The 550 big black and white Holsteins at Haubenschild Farms, near Princeton, spend much of their day in a long, well-ventilated barn, eating immense quantities of bright-green alfalfa hay, ground corn, soybeans, vitamins, and minerals. Three times a day the half-ton animals take the short walk from the so-called loafing barn to the dairy parlor. There Haubenschild family members and employees, standing in a concrete pit that puts them eyeball to pink-and-white udder, milk 20 cows at a time while the others patiently wait their turn.
Each of the Haubenschild Holsteins eats about 90 pounds of food every day, produces eight and a half gallons of milk, and, during the same time period, creates 220 pounds of waste manure (which includes bedding).
Dennis Haubenschild was never satisfied with the waste side of that equation. On a typical large Minnesota dairy farm the tens of thousands of gallons of manure produced end up in an earthen manure pit, or "lagoon." There the dung festers and bubbles, a potential threat to the environment and an irritant to the neighbors, until the farmer puts it into the soil for fertilizer. Methane gas, given off by the decaying manure, is one of the nastiest parts of the environmental threat. Across the country, neighbors of farmers with big smelly manure lagoons are often forced to stay indoors and have sometimes become chronically ill from the gaseous stench.
At the Haubenschild place, not one plop of manure is wasted. Twice a day employees in knee-high rubber boots scrape the concrete barn floor clean of dung, urine, and the shredded newspaper used for cow bedding. They scrape this goulash down a drain into a labyrinth of underground pipes. The first stop for the manure is what one of the generator's California-based design engineers, Mark Moser, likens to a milkshake machine. There the manure is blended into a creamy brown slurry, which then creeps slowly through more pipes to the heart of the system.
The digester pit itself is like an underground Hubert H. Humphrey Metrodome; 130 feet long, 30 feet wide, and 14 feet deep, it's covered by a very tough, antiseptic-looking white fabric. The methane gas rising from the manure keeps the cloth dome inflated.
It takes 21 days for the manure to inch through the system. At the rear end the odorless poop--now called digestate--plops slowly into a conventional lagoon. "This stuff is something like compost," explains Haubenschild, who puts the relatively clean waste on his fields.
"It has great microbial activity and the water-holding capacity is tremendous," he gloats. "We think it will be great for the soil."
The methane, meanwhile, travels from the digester pit up yet another underground pipe studded by numerous meters, valves, and electronic gadgets that control the flow of methane into the generator's engine, which roars--day and night--so loudly that human speech is impossible to hear nearby.
The resulting electricity flows out onto the grid, just like power created by nuclear and coal-fired plants. Each of Haubenschild's dairy cows generates nearly 31 kilowatt hours of electricity per week. That's enough for the herd to power the Haubenschilds' farm plus 50 homes.
In its initial year of operation the manure burner will send $50,000 worth of electricity out through its flickering gauges and thick wires and onto the electrical grid. East Central Energy of Cambridge, Haubenschild Farms' electrical utility, pays seven and a quarter cents per kilowatt hour for the cow-generated power, which it distributes to some western suburbs of the Twin Cities.
Haubenschild and his engineers were not satisfied with merely capturing electricity generated by the process. As the Cat engine labors to transform methane to electricity it gives off lots of waste heat. But Mark Moser, one of the system's California-based design engineers, gets a wild look in his eyes when the word waste is uttered. In a room near the milking parlor are five large water tanks connected to still more underground pipes. The waste from the generator engine heats the water, which keeps people and cows in the barns warm and, more important, the bacteria in the digester pit at a cozy 100 degrees. Last winter, Haubenschild used no propane for heat.
When Haubenschild's big electrical generator roared to life with its first sniff of methane gas in the fall of 1999, it was the culmination of 20 years of dreaming on the farmer's part. For a quarter of a century, farmers and alternative-energy tinkerers have known that livestock manure is a potential source of energy. Some manure-fired electrical generators were built on farms in the Seventies and Eighties. But even though designers quickly smoothed minor technical glitches that had plagued the machines, the manure-fired engines remained prohibitively expensive. Haubenschild's generator, built by Caterpillar, cost $300,000; much of that was paid by public funds.
At the close of the 1980s, according to the U.S. Environmental Protection Agency, there were 13 on-farm generators operating throughout the nation. By the end of the Nineties that number had more than doubled. The 28 generators in service today capture the equivalent of 27,500 tons of carbon before it entered the atmosphere.
The reason for the small but dramatic increase isn't that the technology improved. More generators have appeared mainly because small farms are disappearing. During the last decade, thousands of small dairy farm operators put away their milking equipment for the last time, closed their barns and were replaced by bigger farms with large numbers of livestock. Big farms equal lots of manure, and lots of manure equals lots of methane--enough to make a system like Haubenschild's economically feasible.