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When the giant Plessis-Gassot landfill opened its gates outside Paris in the 1960s, Charles de Gaulle was France’s president and Brigitte Bardot its most famous movie star.
Since then, the landfill has gobbled up millions of tons of refuse thrown out by generations of Parisians. That trash is now playing a bright role in France’s renewable energy future. It supplies the country’s largest landfill power plant with enough methane-rich biogas (also called landfill gas) to generate electricity for more than 40,000 French homes.
The plant also gives off enough heat to make the nearby town of Plessis-Gassot the first French municipality with a district heating system fueled by landfill gas. The town hall, church, community hall and residences connected to its heat pipes could see their heating bills fall by a whopping 92 percent as a result.
Trucks unload waste from a tipping floor that can lift 60 metric tons to an angle of 63 degrees.
Because the plant is replacing electricity generated by conventional fossil fuels, the Plessis-Gassot plant has a 15-year contract to sell power back to the grid at a rate exceeding €0.1 ($0.14) per kilowatt hour. “It’s a great business model,” says Didier Lartigue, managing director of Clarke Energy in France, which built the plant for the energy and waste management company Veolia. “The gas is basically free and when we recover the heat from process, it’s an additional bonus.” (French off-peak and peak electricity tariffs range from €0.1 to €0.15.)
France plans to generate 23 percent of its energy from renewable energy sources by 2020. They include solar and wind power, but also biomass and landfill gas.
Wellheads vent biogas from underground landfill gas cells holding compacted waste. The bottom of each cell sits about 50 feet deep and covers 25 acres. It takes 18 months to fill a cell. Each cell produces gas for about 25 years.
The gas is produced when anaerobic bacteria decompose organic waste in an airless environment, like deep inside a compact mountain of trash. Landfill gas contains mostly energy-rich methane mixed with impurities like carbon dioxide and nitrogen. It is similar in composition to natural gas, but dirtier.
The Plessis-Gassot power plant is using 10 advanced Jenbacher gas engines to produce the heat and electricity. Using landfill gas to make electricity is not a new idea, but the engines, which are manufactured by GE in Austria, can be up to 42 percent efficient in converting gas to power. (The system total efficiency including heat is 85 percent.) They replace an older boiler system that was 22 percent efficient.
The engine’s sturdy design allows them to gobble up biogas generated from pretty much anything, including cheese whey, whiskey mash and discarded school lunches.
There are close to 2,000 Jenbachers at work at landfills in 30 countries, including Brazil, the Philippines and the U.S.
The Jenbacher engines, which are part of GE’s ecomagination program, belong to the company’s new Distributed Power business. Distributed power technology allows customers to generate their own power near the point of use, rather than relying on a centralized grid miles away. The concept is taking hold in the developing world, but also at industrial dynamos like France.
That’s because power generation is shifting from a centralized to a decentralized model, says Wouter-Jan van der Wurff, a GE gas engine product line leader. “We have the capability to supply engines for power generation and combined heat and power to maximize fuel efficiency where customers need it,” he says.
Top Image: This illustration shows what a Jenbacher looks like on the inside.