But his 750 cows are also in another business with a different product line: Every one of the half-ton beasts generates 4 kilowatt hours of electricity a day.

Locals call it "cow power," and it keeps the lights burning and supper warm in 75 rural Minnesota homes north of Minneapolis.

The cow-to-electricity operation on Mr. Haubenschild's farm is part of a born-again interest in putting to good use a problematic farm-waste product - that is, gigantic loads of manure. While overall investment in such "waste-to-energy" efforts is small, in the range of $20 million, interest is higher today than at any point since the 1980s, say enthusiasts.

For Haubenschild, the benefits are numerous. The manure is contained in a covered pit, so his downwind neighbors can smell the daisies instead of nose-stinging cow excrement. The pit is cement-lined, so the waste won't seep into the groundwater or run off into rivers and streams. The methane gas that is produced as the manure decomposes is channeled into use as a renewable energy source, rather than dispersing into the atmosphere, where it would contribute to global warming. What's more, his cows generated $81,000 worth of electricity last year, helping to keep the farm in the black during times of low milk prices.

If it's such a brilliant solution, what took so long?

The answer, as is often the case in localized energy projects, is money. Dairy farms already operate close to the margin, and finding the dollars for the initial investment is no easy matter. Methane-fired electricity generators don't come cheap, and they need to be individually designed (bring on the engineering consultants) to fit the circumstances of each farm.

A harmonic convergence

Haubenschild, who has been interested in this renewable technology since the 1970s, finally saw his opportunity in the late 1990s - and seized it. The US Environmental Protection Agency was increasingly concerned about methane gas (a greenhouse gas 21 times as potent as carbon dioxide), and Minnesota agriculture officials, meanwhile, were fretting over declining farm incomes. With a patchwork of state and federal grants, and with help from the University of Minnesota and a nonprofit group called the Minnesota Project, Haubenschild was able to build a $350,000 electricity-generating plant on his 1,000-acre farm. His idea was that the plant would demonstrate that his dream of electricity from manure was feasible.

He was right.

"I had no doubt that it would work," Haubenschild says. "It just took quite a few years to tie everything together."

When Haubenschild's system was completed in 1999, his was one of only 31 electricity-generating methane harvesters on US farms. But its success exceeded even the engineers' expectations, and published reports about its merits are reviving interest in the technology.

"As of spring 2002, there were over 40 digester systems in operation at livestock farms in the United States, with dozens more in the planning stage," the Minnesota Project wrote in its August report on Haubenschild's generator.

One man who was not surprised by the results is Dick Waybright of Mason Dixon Farms, near Gettysburg, Pa. He has used a similar system for more than two decades.

It is an "important part of our profit picture. We get 30 percent or better annual return on our investment," says Mr. Waybright, who milks 2,150 cows with his sons.

Mason Dixon Farms' methane-to- energy system was part of a wave of such projects built in the 1970s and '80s. But Waybright's experience was not the norm. Often, systems built during that time failed because of poor engineering or poor construction. Ultimately, bad publicity snuffed out further interest.

But the dream of profits from manure persisted in the minds of inventive farmers like Haubenschild and engineers interested in renewable energy. The Haubenschild system is part of a trend toward on-farm energy production.

So, how does it work?

The Haubenschild design begins, plainly enough, with a 350,000-gallon cement pit full of manure. The pit is also heated. And it has an inflatable, snow-white fabric cover that keeps heat (and odor) in and oxygen out.

Mark Mosser of Resource Conservation Management of Berkeley, Calif., the firm that designed the cow-to-electricity system, likens it to a giant tube of toothpaste open on both ends.

"Today's manure enters the tube and pushes yesterday's manure forward," he said during a farm tour.

The manure spends two to three weeks in the pit. There, it is introduced to anaerobic, or oxygen-hating, bacteria, a process that emits methane. Engineers have a polite term for the pit and its contents: a methane digester.

"The methane flows up and out the pit into pipes, where it's metered into the generator engine," Mosser says. The engine, in short, burns methane gas to make electricity. The electricity is sufficient to power both the Haubenschild farm and nearby homes.

Before the manure enters the pit, it slides down a series of pipes into a vat that the engineer likens to a large milkshake mixer. There, a milkshake-consistency slurry of manure and shredded-newspaper cow bedding is prepared for the hungry bacteria.

One reason for the system's surprisingly efficient performance is the cellulose-rich newspaper. Anaerobic bacteria prefer newspaper shakes to those made from straw bedding.

"We use a thousand pounds a day," says Bryan Haubenschild, Dennis's son. "We get it free from a local publisher."

The methane-fired engine itself also produces "waste" - in the form of heat. That waste heat is used to warm large tanks of water, and the water, in turn, is used to heat the barn. That replaced $4,000 worth of propane.

The key to converting all these waste products to electricity is to sell the electricity profitably. Haubenschild sells his to the local utility for 7.3 cents per kilowatt hour. That happens to be the retail rate that the utility charges for a farm his size.

"This project is an opportunity to make use of renewable energy and promote sustainable agriculture," says Henry Fisher of East Central Energy. "We roll the energy into our 'green power' program, where we can charge a premium over the retail rate to cover distribution costs." Despite the higher cost, ratepayers have signed on to use all the "green" power the utility has to offer. It's a testament to the marketing appeal of what East Central Energy calls cow power.

In addition to being popular with customers, profitable for farmers, and friendly to the environment, the cow power generator has operated with a high degree of reliability.

"Haubenschild Farms has operated the generator at over 95 percent availability," wrote Carl Nelson and John Lamb, authors of the Minnesota Project report. "This far exceeds even the highest-performing coal plants."

One drawback with cow-to-electricity systems, says Mr. Nelson, is that they operate efficiently only on farms with 400 or more cows. That's six or seven times the average size of a Minnesota dairy herd. "We'd like to see design and engineering that would make these systems feasible on smaller farms," he says.