Cow belches and flatulence are infamous for their surprisingly high contributions to the climate crisis. Studies blame agriculture for as much as 40 percent of human-caused methane emissions, with cows and resulting manure ponds contributing a significant and growing fraction. Nevertheless, Vermont, with its green profile and well-known cow populations, is well-situated to capitalize on an opportunity to solve this problem.
That’s the view of Alex DePillis, who works on agriculture and energy projects for the Vermont Agency of Agriculture. DePillis promotes methane digesters as a way of capturing and using that methane, which he argues gives “carbon-negative” fuel.
“The classic manure digester is an extension of the cow stomach,” DePillis explains. “It’s just letting that same manure ferment another 20 to 30 days, and you get methane and carbon dioxide.” The process requires some external heat, but “with good insulation,” it’s not much, DePillis says. And if the biomethane—also called renewable natural gas—is burned on site to generate electricity, the heat needed is available as a byproduct.
The 800-cow Maxwell’s Neighborhood Farm in Coventry uses its methane energy resource in that way. Located in the same town as the landfill where Washington Electric Co-op collects methane from rotting garbage and burns it for electricity, the farm has a manure-fueled generator that can power about 200 homes. There, excess heat is also piped into the soil in a high-hoop greenhouse, extending the growing season and allowing the farm to get early tomatoes to market.
The Paris-based International Energy Agency released its annual report on renewable energy in October, and it calls biomethane “significantly under-exploited,” only using 6 percent of inputs available. Potential inputs include not just manure, but also food scraps, crop residue, and other organic matter.
With more than 27 million vehicles worldwide fueled by natural gas, the market for transportation already exists in many places. Despite President Donald Trump’s withdrawal of the U.S. from the Paris Agreement on climate change policies, the U.S. leads the world in using biomethane for transportation and has doubled its use in the past three years—in large part because of federal and state financial incentives, according to the IEA report.
Manure digesters can operate on a smaller scale than the 800-cow farm in Coventry. Keewaydin Farm in Stowe, a third-generation farm run by Les and Claire Pike, milks about 90 cows. A digester installed in 2011 fuels an 8-kW generator that powers the farm and sells excess electricity to the grid. For any size dairy farm, an on-farm generator also provides much-needed backup during power outages.
The potential of larger dairy farms to power Vermont with energy from their manure plus added food waste is surprisingly high. DePillis has calculated, based on a project in Salisbury, that digesters on the state’s 10 largest dairy farms could replace nearly 15 percent of Vermont’s natural gas consumption or nearly 20 percent of its on-road diesel use. “There’s real potential,” he says.
To achieve the potential requires deliberate choices, DePillis says. “In Salisbury, just the permitting for this one project took a year or so, and now they have to build the thing. There’s serious ramping up that has to happen. Capital has to come to the table. There’s probably got to be some kind of policies to create the market for the gas. Yes, we have the manure and the farms—that’s just technical potential.”
Because methane emissions from manure and other sources are already happening, capturing that biomethane can create a positive double-whammy for greenhouse gas emissions.
“If you can capture the methane and burn it, you are destroying a greenhouse gas,” DePillis explains. (Burning methane converts it to carbon dioxide, which is also a greenhouse gas, but methane is 20–80 times more powerful in causing climate change.) “And then if you use it in a vehicle, you’re offsetting the diesel emissions. So using methane from a dairy source is carbon negative, and it’s very unusual to have a carbon-negative transportation fuel.”
With farms not being charged for polluting the air with methane emissions, the economics of biomethane currently require subsidies to make projects work. Funding from the state’s Clean Energy Development Fund and other sources has already underwritten much of the development of the dozen or more digesters in operation. However, DePillis would like to see a larger role for biomethane in Vermont’s energy investments, and in the state’s calculations of its greenhouse gas emissions.
“The sooner the methane is captured and destroyed, while powering vehicles or things, the better for our climate policy,” DePillis says.
Vermonters who want to support biomethane development can enroll in GMP’s Cow Power program. Customers can pay a premium to get electricity from on-farm digesters.