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When it comes to solar energy in Philadelphia, which has far fewer solar-viable houses than its peers, the Northeast is winning.

Most neighborhoods and zip codes in that area of Philly have a greater percentage of roofs that create solar energy than the city average, which is .39 percent. That data comes from a new tool released by Google. Called Project Sunroof, it allows users to see how many structures in a given zip code, city, county or state are topped with solar panels. It also estimates how much sunlight hits each roof, and how many roofs could handle being turned into solar energy producers (are solar-viable).

Billy Penn created a solar-powered index of Philly neighborhoods by taking the total number of equipped roofs in a given zip code and dividing it by the number of solar-viable roofs in the same area.

In the Far Northeast’s 19116 zip code, which includes Somerton, 1.21 percent of roofs viable for solar energy have panels installed — 70 of them in total. Rhawnhurst’s rating is 1.04 percent. Other Northeast zip codes range from 0.5 to 1 percent, all well above the Philadelphia average. The single neighborhood with the highest solar share is Chestnut Hill, at 1.27 percent.

Solar by zip code

This map breaks down the percentage of viable roofs that have solar energy by zip code:

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Per several studies, the best predictor for whether people will install solar on their house has nothing to do with income, race or class. It’s all about whether their neighbors have it.

That’s not great news for progress in Philly, since no neighborhood boasts a large portion of solar roofs, and neither does the city as a whole. Project Sunroof suggests solar panels cover just 495 out of an approximate 128,000 viable roofs (the city has estimated we have around 350 solar roofs). However, the tool also notes that the vast majority of the city’s housing stock isn’t solar viable. The other 350,000 or so roofs here either couldn’t handle solar or couldn’t efficiently use it, according to Google.

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That 29 percent viability share for Philly is lower than most other East Coast cities. In New York, 76 percent are solar-viable. In Washington, it’s 47 percent. Pittsburgh gets a 57 percent viability rating. Sunbelt cities like Houston (82 percent) and Phoenix (92 percent) are even more viable.

Some Philadelphia neighborhoods fall far below the 29 percent solar-viability rating. Olney gets a 13 percent score, for instance, while Mayfair has a dismal 3 percent.

Old houses and big trees

Philadelphia lags behind for a few reasons, including the average age of our housing stock — about 55 percent of it was built before 1950. Many older houses aren’t able to be equipped with solar panels, or at least not enough to provide the minimum 2 kilowatts of energy needed to be considered viable by Google (and certainly not enough for the 4 to 5 kilowatts that would really allow someone to save money on an energy bill).

In 2014, City Council set a goal of producing enough solar energy to power 25,000 homes by 2025. So far, the 10 total megawatts produced by Philly’s 350-plus solar roofs would likely power somewhere between 1,500 and 2,000 homes.

The city’s tree canopy is another factor. Emily Schapira, executive director of the Philadelphia Energy Authority, lives in West Oak Lane and noted that the tree cover impacts solar capabilities of the neighborhood. Per the Project Sunroof, West Oak Lane’s two zip codes come in at 27 percent and 16 percent solar viability, respectively.

How to bring more solar roofs to Philly

Schapira did suggest that people interested in solar should get their house checked out — even if Google’s tool shows the house as not viable. She’s speaking from experience: At first glance, it appeared that nearly 10 percent of 500 or so applicants for a city program called Solarize Philly wouldn’t be viable. But after a more thorough examination, program organizers determined half of those thought unfit could actually be equipped with solar.

“As we’ve been going through prescreens, we made a second pass and found a tree had been cut down,” Schapira said, “or the roof just didn’t have the shading that Google thought it did.”

The city will announce open enrollment program for its Solarize Philly program today. Neighbors will be able to work together to have their homes assessed for viability, and installation costs will be discounted based on how many homeowners move forward. The initial sign-up period will run through Sept. 30.

Mark Dent is a reporter/curator at BillyPenn. He previously worked for the Pittsburgh Post-Gazette, where he covered the Jerry Sandusky scandal, Penn State football and the Penn State administration. His...