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Light on Landfills: Solar energy covers turn maxed-out landfills into solar farms


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Hickory Ridge landfill solar cover as seen by air when flying into Atlanta's Hartsfield Jackson International Airport (Photo courtesy of HDR Engineering Inc.)

Hickory Ridge landfill outside of Atlanta, GA, is full. Like most landfills that reach capacity, it was capped to contain its noxious mix of debris that will slowly degrade over the decades and centuries to come. But unlike most, Hickory Ridge glistens on a sunny day due its over 7,000 thin-film photovoltaic solar panels plastered to a geomembrane that has been stretched over the hill like a swim cap.

The goal for this new capping system is to create an alternative to traditional landfill covers that will create revenue, boost renewable energy use, and utilize obsolete land, said Mark Roberts, Senior Project Manager for HDR Engineering Inc., the company which developed the technology.

Normally when a landfill closes, the waste is sealed using a polyethylene cap, buried under a couple feet of compacted soil and seeded with grass. The grassy knoll is then effectively useless, albeit somewhat pleasing to the eye.

In contrast, a solar energy cover aims to eliminate the typical maintenance costs of mowing and soil replacement, and instead allows a closed landfill to continue being useful by generating revenue through renewable energy production. This new system uses a durable geomembrane constructed for roofs and fastens it to the landfill with vertical anchor trenches. The geomembrane-covered landfill slopes then serve as a secure and clean surface for the solar panels.

Much of the cost associated with solar caps occurs during the initial stage of buying and installing the solar panels (the project at Hickory Ridge cost roughly $5 million, $2 million of which was offset by federal stimulus money through the Georgia Environmental Finance Authority). This cost (Republic Services, the owner of Hickory Ridge landfill, was unable to disclose the agreed rate) will slowly be regained as the solar energy is sold back to the local utility.

This is exactly what’s taking place at Hickory Ridge. It’s now the world’s largest solar cap, producing 1 megawatt (MW) of electricity, which is enough to power about 225 homes, or offset the total energy use of the landfill itself. And, it’s not the lone example.

The first solar energy cover was installed in San Antonio, TX., in 2008 at a landfill called Tessman Road. Others exist in Mass., NY, and NJ. According to the Environmental Protection Agency, there are about 10,000 old municipal landfills in the United States that could potentially serve as the groundwork for renewable energy projects. Many of these landfills are located on the outskirts of cities and already possess the necessary infrastructure for solar power. Hickory Ridge landfill did.

The view while climbing Hickory Ridge landfill (Photo courtesy of HDR Engineering Inc.)

And as I climbed the green rubbery slopes of Hickory Ridge landfill last Thursday, its solar-covered apex loomed above prompting me to think about this odd nexus of materials – garbage and solar. Not only was I observing a fairly new achievement in engineering, to me it also seemed to be something more meaningful. Below my feet were 9 million cubic yards of garbage, a stark representation of our world’s waste, yet, it had been capped with solar panels, a symbol for abundant, clean energy. It was like walking through the streets of Rome and seeing advancements in civilizations built upon one another.

I was witnessing a small step forward.

“We’re trying to change the perception that landfills are the great evil,” said Andy Keith, Environmental Specialist, Republic Services, “They aren’t evil. They can be sources of green energy and could be an asset to the community instead of a liability.”

Keith is drawing on a when given lemons make lemonade way of thinking, and it’s helping spur innovation.

While the future is literally bright for solar energy covered landfills, landfills are not the final destination for these caps. HDR Engineering Inc. is looking to design these solar energy covers for coal combustion product monofills and impoundments around the country and internationally, and the EPA is looking to use them for brownfields.

Robynne Boyd About the Author: Robynne Boyd began writing about people and the planet when living barefoot and by campfire on the North Shore of Kauai, Hawaii. Over a decade later and now fully dependent on electricity, she continues this work as an editor for IISD Reporting Services. When not in search of misplaced commas and terser prose, Robynne writes about environment and energy. She lives in Atlanta, Georgia.

The views expressed are those of the author and are not necessarily those of Scientific American.



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Comments 8 Comments

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  1. 1. jfcov 11:15 am 03/30/2012

    So THAT’s what the big green thing is all about — I’ve seen it a few times! I’m so glad to know this.

    Now for a novice’s question — can the solar power be used to degrade the trash lurking underneath? As someone decidedly un-scientific, I’m picturing the heat and energy from all this collection getting funneled down into the ground to incinerate the landfill and renew the land. Possible? Or pipe dream?

    Link to this
  2. 2. rboyd 12:07 pm 03/30/2012

    Yes, the solar cap can be viewed out an airplane window when landing in Atlanta.

    To answer your question, jfcov: the solar panels will not help biodegrade the trash – that’s up to the oxygen-deprived microbes trapped in the giant garbage heap. However, as the organic material decomposes, methane gas is released, which can also be used as fuel. So landfill owners can mine their trash for a couple sources of energy. This will also be taking place shortly at the Hickory Ridge landfill. Until now the methane gas has been burned off.

    Link to this
  3. 3. Heteromeles 7:32 pm 03/30/2012

    I showed this blog to someone I know who’s in the waste management field in a major US city. Said person shall remain anonymous, due to the comments:

    “Where to start? Oh, I know–an analogy. This is like putting a thin rubber cover over a bubbling, very acidic stew of chemicals that will slump away from the cover or push it up. The stew will eat up the solar rubber cover as soon as the geomembrane, about a foot under the final landfill soil cover,degrades–about 15 to 20 years–depending on the garbage underneath and the chemical reactions generated. There seems to be no mention of methane removal or leachate removal and treatment, so one might expect some very interesting ballooning effects, sudden slumping under the solar rubber cap, or spectacular rips of the solar cover depending on rainfall amounts, lightning storms, accumulation of volatile organic gases, cracks in the landfill cap and a myriad of other fascinating possibilities. I suspect the makers of this cover do not expect it to last that long–then another $5 million to replace it?”

    As people have observed with desert solar, the key question on big solar plants is whether they break even before they either break down or run out of some crucial resource. In desert solar, that resource is the water the plant needs to wash its panels down, and that water evaporates off the drying panels. If they’re draining an aquifer, the lifespan of the plant is limited by how much water is left in that ground. Note that this water is lost to the air, not recycled.

    Here, I think my friend is right: that plant has a life limited by how fast the landfill breaks it down. Hopefully it will break even before it breaks down, but if they’re planning on breaking even in 20 years, they may be in trouble.

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  4. 4. kiteman 4:30 pm 03/31/2012

    There must be an enormous run-off of water when it rains. I wouldn’t like to be driving along that road at the bottom, when there is a sudden downpour. What actually is wrong with a grass covered hill? The grass can be kept neatly trimmed by a flock of sheep.

    Link to this
  5. 5. rboyd 3:15 pm 04/2/2012

    To answer a number of questions/comments raised: Methane removal and leachate removal, as well as water run-off collection, are all part of the project at Hickory Ridge landfill. The methane has been collected and burned off since 1999, and it is now beginning to be captured for energy generation.

    As for the lifespan of the geomembrane with solar panels, it is about 25 years.

    Link to this
  6. 6. Sockrates 2:45 pm 04/5/2012

    To claim that the vegetated cover of a landfill is “effectively useless” is misguided and wrong. Such covers can be, and often are, extremely valuable for a succession of plant species as well as habitat for birds, butterflies, other insects and other species. A system that provides habitat with foraging, mating, nesting, resting and other opportunities and associated ecological benefits is by no means “useless.” Depending on the location of a landfill and its actual or potential use by various species, the benefits of vegetated habitat may parallel or exceed the benefits from other, more anthropocentric uses.

    Link to this
  7. 7. Rose Wilson 7:20 am 09/23/2012

    nice,but i also think That grass can be kept neatly trimmed by a flock of sheep.
    solar power

    Link to this
  8. 8. nrios624 7:46 pm 04/24/2013

    More on the gas emitted and runoff. This came from the HDR,Inc. webpage:
    “The solar energy cover helps avoid thousands of tons of greenhouse gases that would be emitted from the mowing and soil replacement activities needed for long-term care of a grass-covered cap. Because rainwater runs off the geomembrane liner like water coming off a roof into a gutter, reusable water can be harvested without the need for sedimentation and cleaning.”

    http://www.hdrinc.com/portfolio/hickory-ridge-landfill-solar-energy-cover

    Link to this

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