Using the satellite tool Google Project Sunroof, which maps existing rooftop solar installations, the group found more than 4,000 houses with rooftop solar and 4,000 neighboring houses without solar.
They then matched the addresses with political and voting behavior data purchased from a political data company.
For each address, they acquired information like party affiliation, voting activity, whether the household rented or owned the property, and basic socioeconomic and demographic data.
After crunching the numbers, they found that 34 percent of properties with solar belonged to registered Democrats, and 20 percent belonged to registered Republicans. (The remaining 46 percent were independents or unregistered.)
The neighboring, non-solar houses were split along similar lines.
“We’re not actually seeing Democrats have solar and Republicans don’t,” Mildenberger said. “This is reasonably strong evidence that people are not deciding to adopt solar out of some sort of ideological preference.” He attributes the higher number of Democrats with panels to the fact that areas with more Democrats, like California, also tend to have more solar panels in general.
Mildenberger’s work builds on similar findings from an earlier study by a group out of UC-Berkeley looking at political affiliation and rooftop solar in just two states: Texas and New York. While those researchers didn’t have the granular address data that Mildenberger’s group worked with, they found that Republican-majority communities had installed rooftop solar panels at the same or greater rates than Democratic-majority communities.
“Both papers are pointing to this fact that Republicans are given this image that they are not participating in the solar revolution, but they are,” said Deborah Sunter, a co-author of the earlier paper who’s now an assistant professor at Tufts. “There’s a mismatch between what the constituents are doing and what the politicians are advocating for.” In several states, like Ohio and Kentucky, Republican-led legislatures are rolling back incentives for renewable energy.
But the new study suggests that could change. That’s because people with rooftop solar were significantly more likely to vote than those without.