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Climatic Causes for Failures




Frequency of external conditions as a cause of failure

Data source: [WMEP 2006]



While as a cause of breakdowns grid outages are not dependent on season or location, the other external conditions, as can be seen in the illustrations, show both a clear seasonal and geographic dependency. For example, most damage and interruptions to operations caused by direct or indirect lightning damage – i.e. voltage surge damage following lightning strikes into the electricity grid – are reported during the summer. Triggered by summer thunderstorms, the probability of a lighting strike in the months from June to August reaches, on average over many years, values of around 15 percent (i.e. 15 reports in 100 months of operation). Despite lightning protection systems now being used as standard, the frequency of breakdowns caused by lightning is thus around the same as that of the other external causes. As most operational problems caused by ice accretion arise between December and March (a period with normally good weather conditions), a significant loss of yield can sometimes be expected in the case of such breakdowns.




Regional distribution of external conditions as a cause of failure

Data source: [WMEP 2006]


Especially in the higher locations of Germany’s low mountain ranges, for which numerous cases of icing are reported as it is, weather conditions that encourage the formation of ice can still occur well into the spring. For such low mountain locations it can also be seen that storms present a significantly higher risk as a cause of turbine malfunctions.


The two figures above are taken from the WMEP claims database. This database was established between 1989 and 2006 with the help of the "Scientific Measurement and Evaluation Programme" (WMEP) as part of the "250 MW Wind" programme. During this period, 193,000 monthly energy supply reports and 64,000 reports on maintenance & repair measures for approx. 1,500 wind turbines were collected and analysed. The aim of WMEP was to collect statistically proven empirical values on the practical use of wind energy on a scale relevant to the energy industry and to evaluate them according to uniform criteria. The results of the project still represent one of the few reliable sources of information regarding the reliability of the turbines and their components.