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.

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.