Wind Power from the Darrieus Wind Turbine
An Introduction to Darrieus Wind Turbine
The power of the wind has been harnessed for centuries, driving ships to new and unexplored harbors and giving the gift of flight to mankind. Wind is a clean source of energy that is easily implemented and highly effective. But at this point in time,less then 1 percent of the energy produced by the United States is derived from wind power 1.
As the amount of pollutants entering our atmosphere from burning fossil fuels such as coal and oil continues to grow, the demand for clean, efficient energy that won’t damage the environment has the world searching for answers. Alternate forms of energy are being sought out and various methods of harnessing that energy have been researched and developed and put into action around the world. In the case of wind energy, one method of harnessing that power has been the Darrieus Wind Turbine.
The Darrieus Wind Turbine is a vertical axis turbine or VAWT, which means that the main rotor shaft runs vertically. The Darrieus Turbine dates back to 1927, when French aeronautical engineer Georges Jean Marie Darrieus patented this innovative turbine design. The Darrieus Wind Turbine resembles a gigantic eggbeater and has two main advantages. The first main advantage is that the equipment including the gear box and the generator can be placed close to the ground. The second advantage to this type of wind turbine is that you don’t need a new mechanism to turn the rotor against the wind 2.
The Darrieus Wind Turbine is a lift-type vertical axis turbine and can function effectively no matter which way the wind is blowing. This wind turbine is powered by the lift forces that are created by a set of airfoils, which are the actual wing-shaped blades of the turbine. These allow the turbine to reach speeds that are higher than the actual speed of the wind, which makes them well suited to generating electricity.
As the airfoils move forward through the air, the air flow creates an angle of attack that generates a force that gives a positive torque to the shaft of the turbine and helps it move in the direction it is already rotating. The same principles apply to a helicopter. That energy coming from the torque and the speed of the airfoils is then converted into electricity.
The Evolution of the Darrieus Wind Turbine
Several unique disadvantages have been discovered to the Darrieus wind turbine that have lead engineers to continue to modify the design although the general theory behind the Darrieus model still comes into play. The main disadvantages to the original design include the following:
- The efficiency of the vertical axis turbine in and of itself isn’t very remarkable. The stress that the design experiences from the high winds can often damage the turbine and cause the eggbeater shafts to bend.
- The Darrieus isn’t a self-starting turbine. It needs a push to get started. Some models that are connected to the grid have a small powered motor to begin the rotation.
- Because wind speeds are close to ground level, there is very low wind speed on the lower part of the rotor.
- The Darrieus Wind Turbine may need multiple guy wires to give it extra stability, but this isn’t practical in a farming environment and can make the entire design extremely unattractive.
- To replace the main bearing of the rotor, you have to actually remove the rotor, which means practically tearing the whole machine down 3. That’s why a lot of Darrieus turbines today are not functioning.
Because of these pretty serious limitations of the Darrieus Wind Turbine, several modifications have been made to enhance the productivity, efficiency, and the downtime of the design.
One common design alteration is called the giromill, which replaced the eggbeater design with straight vertical blades that are attached to a central tower. This design is cheaper and easier to build than the original Darrieus, however, they are less efficient and can at times struggle to keep up a steady rate of rotation 4
Another type of Darrieus design is called the Cycloturbine. This design mounts the blades around the vertical axis, which allows them to be appropriately pitched so they always have an angle of attack and are self-starting, a distinct advantage over the original Darrieus design.
One very recent design of the Darrieus wind turbine is what is being called the Windspire by Mariah Power. The Windspire is being used mostly for residential areas as the unit starts at only $6,500. It still follows the same principles of the Darrieus turbine design, but has abandoned the eggbeater shape for a more sleek and efficient design, not to mention more elegant. The Windspire is even being sold today as a sculpture for hotels and other commercial settings.
Darrieus Wind Turbines at Work throughout the World
There are several Darrieus Wind Turbines with the original eggbeater design still at work today, although most have been reduced to operating on rare occasions to extend the lifetime of the turbine. The largest Darrieus wind turbine is the Eole located in Cap-Chat, Quebec. It is almost 100 m tall and about 60 m wide 5 .
Another smaller turbine is located in the Sandia Laboratory in Bushland, Texas and stands 42 M high and 34 m wide. There was also an attempt to implement the Darrieus wind turbine on a large scale effort in California by the FloWind Corporation; however, the company went bankrupt in 1997.
While the original Darrieus wind turbine design is not as effective or applicable on a large scale model as we need it to be, it did lay the groundwork for further research and development of wind turbines throughout the world. Wind power is an excellent choice for providing clean, safe and reliable energy without harming the environment, and it is only by further exploration into more effective designs for the turbines that we can ultimately be free of energy sources that negatively impact the environment with harsh emissions and pollutants.
1. American Wind energy Association, Wind Power – Clean and Reliable. Http://www.awea.org/utility/pdf/wind_and_reliability_factsheet.pdf.
2. Wind Turbines: Horizontal or Vertical Axis Machines? http://www.windpower.org/EN/tour/design/horver.htm
3. American Wind energy Association, Wind Power – Clean and Reliable. Http://www.awea.org/utility/pdf/wind_and_reliability_factsheet.pdf
4. Giromill Darrieus Wind Turbines. http://www.reuk.co.uk/Giromill-Darrieus-Wind-Turbines.htm
5. Darrieus Wind Turbine Analysis. http://www.windturbine-analysis.netfirms.com/
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