may be revised later.
License: EIA data is a U.S. Government work in the public domain. See EIA copyrights and reuse.
Attribution: We cite EIA as “Source: U.S. Energy Information Administration (Mon YYYY)”. EIA does not endorse this site, its calculators or any derived figures.

What we use: Annual and monthly AC production per kW for a representative location in each state, from the PVWatts v8 API (version 8.5.0), computed in advance and cached; we never call the API when you load a page.
Attribution: Solar production estimates: PVWatts® by the National Laboratory of the Rockies (formerly NREL), U.S. Department of Energy. Used under the laboratory’s data notice; DOE/NLR do not endorse this site.

What we use: EPA combined electricity consumption (kWh per 100 miles) and range for 35 current electric vehicles, from the public vehicles.csv file (version of Tue, 29 Sep 2026 19:47:00 GMT). We use the data only, not vehicle photos.

What we use: The category of compensation for exported solar generation in each state, from the map “Distributed Generation Customer Credit Rates for Excess Generation” (May 2026). Source: DSIRE / NC Clean Energy Technology Center, “Distributed Generation Customer Credit Rates for Excess Generation” (May 2026). Rules for individual utilities, co-ops and municipal utilities can differ.

What we use: Statewide annual heating degree days (base 65 °F) from Climate at a Glance, 2016–2025 and 2020, to adjust heating estimates to typical weather and to size heat pumps. Public domain. Alaska and Hawaii have no statewide series; DC uses Maryland.

What we use: Water heater test constants (10 CFR 430 Subpart B, Appendix E) and federal minimum efficiency standards (10 CFR 430.32); the ENERGY STAR room air conditioner sizing chart and adjustments. ENERGY STAR does not endorse this site.

What we use: The default installed price for residential solar ($3.6/W): Berkeley Lab, U.S. Distributed Solar and Storage: 2026 Data Update (Aug 2026).

If you believe a figure differs from the source, please let us know. Changes are listed in the update log.