COVENTRY, Vt.—The Washington Electric Co-op is one of two Vermont electric utilities with a 100 percent renewable energy portfolio, thanks in large part to its 8-megawatt generator fired by waste methane on Vermont’s only operating landfill. Washington Electric’s Coventry landfill facility produces enough electricity from waste methane to power approximately 6,000 homes and generates more than half of Washington Electric’s electricity.
As organic landfill waste decomposes, it naturally produces methane. Unless captured and converted to energy, the powerful greenhouse gas either would be released into the atmosphere, or burned off by the landfill operators. “If no generator was here, the landfill would burn it off in a flare,” said Patricia Richards, general manager for Washington Electric, comparing it to “a great big candlestick literally burning the gas. No electricity is produced and it’s just wasted into the atmosphere.”
“We’re a small cooperative, we’re not-for-profit. We have roughly 11,000 member-customers and the Coventry Landfill project is our anchor power supply resource that serves our membership,” said Richards. “The power plant serves over half of the energy needs of our membership.”
The idea for this methane generator emerged when Washington Electric Co-op set out to replace the electricity it was buying from the Vermont Yankee nuclear power plant. “We said, ‘Hey, we want to do renewable power. What about a landfill? Could we build a power plant like this in Vermont and produce renewable power instead of taking power from a Vermont Yankee type resource?’ In 2002, the contract ended with Vermont Yankee and, in 2005, this project came online,” Richards said.
Vermont Yankee, which was built in 1972, stopped producing electricity in December 2014. The Coventry generator first came on line with three engines in 2005. Since then, two more engines have been added.
The $14.2 million landfill gas-to-energy generator at Coventry “completely did away with [our reliance on] Vermont Yankee. We replaced a base-load resource with another base-load resource, which was renewable,” Richards said.
“It runs 24 hours a day, 365 days a year. It’s on all the time,” she said. “So literally, constantly there’s being electricity produced here.”
“This power is really affordable. It’s the cheapest resource in our mix. It’s six cents a kilowatt hour,” she said.
HOW DOES IT WORK?
Richards likes to describe the plant, which employs three Vermonters full-time, in stages. “The landfill and extraction of gas off of the landfill is stage one. There are several wells that are drilled into the landfill itself. There’s over 80 to 90 wells,” she said. “We collect all the gas from those wells into one pipe and they come into a staging area outside the Coventry plant. That’s where the actual treatment of the gas begins.”
“As the gas is collected, it essentially becomes naturally compressed, and it comes off the landfill really, really hot,” she notes. “It’s 140 degrees.”
“The microbes are doing the decomposition inside the landfill. We collect all that gas … Basically, water particles start to drip off the gas and the rest of the gas comes into the building,” she said.
In the next stage, the gas passes through “a scrubbing system” to remove toxic particles and other pollutants. After the gas is scrubbed, it goes to the engine room to be burned, producing electricity.
“We’ve got five engines and their technical capacity is 1.6 megawatts each,” she said. The facility has proven so effective for Washington Electric and its members that it has been expanded two times – in 2007 and 2009. The $1.7 million investment currently underway will upgrade the turbines and further improve air quality by installing a new scrubbing system.
The methane generator abides by “very stringent federal and state standards regarding emissions,” Richards said. “We want to be on as many controls as we can to make sure we are not making pollutants.”
To help finance the project, Washington Electric secured the funding through federal Clean Renewable Energy Bonds, or CREBs.