January 19, 2013

'Cow power' turns manure, food waste into mighty electricity source

Exeter Agri-Energy on track to produce about 8,000 megawatt-hours of electricity a year, enough to power 800 typical homes

By Ben McCanna bmccanna@centralmaine.com
Staff Writer

EXETER -- Calling it a win-win situation is an understatement.

click image to enlarge

Two of the 1,000 cows at the Stonyvale Farm in Exeter. Waste from the cows and food products are used to produce gas to power electric generators.

Staff photo by David Leaming

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John Wintle monitors the engine inside the control room, where gas produced by mixing cow manure and food waste powers a generator and produces 5.2 million kilowatt-hours of electricity, at the Stonyvale Farm in Exeter.

Staff photo by David Leaming

Additional Photos Below

Every day in rural Penobscot County, a large dairy farm harnesses clean-burning gas from cow manure and food waste, and it generates enough electricity to power 800 homes continuously. The process, commonly known as cow power, has the potential to earn the facility $800,000 a year. It also creates byproducts -- animal bedding and a less-odorous fertilizer -- that save the farm about $100,000 a year.

Cow power is more consistent than solar and wind energy, and it eliminates greenhouses gases that otherwise would enter the atmosphere.

The $5.5 million project could pay for itself in five years. After that, it's all gravy.

So why aren't more farms doing it?

How to get 'green' from brown

For five generations, the Fogler family has milked cows on a pastoral setting of open fields, mixed hardwoods and red barns.

Now the scene includes a distinctly modern facility.

About a mile from the nearest stretch of pavement are two large domes, two towers that occasionally spew flames, a trailer-sized power generator and more. The site's unconventional appearance sometimes causes passing motorists to pause in the middle of the dirt road to ask John Wintle what it is.

Wintle, the plant and engineering manager for Exeter Agri-Energy, said there's no quick answer.

"Each question leads to more questions," he said.

For the past 13 months, Exeter Agri-Energy has been combining cow manure and industrial food waste at this location. In its first year, the company generated 5,200 megawatt-hours for the grid, which earned the farm about $520,000 from Bangor Hydro Electric. Now that the kinks have been worked out, the facility is on track to produce about 8,000 megawatt-hours a year. At 10 cents per kilowatt hour, that's $800,000.

The project was installed in four months beginning in August 2011. It cost $5.5 million and received $2.8 million in grants from Efficiency Maine, the U.S. Department of Agriculture and the U.S. Treasury Department. The facility is a subsidiary of the Foglers' Stonyvale Farm, which hosts the project on its land.

Stonyvale also supplies the system with 20,000 gallons of raw cow manure every day.

The manure, which is produced by 1,800 cows, is plowed from the barn floors by a skid steer and diverted into a pumphouse. From there, the manure is pumped about 1,000 feet through underground pipes to Exeter Agri-Energy, where it enters the facility's anaerobic digesters -- two silolike containers that each hold about 400,000 gallons of manure and food waste.

The food waste arrives nearly every day in an 8,000-gallon tanker truck. The waste comes from grease traps and food processors throughout New England and is delivered by a subcontractor. From the trucks, the waste is pumped into holding tanks, where it flows into the digesters and mixes with the manure.

The digesters are heated to 104 degrees, which creates optimal conditions for the bacteria that are naturally present in cow manure. As the bacteria feed and multiply, the mixture exudes biogas -- about 60 percent methane and 40 percent carbon dioxide.

As the gas pressure builds, the containers' rubber tops expand like balloons and give the containers a domelike appearance. When pressure is sufficient, gas travels through pipes to a 1-megawatt generator.

The generator runs almost constantly throughout the year, except during maintenance periods. The exhaust leaves the generator through a short stainless steel stack, about the size of an exhaust pipe on a farm tractor.

Travis Fogler, operations manager for Stonyvale Farm, said the gas burns cleanly.

"When you look at the rain cap on the exhaust, it's just clean," he said. "If that was a diesel engine, the cap would be black from all the carbon. It's just not there."

(Continued on page 2)

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Additional Photos

click image to enlarge

Adam Wintle, left, Travis Fogler and John Wintle walk past the two digester buildings, where food waste and cow manure are mixed to produce gas that powers a generator for electricity, at Stonyvale Farm in Exeter.

Staff photo by David Leaming

click image to enlarge

Stonyvale Farm worker Joachin Hershbine pushes cow manure into a transport system that takes the manure to a digester, where it is mixed with food waste. The gases produced are used to power an electric generator at the Exeter farm.

Staff photo by David Leaming

click image to enlarge

John Wintle watches as food waste is unloaded in one of the receiving tanks at Exeter Agri-Energy, at the Stonyvale dairy farm in Exeter. The waste is mixed with cow manure and produces gas that is used to power a generator to make electricity.

Staff photo by David Leaming

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