How I count installers and calculate payback

Which cities get a page

A city page is built only when we have: the utilities serving the city, NREL production, a current residential rate, an export credit or rule for every utility checked in a primary source within 90 days, and installer names in utility records. Missing any of these, the page is not published.

Installers

• Systems by company — residential systems in Lawrence Berkeley National Laboratory's Tracking the Sun public data (utility interconnection records), for ZIP codes whose center lies within an equal-area radius of the city center. The latest public release covers installs through early 2024; each page shows the years used.
• Earliest record — the first system under that company name in the same ZIP codes. Renamed or acquired companies can appear under older names.
• Leased / PPA and battery shares — share of the company's systems marked third-party-owned or with battery storage. Shown only where the utility reports these fields.
• We do not publish historic prices from these records: they predate the 2026 market and are not a guide to what you will pay today.

Prices and payback

• Today's price — the average price per watt of current quotes from a named marketplace, with its update date. Quotes are not signed contracts.
• Production — NREL PVWatts v8 for the city center: 1 kW DC, fixed roof mount, 20° tilt, south-facing, 14% losses.
• Utilities — utilities serving a 3×3 grid of points inside the city radius (NREL utility rates API). A utility counts as serving the city when it covers at least 3 of the 9 points; utilities found at fewer points are named as serving parts of the area, without rates or payback.
• Typical energy charge — median energy charge of standard residential plans effective today in the OpenEI Utility Rate Database. Solar, export, low-income, demand, pilot, prepaid, EV and closed plans are excluded. Fixed monthly charges, adjustors and taxes are not included, so real bills are usually higher.
• Export credits and state rules — utility tariffs, state statutes and regulators, checked by hand with the date shown on each page.

Yearly savings = production × 50% × typical energy charge + production × 50% × export credit. Payback = (price per watt × system size − state tax credit) ÷ yearly savings.

Estimate from your bill

The calculator works for any US ZIP. Yearly use = monthly bill × 12 ÷ energy charge; system size = yearly use ÷ production per kW (rounded to 0.5 kW, 2–20 kW); cost = size × price per watt, shown as ±15%. Energy charge and export credit come from my checked data in covered cities; elsewhere the energy charge is the utility's average residential rate from the NREL utility rates API, and because the export credit is unknown the payback is shown for two cases: exports credited at the full retail rate, and exports earning nothing. Price per watt is the city average from EnergySage where I have it, otherwise EnergySage's state average (updated 2026-06-30) or the US average.

Quote checker

The quote checker uses the same data for the ZIP codes of covered cities. You enter the price and size from your quote and can change the energy charge, export credit and the share of power used at home (30%, 50% or 70%). Where a utility has no single export rate, the field starts empty and the estimate counts exports at $0 until you enter a value.

What the numbers leave out

• How much of your production you use at home — it depends on when you use electricity; we assume half.
• Future rate increases, panel degradation, financing costs, maintenance and inverter replacement.
• The federal Residential Clean Energy Credit, which is not available for property placed in service after December 31, 2025 (IRS).
• Reviews, workmanship and warranty terms of individual companies.