3 GW of potential solar capacity on San Francisco roofs

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19th century writer Mark Twain is often credited with saying that the coldest winter he ever spent was a summer in San Francisco. With the city’s odd weather patterns and intense summer fog, it may surprise many that San Francisco also hosts an excellent potential for rooftop PV.

Solar mapping provider Mapdwell reports that San Francisco has the potential to host 3 GW of high-yield rooftop solar, according to their latest mapping. This follows a similar study of New York City, where Mapdwell found over 11 GW of capacity across the city’s five boroughs.

This is a particularly high capacity for San Francisco, as the city covers only 47 square miles with a mere 850,000 inhabitants, one-tenth the population of New York. One factor may be that the city is less dense, however Mapdwell was not available to comment on their findings by press time.

Neither San Francisco nor New York City offer the kinds of high capacity factors that PV plants in the Southwest, Texas and other regions offer. Based on Mapdwell’s numbers San Francsico’s 2.99 GW could generate 3.99 GWh annually, at an average capacity factor of 15%.

Solar is slightly less productive in New York, with 11.4 GW of capacity offering a potential of 13.3 GWh, for an average 13% capacity factor, or roughly half that of a typical utility-scale project in the desert Southwest.

Mapdwell’s maps of major cities provide property owners with individual assessment of their building’s potential, much like Google’s new Project Sunroof. The company’s tools were developed by a team at Massachusetts Institute of Technology, and Boston was one of the first cities that it mapped.

Similarly to Project Sunroof, Mapdwell also offers references to local installers, however its financial and incentive analysis does not include the inputs that Google’s project does. It does cover more geography. While Project Sunroof looks only at the Boston Metro area, San Francisco and Fresno, Mapdwell is already covering areas in the state of Oregon, Washtington D.C. and New York City.