How to turn trash into treasure: Put solar panels over landfills

There’s a lot of open land waiting to be covered with solar panels — as long as you don’t mind building on top of trash. 

Take the recently opened 5.2-megawatt Solar Star Urbana Landfill project from solar developer Nexamp. Built on a 40-acre closed landfill outside Urbana, Illinois, the project has turned a trash dump unsuitable for almost any other productive use into a clean-energy resource for low- and moderate-income residents able to tap its output at low rates under a state program.

The Boston-based developer has built similar landfill solar farms in California, Massachusetts and New York. ​“We want to do more of these projects,” Ethan Gyles, the company’s director of channel development, said in an interview this month. ​“Landfill and brownfield projects are a win-win for everyone. It’s land that typically can’t be developed for other productive use.”

The U.S. will need millions of acres of solar panels to decarbonize its power grid. Closed landfills, which are defined as landfills that are no longer accepting solid waste, could provide a significant portion of that total, according to a new report from nonprofit research organization RMI. (Canary Media is an independent subsidiary of RMI.)

Out of the 10,000 closed landfills across the country, at least 4,000 of them could host solar projects, the report concludes. The total generation capacity of solar at these sites could exceed 63 gigawatts, more than two-thirds of the country’s entire solar capacity installed through 2020.

Thousands of other closed landfills may be able to host additional gigawatts, but RMI lacked data from many states that would have been necessary to carry out a comprehensive analysis, said Matthew Popkin, the manager on RMI’s urban transformation team who co-wrote the report.

As of last year, only about 500 megawatts of U.S. landfill solar projects had been completed, according to data from the U.S. Environmental Protection Agency, so there’s tremendous room for growth. Three-fourths of the existing projects have been built in Massachusetts, Connecticut, New Jersey and New York, states that have a combination of incentives and regulatory structures to encourage solar developers to build over landfills.

“If you look outside of those four states, there are solar projects [on landfills] happening — but they’re happening slowly and from the ground up,” Popkin said. ​“What this report hopefully shows is that these are not one-off projects, but a real opportunity for scale and impact.”

The pros and cons of building solar on closed landfills 

Popkin, who worked on urban land redevelopment and revitalization projects before joining RMI, highlighted a host of reasons for cities, counties and states to target landfills for solar development. The most obvious reason is that, unlike undeveloped land or farmland, there’s little else to be done with a closed landfill.

“Think of the avoided cost of using a closed landfill that couldn’t be used for anything else, versus another plot of land that could house a school or a hospital or housing,” he said. 

Landfills also tend to be located in areas that ​“have been marginalized for years,” including low-income communities, Popkin said. Solar farms can offer clean energy to surrounding communities as well as generate revenue to offset the maintenance costs borne by local governments that manage landfill sites.

Building solar on closed landfills comes with engineering and regulatory challenges that make these projects a bit more expensive than solar built on open land, however, Gyles said. 

“One is environmental liability,” he said. Closed landfills have to manage groundwater contamination and the emissions of methane and carbon dioxide from rotting trash.

Cities, counties or private owners of landfills can certainly use revenue from solar projects, in the form of land leases or other payment structures, to help cover some of those costs, he said. But landfill owners that insist solar developers take on liability for environmental compliance aren’t likely to close the deal. ​“The solar economics are not always going to be able to absorb that kind of responsibility or risk,” he said.

There’s also the issue of the land itself, Gyles said. Closed landfills are ​“capped,” or covered up with a combination of soil, clay and materials like asphalt or concrete, to contain the underlying waste and divert water so it doesn’t seep through.

These caps can’t be pierced by the steel pilings that anchor most solar arrays to the ground, so landfill solar projects have to use concrete blocks as ballast instead, which adds time and cost, he said. (This also precludes the use of tracker systems that shift the orientation of solar panels to follow the sun, which haven’t yet been designed for use on concrete ballast foundations, Gyles pointed out.)

Capped landfills also slowly settle over time as the underlying waste decomposes and breaks down, which can shift the ground underneath in ways that could damage or destroy the solar panels on top of it, Gyles said. That’s why developers including Nexamp target landfills that have been capped for at least a decade, which is enough time for the most dramatic settling to have already occurred.

All of these complications add about 15 to 20 percent to the cost of a landfill solar project compared to one built on open, undisturbed land, according to Nexamp and other solar developers. That’s enough of a premium to require some kind of financial incentive to make landfills worthwhile targets for developers.

Lining up incentives, getting communities involved

Closed landfills also tend to have a smaller footprint than the sprawling sites of the utility-scale projects that have dominated U.S. solar development to date, Gyles noted. To make these smaller-scale projects worthwhile, regulatory structures such as state community solar programs and virtual net-metering are needed, allowing smaller-scale projects to earn revenue to make up for their relative lack of size.

Popkin highlighted several ways that the states that have dominated landfill solar so far have created structures to support this growth. The Solar Massachusetts Renewable Target Program (SMART), for instance, sets the payment levels that solar projects receive from utilities and allows projects to ​“stack” increases in those payments, known as ​“adders,” that boost the value of the solar power they generate — including one adder of 4 cents per kilowatt-hour for landfill projects and another of 6 cents per kilowatt-hour for community solar projects serving low-income customers. SMART also disincentivizes projects built on undeveloped land. Other states, including New Jersey and Illinois, have set specific targets for brownfield solar development as a portion of their overall renewable energy goals.

Gyles pointed out that Nexamp’s Urbana project tapped into the Illinois Solar for All program, which offers increased payments to projects that sign up lower-income customers for the solar power they generate. The company’s other landfill projects have relied on similar community-solar or virtual-net-metering structures that ensure the power they’re generating can secure a predictable return.

Aligning efforts between multiple local governments and community groups can help landfill solar projects get off the ground, Popkin said. Annapolis, Maryland’s 16.8-megawatt landfill solar project sells power to the city, Anne Arundel County and the county’s board of education, for example.

Landfill solar development can be combined with other community projects to bring multiple benefits to the local populace, he added. The proposed 52-megawatt Sunnyside Energy Project development in Houston, Texas will offer nearby low-income residents the opportunity to buy solar power at cheap rates and will include a community center and agricultural training hub to support the neighborhood surrounding the landfill, for example.

“Communities across the country are trying to meet ambitious climate goals,” Popkin said. ​“More often than not, they want to do as much as possible locally, because you get local jobs and economic development. […] We’d encourage cities and counties to be ambitious with this.”