Lightning Location System Data from Wind Power Plants Compared to Meteorological Conditions of Warm- and Cold Thunderstorm Events

Five years of Lightning Location System (LLS) data from five different wind turbine sites in Europe are analysed. The sites are located in Croatia, Italy, Spain, France and one offshore wind power plant in the North sea. Each location exhibits individual characteristic properties in terms of topography, height above mean sea level (AMSL), and average ground flash density.

For three sites, the most severe lightning events have been identified during the warm and cold months whereas the other two locations exhibit severe lightning detections mainly during the warm months. In this work severity is a measure of lightning observations per day. Statistics about the monthly exposure of the wind turbines are provided.

In order to complement the analysis, meteorological parameters related to the lightning events were analysed. Radio sounding measurements provide an analysis of the condition of the atmosphere, in which an electrically charged thundercloud is formed. Furthermore, the reflectivity data from a radar station is used in order to identify convective cores, cloud shape and height of its top and base, and the motion direction of the thunderstorm clouds.

With this approach, distinct differences between warm and cold season thunderstorms can be identified. In total, 27 severe thunderstorms events, which were detected by a LLS in the vicinity of the wind turbines, are investigated. The analysis of cold season thunderstorms shows that lightning discharges are triggered in a very big area over a long time period (up to 18 hours).

As characteristic for cold season storms, the altitude of the charge separating -10◦ C isotherm is around 2000 meters above terrain and the wind velocity is above 12 meters per second. Warm season thunderstorms develop faster, and the overall lifetime of such an episode can vary from tens of minutes to several hours in the case of new storms being continuously developed in the same area.

The distance of the charge separating -10◦ C and the ground is usually larger than 3000 meters. This analyse provides information about the different thunderstorm types which trigger lightning discharges on wind turbines.