Utility tariffs: OpenEI Utility Rate Database
The Utility Rate Database (URDB), hosted on OpenEI with support from NREL, records residential tariffs for thousands of US utilities under a Creative Commons Attribution 4.0 licence. HomeWattCost models 80 utilities in 50 states and the District of Columbia, choosing the largest utilities in each state that have a current, complete residential tariff in URDB. Each month it downloads the full URDB export and follows each plan to its newest version. Export used: September 28, 2026. Tariffs last checked September 28, 2026.
Utility customers and billed prices: EIA-861
EIA’s annual survey of electric utilities (Form EIA-861, 2024 data) gives each utility’s residential customers, ownership, revenue and sales. HomeWattCost uses the billed price (revenue ÷ sales) to reject tariffs whose modelled price does not match reality.
State prices, use, gas and gasoline: U.S. Energy Information Administration
Monthly residential electricity price, sales and customer counts by state (latest month July 2026); residential natural gas price, volume, customers and heat content by state; and the retail price of regular gasoline by state or PADD region, all from EIA’s open-data bulk files. EIA data are in the public domain.
Vehicle efficiency: EPA and DOE
EV efficiency (combined kWh per 100 miles) and range for 30 models come from the EPA/DOE fuel economy dataset on fueleconomy.gov, newest model year of each version. Dataset published September 18, 2026.
Home load shapes: NREL ResStock
Hourly electricity use and space-heating demand of a typical single-family home in each state come from NREL’s End-Use Load Profiles for the U.S. Building Stock (ResStock 2025 release, 2018 weather), CC BY 4.0.
Solar production: NREL PVWatts
Hour-by-hour production per kW for each state comes from PVWatts v8 at the state’s 2020 centre of population (U.S. Census Bureau).
Refresh
A script downloads these files each month, validates them (a run that fails keeps the previous data), compares every tariff with its previous version and rebuilds the site. Tariff changes appear on the rate changes page. For the formulas, see the methodology.