Options for a closed landfill are limited, as it can be hard to find developers willing to invest in projects for the sites. While there are examples of passive walking parks and ball fields — including the development of the largest former landfill in the world into a park — it can also be difficult to convince communities and consumers to choose to spend time on a covered landfill.

And even if nobody wants to live near or use the land, the landfill owner is responsible for maintaining the cover for decades. Without advanced planning, the 30-year (or sometimes longer) time period for maintaining the site can be a huge cost sink.

Capturing methane to sell as electricity — or compressed natural gas — has long been a reliable source of income for landfill owners. In more recent years, a second source of income has been catching on for landfill operators — solar panels.

An easy match?

Solar panels are an easy, passive way for site owners to generate income. Once installed, panels will generate electricity which can be sold back to the local utility. 

"It's a nice, steady revenue stream that's coming back to the community or to the private landfill owner," said Jeff Murray, president of the Solid Waste Association of North America. Murray is a registered professional engineer in Raleigh, North Carolina, where he works as an associate and solid waste section manager for HDR.

It doesn't take a lot of creative thinking to realize that closed landfill sites can be good locations for solar panels. They're large, mostly-flat areas without shade from trees. If the landfill wasn't covered flat, then it's at least got one south-facing slope that's highly efficient for capturing solar energy.

The same could be said, though, of other sites including old farmland or even just an open field. However, there are two factors that help landfills stand out.

The first is that, by their very nature, landfills have to be fenced off — first to protect operations and keep people from getting injured, and then later to protect the cover from getting damaged. Those already-necessary barriers can be a cost-saver for solar panel installers.

Secondly, and perhaps more importantly, many landfill sites will already have interchanges and connections to the power grid. Instead of having to build all-new infrastructure to connect solar panels to sell electricity, developers can plug into what's at the site already.

Obstacles

Of course, panels would have to be installed carefully, as to not compromise the final cover system. In that same vein, it would be easy to worry about settlement as material in the landfill ages. 

However, the slow rate of decay takes away much of that concern. This is especially true since objects such as bath tubs are no longer included in with general waste, assuaging fears of differential settlement. Ultimately, according to Murray, the changing slope of a covered landfill shouldn't keep projects from taking off.

"That concern shouldn't stop you from looking at development of solar fields," He said.

In fact, the biggest concern may come down to cost. Building on a landfill can be expensive and involve significant red tape.

Jesse Grossman, CEO of Soltage, a solar company that's installed on several landfills, said there are multiple parts that make developing on a landfill more expensive.

You may have to rewrite post-closure permits for landfills to allow solar panels to go on top. There are local and state regulatory agencies to deal with. Construction has to be carefully vetted so the cap isn't damaged, and labor costs on a landfill may be higher, too.

To make up for those added costs, Grossman said, governments can sweeten the deal for developers.

"State regulatory agencies, state-level governments, really need to send the market the right signals to go ahead and do solar landfill development," Grossman said. Those signals could look like tax credits or tax incentives, specifically for developing on landfills, to make up for the extra associated cost.

Additionally, Grossman said, solar developers would likely be looking for landfills that have been closed for at least 10 years, so that settlement is not as much of a factor.

Ultimately, it may come down to a simple equation — can you make enough money selling electricity back to the grid to make up for the cost of development and maintenance? 

"From a landfill owners perspective, it's certainly something that should be looked at as part of your overall post-closure and your master plan of your facility, especially if you're in a state that has a good portfolio for renewable energy credits, and if the federal government continues to provide federal tax credits for solar development," SWANA's Murray said.

Recent solar projects

Rochester, NY

Rochester officials used old iron slag to level off a notorious remediated landfill in the city's west side. On top of the 7-acre refinished slab, AES Distributed Energy of Colorado installed 7,800 solar panels, capable of generating up to 2.6 megawatts of electricity. The panels will be used to power Rochester City Hall and an operations center for the city.

The Emerson Street Landfill was city-operated and closed in 1972. After it was turned over to the state for redevelopment, it was classified as a hazardous waste disposal area and has required extensive remediation. The site was dedicated in late October.

Randolph, Plainville and East Bridgewater, MA

Republic Services unveiled in September a total of 41,000 solar panels across three closed landfills in Massachusetts. The 13.5 MW project can power an estimated 1,900 households and was designed for a 40-year lifespan.

Soltage was behind the project, with investment from Basalt Infrastructure Partners and Eastern Bank. The projects benefited from a favorable regulatory climate and incentives for renewable energy projects in Massachusetts.

Williamstown, MA

Made possible because of a partnership with neighboring Williams College, city officials said the site was generating power as of Nov. 17. Firstar Bank provided financing for the project.

The site has a 19 MW capacity. Because the town's fiscal plan was built without accounting for the savings from the solar project, the town will likely see some savings between the time the project went online and late June.

Northhampton, MA

The city installed part of a 15-acre, 3.17 MW solar facility on a landfill that shut down in 2013. Ameresco has a 20-year lease to own and operate the installation. The panels are split up, with 2.5 MW on the capped landfill and the rest located on an adjacent plot.

Officials expect the 9,920 panels will generate 45% of the electricity used by municipal buildings. That's expected to save the city $7.5 million over 20 years.

Tyngsborough, MA

In 2015, Tyngsborough reached an agreement with Citizens Energy Corporation to build a solar array on a capped landfill — The Charles George Reclamation Trust Landfill, a Superfund site. Before EPA-supervised remediation, the site was contaminating soil, groundwater, air and sediment.

In late November this year, the EPA announced the opening of a 70-acre, 3.56 MW solar array on the site. EPA worked with Citizens Energy Corporation and the Massachusetts Department of Environmental Protection to make sure construction didn't damage the cap or otherwise harm remediation efforts.

#ICYM: Yesterday, @EPA and partners celebrated the redevelopment at Charles George Landfill #Superfund Site in Tyngsborough, MA - a 3.56 megawatt solar plant https://t.co/bsGF2QXmkw pic.twitter.com/Q5ARHZqVmn

— EPA New England (@EPAnewengland) December 1, 2017

Potential solar projects

Ulster, NY

Tesla's SolarCity is constructing a 6,120-panel array on 29 acres in Ulster to meet at least 20% of the county government's power needs.

The 1.9 MW project has a projected annual output of 3 million KW. Officials expect the array to be constructed by the end of the year and operational by March. The town sold the capped landfill to the Resource Recovery Agency in 1993. To make it easier for the county to undertake the solar project, the town waived its right to buy back the land in 2015.

West Haven, CT

SolarUS wants to install a 4 to 5 MW solar project on a landfill that closed in the '80s. The panels would be located on two privately-held properties in West Haven, CT. According to estimates, the solar installation would save the city around $1.46 million over 20 years.

Solid Waste Disposal Inc. of Connecticut owns the property. However, the company last filed as active with the secretary of state's office in 2014, and officers identified on the filing have since died. Its mailing address is a now-vacant drive which closed in 2015. The city will likely attempt to negotiate with whoever owns the company — which has a substantial debt with the city.

Cooper Township, MI

Cooper Township officials are fielding offers from two solar companies to develop on the site of a former paper mill landfill. Cypress Creek appears ready to sign a contract with the township.

However, officials have expressed interest in Harvest Energy Solutions, a company that would operate a community solar program, rather than selling electricity back to the local utility company. The township has already changed its zoning rules to make it easier to develop a large solar project.

Annapolis, MD

BQ Energy LLC has started constructing an 16.8 MW solar array over an 80-acre landfill in Annapolis, MD. The project is slated for completion in spring 2018. The more than 50,000 solar panels will reportedly make up the largest solar array built on a covered landfill.

Once completed, the array will be turned over to Building Energy Development US. The City of Annapolis, Anne Arundel County and the Anne Arundel County Board of Education all signed power purchase agreements for electricity generated from the site to power government buildings and operations.