Gigawatts of solar could be built in the open land around US interstate highways

When Allie Kelly, executive director of the Georgia-based nonprofit The Ray, looks at the open land alongside U.S. interstate highway offramps and intersections, she sees tens of thousands of acres where solar panels could bloom, providing a significant fraction of the country’s clean power.

She also sees a local clean energy resource that can power roadside electric-vehicle chargers, provide revenues for cash-strapped state transportation agencies, and boost the economies of communities harmed by the country’s 65-year-old nation-spanning highway system.

Sure, there are challenges to developing solar PV in federal highway rights of way. But in the past year, some of the biggest roadblocks have been cleared away. Most notably, the Federal Highway Administration in April instructed state agencies to put those rights of way to use for ​“clean energy and connectivity” projects like high-voltage transmission, broadband internet, EV charging and solar and wind power.

“The right of way is that forgotten asset,” Kelly said in an interview last week. ​“This is land that will never be farmed, never be utilized,” but could be used ​“to go big to solve the climate crisis.”

Figuring out just how big solar could get along the U.S. interstate highway network has been one of The Ray’s missions since its 2014 founding as a test bed for technology along an 18-mile-long stretch of Interstate 85 in western Georgia. The group’s first project was a 1-megawatt solar array and an EV charging station at a rest stop near the Alabama border.

A handful of other solar projects on state-managed interstate rights of way have been built in Oregon and Massachusetts, and the Maine and Maryland transportation departments are targeting solar development as well, she said. But the scope of development so far pales in comparison to its potential, she said.

A study from the Webber Energy Group at the University of Texas at Austin last year found 200 miles along the major interstate interchanges in the lower 48 states suitable for solar development, capable of supporting 23 gigawatts of solar PV. That’s nearly a quarter of the 103 gigawatts of distributed solar a recent study forecasts the U.S. will need by 2030 to reach the Biden administration’s goal of zero power-sector carbon emissions by 2035.

Solar projects along highway interchanges fall into an intermediate size category — not as big as utility-scale solar farms, not as small as rooftop solar projects. A typical interstate interchange has about 20 acres of open land, which could support an average of about 4 megawatts of solar PV capacity, Kelly said.

While smaller-scale solar projects are seen as a valuable accompaniment to the utility-scale solar and wind farms needed to decarbonize the power grid, the economics behind intermediate-scale projects aren’t as strong.

But highway-sited solar could create an interesting new market niche for intermediate-size projects. The Webber study calculated that solar built at interstate interchanges could provide $4 billion per year for state transportation departments that own and maintain the rights of way along interstate highways. Today, those rights of way are ​“a deep liability” for state agencies, Kelly said.

The prospect of generating revenue at these sites could create strong incentives for transportation departments to work with project developers and utilities to find ways to make solar projects pencil out. Georgia Power’s 25-year deal for The Ray’s first solar project pays the Georgia Department of Transportation for use of the land. It also puts the utility in charge of operating the LED rampway lights at the highway exits, and maintaining the native plants between solar panels that provide habitat for bees that pollinate local blueberry farms.

Solar along highways could also help provide the massive amount of EV charging needed to support the switch from fossil-fueled to battery-powered vehicles, Kelly said. High-voltage fast chargers use enormous quantities of electricity, prompting many of the highway charging sites using them to build solar and batteries. ​“You can imagine that 4-megawatt solar site could provide the power for storage-backed EV charging,” Kelly said.

Making roadside solar work at nationwide scale 

Whether solar developers can be lured into doing projects in the unfamiliar environment of highway rights of way is an open question. But if a good model can be developed, it can scale.

“The national highway system was built relatively the same in all 48 states,” Kelly said. ​“Whatever we prove successful and safe in one area of the national highway system can be replicated at other sites.” (She noted that the sites identified by the University of Texas study don’t include highway medians, which would be challenging for construction and maintenance vehicles to access without blocking lanes.)

Highways tend to be relatively close to power grid infrastructure, she added, which could make roadside solar cheaper and easier to interconnect to the grid than solar on further-off rural areas with cheap land.

Last week, The Ray unveiled a project with Esri, a major global vendor of geographic information system (GIS) computer mapping technology, that aims to give developers and utilities detailed information about highway solar sites. It will combine state transportation department data with Esri’s in-house data on factors like solar radiation, vegetation cover and the layout of solar sites in relation to highway scenic overlooks.

“We have a whole range of fairly detailed surface data,” said Terry Bills, Esri global transportation industry director. The company already works with both state transportation departments and solar developers, giving them data to ​“literally calculate, parcel by parcel across the entire state, the solar potential” of different right-of-way sites. This screenshot indicates the tool’s assessment of a section of interstate highway in Iowa, with solar potential ranked from high (red) to lower (orange to yellow). 

The Ray is developing the Esri tool for use with Texas’ and Arizona’s transportation departments and the Pennsylvania Turnpike Commission, and is looking for more partners, Kelly said.

This kind of data could become far more valuable now that the federal government is encouraging states to use highway rights of way to support clean energy, she added. Prior to the Federal Highway Administration’s April guidance, ​“the federal government wasn’t on the same page in terms of how to treat these projects,” Kelly said, leaving individual agency field offices with discretion on how to deal with proposals like The Ray’s solar installation.

The Federal Highway Administration has now clarified that it can support ​“public-private partnerships to develop renewable energy projects,” including those that involve land leases, licensing agreements and power purchase agreements. Its guidance also aligns federal policy with the Biden administration’s interest in using highways as routes for high-voltage transmission corridors and for laying broadband fiber to communities now lacking high-speed internet access.

This kind of federal guidance ​“sets the pattern in a way that can be replicated across the country,” John Porcari, managing partner of 3P Enterprises and former U.S. Department of Transportation deputy secretary, told Canary Media in an April interview. Transmission grid developers are already exploring highway rights of way for underground high-voltage direct current corridors, but local clean energy projects could offer ​“not just a lot of additional power, but power in different places with different interconnections.”

The Biden administration has also pledged billions in infrastructure funding to aid communities harmed by the building of the interstate highway system from the 1950s to the 1970s. Many communities of color were targeted for highways that demolished homes and businesses and separated them from their neighbors.

“I don’t need to tell you that the national highway system broke communities,” Kelly said. In the future, low-income communities clustered along the interstate highways could benefit from projects that deliver clean energy and reduce air pollution, she said.