It’s getting harder to build large wind farms in the U.S. as the industry faces major political roadblocks. But a different kind of wind power could grow more quickly: small turbines that sit on the edge of rooftops rather than fields.

A startup called Accelerate Wind designed a system that takes advantage of the fact that when wind hits a building, it speeds up to flow over the edge.

Founder Erika Boeing, a mechanical engineer, started considering the idea while she was on a Fulbright Scholarship in the Netherlands. One night, while sitting in a brewery, she looked at the buildings across the street and suddenly had the thought that wind could be harnessed on roofs.

“I went home, and when I did the math, I realized that there’s actually a ton of power right at the edge of the roof,” she says. The wind speeds up naturally as the sharp edge of the building forces the air to change direction. With grants, she started developing the idea in a startup program at Argonne National Labortory.

A handful of other startups have also designed rooftop wind turbines. But Accelerate Wind added something new—a patented airfoil that hangs over the edge of the building to maximize the speed of the wind hitting the turbines. Without it, you’d need tall turbines to generate much power. “We’re able to capture more power lower to the ground, because we have a spoiler that lets us really use all the wind that’s accelerated by the building,” Boeing says.

On a warehouse or big-box store that already has solar power covering the roof, the turbines can add an average of 25% more power generation. The tech sits on the edge in space that would otherwise be unused.

The potential is huge. The company used an AI tool to analyze all of the buildings in the U.S. Around 375,000 could potentially install the tech, accommodating roughly 2 million turbines—enough to generate the amount of energy used by 29 million homes. (Though the current product is designed for large, flat roofs, the company may also later design a system that could work on single-family homes, adding to the total space available.)

After spending years developing and testing the tech, the startup will soon begin deploying it in pilots at commercial buildings for several large companies, as well as at Ellsworth Air Force Base in South Dakota. It’s a way to make buildings more resilient, so they still have access to power if the grid goes down. Wind power is often strongest at night, when solar power isn’t available. Building owners can save money on power bills. (For some buildings that use relatively little power, such as warehouses, solar and wind on the roof could potentially supply all of the energy needed.)

It’s also helpful for climate goals. “For customers focused on decarbonization, there’s been a big push to generate energy on site, because then you know that you’re directly retiring the electrons that you are generating,” Boeing says. And while building large renewable energy projects is slow, and getting slower thanks to the current federal government, getting permits for rooftop wind is essentially as straightforward as adding rooftop solar.

As the company grows, it plans to work with solar installers to install its equipment alongside solar panels. The payback period is comparable to solar—and in especially windy areas, it can be even more cost-effective.