Topped off with solar
Waste management company Republic
Services has taken creativity and resourcefulness to a whole other
level, installing 10 acres of solar panels on a closed landfill in
Georgia, and the project is now producing close to one megawatt of
The 88-acre Hickory Ridge landfill near Atlanta, Georgia, was filled to
capacity. Having lived out its useful life as a safe disposal facility,
the gates were closed, and site staff began preparing for post-closure
and the 30 years of environmental monitoring required by federal
Normally a synthetic cover would be
placed over the waste, followed by soil and grass, keeping liquids out
and gases contained, returning the hill to something resembling the
surrounding landscape. But waste handler Republic Services proposed
another option, one that meant continued usefulness—as a
generator of renewable energy.
"We did a pilot project in 2009 at our
Tessman Road Landfill in San Antonio, Texas. That was about an acre,
and we learned a lot," says David Stuart, area environmental manager
for Republic Services.
Republic's Brian Martz and Tony Walker
wanted to use the same flexible laminate-type photovoltaic (PV) solar
collection strips developed by Uni-Solar for the Georgia landfill. The
strips are attached directly to the synthetic geomembrane used to cover
and close a landfill.
With a successful pilot under their
belt, the team set out to put an even bigger project on the ground.
With a combination of company investment and a $2 million award from
Georgia Environmental Finance Authority (GEFA), the project encompasses
ten acres and generates one megawatt of power (double what Republic
would have been able to do on its own).
The state approved the switch from the
more traditional closure method to an exposed geomembrane with affixed
"We needed to put on a 45-acre closure
cap to finish the closure," says Stuart. "GEFA assisted with some
funds, allowing us to go from a 5-acre installation to a 10-acre
installation, covering the entire south side of the landfill."
One of the biggest challenges with
landfill closure designs is the instability of the surface due to
settlement over time.
"By their very nature, landfills
change over time as materials decompose and require less space," says
The flexible liner and flexible solar
panels ensure that the integrity of the system remains intact over
At the Texas location, the team
secured the flexible panels using special glue on the surface of the
exposed geomembrane. This system was complicated by dust, variation in
temperature, moisture, and other environmental changes, which made it
difficult to get a good seal between the panels and the liner.
For the Hickory Ridge Landfill project, partner Carlisle Energy affixed
the panels and the liner product together into what they call a Power
Mat.The mats are rolled up and shipped, then unrolled at the site. The
combined materials were laid down at one time, eliminating the need for
bonding the materials on site. The Power Mats come in various sizes,
but each contains
One of the biggest challenges
with landfill closure designs is the instability of the surface due to
settlement over time. Landfills change over time as materials decompose
and require less space. On the Hickory Ridge landfill project (above)
the flexible liner and flexible solar panels ensure that the integrity
of the system remains intact over time.
36 solar panels and has a life span of 25 years.
The Power Mats may be flexible, but they aren't as efficient as
standard solar panels. Each mat generates about 5.2 kilowatts.
"We have 6,984 flexible solar panels in our project," says Stuart.
"With that kind of solar power, we're able to generate about one
megawatt of power from the Hickory Ridge site, which is about enough to
power 224 homes."
Georgia Power has an agreement to purchase that 1 megawatt at avoided
cost and is currently building a power station at the Republic
Republic quickly discovered that the Power Mats didn't just generate
power, they also helped create cleaner storm water.
"We get about 40 to 50 inches of rainfall a year in Georgia, and we
have a lot of silty, sandy clay," explains Stuart. "A lot of times, if
it's raining, you'll see rivers and creeks looking muddy. The runoff
from the panels is so clean that our storm water management pond has
With maintenance and monitoring mandatory at closed landfill sites for
three decades, Republic says maintenance for the solar panels trumps
upkeep of soils and grass.
"Solar has lower long-term maintenance costs," says Stuart. "You don't
have to mow it every quarter or repair washouts. There are so many
things that you don't have to do whenever you get away from dirt."
Maintaining the solar panels requires someone to walk the surface,
checking for any kind of delaminating. "We also look for things like
settlement that may have caused a low spot that's holding water in the
landfill. Or possibly a trapped gas bubble," says Stuart.
The real economic benefit of solar landfill covers comes from the
diverted or avoided costs of closure expenses. Republic is evaluating
the possibility of applying solar covers on other landfills slated for
"Each of our landfills is evaluated individually as a candidate," says
Stuart. "It won't be right for every location, but we have certainly
seen the benefits at the sites where we have already installed this
The solar energy cover was
installed in relatively short order. The project, which included
capping the entire 45 acres with geomembrane and 10 of those acres with
solar, took just 11 months.
"Now we're looking in locations where we feel the regulators would be
open to considering it. That's really a huge driver for it—the
state agencies that regulate landfills must be on board and approve of
this now tested technology."
He added, "State regulators want to keep gas in and water out of the
landfill. They also want these sites to be aesthetically pleasing. This
technology meets all of those criteria."
In 2010, Republic Services sold the solar energy cover technology to
Carlisle Energy for further development and now works with the group on
refining the technology and installing it on approved sites. Looking at
future installations, Carlisle is continuing to improve not only the
flexible solar panels but the installation technology as well. The
lessons learned at Hickory Ridge—the first large-scale
installation in the United States—will make future projects more
efficient and thereby more financially feasible.
To prepare for the installation, an earthwork contractor and crew
smoothed the ground and prepared the surface to accept the synthetic
cover. Installation included anchor trenches spaced about every 70 feet
to hold the geomembrane in place.
A 14-person installation crew drove the liner up to the area, unrolled
it, and put it in place. From there, the crew included workers to weld
the separate pieces together and others to observe, document, and test
what was done to make sure it conformed to engineering standards. They
measured strength, durability, and resistance to stress. Finally, an
electrical crew wired it all up.
In all, the solar energy cover was installed in relatively short order.
The project, which included capping the entire 45 acres with
geomembrane and 10 of those acres with solar, took just 11 months. That
included downtime for winter snowstorms and freezing conditions as well
as for strong winds.
For Stuart, the highlight of the project was being involved in
something relevant to the future of the landfill business. "To me, this
is a better fit than just growing grass. To make a dormant resource
productive—a resource we are already taking care of for the next
The project is also something the state should be proud of. "It's very
forward-thinking from Georgia's standpoint. Sometimes states bear some
scrutiny when they go outside the box. But in this case, it was just
the right time, the right match," said Stuart.
In the end, it's easy to see why refuse-to-renewable-energy is the way
to go, he added.