Yesterday Google announced that it has expanded its online solar assessment tool Project Sunroof to at least some portion of all 50 U.S. states, to now cover 60 million buildings. When the project started in 2015 it was only available in parts of Northern California and the Boston metro area, but Google had reached parts of 42 states by late 2016.
The technology company has also revealed that 79% of the buildings which it analyzed have enough unshaded area to host PV modules. However, this was highly variable by state, with 90% of homes in Hawaii, Arizona, Nevada and New Mexico deemed viable, but only around 60% in Pennsylvania, Maine and Minnesota.
The company has provided numbers for the potential output of rooftop solar in various cities, estimating that Houston could generate 19 GWh annually with rooftop solar, Los Angeles 15 GWh and Phoenix 12 GWh.
However, these numbers suggest that Project Sunroof, like other online tools, is not taking into account policy limitations. Google lists New York City’s rooftop solar potential as 9 GWh, but like the more than 11 GW estimate provided by Mapdwell, this does not take into account the 6-foot setback on flat roofs mandated by the New York City Fire Department (the issue of this setback and other market barriers was covered in detail in the July 2016 global print edition of pv magazine).
Regardless, the central message – that there is truly nearly unlimited untapped potential for rooftop solar in the United States – remains valid. GTM Research estimates that even in solar market leader California only 8% of the viable roofs host solar PV systems.
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