Initial investigation of influence of wind farms to lightning events

Wind turbines are very exposed structures to lightning due to their height and installation in unshielded areas and are therefore expected to influence the local lightning activity. However, it is unknown in what quality and quantity lightning is influenced. The following paper presents a study conducted at wind farms in Germany showing to what extent lightning activity is influenced by wind turbines. Conducting the analysis all lightning strokes of more than 50 wind farms over the period of 10 years were analyzed before and after the construction of the considered wind farms using the lightning detection system BLIDS [1]. Thereby both onshore and offshore wind farms are investigated. Examining lightning density, amplitudes and probability distributions of the considered wind farms a significant increase in lightning frequency was observed inside the impact area of the wind turbines both for onshore and offshore wind farms. With regard to amplitudes of negative lightning strokes no specific conclusion could be drawn for onshore wind turbines while amplitudes at offshore wind farm increased extremely. The data obtained during current initial investigation can be used for further study to estimate the average number of lightning flashes to a single or a group of wind turbines. That can help to design a sufficient lightning and overvoltage protection system for wind turbines. However, one should take into account that detection efficiency (DE) of lightning detection systems for ground-to-cloud flashes (upward lightning) in special cases is reduced compared to cloud-to-ground flashes (downward lightning). In [2] a DE of 43 % is reported and explained by the fact that the ground-to-cloud lightning currents often are an initial continuous current only (ICCOnly), free from any superimposed impulse currents and therefore cannot be detected by lightning detection system at all. However, this type of flashes could pose a risk to wind turbines because of their enormous high transfered charge values which can easily exceed 300 As. This specific type of ground-to-cloud flashes cannot be considered in this study because of reason mentioned above.