Tony Walker

You've heard the expression, “one man's trash is another man's treasure.” At Tessman Road Landfill in San Antonio, trash is being used to produce two treasures: gas and electricity. For decades, the gas produced naturally through the decomposition of waste has been tapped as a renewable energy source. Now, Republic Services, which owns the Tessman Road facility, is taking the generation of green energy at landfills one step further by capping a closed portion of a landfill in an environmentally sustainable manner to collect solar energy for conversion into electricity.

Partnering with CPS Energy, the company directed its engineering design firm, HDR Inc., Jacksonville, Fla., and contractor, American Environmental Group, Richfield, Ohio, to redesign the current landfill closure method to incorporate an exposed geomembrane cover system that would serve as a mounting surface for flexible photovoltaic (solar) panels.

The geomembrane needed to offer decades of performance with minimal maintenance, provide superior containment, stability and protection for the environment, and meet the rules and regulations of the Texas Commission on Environmental Quality. The geomembrane cover is anchored directly into the landfill, providing a stable surface for solar power generation while minimizing the erosion and settlement concerns of traditional landfill cover designs.

The geomembrane is a thermoplastic polyolefin (TPO) that is designed in a patina green color to blend into the surrounding landscape and cover the entire closure area. The TPO is a very durable product that maintains its flexibility and offers superior weatherability and long-term performance.

Renewable energy is generated from flexible, laminate-type photovoltaic solar modules, manufactured by United Solar, Rochester, Mich. The modules are 1/100 of an inch thick (the equivalent of two stacked nickels). Each solar module is approximately 15 inches wide by 18 feet long. The modules can be applied side-by-side or end-to-end, which allows greater freedom in designing grid layouts that maximize solar collection while adapting to a landfill's natural contours. The solar modules are black, matte panels that do not reflect light. They are typically arrayed on a south-facing slope and a top deck of the landfill to maximize their hours of sunlight exposure throughout the year.

The panels convert the Sun's rays into renewable energy, while the geomembrane substrate provides an environmentally safe and economical method for capping closed areas of landfills. Landfill side slopes are ideal for solar energy collection because they are large, flat surfaces angled in a way that optimizes their exposure to the Sun's rays. Also, landfills typically are large open areas with excellent stormwater runoff potential, utility connections and controlled site access.

In addition to generating renewable energy, the solar energy cover (SEC) is scientifically engineered to outperform traditional cover systems through rapid removal of precipitation — eliminating water infiltration — and increased final cover stability. Also, because there is no soil loss from wind and rain, the cover performs as designed over time, whereas traditional cover systems may be adversely affected by erosion. SECs are also easily inspected and repaired, helping to reduce annual operation and maintenance costs.

The solar panels require dusting or cleaning periodically in order to maintain the efficient collection of solar energy. If a solar panel loses its ability to absorb solar energy, it can easily be replaced. Since the TPO incorporates a reinforcing material to resist punctures, it is suitable for long-term outdoor use in hot and cold climates and can withstand extreme weather conditions.

SEC systems also generate revenue for the community through investment, reuse of commercial property and the creation of new jobs, while helping to reduce carbon dioxide emissions. Tapping the sustainable energy power potential of landfill gas and solar collection turns closed landfills into “energy parks” and allows communities to benefit from the long-term use of areas that would otherwise remain nonproductive.

Today, more than ever, people understand the need to intelligently manage waste. For a growing percentage of the population, this means looking for more opportunities to reduce, reuse and recycle. In addition to providing safe waste disposal, landfills now offer the benefit of sustainable, green energy production.

Tony Walker is manager in engineering for Phoenix-based Republic Services.

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