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Rooftop Solar Potential

By George Harvey

The Department of Energy’s National Renewable Energy Laboratory has released a report, “Rooftop Solar Photovoltaic Technical Potential in the United States: A Detailed Assessment.” Its conclusions were surprising, partly because they showed earlier estimates were far off the mark. The report can be seen at bit.ly/rooftop-solar-report.

The new calculations increased significantly the estimates of the percentages of our current electrical demand that could be generated from rooftops. This is true for not only the country as a whole, but for nearly every state. But what is really shocking is which states showed the greatest values. California is rated highest, and theoretically able to generate an impressive 74.2% of its demand from its rooftops. Surprising, however, the next six states are Maine (60.0%), Vermont (60.0%), Rhode Island (56.6%), New Hampshire (53.4%), Connecticut (49.8%), and Massachusetts (47.0%).

While our minds could go to the idea that rooftop solar could be augmented with such things as canopies over parking lots and sidewalks to fill all our needs, we should be careful not to fantasize overly. We will certainly not develop 100% of available rooftops and would be lucky to get half of that. Furthermore, we will very likely need to triple our demand, so we can cover the needs of heating and transportation without fossil fuels. Additionally, we need diversified power sources for several reasons. Nevertheless, this is very positive news.

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