80% of rooftops can hold solar — Google

Source: Christa Marshall, E&E News reporter • Posted: Friday, March 24, 2017

Wondering whether solar power might be viable for your roof? Google wants to provide an answer.

The technology giant expanded its “Project Sunroof” program into all 50 states this month and found that nearly 80 percent of rooftops it assessed around the country are suitable for solar power. That doesn’t mean those 60 million buildings are likely to adopt panels — only that they technically can, according to Google.

The company is aiming to fill a data gap on how much solar power is viable — a factor that hasn’t always been easy to measure because of the difficulty of tracking how things like weather and shade from trees affect power generation in a given location.

Project Sunroof allows anyone with a computer to plug in a ZIP code and find out whether it is in viable solar territory. When the program launched two years ago, it only covered a few cities.

The project uses Google Earth and Google maps technology to build 3-D models of rooftops around the country by assessing everything from weather patterns to shade from nearby buildings. The project can calculate the amount of sunlight received by all parts of a roof over a year and also estimate how much power could be produced in a tested spot. In many of the locations, users can estimate potential energy savings.

Overall, Google ranked Houston at the top of U.S. cities, with 18,940 gigawatt-hours of annual solar generation potential. Los Angeles; Phoenix; San Antonio; New York; San Diego; Jacksonville, Fla.; Oklahoma City; Dallas; and Albuquerque, N.M., round out the top 10.

“If the top ten cities reached their full rooftop solar potential, they’d produce enough energy to power 8 million homes,” Google said in a statement.

More than 60 percent of rooftops in states not known for being sunny, like Minnesota and Maine, are suitable for solar, according to the data. Ninety percent of homes in Hawaii, Arizona and Nevada are “technically viable,” Google said.

There are many limitations to the project, including that it doesn’t assess costs and policies like renewable portfolio standards in the first place. It’s also difficult to track changes to buildings, and there are differing numbers on rooftop potential.

Last year, the National Renewable Energy Laboratory reported rooftop solar holds the potential to generate 1,432 terawatt-hours of annual energy, or about 40 percent of national electricity sales (E&E News PM, March 24, 2016).

Solar currently provides 1.4 percent of U.S. electricity, up from about 0.1 percent seven years ago, according to the Energy Department.