The Power of Poo
Farmers generate energy, save money and help the environment, with a little help from some dung.
I saw the monstrous blue tank before I saw the New Hope View sign. Even though the tank was set back from the road, it stuck out like a sore thumb nestled among the bucolic hillsides. As I turned into the driveway, I couldn’t help but wonder if other passersby knew what it held—three million gallons of liquefied cow dung.
New Hope View Dairy Farm is one of 15 farms in New York State generating electricity from an ever-plentiful, if rather unlikely source: cow manure. At New Hope View in Homer, New York the 1,000 dairy cows produce enough poo to power the entire farm.
This process of converting manure to electricity—called anaerobic digestion—is being done on farms throughout the United States and is becoming more widespread as energy costs soar.
Wisconsin leads the pack with 20 farms producing biogas, the gas captured from the poo, about 60 percent of which is methane. A utility company in Vermont offers its customers the option of buying cow-power, and some California dairy farms just signed a contract with Pacific Gas & Electric.
The benefits are multifold for farmers. Anaerobic digesters don’t just turn manure into electricity; they also create, as a byproduct, a nutrient rich, odor-free fertilizer as well as a solid that farmers can use for compost or cow bedding. Plus, there are environmental benefits. Manure emits methane, a greenhouse gas with 20 times the heat trapping potential as carbon dioxide. Capturing the methane to use for electricity prevents it from entering the atmosphere. The neighbors are also appreciative, as anaerobic digestion greatly reduces the stinky smell.
“It’s cleaning the environment and tapping an untapped resource,” says Trevor Head, owner of New Hope View Dairy Farm.
Anaerobic digestion also offers farmers an added source of income—they can save money on electricity, cow bedding or compost, and possibly make extra money by selling leftover electricity or solids.
In order to make money, though, you have to spend money. And the biggest hurdle to overcome is price. Initial capital investment, which can be over $1 million, is often a disincentive, and the eventual payback can take years. Another problem is maintenance. Dairy farmers are in the business of making milk, not electricity. Operating an anaerobic digestion system is time away from their main job.
Head and I tromp across the field to get a better look at his digester, where the process of converting manure to electricity begins. Standing next to the cow barn, he points to a long white dome popping out of the ground in front of the gargantuan blue tank holding the liquid poo. That’s the digester. It is a long, cylindrical, airtight, underground tank kept at 100 degrees Fahrenheit—the same temperature as a cow’s stomach.
He collects manure from the cows and loads it into the digester. Bacteria, which come free of charge with the cow pies, go to work breaking down the dung. “The digester is a living, breathing organism, just like a cow,” he says.
There are two types of bacteria in a cow’s stomach that get passed out with poop. The first one breaks the poo down into acids. The second type breaks the acids down into a gas. Besides the 60 percent that is methane, the rest of the gas is mainly carbon dioxide, with trace amounts of hydrogen sulfide and ammonia.
Head says the manure takes about three weeks to fully break down. As it breaks down, it moves along the length of the digester. It goes in one end and comes out the other, just like in a cow. Standing in such close proximity to the digester, I’m not disappointed that the poop and its accompanying odor is kept underground.
An underground PVC pipe carries the biogas to a microturbine in the utility room. Head and I walk toward the utility room where the loud whirring of the microturbine can be heard long before setting foot inside.
The biogas from the manure has two main tasks. The first is to heat the water that keeps the digester at 100 degrees Fahrenheit. Secondly, it powers the microturbine, which generates electricity for the farm. If more biogas than is needed to continuously power Head’s 70-kilowatt microturbine is generated, the remainder is burned off.
Head points about 30 feet away from the utility room to a long pole that looks a bit like an oversized tiki torch. Every so often a billow of steam drifts out the top. It is the extra biogas being burned off.
“It’s a balancing act,” Head says. Ideally, you wouldn’t have any leftover gas. Or the leftover gas could be used for other things—Head wouldn’t mind if he could use it to heat his house, for instance. But that would require a very long pipe to channel the gas to his house a mile away. Selling electricity back to the grid is even more complicated and requires a purer biogas and cooperation from the local utility company.