The report was published by Environment California and is available for download.
San Diego has 4,507 rooftop systems that have been installed, compared to a little over 4,000 in runner-up Los Angeles, a city with a much larger population, according to the report by Environment California.
San Jose, San Francisco and Fresno rounded-out the top five.
Within San Diego County, Escondido ranked 17th with 709 systems, Poway was 26th with 544 and El Cajon was 28th with 533.
In generating capacity, San Diego was tops with 36,775 kilowatts that are tied to the electrical grid, just ahead of Los Angeles. Poway ranked 41st, Escondido was 48th and Chula Vista 50th.