Published: June 30, 2008 10:24 am      

Minn. farmer turns manure to power

BROOTEN, Minn. — Milk isn't the only product produced by 158 dairy cows on Jerry Jennissen's central Minnesota farm.

Thanks to a digester that converts methane from cow manure into electricity, Jennisen is hoping to produce enough power not only to power his own farm but also sell back unused power to his utility.

"It's a product, just like milk, that you're going to sell," Jennissen told the St. Cloud Times.

With energy prices skyrocketing and global climate change a major concern, the Jennissens agreed to participate in a pilot project sponsored by the nonprofit Minnesota Project along with several governmental bodies and power companies, to test whether the technology used can be profitable for an average-sized dairy farm.

Jennissen said he'd been aware of digester technology but never seriously thought about installing one because of the hefty price tag. But he jumped at the chance when the Minnesota Project, which makes grants to foster green technology, asked him to be the test site.

The Jennissens got $329,000 in grant money, including $211,000 that came from state lottery proceeds. The total project cost was $460,000, Jennissen said.

The Jennissens took three years to find a company that could build a suitable digester, finally settling on Utah-based Andigen. Construction started last September and isn't quite finished, although the digester started operating on May 17.

Twice a day, manure from the Jennissen's barn is scraped into a pit where an agitator keeps it moving continuously. The manure is pumped through a heat exchanger, where it's heated to about 103 degrees, after which it flows into the bottom of the digester tank where bacteria convert the organic matter to biogas, a mixture of carbon dioxide, methane and other gases.

The gas is piped off at the top of the digester and sent to a gasoline engine that's been modified to burn methane. The engine runs a generator that produces electricity.

The leftover manure is pumped from the top of the tank, where the liquid is sent to a storage tank. The solids — undigested fiber material now free of disease-causing pathogens — are removed and used as bedding for the cows, saving the cost of more expensive wood shavings or straw.

Right now, about 60 percent of the electricity produced by the digester is in use at the Jennissen's farm, while the rest is sold back to the utility company. As more bacteria grows the system should become more efficient, Jennissen said, who hopes to increase his herd to 170 cows and eventually produce 430 kilowatts of electricity per day — selling back 70 percent or more.

Since methane is considered a greenhouse gas, Jennissen can sell his environmental savings as carbon credits. As part of a trading system designed to reduce global warming, such credits can be bought and sold by businesses and individuals looking to shrink their carbon footprint.

Jennissen isn't the first Minnesota farmer to employ such technology. In 1999, Princeton-area farmer Dennis Haubenschild installed the state's first digester at his 900-cow farm. But that's much larger than the average Minnesota dairy farm of 100-200 cows.

More farmers are considering installing digesters because of energy costs and environmental concerns, said Phil Wirth, vice president of Genex Farm Systems.

"There's a tremendous amount of interest," Wirth said. But he said without grant money, the cost is still prohibitive for most farms.



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