Each county gets one number, with a 95% range, a breakdown by city and ZIP, a check against utility records, and the list of addresses known to have solar.
54,336 single-family houses have solar panels
The address list and its Excel and CSV files open after you tap your name and type your PIN.
The county assessor's parcel records give the full list of single-family houses, so every house is counted once.
Every city and town permit portal with online records is collected and matched to its parcel. These are the addresses in the list.
Thousands of randomly chosen houses are inspected on the county's own aerial photos, to confirm the permit homes and to find panels with no permit on file.
The total is compared with the residential solar customers that utilities report to the U.S. Energy Information Administration each month.