Garbage in, megawatts out at new landfill gas power plant

By on April 24, 2014

The Nelson Gardens landfill was teaming with activity for years as steady streams of garbage trucks dumped their “not-so-precious” cargo at the site – broken toasters, empty hairspray bottles, mangled Trix cereal boxes, moldy fruits and vegetables, 9 Lives pet food cans, and tons of other household waste.

Like other landfills, this 277-acre dumping site in Southwest San Antonio eventually grew to mountainous proportions. It closed more than two decades ago.

In 2013, however, activity at Nelson Gardens picked up again as large trucks once again were making deliveries: yards of piping, generators the size of small SUVs, as well as other pieces of industrial equipment.

This material wasn’t waste from construction projects or commercial operations. Rather, it was used to construct a 4.2 megawatt (MW) gas-to-electricity power plant that is now providing clean energy for CPS Energy customers.

Thomas Kennedy, a principal at Nelson Gardens Energy and its affiliate Greenfield Energy, explains how it works: “Decomposing wastes create various gases including methane. We’re piping these gases to our plant built at the landfill, cleaning it, compressing it and using it as fuel for the four engines that are driving four generators to make electricity.”

That electricity is then fed into CPS Energy’s distribution system, and eventually makes its way to customers.

Commercial operations began on April 1, and the plant produces enough energy to power almost 2,000 homes on average, says Raul Cardenas, CPS Energy’s renewable/emissions program manager. CPS Energy signed a 15-year agreement with Nelson Gardens Energy of Liverpool, N.Y., to purchase the power.

The landfill gas-to-electricity power plant concept is not new to the energy industry, or to CPS Energy. Customers began receiving power from the Covel landfill plant in 2005. Adjacent to Nelson Gardens, it generates 9.6 MW.

“One of the greatest benefits of this type of power,” says Cardenas, “is that it’s always producing. It’s a steady source of energy, and it contributes to our renewable energy portfolio.”

In addition to 13.8 MW of power from landfills, CPS Energy has contracts in place for more than 444 MW of solar and 1,059 MW of wind energy.

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