By Cory Marquart, Assistant Scientist, Renewable Energy
For the past 16 years, wind turbines have overlooked the Pomme de Terre River east of Morris, MN. These turbines have produced power for projects at the University of Minnesota West Central Research and Outreach Center’s (WCROC) Renewable Hydrogen and Ammonia Pilot Plant as well as power the University of Minnesota Morris (UMN Morris) campus. During periods of high wind, excess power is generated and then is sent to the Otter Tail Power Company grid. The north UMN turbine is operated by WCROC and the south turbine by UMN Morris. The electrical line is owned by the UMN and power flows from the turbines along State Highway 329 to the UMN Morris campus. These two turbines are both 1.65 MW (1,650 kW) Vestas V82 models. The turbines blades are 41 meters (134.5 feet) long. The major parts of the turbine are the tower, rotor/hub, blades and the nacelle, as shown in Figure 1.
WCROC’s turbine has a 70-meter (230 feet) tower split in 3 sections and the UMN Morris turbine has an 80-meter (262 feet) tower split into 4 sections. Even though adding 10 meters (approximately 33 feet) to the tower height may not seem like much, every 10 meters adds 1 meter/second (m/s, 2.24 mph) in wind velocity. It has been shown that the power generated from wind is directly proportional to the cube of the wind speed. This means that doubling the wind speed will result in eight times more energy. In theory, by adding 10 meters in tower height and 1 m/s of wind velocity may add almost 30% more energy production. In comparing the production numbers between the two turbines there has been approximately 16% more production from the 80-meter tall turbine.
The turbines are controlled by a computer located at the base of the tower, which monitors the wind speed and direction via anemometers located on top of the nacelle. The turbines start creating electricity at 8 mph and reaches peak production at 26 mph. Once the wind speeds reach 26 mph, the blades pitch slightly into the wind so excess energy is not transferred to the generator. The pitching procedure will continue until wind speeds exceed 50 mph; the computer will then pitch the blades completely parallel to the ground and shut down the generation process until wind speeds have subsided. The turbines face into the wind and the process of turning the nacelle/hub/blades to the direction of the wind is called yawing.
Service and maintenance on the turbines is completed by the original equipment manufacturer (OEM), Vestas. This service includes semi-annual maintenance as well as any minor repairs that need to be done on the turbines. The cost is a flat fee and all service and minor repairs are covered under this agreement.
In the fall of 2004, WCROC began construction of their wind turbine. The first step in the process was civil work to prepare the ground and pour the concrete for the foundation. The foundation used for this turbine is called the “Patrick-Henderson” design. The design has a smaller footprint than other foundations and also uses less concrete as a steel culvert is inserted upright into the hole and then rebar and concrete are added. This foundation then serves as a ballast. The drawback of this design is that it can only be used with certain turbines, towers, and in soil types.
In early winter of 2005 after the concrete had cured, the process of erecting of the turbine began. Originally, WCROC wanted an 80-meter tower, but a crane to build something that high was not readily accessible. The closest crane with the capability to build as this height was located in Kansas City, MO, of which would have been very costly to procure. Cranes for building a 70-meter tower were available at closer locations and that is what was used. The crane arrived in approximately fifteen semi tractor-trailers loads to the site and it required a week to put together. The turbine parts arrived via eight semi tractor-trailers shortly after. The turbine was raised in 3 days. Once the turbine was installed, the electrical controls were assembled and connected.
In a similar manner, UMN Morris started construction of their turbine during the fall of 2010 and the turbine was constructed during the winter of 2011. As the development of wind farms grew over the time from WCROC’s turbine to the new one, the amount of larger cranes became available and UMN Morris was able to secure and install an 80-meter tower. UMN Morris’ turbine requires a different foundation to that of WCROC’s because of the 80 meter tower height.
On March 8, 2005 WCROC’s turbine began producing power. Through the end of 2020, this turbine has produced more than 76,000,000 kWh of electricity, which is roughly 4,800,000 kWh per year. This is enough electricity to power 500 homes and covers approximately half of UMM’s campus load. Table 1 lists the monthly average wind production from March 2005 through December 2020. From the table, it can be seen that the best months for production in Morris is November (474,978 kWh) and April (472,213 kWh).
|Month||Average Wind Production (kWh)|
Capacity factor is one way to measure the efficiency of a wind turbine and is defined by the amount of electricity a wind turbine produces compared to the amount of electricity produced at a maximum output all day every day. The net capacity factor for WCROC’s wind turbine is approximately 33%. This means the turbine produces 33% of the maximum it could if the wind speeds were sufficient for maximum output (1.65 MW) all hours of the year. Some power is lost on the line and is used by the wind turbine itself for operation including lights so this is also subtracted to arrive at a net amount of generation.