By Don Willmott


When it comes to alternative energy sources, cows haven’t yet reached a tipping point, but they’re getting there. When Vermont’s Green Mountain Power reduced its electricity rates this summer, there may have been some bloated bovines to thank. The company’s Cow Power program turns methane captured from locally sourced manure into electricity, with customers opting in and paying a slight premium to help the project grow as farmers reap a small reward for providing the smelly stuff.

The digester at Vermont’s Blue Spruce Farm is 14 feet deep. (Source: Green Mountain Power)

How does it work? A single cow produces more than 30 gallons of manure a day, and a typical Cow Power farm—there are a dozen so far—has 1,000 cows doing their daily business. Green Mountain Power creates incentives for the dairy farmers to take that manure and shovel it into an anaerobic digester on site at the farm. The digester—think of it as a giant septic tank—holds 21 days worth of waste at about 100°F while bacteria convert it into various products, one of which is methane gas. That gas is then piped to a modified natural gas engine, which spins an electric generator to create electricity. Heat generated from the process is repurposed to keep the digester warm, which offsets fuel purchases on the farm. The energy generated is fed into the Green Mountain Power grid for distribution to customers. One cow's waste can produce enough electricity to run two 100-watt light bulbs for 24 hours, and the entire program generates 16 million kilowatt hours per year—or enough to power nearly 2,500 homes.

The methane extracted from the manure powers an engine to create the electricity that is fed back to the grid. (Source: Green Mountain Power)

What’s left over? The farmers process the digested manure through a mechanical separator. The resulting odorless solids can replace sawdust or sand as bedding for the animals, and gardeners can also use it to enrich their soil. The leftover liquids are also nutrient-rich and can be further processed into fertilizer. Amazing, isn’t it? Nothing goes to waste.

For every kilowatt-hour requested by customers and provided by a Vermont farm, Green Mountain Power pays the farmer at rates set by the state, plus a Cow Power bonus of four cents.

Separators pull out undigested fibers and process digested manure into fertilizer for the farm to use or sell. (Source: Green Mountain Power)

If customer demand exceeds Cow Power supply at any given time, Green Mountain Power attempts to acquire and retire premium renewable energy certificates from other regional renewable energy providers to support renewables in a broader way. Some big Vermont businesses and organizations (Killington Resort, Long Trail Brewing Company, Middlebury College, The Equinox Resort, and more) have signed on to help.

Environmentalists—and vegetarians—often point out that raising cattle for beef in the U.S. requires 28 times as much land and 11 times as much irrigation water per calorie as dairy products, poultry, pork, or eggs. So in addition to serving as a sustainable energy source, cow power helps cows offset each other in a macro sort of way and yield a slightly more sustainable steak or a lower-impact cheeseburger… with plenty of Vermont cheddar on top.


Don Willmott is a New York-based journalist who writes about technology, travel, and the environment for a wide variety of publications and websites.

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