Manure Today, Electricity Tomorrow

by Emily Gertz

Published October 08, 2008 @ 07:30AM PST

Norm Audet founded Blue Spruce Farm in 1965 with 30 cows; today, his three sons and their children operate farm, which has grown to 2,200 acres and 1,500 cows.  Since 2005, the farm's Holsteins have been creating two streams of income: about 24 million pounds of milk a year, and over 1.3 million kilowatt hours of electricity.

This Vermont farm and three others are part of the Cow Power program run by Central Vermont Public Service (CVPS).  This program is proof that smart methods for generating significant amounts of clean energy already exist for those ready to take advantage of them.

Inside Blue Spruce's sprawling open-air barn, the Audet's dairy cows produce around 45,000 gallons of manure a day -- 30 gallons per cow. Scrapers move slowly along the barn floors, pushing the manure into a pipe that goes to a bunker-like, concrete holding tank called a digester.

The manure sits in the digester for about 21 days, held at a steady a temperature of 101 degrees Fahrenheit, while anerobic bacteria break down and transform it into a nearly odorless mix of liquid and solids, giving off heat and methane.  This treatment also kills pathogens and weed seeds that would otherwise end up spread over the farm.

The methane is piped out to power a generator, which generates electricity and sends it out to join up with Vermont's energy grid.  The liquid is sent to a holding pond to be used as fertilizer.  The solids -- virtually sterile after being baked at high heat for three weeks -- are piled up in an enormous barn to be used as cow bedding, saving the farm tens of thousands of dollars a year in sawdust.  Between the energy payments and savings like these, the Audets expect to recoup their $2 million investment in the methane harvesting system in about seven years.

In 2007 the four Cow Power farms produced approximately 5.9 million kilowatt hours of energy, enough to power 980 average Vermont homes, according to David Dunn, a spokesperson for CVPS.  This year, they've already generated 5.5 million kilowatt hours, enough for about 1230 average Vermont homes.

About 4,000 CVPS customers (out of 158,000 total) have signed up for Cow Power, and so have a number of businesses and at least one educational institution, Green Mountain College.  They can opt to have some or all of their energy come from the program, paying a small premium of 4 cents per kilowatt hour on top of the average charge of 12.5 cents per kilowatt hour.

Along with keeping methane (a powerful greenhouse gas) out of the atmosphere, this power-generating process has other compelling benefits.  The dairy farms gain some financial stability: the income from power generation is a hedge against variable commodity prices for milk.  They also get a better way to manage manure, which can become an environmental pollutant if it runs off into nearby water sources or land. In turn, utility customers get a green power option that helps preserve Vermont's iconic, open rural landscape, and keeps people working on the land.

Image credit: Emily Gertz