Green Power

Cows at Green Mountain Dairy not only produced milk and manure; recently they have generated something else: electricity, methane gas from cow manure is converted into electricity that is sold to the power utility’s grid.

A mechanical scraper sweeps the animals’ waste into a large drain. The waste is then pumped into a huge sealed concrete tank known as a digester, which holds 21 days’ worth of waste and is kept at a temperature of 101 degrees Fahrenheit. Anaerobic bacteria break down the organic matter in the waste, producing a mix of methane and other gases, known as bio-gas. The gas is burned in an engine that runs an electrical generator. A 1,050 cows farm can produces roughly 250 to 300 kilowatts of electricity daily, enough to power 300 to 350 homes.

The digester produces more than electricity. After 21 days, the waste is pumped through a separator, which siphons off the liquid into a silo and drops the solids into a barn. The liquid manure is used as fertilizer, while the solids are used for cow bedding. The bedding saves the farm owner thousands of dollars a month on sawdust, and they sell the excess to garden stores.