By Nora Caley
When people think of renewable energy and buried waste, they think of Massachusetts. Or at least they might, as the state has been active lately in helping municipalities build solar farms on landfills.
According to the Massachusetts Department of Environmental Protection (MassDEP), there are currently 39 solar-on-landfill projects permitted by the agency that will produce a total of more than 78 MW of energy. (There are also two wind projects generating 3.6 MW of energy.) Some of the projects are complete, and several are under construction.
Other states, such as California and New York, have built solar projects on landfills, but Massachusetts has been especially enthusiastic over the past few years. In 2010, the state approved what was reportedly the first post-closure use permit for solar for the 2 MW Greenfield Solar Field on a landfill in Greenfield, Mass.
MassDEP even offers a 46-page "Guide to Developing Solar Photovoltaics at Massachusetts Landfills." According to the guidebook, municipalities are looking for ways to generate revenue, the state has a robust solar renewable energy credits market, and the investor-owned utilities allow net metering. Also according to the guide, the commonwealth has more than 490 landfills, 466 of which are now inactive or closed.
Industry experts say some of those landfills are prime real estate for solar projects, but there are challenges. One challenge is the slope of the land.
"Greenfield had a large expanse of 23 acres of relatively level land, and that's somewhat unusual," says David Andrews, senior geoenvironmental engineer for TRC, the engineering firm that performed geotechnical services for the project. He explains that most landfills have steep slopes because building pyramid-like mounds enables the landfill to maximize its space, making many landfills unsuitable for ground-mounted solar panels.
Another challenge is the structures cannot permeate the top layer of soil and the membrane that keeps water out. "Essentially, it's more like putting a solar array on the roof than on the ground," Andrews says. "You can't do things that would make the roof leak. On a landfill, you can't drive loaded semis if there isn't a prepared road, and you use lightweight equipment."
According to the permit application, the Greenfield project included excavating six inches of the vegetative support layer and pouring concrete footings for the PV racks, which were bolted onto the footings. The transmission wiring was buried at the base of the vegetative support layer.
That project was completed in June 2012. TRC also received approval for a 2 MW solar farm on 11 acres of the Pittsfield Municipal Landfill. The company does plan to work on more of these projects.
"The potential is enormous," Andrews says.
Justin Gravatt, project development manager for Gemma Power Systems, agrees that landfills present a great opportunity for solar projects. "It is land that is usually elevated and free of trees," he says. "And it's usually a maintenance expense for the town, but putting a solar plant on the landfill generates revenue."
Maintenance includes mowing the grass and making sure trees do not grow on the land, so that roots do not penetrate the top layer. The solar panels cannot penetrate the soil either.
"It has to be a ballasted system," Gravatt says.
Gemma Power Systems, an EPC contractor that is a subsidiary of Argan Inc., built a 5.7 MW solar energy facility on a closed, capped landfill in Canton, Mass. The 12.5-acre project was completed in August 2012. The company is currently building the 6 MW Ravenbrook Landfill Solar Project on a landfill in Carver, Mass. That project is scheduled for completion this summer.
Gravatt says another advantage of building solar on landfills is that there is usually no public pushback. "Generally, the residents have very little resistance to putting a solar farm on a landfill versus a farmer's field," he says. "If you propose solar on a farm, people will say you are taking away from agricultural productivity and ruining the bucolic nature of the area, and it's not aesthetically pleasing."