EGU2020-3337
https://doi.org/10.5194/egusphere-egu2020-3337
EGU General Assembly 2020
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Probability of lightning strikes to wind turbines in Europe during winter months

Gerhard Diendorfer
Gerhard Diendorfer
  • OVE Service GmbH, ALDIS, Vienna, Austria (g.diendorfer@ove.at)

Upward lightning triggered by elevated objects, such as wind turbines (WT), may increase significantly the number of lightning strikes to these objects. In the recently publishes 2nd edition of the international standard IEC 61400-24 an environmental factor CDWL for winter lightning conditions was introduced to account for this additional lightning risk in the lightning exposure assessment of a WT. Values for CDWL should be 4 (in medium winter lightning activity areas) or 6 (high activity areas) or even higher in special cases. The main challenge is to get reliable data about the winter lightning activity for a given region and for first estimates maps of winter lightning activity for the continents are given in IEC 62400-24, Annex B.

A different approach is used in this contribution. As there is already a high number of WT installed in Europe, we have investigated the number (percentage) of existing WT that was at least struck one time in the winter periods of 2017/18 an 2018/19 based on data of the EUCLID lightning location system.

We have extracted the locations of 10.225 WT sites in Europe in the area from 45°N - 50°N and 10°W -30°E form OpenStreetMap database. Then we checked if there were any lightning strikes located by EUCLID within a 0.003° circular area (is about a 300 m radius) around each of these turbines during the cold season (October to April) in 2017/18 and 2018/2019, respectively. Out of the 10.225 WT 1.131 (11,1 %) and 913 (8,9 %) have been struck by lightning in cold season 2017/18 and 2018/19, respectively. It is worth noting, that only 101 WT (1%) were struck in both seasons, indicating that it is more a dependency on regional meteorological conditions changing from year to year, rather than on a specific group of WT. EUCLID detected flashes are likely to represent only about one half of the real occurring upward flashes from the WT. ICCOnly type upward lightning, which are discharges with current waveforms not followed by any return strokes are typically not detected by lightning location systems, and on instrumented towers this type of discharges makes up about 50% of all upward lightning. But there is a high chance, that a large fraction of this ICCOnly discharges were triggered by the same WT, where EUCLID detected some strokes.

In terms of dependency of the altitude of the WT site above sea level we observe a clear increase of probability of WT lightning with increasing altitude. About 10 % (29/315) of the 315 WT at altitudes up to 50 m ASL are struck by lightning increasing to almost 50 % (15/31) for WT at sites of 950 to 1000 m altitudes ASL. No clear trend is observed for higher altitudes, likely due to the low number of WT above 1000 m.

The obtained 10 % of the WTs triggering at least one upward lighting per cold season demonstrates the high probability of lightning to WT and emphasizes the need of proper protection of the WTs mechanical structure (rotor blades) as well as the entire electrical installation.

How to cite: Diendorfer, G.: Probability of lightning strikes to wind turbines in Europe during winter months, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3337, https://doi.org/10.5194/egusphere-egu2020-3337, 2020

Comments on the presentation

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Presentation version 1 – uploaded on 16 Apr 2020
  • CC1: Comment on EGU2020-3337, Kenneth Cummins, 02 May 2020

    Hi Gerhard.

    Hope all is going well.

    I like this study, and I like seeing that many of the strikes to windfarms occur at the edges of the farms!

    Have you looked at strike probability as a function of local height above "ground" level? It will also

    depend on the distance to other "collectors" and their relative height.

    Cheers,

     

    Ken

    • AC1: Reply to CC1, Gerhard Diendorfer, 03 May 2020

      Thanks Ken for your interest in the project.

      By heigth above ground you mean the height or the wind turbine tower plus the length of the rotor blade?

      Regading the position within a windfarm, I dot see a clear picture (needs further systematc analysis). I assume there will be some difference if all turbines of the wind farm are on the same height (e.g. offshore wind farms) or if the turbines are at different heights above sea level (mountain ridge).

  • CC2: Comment on EGU2020-3337, Ute Ebert, 05 May 2020

    Hi Gerard,

     

    I have the same question: you give the height above sea level, but what about the height above the surrounding terrotory in a mountain area? Top of the  mountain or on a slope? Or are WTs always on the top of the mountain?

    Furthermore, I am not familiar with your terminology of "ICC_only".

    Gruesse,

    Ute Ebert

    • AC2: Reply to CC2, Gerhard Diendorfer, 05 May 2020

      ICC_Only is a type of upward discharges, where there is only the upward leader with current in the range of some hundreds of  amps, not followed by any return strokes occurring in the channel established by the upward leader (see G. Diendorfer, H. Pichler and M. Mair, "Some Parameters of Negative Upward-Initiated Lightning to the Gaisberg Tower (2000–2007)," in IEEE Transactions on Electromagnetic Compatibility, vol. 51, no. 3, pp. 443-452, Aug. 2009.)

      You are right, the relative height would be an interestig parameter to look at in the future. This requires some more effort to "define" a value for this relative height each of the thousands of turbines analyzed.

       

      • CC3: Reply to AC2, Ute Ebert, 05 May 2020

        Hundreds of amps is not much. How long does the current last? How much energy is deposited approximately in the blade?

        • AC3: Reply to CC3, Gerhard Diendorfer, 06 May 2020

          For upward initiated lightning at the Gaisberg Tower we obtained a median initial stage (IS)-current durations in upward negative, positive, and bipolar flashes were 275, 96, and 282 ms, respectively (DOI: 10.1109/TEMC.2019.2916047)

          We typically measure the charge transferred to the tower by the different current components. The initial continuing current (ICC) can transfer up to several hundreds of Coulombs. Median at Gaisberg Tower is 33 C (DOI:10.1109/TEMC.2009.2021616), maximum at Gaisberg Tower was 783 C in a single flash.