Republic Services, Inc. recently completed a flexible, photovoltaic cap on the closed Hickory Ridge landfill near Atlanta in what the company hopes will be just the first commercial-scale application of the technology. The 1-megawatt array covers just a 10-acre portion of the 45-acre cap and provides power for the local community while protecting it from pollution and waste from the site.
The cap performs a dual-purpose, said Tony Walker, the Republic Service engineer that oversaw the project.
“In the landfill industry, we have to use a membrane we call a geomembrane, a plastic liner,” he said.
A liner is at the bottom of the landfill and on top. It’s used to contains waste, keep rainwater out, contain landfill gas and keep out rodents, according to Walker.
In most cases, the top liner is covered with three feet or more of soil to protect the cap from exposure. But in this case the company used a sturdier material as a liner.
“A material you’d see in commercial rooftops,” Walker said.
The material can better withstand ultraviolet radiation and is ideal for Uni-Solar’s flexible photovoltaics, which were used in the project. In fact, the project is expected to have a 30-year lifespan, he said.
By using the more robust material and placing solar directly on the membrane, it helps reduce costs over other PV systems on landfills, which require the layers of soil over the cap.
“We like the market where we change the cap design. We get the benefit from the solar generation from the cap, and the financials are a lot better,” Walker said.
Another reason the method was chosen is because the site is still going through what Walker called “closure,” meaning it was recently capped and still going through the digestion process and producing landfill gasses like methane.
He said it’s hard to put much on them as they’re going through the process.
The cap also is collecting methane gas that’s coming from the site.
“That site’s becoming an energy park,” Walker said. “We collect the methane out of the landfill. That gas will be run to a developer onsite.”
The developer will collect the gas and send it to an industrial facility where it will be used onsite.
The company is hoping to use the same mechanism at other sites, according to Walker.
“We’re just introducing this to the EPA to show that this can be a capping alternative for the solid waste industry,” he said.
A lot of facilities need capping, but there are many things that must be done prior to adding a cap like this with a solar installation.
Still, he wouldn’t recommend the geomembrane cap for older, closed landfills.
“I’d look at crystalline on an old-closed landfill. I could put it on a floating ballast,” Walker said.
Regardless, there are many, many landfills that could be ripe for a second life as a solar-power producer.
“There are probably over 100,000 closed landfills in the U.S. alone. Most are close to urban settings,” Walker said.
As such they’re close to existing power lines.
“We think it’s an ideal location for this type of technology,” he said.
Image courtesy of Carlisle Construction Materials, which built the cap.