Ice throw

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Snow-covered sign warning of falling ice in front of a high transmission tower on the Feldberg .

The term ice throw is mostly used in connection with wind turbines and describes the falling and shedding of ice from the rotor blades. However, the risk of falling pieces of ice when the weather is appropriate comes from tall buildings and structures.

Emergence

In unfavorable weather conditions (high humidity or fog or rain together with temperatures around freezing point or below), layers of ice can form on the rotor blades of wind turbines. Until the ice switches off or when the system starts up again, centripetal force , bending of the rotor blades or thawing of the ice pieces can cause them to fall or be thrown in the direction of rotation. These are usually thin, leaf-like, more rarely compact pieces of ice and, in extreme cases, heavy pieces of ice. In particular, wind turbines in low mountain ranges and alpine regions can cause ice fall and ice throw.

Effects

In endangered locations, wind turbines must be equipped with ice detection and ice shutdown systems to avoid ice throwing. There are different, manufacturer-dependent and manufacturer-independent systems. In addition, warning signs must be set up in the vicinity of the wind turbine (s). When the systems are switched off, the area around the tower and under the rotor blades is at risk, and the deflection by the wind must be taken into account. Smaller pieces of ice can also be thrown into greater distances during operation before the shutdown or when restarting by rotating the rotor. In theory, distances of several hundred meters are possible. In reality, critical ice throw never occurs at the nominal speed , because ice weather conditions are often weak winds, even the formation of ice in a millimeter thickness reduces the lift and speed of the rotor and the ice is thrown off in small pieces by the centripetal force acting on it. The parameters for the throwing distance are speed, system height, rotor diameter, deflecting wind speed across the throwing direction and ice shape (see also air resistance ).

Hazard potential

Warning notice of ice throwing in a wind farm

Icy rotor blade of a wind turbine near a motorway in Northern Germany. Due to the proximity to the motorway, an ice detection system had to be installed that stopped the system. The ice formed on the leading edge.

The risk of ice throwing lies in property damage and personal injury , occurs only for a few hours a year and is limited to the area around the facility (a few hundred meters). Through appropriate planning, ice shutdown systems and warning signs, personal injury could be avoided in Germany despite over one hundred thousand cumulative years of system operation. The risk of fatal injuries cannot be ruled out, but is assessed by insurance companies, authorities and operators to be extremely low. There is no risk to residential buildings and settlements, as wind turbines are several hundred meters away from them in order to comply with noise levels. Roads and paths near wind turbines should be avoided by unprotected people when the weather is icy and ice can be seen. Closed vehicles offer protection, but could be damaged, which has not yet been documented. In the case of vehicles in motion, reflexive reactions on the part of the driver could lead to accidents in the event of a hit; this has not yet been documented either. Individual, older wind turbines were and will be provided with the requirement to cease operation in icy weather conditions. Some manufacturers offer rotor blade de-icing systems that can reduce or prevent ice formation and thus enable continuous operation even in cold climate regions with a high risk of frost .

With the approx. 23,500 wind turbines in Germany, there has so far been neither personal injury nor material damage worth mentioning. The risk is rather low for the following reasons:

• The necessary weather conditions for the formation of thick layers of ice occur very rarely.
• The shedding of the ice layer takes place in a very short period of time, preferably after a run-up.
• The formation of thick layers of ice during operation of the rotor does not take place.

Future developments

Ice detection systems are continually being improved, so that modern and future wind turbines pose a lower potential risk than older systems. In order to minimize the risk in the vicinity of roads and paths, the authorities issue corresponding requirements on distances and operating modes.

Individual evidence

1. ↑ Statistics - number of plants in Germany 2013 ( German ) Bundesverband WindEnergie. Archived from the original on April 25, 2014. Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. Retrieved May 19, 2014.