Vermont electric co-op looks to landfill for ethane recovery
By Steve Thompson
USDA Rural Development
Editor's note: This is the second in a series
of articles on farm and utility cooperatives
that are producing, or using, alternative fuels.
In upcoming issues, the focus will
shift to wind and solar power, and then to ethanol.
ermont is a "green" state (its name, after all, means "Green Mountain"), and many Vermonters are not very enthusiastic about nuclear power. So when the end of Washington Electric Cooperative's contract with a nuclear power plant was in sight, the co-op looked around for a practical source of renewable energy.
"We consider ourselves a "green" co-op," says General Manager Avram Patt from the co-op's offices in East Montpelier. "Both our board and our members wanted to find a source of electric power that's environmentally sound."
Vermont Yankee Nuclear Power Corporation operates a 550-megawatt nuclear power plant in Vernon, and supplies 30 percent of Washington Electric's 10-to-14 megawatt power needs. "That's a significant chunk of our power needs," says Patt. "So we need a baseload source-reliable and economically feasible generation that isn't dependent on weather or other variable factors."
That leaves out solar and wind power-technologies that are considered highly desirable as renewable energy sources, but are not suitable for baseload generation because of their very nature. Solar power generation is greatly affected by cloud cover, and, of course, does not operate at all at night. Wind generation is useful in some circumstances, depending on geographic location. However, in most areas wind produces the least power at times when it is most needed: hot, still days in which customers' air conditioners maximize power demand.
Both of these technologies while excellent for some uses are limited by the lack of a workable means to store for later use the power generated during periods of low demand. So they are practical primarily as supplemental sources of power. Both are also significantly more expensive than more conventional energy sources.
The co-op found what it was looking for in, of all places, a huge landfill
located in a nearby state. As the materials buried in landfills decay, the action of microbes produces methane gas. The gas can be burned in conventional steam-turbine power plants, or in smaller gas-turbine generators. The technology for using landfill gas is well developed and in use in dozens of areas around the country, and its cost is significantly lower than wind or solar power. Best of all, recovering landfill gas and burning it reduces the net amount of atmospheric methane, a gas that is considered 27 times more destructive as a greenhouse gas than is carbon dioxide produced by its combustion.
Competitive energy prices
Landfills across the country use this technology. The use of landfill methane is not free a sizeable investment is required for infrastructure to mine it from a landfill. However, while wind and solar sources enjoy the greatest state and federal green power incentives available to utilities, methane recovery can also receive financial benefits (see sidebar). With the incentives available, the co-op's board of directors determined that they could provide landfill-generated power to their customers at prices competitive with market forecasts.
Washington Electric is a long-time borrower and customer of the Rural Electric Administration and now the Rural Utilities Service (RUS), an agency of USDA Rural Development. The co-op is now working out the details of a financing plan with assistance from RUS, which has program funding to help electrical co-ops take advantage of renewable energy sources. The primary contractors chosen to build the facility are La Capra Associates of Boston.
Blaine Stockton, RUS assistant administrator, sees a growing role for the agency in the trend to "green" power. "Encouraging the use of renewable energy is not only the policy of the federal government," he says, "it's also what many utility co-op members want. It's an important part of our job to help rural electric co-ops find sources of renewable energy they can provide their customers at attractive prices; and we see that role growing more important in the future."
Avram Patt says the project is compatible both with the co-op's desire for clean energy and with its commitment to providing low-cost power for its members. "We're especially concerned with reducing the volatility of our costs," he says. "We're interested in long-term commitments bringing our ownership and financing abilities to bear to keep our prices down."
Uncomplicated technology
The technology involved is well established and uncomplicated. A membrane lines the bottom of all new landfills. This is to prevent leakage of polluting substances into the water table and soil, but it also serves to help seal in the methane and other gases produced by microbial action on garbage. Vertical-slotted pipes made of plastic are installed and surrounded by porous rock, which acts as a moisture barrier. A membrane is installed over the top of the fill, and a fan is used to create a slight negative pressure, drawing the gas as it is generated through the pipes. With existing landfills, holes are drilled into the fill, into which the slotted pipes are inserted.
Once the gas is extracted, it is scrubbed to remove acids and dehumidified. The condensate is returned to the landfill. It is then compressed, stored and used to power one or more generators. The Washington Electric Cooperative's installation will use a clean-burning gas turbine similar to an aircraft jet engine to combust the fuel, instead of the more traditional method of burning it in a boiler to generate steam that in turn drives a generator. There is no release of gases into the atmosphere except through the exhaust stack.
A landfill gas installation provides a reliable source of power for some 30 years, although gas production does decline somewhat over the life of the installation, says Ralph Overend, a researcher at the National Renewable Energy Laboratory (NREL) in Denver. "At the end of the 30 years, you've used it up, so you walk away and start over," he says. However, while any single installation is not a permanent source of power, the supply of producing land-fills promises never to run out truly a renewable energy source.
