Texas is known for doing things big. In this case, a first-of-its-kind application for generating solar electricity by covering a solid waste landfill with a flexible membrane containing photovoltaic (PV) cells.
On April 1, 2009, Republic Services Inc. fired up the first 134 (kW) solar power system that is powered by one-quarter-inch-thick PV collection strips made by Uni-Solar. The flexible strips are adhered to a heavy-duty geomembrane that covers 5.6 acres of the 680-acre Tessman Road Landfill in San Antonio. Republic, one of the largest waste-management companies in the United States, operates 213 land-fills in 40 states and believes that up to 2,350 acres could be covered this way. According to Republic, that would be enough to power 47,000 homes a year.
To appreciate the technology’s significance, an understanding of traditional landfill treatment is needed. Once a landfill is full, the usual method is to cover it with a geomembrane (sheets of flexible plastic) and cap it with a layer of soil. Depending on permit requirements, the soil layer is from 1 to 3 feet deep and usually must have a high clay content. This type of soil often is hard to find, must be excavated, often trucked over long distances and carefully spread over the geomembrane so it is not damaged. It’s expensive.
As a capped landfill ages, it can settle unevenly, potentially causing geomembrane problems that must be continually repaired. Before capping many landfills, a network of pipes is installed to capture biogas produced though waste decomposition. The biogas is used as an energy source. The new Republic solar cover complements Tessman Road’s existing biogas-to-energy system that has been in operation since 2002.
In addition to using real estate that would otherwise be unproductive, Republic’s green-colored solar blanket also eliminated the need for a soil layer—a large cost saving, not only for the initial capping, but also for ongoing maintenance. It was possible because of the durability of the substrate, an enhanced roofing material made by Firestone.
The solar cover is attached directly into the landfill with a series of horizontal and vertical anchors that strengthen the liner system by limiting the stresses and strains the material encounters during a storm. This design provides a stable cover system that protects the land-fill during storms and wind events. A major advantage over soil capping is that a cover section can be pulled back easily to remediate for landfill settling.
“Capping with soil presents a huge maintenance issue for us. With the solar cover, we have complete water runoff with no sediment, no erosion, no vegetation and we can visually inspect the liner,” said Tony Walker, Republic’s project manager.
The solar cover also helps prevent oxygen intrusion into the landfill, which can result in better quality biogas.
“By tapping the sustainable energy power potential of landfill gas and solar collection, we turn closed landfills into ‘energy parks’ and allow communities to benefit from the long-term use of areas that would otherwise remain nonproductive,” Walker said. “We are cur-rently looking at other sites in Illinois, Georgia and Nevada, but we will have to work with the state regulatory agencies to obtain permits to install the solar cover system.”