WILLMAR -- A failed motor shut down one of Willmar Municipal Utilities' two wind turbines on Sunday, but the motor was replaced this week and the turbine returned to service Thursday, according to Wes Hompe, utility staff electrical engineer.
He said the problem was investigated Monday by technicians for turbine supplier DeWind Company of Round Rock, Texas. DeWind has technicians in the state.
Both turbines are located near Willmar Senior High School. The outage occurred in Turbine No. 4, the south tower closest to the school. No. 3 is the north tower.
Hompe said turbines are complex: a system of interacting components that depend on each other to make the whole system work. He said one link in the chain causes the system to shut down until that link can be fixed.
Hompe said the turbines ran for the past six weeks when there was wind. Each unit can produce 2 megawatts if the wind speed is close to 25 mph; however, production starts at 8 mph and ramps up from there.
The month of April was the highest production month for both units. Since the units began commercial operation in September 2009, 935,277 kilowatts of power has been produced.
Availability -- defined as how much of the time a turbine is available to produce when not down for maintenance or repairs -- has been improving. The national average percentage of availability is in the upper 80s, and Willmar's turbines have been averaging in the 90s, Hompe said.
So far this year, availability for No. 3 was 99.7 percent in January, 86.9 percent in February, 63.74 percent in March and 98.1 percent in April. Availability for No. 4 during the same period was 96.8, 92.7, 75.7 and 99.5. March was down due to a motor and pump that needed maintenance.
Hompe said the trend is obviously better and the utility is hoping to maintain availability at or above 95 percent.
"Like I have been saying for the last year or so, once those first-year bugs are worked out and these occasional problems are taken care of, the equipment should run a whole lot more dependably,'' Hompe said.
"We're seeing that trend where the problems that do arise are less and less frequent. That's what we expected and that's what we're seeing.''
While the local power plant was down from about mid-April through Wednesday for annual maintenance and overhaul, the turbines were providing locally generated power when the wind was blowing. Typically, April and May, along with October and November, are the windiest months and the windiest time is from midnight to 4 a.m.
Power plant maintenance is scheduled for April because the demand for electricity in Willmar and the Upper Midwest is typically down during this time of year, said Hompe.
Late next week, either one or both turbines will be shut down occasionally for training. An instructor from DeWind's German headquarters will provide further operation and safety training to Willmar utility employees who one day will take over those functions.
The state mandate for electric utilities in Minnesota to provide 25 percent of energy from renewable sources by 2025 triggered Willmar Utilities to investigate wind power. The planning phase began in 2002 when Willmar borrowed a wind monitoring tower for 18 months from the Minnesota Department of Commerce.
Data showed wind speed was sufficient for turbines that were being built at that time. Like computers, turbines have been improving, he said.
Hompe said wind power is meant to supplement, not substitute for, baseload generation.
"You need power 24/7 and obviously wind doesn't do that, so you've got to have something else,'' he said. "Dispatchable power is very important and if some day we can find dispatchable renewable power that's cost-effective, great.''