Icing on wind turbine’s blades
Wind power generation in cold climate has various challenges in all stages of the project: site assessment, construction and operation. The most known problem in low temperature is icing formation on the blades of the turbine and two of the main consequences of this event is reduction on electricity generation (lower profitability and efficiency) and increasing of aerodynamic loads (more shutdowns and decrease of life-time of the machine).
Icing was the topic of my research at LUT University, in Finland, and in Peter the Great St. Petersburg Polytechnic University, in Russia. If you want to read about the results, take a look at the following article:
How the icing event affects on the wind plant performance? Wind turbines have a specific design with a complex system, so each part of the machine has a functionality. The accumulation of ice on the surface of the blades changes its shape and mass, causing an unbalance on the rotor that is rotated mainly by the lift force that comes from the wind. In order words, the interaction between the wind and the turbine is now modified, so the control system is not actuating with the optimum operational point.
Adriána Hudecz studied in deep the icing event in wind turbines in her doctoral thesis “Icing Problems of Wind Turbines Blades in Cold Weather”, in the Technical University of Denmark, and if you are interested in this topic I highly recommend to read her work (clique here for more information).
There are 02 types of atmospheric icing: in-cloud icing (rime glaze and mixed ice) and precipitation icing (freezing rain and wet snow). Glaze ice is formed when the temperature is just below 0 ℃ to -4 ℃ and a combination of conditions such as high wind and high water content. Rime ice occurs when the temperature is between -4 ℃ and -12 ℃ and the ice is white and opaque. The mixed ice is a combination of the previous two and it usually occurs when the temperature is decreasing. The following image shows examples of rime and glaze ice.
In order to study the effects of the ice formation in turbine blades, Adriána Hudecz made an experimental investigation of the effects of glaze, rime and mixed ice buildup on NACA 64–618 airfoil profile in the Collaborative Climatic Wind Tunnel (CWT) in Denmark. The scheme of the wind tunnel is represented on the top of the following image and the results for ice accretion on the airfoil section at the bottom, for various climate conditions.
It is possible to notice that each condition results in a different ice formation on the blade and the impacts of it are somehow different, but when it comes to the forces acting on the blade, Adriána Hudecz says: “ …the difference between the immediate reduction of lift coefficient for the different ice types is not significant, which indicates that the initial degradation is independent of the ice formation type for the same angle of attack” and she points out that the surface roughness has a more significant influence on the initial lift coefficient than the shape of airfoil.. Another important observation is that the angle of attack has a high influence on the mass and on the shape of ice deposit.
Check out this publication: Wind Energy in Europe and Data Science
In the last decades many studies have been made in order to detect the icing formation on the wind turbine and how this event affects on the power production. One of them was made by Blasco, Palacios and Schmitz in 2016 and it is called “Effect of icing roughness on wind turbine power production” at The Pennsylvania State University in US. In this study, the researchers created ice shapes in some selected conditions and a mold with this shape was made and the aerodynamic forces were measured so the degradation could be calculated and predicted. The results of this study showed a 25–30% of power loss between some different condition cases when any optimization method is applied. The next image show the methodology implement in this study.
There are some ways to detect ice on the wind turbine such as laser monitoring points, combination of low temperature and high humidity, cloud based height, comparing the results of heated and unheated anemometers, by analyzing the power production of the plant and so on. If the wind turbine is generating less energy than it should and the temperature is below 0 ℃, so the probability of icing is high.
Check out this article: How Artificial Intelligence is changing the Energy Sector
In order to help developers, operators and investors of wind plants, maps of icing were created in regions like Scandinavia, Russia and Central Europe with observational or meso-scale model approach. Maps of icing are only a first indicator of this event because the amount of icing and its frequency depends mainly on the air temperature, relative humidity and other parameters. The following image shows the map of power losses due to icing of Finland.
This area of research is relatively new and there are still some lack of information about how to detect icing, how to mitigate it and what are the consequences of it.
For the reduction of carbon emissions, wind energy plays an important role and it is being investigated in all continents and in all climates. This source of energy might be the most important on the extremes of the earth where the darkness is covering the area most of the year so new technologies need to be developed to keep energy generation quality with sustainability standards.
Thanks for reading! Follow me in social media:
- Twitter: @afonso_lugo
- LinkedIn: Afonso Lugo
