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Frequently Asked Questions About Carleton's First Wind Turbine

The turbine is sited on a high point at 93.11 degrees west latitude and 44.46 degrees north longitude about 1-1/2 miles east of the campus. It is visible from several sites on campus. The turbine was delivered on August 27, 2004, and constructed from August 28-31. It began supplying clean energy to the electrical grid on September 16, 2004. Some frequently asked questions and answers about this turbine are below.

Why did Carleton College decide to purchase and operate a wind turbine?

Global concerns about the environmental impact of fossil fueled and nuclear power plants were part of the decision. The ENTS program at Carleton and a local organization, RENEW, brought attention to renewable energy options that Carleton could investigate. The advance in wind power technology in the last few years and the increasing number of turbines being installed suggested an opportunity for investing funds for a comparable rate of return while contributing to a healthier environment.

How much energy will the turbine provide?

The energy produced depends on the wind speed rather dramatically. At full power in a 27 mile per hour wind the generator will output energy at a rate of 1.65 million watts. This would operate 1650 one thousand watt toasters. In a 17 mile per hour wind the output power is about 0.7 million watts, which would operate 700 toasters. This amount of power is more in line with measured average wind speeds in this area. On a yearly basis, this turbine should produce about 5-6 million kilowatt hours of electricity needed for 500-600 homes.

Why is it so huge?

The energy in the wind is directly related to the volume of air impacting the blades. The larger the diameter of the blades the more energy they can capture. The diameter of the blades is 82 meters to about 270 feet. The span of the blades is larger than most turbines in order to capture the winds at lower speeds. Wind speed is also greater high above the ground. The hub of the blades is 230 feet above the base. The turbine sits on a 70 meter tower which is common in Minnesota. However, 80 meter towers are becoming more popular because of the additional wind speeds. Carleton considered the wind and cost for each and decided it was more economical at this location for a 70 meter tower.

Who built it?

The Danish company N.E.G. Micon, recently acquired by Vestas, designed the unit and built most of the parts except the tower, which was built in the U.S. Several subcontractors were involved in putting it together.

Why do the blades turn so slowly?

The blades turn at the standard operating speed of 14.3 revolutions per minute, the tips of the rotor are moving at 139 miles per hour. Large stresses are incurred at these speeds particularly in gusty conditions. The blades are made from carbon, epoxy and wood with a steel mounting flange. The shape of the tips is very important in reducing drag and noise and providing some over speeding protection.

Will the turbine provide power if there is a general power outage in town?

This design requires a small amount of power from the energy company to energize the generator coils so that it will not produce back up power for the town if there is a city wide outage. However, if there should be a supply shortage such as a brown out due to peak demand it would help provide power.

How long will the turbine last?

It is designed for a 20 year life. All the components are very robust and require a minimum of maintenance with many automatic features controlling start up and shut down. Spare parts are readily available.

What’s inside the nacelle on top of the tower?

Let’s start with the rotor hub. The three blades can be rotated on their axes to change the angle/pitch of the blade relative to the wind for maximum efficiency and safety. This is done with hydraulic pressure which is fed through the rotating, hollow drive shaft which is supported in massive ball bearings. This drive shaft is coupled to a geared speed increaser, weighing 17 tons which increases the speed to 1200 r.p.m. A disk brake is next in line which is used in emergency situations and for maintenance. Finally, the generator, which is a special 3-phase, 600 volt ac generator which produces the 60 cycle power compatible with the power line is tied to the drive train.

What’s in the tower and the attached cabinet?

The tower, made of ½ inch thick welded steel in three sections, has a ladder for access to the nacelle and contains all the controlling electronics and cable that come from and lead to the generator. The transformer that steps the voltage up from 600 volts to 13,800 volts for line distribution is housed in the cabinet just to the north of the tower base. It has cooling fins on the south side.

How will the power be monitored?

A phone line is connected to the college that will provide the performance data which will be made accessible by the college Web site. There are sensors on top of the nacelle that provide wind speed and direction for controlling the orientation of the blades into the wind and provide lightning protection.

How is Carleton paying for the wind turbine?

Carleton is using college funds to pay for the capital cost of the 1.8 million wind turbine. In order to amortize the capital cost, the electrical power will be sold to Xcel Energy Company. A $150,000 grant was given to Carleton from the Minnesota Department of Commerce to help with the costs. In addition, the Minnesota Department of Commerce will provide production incentives for each kilowatt hour of electricity produced for the first ten years. These funding sources will allow Carleton to pay back the turbine cost in 10–12 years.