LE SUEUR, Minn. -- One of Minnesota's most ambitious green energy projects is flipping the "on" switch.
The odd-looking power plant, completed in November, is a collection of tanks and fabric bubbles resembling domed stadiums. Inside, bacteria in giant heated tanks are digesting corn silage and manure to produce methane, a flammable gas that's fed into the engines that generate electricity.
This city, famous for the Green Giant brand, is now home to one of the largest biogas power stations in the world.
"This is the newest and best technology available," said LeRoy Koppendrayer, board chairman of the plant's operating company, a unit of the Minnesota Municipal Power Agency.
Yet not everybody is jolly about the plant. Critics have questioned whether the benefits have been oversold and the risks understated.
The plant's output isn't huge, equivalent to about four wind turbines. Yet the facility, called the Hometown BioEnergy Project, promises to deliver cheap, renewable power when customers need it -- not just at the whim of nature like wind power.
Three fabric domes store methane from the constantly running anaerobic digesters. They're designed to feed the biogas to generators that run 12 to 16 hours a day when electrical demand peaks, typically daytime and evening.
"We see ourselves being more financially effective by storing the gas and making electricity when it has greater value," said Derick Dahlen, CEO of Avant Energy, a Minneapolis-based company that developed the biogas project and has long managed the municipal power agency.
The project is a big commitment to a still-developing technology.
About 2,000 U.S. sites produce biogas -- mostly farms, wastewater treatment plants and landfills -- though not all generate power. The nation's total biogas electrical output is 158 megawatts, about the output of a single 1950s-era coal power plant, according to Bloomberg data.
In Europe, biogas technology is more common, thanks to generous price supports. Germany has the most, about 7,000 biogas plants, said Mackinnon Lawrence, a Navigant Research analyst who has studied the biogas industry. He said biogas has benefits and challenges.
"It is a fickle process," Mr. Lawrence said, especially with manure, a common feedstock. "It has to be the right temperature, the right mix of organisms. You are constantly brewing this thing."
The key maintenance challenge is engines corroding from hydrogen sulfide, which also stinks. The Le Sueur plant has scrubbers to clean the gas, and hopes to avoid problems.
Even before construction, the Hometown BioEnergy plant's price tag climbed 50 percent, to $45 million, from the original estimate.
"This is the challenge of doing a first-of-its-kind-type project," said Avant's CEO. "We didn't have a good benchmark price for a facility like this in the U.S."
The project is funded mainly with municipal bonds and a nearly $9 million federal stimulus grant. The project's nearly $11 million in soft costs -- for development, engineering and project management -- chewed up 24 percent of the budget. That's higher than wind energy projects, and most of the money went to Avant.
"One of the questions we kept raising over and over is whether there is any risk that falls back on Avant, but they make their money without any documented risk of any sort," said John Schultz, a Le Sueur City Council member.
The question is whether the Hometown BioEnergy plant's larger scale, innovative technology and storage will provide game-changing benefits.