An icy Arctic gale sweeping down upon north-central Iowa warms Dwight Pierson's heart. He's superintendent of the Forest City Community School District, which has a 600-kW wind turbine on its campus.
"When we get a nor’wester coming in, the wind may blow at 45 mph for 24 hours straight,” Pierson says. “We call that a ‘ka-ching’ day. Under those conditions, our turbine can produce $600 to $1,000 worth of electricity in a day.”
Every day isn’t like that, of course. Pierson estimates that Forest City, which is 34 miles northwest of Mason City, IA, and 15 miles south of the Minnesota state line, has about 100 windy days (defined as days with a wind speed of at least 12 mph) in a year. According to the Iowa Energy Center’s Wind Assessment Study and Turbine Calculator, Forest City’s average annual wind speed is 15.69 mph.
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| The local utility pays the same price for the school district's wind-generated electricty that the school district pays for utility power. |
When the wind blows hard and demand is high, the turbine helps the Forest City Municipal Utility meet the peak electricity needs of Forest City’s 4,700 residents. The utility supplies 1,735 residential customers, 162 commercial customers, and 11 industrial customers—including recreational-vehicle manufacturer Winnebago Industries Inc., which accounts for more than 45% of the total load.
Net Metering
How much electricity the turbine produces has nothing to do with the school district’s consumption. The municipal utility permits net metering (allowing the meter to turn backward to credit the school district for excess electricity it delivers to the grid). The utility pays the same price for the school district’s wind-generated electricity that the school district pays for utility power.
So far, the wind turbine’s revenues have gone to defray its $673,000 cost. An interest-free loan through Iowa’s Alternative Energy Revolving Loan Program provided $250,000, and a local bank financed the other $423,000 at 4.1% interest.
“To date, the wind turbine has been revenue-neutral,” Pierson explains. “When the energy dollars it saves have paid it off in three or four more years, the extra revenues will go into the general fund. That money will be discretionary income—a blessing. We can use it for textbooks and upgrading facilities.”
A Student Project
The impetus for the wind turbine was a student physics project in 1996. Paul Smith, then a high-school junior, and his teacher, Ron Kvale, mounted an anemometer atop the city’s water tower and collected wind data for six weeks. Their research demonstrated that the average wind speed was high enough to justify installation of a wind turbine.
Kvale says the turbine project was “more than just teaching science. I teach kids. You apply everything that’s around you. When we worked on this, it got us into economics and politics, too. It was a good project for the kids who were involved.”
Smith and Kvale shared their monitoring information with the school board and the city council. The school board formed a wind energy task force, on which Smith and Kvale served with Superintendent Pierson, school board members, municipal utility employees, members of the community, and employees of an engineering firm hired to provide technical assistance. After nine months of study, the task force concluded that the project was economically feasible and urged that it go forward.
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| The blades start to turn when the wind blows at 6-10 mph. |
Selecting the Turbine
The study focused on wind turbines of two sizes, 250 kW and 600 kW. The economics were more favorable for a 600-kW machine, so the specifications were written accordingly. Two vendors submitted bids, and the winner was Nordex Energy B.V., a subsidiary of Nordex AG, based in Norderstedt, Germany.
“When we made the recommendation to go ahead with this project,” Pierson recounts, “we were working with another company, Vestas Wind Systems A/S of Randers, Denmark. The Vestas representative was calling on us regularly. We based the specifications on his equipment, but we left them open so anyone could bid on the project. In Iowa we have a low-bid law. When the bids came in, the Nordex contractor had the low bid. We couldn’t find a reason why we shouldn’t accept it.”
That is how Nordex came to install its first and to this day its only model N-43 in the United States. Most of the 538 N-43s now twirling worldwide are in China (160), Germany (113), Egypt (105), and France (47).
The location chosen for the wind turbine was 900 feet from the school buildings, far enough away so ice thrown off the rotor blades couldn’t reach the buildings. Pierson says that hasn’t been a serious concern. “I can count the number of days on both hands that we’ve had the turbine down for ice,” he says, “and I’ve never had reports of ice being thrown anywhere.”
The local contractor poured the concrete footings for the tower in the fall of 1998. Because the tower was late in arriving, the installation had to be completed in extreme winter cold, requiring the cables to be heated foot by foot.
Creating an Expert
Initially, a local heating and air conditioning contractor maintained the wind turbine, but that arrangement proved unsatisfactory. “He would be out installing a furnace and might not hear our call,” Pierson says. “If the turbine went down on a windy day, it might have been six or eight hours before he got around to servicing it. That bothered us.”
The solution was to send school custodian Dan Millard to France for three weeks to learn turbine maintenance. Now Millard is on hand, or available almost instantly via pager, to make adjustments as needed. “For simple trouble-shooting, it’s ready to go on a short-term, quick-decision basis,” Pierson says. “We’ve saved a lot of downtime that way. Our investment [in Millard’s training] has paid off many times over.”
Nordex provides around-the-clock remote monitoring from overseas over a dedicated telephone line, as well as major maintenance, sending technicians to Forest City for annual inspections and preventive care.
Pierson says the district spends about $5,000 a year to maintain the wind turbine. In 2001, a major breakdown cost an additional $70,000 and prolonged the machine’s payback period.
When the turbine began operating in 1999, it was a novelty in the region, so local maintenance alternatives didn’t exist. “Now we’ve got 300 turbines within a 45-mile radius of Forest City,” Pierson says. “Today we would have different bidders. Some of our local wind farms have offered to get involved when we’re ready. If the contract with Nordex gets too expensive, we would have to reconsider, but so far it’s been a very good arrangement.”
Small and Simple
The N-43 is Nordex’s smallest and simplest wind turbine. It is stall-regulated, which means it lacks mechanical adjustments to alter the pitch of the blades. It also lacks complex controls that would raise the price of the machine and the cost of maintaining it. Nordex characterizes the N-43 as a basic model well-suited to installation in any part of the world.
Like all wind turbines, the N-43 has rotor blades that capture the kinetic energy of the wind. They turn a hub connected to a drive train that converts the wind’s energy into rotational energy. Then a generator converts the drive train’s rotational energy into electricity. The air-cooled asynchronous generator has two sets of windings, a six-pole 125 kW winding for gentle zephyrs, and a four-pole 600 kW winding for stiffer breezes.
The three rotor blades, made of plastic reinforced with glass fibers, are about 75 feet long and are mounted facing upwind. They start to turn when the wind blows at 6 mph to 10 mph. At low wind speeds they rotate at 18.1 rpm and their tips move at 96 mph. As the wind speed increases, the blades rotate at 27.2 rpm, their tips travel at 146 mph, and the electrical output rises. An anemometer and wind vane measure the wind conditions and communicate with computer software that monitors 220 separate values over a 10-minute time span to regulate the speed of the rotor blades and the generator’s operation.
The N-43’s best performance occurs from 31.3 mph (14 meters per second) to 42.5 mph (19 meters per second), when it generates up to 620 kW. If the wind blows too hard—over 55.9 mph—two independent brake systems lock and the blades stop turning.
As the direction and speed of the wind shift, a yaw system consisting of two hydraulic drives and two separate braking systems turns the entire nacelle (machine housing) on a ball-bearing ring to keep the rotor blades facing into the wind.
The tubular steel tower, sandblasted and coated with epoxy for corrosion protection, is a rigid structure with its base cast into the concrete foundation. It stands nearly 160 feet high. The tower is designed so its resonant frequency and that of the turbine won’t interact, minimizing the turbine’s noise level in operation. The design of the generator, gears, and other components also helps to reduce or muffle noise and vibration.
The rotor blades weigh 14 tons, the generator 21.5 tons, the tower 49 tons, and the concrete base 137 tons, for a total weight of 221.5 tons.
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| The tubular steel tower, sandblasted and coated with epoxy for corrosion protection, is a rigid structure with its base cast into the concrete foundation. |
Meeting Green Needs
The wind turbine has helped the Forest City Municipal Utility meet some “green power” requirements imposed by state and federal agencies, Pierson notes. However, because it supplies power intermittently, it can’t be accredited as part of the utility’s generating capacity.
“It’s there when it’s there, it’s good energy, cheap energy, but it’s poor capacity. They can’t guarantee it’ll be there on our peak day,” says Roger Rolleson, the utility’s power plant superintendent.
The utility buys most of its electricity wholesale from the Dairyland Power Cooperative in LaCrosse, WI, which generates much of its output in coal-fired plants along the Mississippi River and in a hydroelectric plant on the Flambeau River in Wisconsin.
Forest City’s own power plant has six diesel generators—three from Cooper Power Systems, a division of Cooper Electric Supply Company in Tinton Falls, NJ; a Worthington generator from Dresser-Rand Company in Olean, NY; and Fairbanks and Colt-Pielstick generators manufactured by Fairbanks-Morse Engine in Beloit, WI.
“Under our contract with Dairyland, they can call us to run for so many hours a year, or we can run in an emergency if the transmission line goes down in a storm,” Rolleson explains. “We can generate about 21 MW, which is more than our summer peak demand of almost 20 MW, but we generally don’t. We can’t afford to with fuel prices so high. Our generators are a good backup for the city, and we get a good rate from Dairyland because we have them. Dairyland accredits our plant as part of its generating capacity.
“The wind turbine at the school is reducing what we purchase, and also what we sell. It works both ways. Whatever the wind turbine generates, we don’t have to buy from Dairyland, but we can’t sell it to the school district either. The wind turbine isn’t helping the city much. We let the school district put it onto our system to help them save on their energy bills.”
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| When the school's wind turbine began operating in 1999, it was a novelty in the region. Today, there are some 300 wind turbines turning withit a 45-mile radius of Forest City. |
Different Numbers
City Clerk Paul Boock, citing 2005 figures, says the wind turbine generated 28.7% of the school district’s total electricity consumption. The school district used an average of 188,060 kWh of electricity a month, or 2,256,720 kWh for the year, of which the wind turbine produced an average of 54,000 kWh a month, or 648,000 kWh for the year.
Compared to Boock’s calculations, Pierson’s analysis of the seven-year period since installation of the wind turbine shows that it has had a more significant impact. The longer time span smooths out the effects of varying wind conditions and down time for maintenance and repairs.
Annually, Pierson says, the wind turbine supplies an average of 887,104 kWh—more than 60% of the 1,440-student school district’s electricity consumption—and yields average revenues of $55,477. That’s only about half a percent of the district’s $11 million annual budget, but over time the savings in energy and dollars mount up. So do the environmental benefits.
The wind turbine began operating in January 1999. As of Feb. 15, 2006, it had generated 6,277,774 kWh of electricity, while keeping out of the atmosphere an estimated 4,708.3 tons of carbon dioxide (based on 1.5 pounds of carbon dioxide for each kilowatt hour generated by burning fossil fuel) and 21.3 tons of sulfur dioxide.
During this time, the turbine generated electricity worth a total of $414,333. That includes $320,166 from wind power feeding into the local utility grid, and $94,167 from the Renewable Energy Production Incentive (REPI), a federal alternative-energy program that pays 1.5 cents for each kilowatt hour generated by the wind turbine. REPI payments will last for 10 years after the turbine began operating.
The Winnebago Connection
Winnebago Industries Inc., employs about 3,000 people in Forest City. Its 200-acre main plant consists of more than 20 buildings with a total of two million square feet (about 60 acres) under roof. Boock says the company has an average demand of 7,260 kW and an average monthly consumption of 2,650,000 kWh, or 31,800,000 kWh a year. In 2005, he says, the municipal utility sold a total of 72,273,801 kWh of electricity.
Russ Daggett, Winnebago’s plant engineering manager, says the firm’s power consumption is closer to 33 million kWh a year. “Our 2005 average peak monthly demand was 7,927 kW, with a maximum of 8224 kW,” he says. “The wind turbine supplies less than 3% of the power we use. It’s absolutely transparent to us, and without it our operations would not be affected.”
The wind turbine would provide maximum benefit to Winnebago and the rest of Forest City, Dagget says, when it shaves the utility’s peak demand for power from Dairyland. This scenario is most likely to occur on a hot summer day with gusty winds. Winnebago would maximize its use of air conditioning during the firm’s busiest season, the school district’s demand would be low due to summer vacation, and the turbine would deliver 600 kW or more to the grid.
On such a day, Daggett says, “there could be a cost impact if the wind turbine isn’t running and delivering 600 kW, and the utility has to buy more power from Dairyland or run its diesel generators. Winnebago would pick up close to half that cost because we use close to half the power. For every kilowatt that machine pumps into the grid, the city would be burning less fuel in those generators.”
A Source of Pride
Pierson says the Forest City government and community have supported the wind-turbine project since its inception. “When the turbine isn’t running, I get 10 times more phone calls about why not than I do about a coach or a curriculum,” he says. “We’ve had tremendous support from the city council, especially with the electrical contract that allows us to trade kilowatt for kilowatt for the power we produce. That’s what made the economics work.”
In the future, the wind turbine promises to be an even greater asset to the school district and to all of Forest City. Currently, Boock reports, the average cost of power for residential and commercial accounts is less than 5.7 cents a kilowatt hour, but the Dairyland contract that supplies power at that favorable rate is due to expire in 2008.
“We’re anticipating a 40% increase from Dairyland, if not more,” Pierson says.