California looks to add solar and transmission along highways

Many states are building solar next to highways. Only one uses them as transmission corridors. A new bill orders California to explore both options.
By Jeff St. John

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An solar array is situated next to a highway interchange in a moderately wooded area
An 8.5-megawatt solar array in a highway interchange in Augusta, Maine — one example of the kind of highway right-of-way clean energy development called for in California’s SB 49 (Maine Department of Transportation)

There’s a lot of empty land along California’s highways — and the state will soon be looking at how it can fill some of it up with solar panels, batteries and power lines to help meet its clean energy targets.

That’s the goal of SB 49, a bill passed by California lawmakers and now awaiting the signature of Governor Gavin Newsom (D). The bill orders the California Department of Transportation to evaluate the suitability” of the land it owns alongside highway roadways, exits and interchanges for developing renewable energy, energy storage and electrical transmission and distribution facilities.

In a statement, State Sen. Josh Becker, the bill’s author, highlighted the potential for SB 49 to get much-needed renewable energy built, support clean energy jobs and earn the state some extra revenue in the process” via lease payments from clean energy developers.

SB 49 isn’t the highest-profile of the climate and energy bills passed in California’s busy legislative session, nor will it lead to immediate building along the rights of way the state’s Department of Transportation owns and manages along 52,000 miles of state highways and nearly 15,000 miles of federal interstate highways that criss-cross California. The bill gives the agency until 2025 to finish analyzing the potential for the land under its control and the steps it must take within state law, and in coordination with state energy and utility regulators, to make the development possible.

But Laura Deehan, state director of nonprofit group Environment California, one of SB 49’s key backers, believes that California could move relatively quickly to turn its highways into clean energy corridors.

This is a no-brainer for our state. Why isn’t it happening?” she said. It seems like this is one of those cases where inertia is the main opponent.” 

Other states are already earning money from solar panels built in the empty land surrounding highways and interchanges.

These projects make up only a tiny fraction of the utility-scale clean energy projects in the U.S. at present, but studies have found potential for gigawatts of solar and thousands of miles of high-voltage transmission using otherwise unusable highway rights of way. Given the challenge of siting and permitting the hundreds of gigawatts of clean energy and transmission grid infrastructure needed to decarbonize the U.S. power grid, land that can’t be used for other purposes should be treated as a windfall for the energy transition, she said. 

Getting solar built alongside highways

Every state has its own rules and regulations for what can be done alongside highways that can complicate its use for clean energy. That land must be kept clear of anything that would imperil driver safety, be maintained to limit environmental harms, and sometimes be kept available for highway expansion. But states including Oregon, the first to explore highway solar, as well as Maine, Maryland and Massachusetts, have set up structures for siting solar and supporting grid infrastructure within state-owned highway rights of way, giving California and other states a template to follow, Deehan noted.

And while states must coordinate their use of federal interstate rights of way with the Federal Highway Administration, that agency has already instructed states to put that land to use for clean energy and connectivity” projects including high-voltage transmission, broadband internet, EV charging, and solar and wind power. That’s an important shift from federal policies that used to prohibit utility infrastructure on interstate rights of way, she said.

California needs a lot more clean energy and grid infrastructure to meet its climate goals, she added — and a lot of the land needed for that expansion is already being used for farming or protected for environmental reasons. Rooftop solar can fill in some of this need, but it comes with its own policy complications.

The search for open space for more solar led Environment California to work with Senator Becker, Deehan said. Then her group got in contact with The Ray, a Georgia-based nonprofit focused on exploring sustainability and safety improvements on interstate highways — including its first project, a 1-megawatt solar array and an EV charging station at a rest stop near the Alabama border.

In 2021, The Ray formed a partnership with Esri, a global provider of geographic information system technology, to map out the parcel-by-parcel suitability of highway rights of way for solar development. That data informed Environment California’s initial study of the potential for solar along highways in Los Angeles, Ventura and San Diego counties. The results indicated that those three counties offer nearly 1 gigawatt of potential roadside solar capacity, enough to power more than 270,000 homes.

A chart of the acreage and potential solar generation capacity along highways in Los Angeles, Ventura and San Diego counties
(The Ray)

David Peters, The Ray’s Western regional manager, noted that a lot of that land isn’t realistically open to solar installations — some of it has too steep a slope [or] not enough insolation,” or other disqualifying characteristics.

Still, there’s a lot of space out there — and if you were in theory to develop it, there’s a huge potential that’s not being utilized at the moment, that we’d hope that California and other states can take advantage of.”

State transportation departments do need to make sure that solar projects don’t create safety hazards — but we’ve worked with a number of states on that,” he said. It’s mainly about making sure you’re far enough back in the setback and that you have fencing.”

Highway-side solar is also a moneymaker for state transportation departments, Peters said. Not only do solar developers pay for leases they hold on the land, but they also take over the duty of maintaining it — costs that states now bear on their own. A 2020 study from the Webber Energy Group at the University of Texas at Austin found that solar built along 200 miles of major interstate interchanges in the lower 48 states could provide a total of $4 billion per year for state transportation departments.

States can also set rules requiring solar developers to improve the land they build on, Peters noted. In Georgia and Maine, solar projects in highway interchanges have included planting pollinator-friendly flowers and crops to support bee and butterfly populations.

One big question is whether states can set up processes that are attractive to solar developers, who tend to focus on low-cost and complication-free sites, to build in highway rights of way. Hopefully SB 49 will help jump-start that,” Deehan said, by creating clear and simple methods for developers to lease and build on state-owned land.

Regulatory structures that support smaller-scale solar projects, such as state community-solar programs, are another key approach to allowing highway-side solar to compete against larger-scale projects for developer interest. A typical highway interchange may contain 10 to 20 acres of open land, enough for 2 to 4 megawatts of solar power, Peters said. The California Public Utilities Commission is in the midst of determining the structure of a new community-solar regime that could make projects of that scale viable for developers, Deehan said.

Once those policies are in place, Peters said, it’s about working with utilities and utility commissions to make sure [that] if it’s grid-tied, it can work out with the transmission and distribution system” — and potentially, using the highway rights of way as thoroughfares for expanding that system, he noted.

Highways as high-voltage transmission corridors? 

Transmission lines already cross highways around the country. But almost no states have taken the next steps needed to open up the land alongside highways for building new transmission lines, despite the clear potential for using those existing corridors to avoid the complex and yearslong land-use battles that now embroil these projects.

The sole exception today is Wisconsin, which passed a law in 2003 that’s led to a regulatory and policy framework that’s allowed 26 transmission projects, constituting hundreds of miles of high-voltage overhead power lines and towers, to be built alongside state and interstate highways.

But there’s little preventing other states from adopting Wisconsin’s playbook, said Randy Satterfield, executive director of the NextGen Highways initiative, a nonprofit group that’s been working with states and utilities to expand the use of highways for transmission development.

NextGen Highways grew out of an effort in Minnesota to review and adapt state policies to allow utilities and grid operators to consider highways as an alternative route for new transmission projects. It expanded to a national coalition this year after winning funding from the Bill Gates–founded Breakthrough Energy, and it is now working with a dozen states, he said.

Highway rights of way offer the greatest bang for the buck” for transmission projects, Satterfield said, because they avoid the painstaking work of securing permission and permits to cross land under the control of hundreds of individual public and private landowners. We could be giving utilities and transmission developers the tools to develop highway rights of way now.”

But inertia stands in the way, he said. From the 1950s until 1989, federal rules prohibited using interstate rights of way for utility infrastructure. That’s changed dramatically in the past few years, however, with the U.S. Department of Transportation now actively encouraging the use of highway rights of way for transmission projects.

Still, there’s some culture and history” at state transportation agencies that is holding them back from taking up this federal encouragement, he said. First, many states — including California — need to pass laws that lift any explicit prohibitions that still exist, he added.

Then, state transportation departments need to work with utility and energy regulators to develop clear processes for planning, permitting and building transmission along highways. Transmission planning is a notoriously complicated field, involving state regulators, utilities and interstate grid operators. NextGen Highways has developed a playbook based on Wisconsin’s past experience that it hopes will help other states manage those complexities, he said.

Satterfield noted that in his former position as an executive at transmission developer American Transmission Co., we would spend three to five years on public engagement, routing and siting before giving an application to the regulator” for a major new transmission line. But in Wisconsin, comparable large-scale transmission projects using existing rights of way are effectively truncating that timeline down to a year or a year and a half.”

Peters noted that The Ray is working with Esri to expand their mapping partnership to include data on transmission development as well as solar development along highways to help California and other states speed up the process.

California is in the midst of planning its own multibillion-dollar transmission grid expansions, a process that takes years of coordination between state agencies, utilities and grid operator CAISO. Satterfield said he hopes that SB 49 prompts the California transportation agency to move as quickly as possible to let highways play a role in the state’s planning.

Given how far behind the U.S. is in building the transmission needed to connect the hundreds of gigawatts of solar and wind power needed to cut carbon emissions, there’s little time to lose, Satterfield said. If we’re going to meet the climate challenge — and we’re already behind the eight ball — we need to start doing things differently.”

Jeff St. John is director of news and special projects at Canary Media. He covers innovative grid technologies, rooftop solar and batteries, clean hydrogen, EV charging and more.