The Power of Poo

Farmers generate energy, save money and help the environment, with a little help from some dung.

This cow's poo helps keep the lights on. [Credit: Monica Heger]
By | Posted October 8, 2008
Posted in: Environment, Featured, Life Science
Tags: , ,

Just how efficient is producing electricity from cow poo? Biogas, which is mostly methane, possesses an energy content of about 600 British Thermal Units (Btu) per cubic foot. This is below natural gas, which has 1,000 Btu per cubic foot.

Translated into real language: Experts estimate that one cow poops enough in its lifetime to power two 100-watt light bulbs for the span of the bulbs’ lives.

Each farm has a slightly different cow to energy ratio depending on the cow, the type of digestion system and how the biogas is used. Head’s farm produces about 55,000 kilowatt-hours of electricity per month, which is average compared to other farms his size.


Surprisingly, most farmers turn to anaerobic digestion not for the electricity, but for waste management. Head says the previous owners of New Hope View installed the digester for that purpose. “As agriculture finds itself closer and closer to urban areas, [waste management] becomes a larger part of being a good neighbor,” he says.

Manure management is more than just a neighborly thing to do. States have requirements for how to dispose of animal waste. There have been problems with excess manure contaminating rivers and streams. Farmers typically have to pay to dispose of it, so anaerobic digestion is an alternative that allows them to get rid of both the waste and smell.

Digestion also produces two other useful products—liquid fertilizer and a pathogen-free dry solid. The liquid fertilizer is what is being stored in the giant blue tank. Apparently, once the biogas is removed, the leftovers don’t smell as bad. I can’t verify, since the tank is sealed tight, so I’ll just have to take Head’s word for it. He stores the fertilizer in the tank until planting season, when he spreads it on the soil, that grows the corn to feed the cows. Head uses the solids as cow bedding.

The pathogen-free solids were what lured farmer Andreas Heer to anaerobic digestion. Heer owns Norswiss Dairy farm, about an hour north of Eau Claire, Wisconsin. He turned to anaerobic digestion because he was in the market for a new cow bedding. Previously, he had been using sawdust and spending about $1,800 every five days. Now, he gets the material from anaerobic digestion, producing around 50 yards a day from his 1,300 cows and hasn’t purchased cow bedding since.

His cows also produce electricity—850 kilowatts per hour, or enough to power 700 homes 24 hours a day, seven days a week. Heer says anaerobic digestion has increased his profits by a quarter of a million dollars per year.

For Heer, anaerobic digestion has been profitable in part because he doesn’t do the whole thing himself. He partners with a company called Environmental Power, which is based in New York. So, while Heer owns the digester, which is on his farm, Environmental Power operates it and sells the biogas to the local power company.

For struggling farmers, jumping into electricity production is no small decision. At New Hope View Dairy, Head’s digestion system cost just under $1 million. The type of system he has typically ranges from $200,000 for 100 dairy cows to $1.8 million for 7,000 dairy cows, according to a report by the National Center for Appropriate Technology. Digestion systems can cost even more, depending how complex the digester is and the type of generator or microturbine used.

Head has only been operating it for a little over a year, so he has yet to determine how long it will take to make up the difference. On average, it takes about five years to recoup the original price. But Heer made a profit after only two years of operation.

Energy from biogas is also more expensive than coal or natural gas. In 2006, the average price of coal was $1.69 per Btu and natural gas was $6.87 per Btu. Biogas on the other hand sold for an average of $7 to $8 per Btu in 2007, according to the Environmental Protection Agency. So while biogas is becoming more competitive with natural gas, it is still well above the price of coal.

Dan Stepan, senior research manager at the Energy and Environmental Research Center, a nonprofit alternative energy developer in North Dakota, says that while the price is definitely a deterrent, farmers can eventually recoup the initial investment. He emphasizes the word eventually, though, and adds that the systems require a lot of time and effort.

“Bacteria are living organisms, and they do require some oversight,” he says. “When you’re dealing with living processes, it’s as much of an art as it is a science.”

Companies like Environmental Power give farmers more of a financial incentive to turn to digestion, since they won’t have to front all of the initial costs. Typically, Environmental Power will own and operate the entire digester system, sometimes having one system for several farms. The savings are variable, according to the company, depending on how much of the process a farmer wants to control.

In turn, they can arrange contracts that provide the farm with reduced electricity and use of the fertilizer and solids. Mark Hall, until recently the senior vice president of Environmental Power, says this method allows them to focus on the operation of the digester and the farms to focus on farming. It also enables them to operate on a much larger scale. For example, they have a project in Texas with 10,000 cows that produces annual biogas equivalent to 4.5 million gallons of oil or 32,000 tons of coal. Recently, Pacific Gas & Electric contracted to buy the farm’s biogas.

“It is impressive the increase in biogas projects that have happened,” Hall says. “But it’s really the tip of the iceberg of things that can be done.”

Hall estimates that there are about 90,000 farms in the United States, including dairy, pig and turkey farms that can make use of anaerobic digestion. Environmental Power is able to make money despite the fact that biogas is more expensive than coal, because utility companies that generate electricity from biogas can get renewable energy certificates. And as more companies and consumers want to go green, biogas is becoming more attractive.

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  1. This is a really great article! But, I have a question. I recently went to a lecture on energy and the environment given by an economist, of all people. But, there was a scientific discussion about the amount of greenhouse gases produced by methane. I don’t remember the specifics, but essentially many people brought up the point that methane has a higher concentration of greenhouse gases per molecule than say carbon dioxide. One, is this accurate? Two, is less methane required for to generate heat/power than other forms of energy so that the higher concentration of carbon dioxide per molecule is essentially canceled out because less methane is needed?

    Stephanie Heger, October 9, 2008 at 3:47 pm
  2. Methane is a more potent greenhouse gas than carbon dioxide–about 20 times more potent. This just means that one molecule of methane traps more heat than one molecule of carbon dioxide.

    By using the biogas from the cows to make energy, you are preventing that methane from entering the atmosphere.

    When you use methane as energy, you are essentially breaking the bonds that hold it together, which creates the heat used as energy. So the end product is no longer methane. One of the byproducts is carbon dioxide. However, you are still emitting less greenhouse gases because you are preventing the methane itself from entering the atmosphere.

    Does that make sense?

    Monica, October 10, 2008 at 12:20 pm
  3. Enlightening article…thanks for explaining the system and process in layman’s terms and for the humorous personal interjections. Such a fresh approach – a serious global concern addressed responsibly without the gloom and doom undertones many writers feel compelled to burdon the reader with. Question: What are the chances that human poo will also find a niche in natural energy production?

    Kay Hunt, October 13, 2008 at 9:48 am
  4. Anaerobic digestion is a very promising technology indeed — some big dairies are generating power from the methane produced and selling it back to the electric grid. (NY Times, Sept. 24, 2008)

    Problem is, it isn’t really cost-effective for smaller dairy farms, which although a dwindling portion of the total in the U.S., still produce half our milk.

    Michigan State University researchers aim to develop scalable, modular technology to digest manure and use the methane to generate electricity — and use the liquid and solid byproducts for additional biofuel, fertilizer, animal bedding, feed and even building materials.

    The story, linked to a wealth of background, can be read at:

    Mark Fellows, October 17, 2008 at 12:17 pm
  5. I think this is a great article. It points out the multiple benefits of biogas production.

    Michel, October 20, 2008 at 12:26 am

    lil_miss_geekiness, December 29, 2008 at 1:24 am
  7. im doing homework right now on poo power but im from the u.k and im only in
    year 7 / eighth grade and out off all of the sites i have been on this make the most sense!
    thank you i can finally finish my homework !

    megan hethear, March 9, 2010 at 1:03 pm
  8. hi im from the u.k and im only in year 7 / 8th grade ! im doing my homework on
    poo power and out of all of the websites i have been on this one makes the most sense !
    thank you sooo much now i can finally finish my homework !

    megan hethear, March 9, 2010 at 1:05 pm
  9. It’s in reality a great and useful piece of information. I’m satisfied that
    you just shared this helpful info with us. Please stay us informed like this.

    Thank you for sharing.

    cosmetic, November 14, 2016 at 4:13 pm
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