Methodology

Data we use

• Electricity price:each state's average residential price from EIA's Electric Power Monthly, July 2026 YTD (year to date); latest month July 2026. We use the year-to-date average rather than a single month to smooth out seasonal swings. Average revenue per kWh across all residential customers, including fixed charges spread over usage. Preliminary estimates.
• Household use and bills: U.S. Energy Information Administration, 2024 Average Monthly Bill- Residential, 2024 (annual).
• Gasoline: EIA weekly retail price for regular gasoline, week of 2026-10-12. EIA publishes state prices for nine states; elsewhere we use the regional (PADD) average and say so on the page.
• Public chargers: U.S. Department of Energy, Alternative Fuels Data Center, Alternative Fueling Station Counts by State, snapshot 2026-10-15 (public stations, currently available).
• Solar output: PVWatts v8 solar model (National Laboratory of the Rockies, formerly NREL, run via its PySAM package) on NASA POWER hourly weather, average of 2015-2024 hourly weather. One location per state (a large city), with 1 kW DC fixed roof mount, 20 degree tilt, facing south (180 degrees), standard module, 14% system losses, 96% inverter efficiency, DC/AC ratio 1.2 (PVWatts defaults except tilt). Checked against the PVWatts web API for eight states: within 8%, 3% on average. We run the model ourselves because the PVWatts web service limits how often it can be queried without an account.
• Vehicle efficiency and range: U.S. EPA and DOE, fueleconomy.gov vehicle data (combined kWh/100 mi, includes charging losses), model years 2026-2027.
• Gasoline car comparison: 25.5 mpg. Average new-vehicle real-world fuel economy was 27.2 mpg, and 1.7 mpg lower without battery-electric and plug-in hybrid vehicles; we use 25.5 mpg for a typical new gasoline vehicle.

Formulas

• EV cost per 100 miles = kWh per 100 miles (EPA) × price per kWh. Monthly figures use 1,000 miles. Reference vehicles: 2026 Tesla Model 3 Standard RWD (24.3 kWh/100 mi); 2026 Chevrolet Equinox EV FWD (31.1 kWh/100 mi); 2026 Chevrolet Silverado EV Ext Range WT (47.8 kWh/100 mi).
• Gasoline cost per 100 miles = 100 ÷ 25.5 mpg × price per gallon.
• Solar system size = yearly household use ÷ PVWatts yearly output per kW. Panel count = system size × 1,000 ÷ 400 W, rounded up.
• Solar value per kW = yearly output per kW × average residential price. This is an upper bound: it assumes every kWh offsets one bought at the full retail rate.
• Break-even price per watt over N years = value per kW per year × N ÷ 1,000. It ignores financing, maintenance, panel degradation, rate changes and rebates.
• Battery hours = 13.5 kWh (Tesla Powerwall 3 datasheet capacity) ÷ average daily household use × 24.

Product data and plug-in solar

• Products on our power station, home battery and plug-in solarguides use only figures published on the maker's own US product page or datasheet, each with its link and the date we checked it. Where a maker does not publish a figure we show it as not stated rather than estimate it.
• Battery Sizer matchesare the cheapest configurations of those products that reach the computed size: one unit plus the maker's own add-on batteries for plug-in systems, at listed prices; or whole units for installed batteries, priced at EnergySage's average installed cost per kWh for the brand.
• Plug-in solar output uses the same PVWatts v8 model and NASA weather as our rooftop figures, with a 1.0 DC-to-AC ratio and three mountings: south-facing at 30°, vertical facing south, and vertical facing east or west. Its value assumes every kWh is used at home.
• Plug-in solar lawsare summarized from the bill or statute on each state legislature's website, with the date reviewed. We list pending bills only when we could confirm them there.

The Go Electric planner

What these figures leave out

• Time-of-use, EV and tiered rate plans, which can make your marginal price higher or lower than the average.
• Public charging prices, which are set by each network and usually exceed home electricity prices.
• Net metering and net billing rules, which decide what exported solar power is worth.
• Roof direction, shading and local weather that differ from the state's reference city.
• State and utility rebates. See incentives.

Updates

The data was last rebuilt on October 15, 2026 by a script that downloads each source file directly from the publisher. We plan to rebuild it monthly, after EIA publishes each Electric Power Monthly. The EV Finder and Home Battery Sizer product lists are refreshed separately by automated research and are labeled as indicative.