Finnish Icing Atlas

Due to Finland's northern location the risk of icing must be taken into account, when planning new wind farms. Ice aggregation on turbine blades changes the aerodynamics of the blade, which causes production loss and hence financial losses to energy companies. In addition, icing poses ice throw risk and possibly increases dynamic loading of wind turbine which might reduce the lifetime of turbine components. In order to avoid the possibility to controlling error, the turbine must be stopped if the cup-anemometer measuring wind speed or the blades are iced. Moreover, the noise level of the turbine increases when blades are frozen.

Icing Atlas is calculated from the same modelled data series than the Finnish Wind Atlas (Tammelin et al., 2011). The basis of the icing calculations is the atmospheric model (AROME) data that is fed to the separate icing model. Icing model is using mainly temperature, liquid water content and wind speed data. Ice aggregation is calculated upon a standard cylinder, described in ISOSTANDARD (ISO - 12494:2001). Diameter of the cylinder is 3 cm and it is one meter tall. In the model the cylinder is assumed to rotate freely around its vertical axis. Therefore, the thickness of ice cover will be uniformly distributed around the cylinder. In addition, the ratio between the ice over standard cylinder and corresponding ice cover on WWD 3MW turbine blade is determined, in order to estimate the effect of icing on wind power production. It should be noticed that in real life ice shapes can be much more complex and production losses thus bigger than the modelling results.

More detailed information on icing of wind turbines and the effects of icing can be found for example from references: IEA Wind Task 19 reports, Tammelin et. al. (2000), Ronsten (2009), Homola et. al. (2010), and conference proceedings of Winterwind and Boreas.

What is icing?

In the context of icing atlas, icing is defined as a process where in-cloud liquid hydrometeors freeze on cold surface. These hydrometeors can be either liquid rain drops or cloud droplets. The hitting rate of the droplets is depending on a size of the droplet. If the droplets are very fine they will more easily follow the flow around the cold object. Larger particles are too heavy to follow the air flow and they more probably collide with the object. The wind speed which drives the flow is also effecting on an intensity of ice aggregation. Stronger winds will favor the collision of finer particles on the target surface.