We have investigated the reliability of more than 6000 modern onshore wind turbines and their subassemblies in Germany over 11 years and particularly changes in reliability of generators, gearboxes and converters in a subse Schleswig Holstein, Germany. We first start by considering the average failure rate of turbine populations and th failure rates of wind turbine subassemblies. This analysis yields some surprising results about which subassembl unreliable. Then we proceed to consider the failure intensity function variation with time for wind turbines in on populations, using the Power Law Process, of three subassemblies; generator, gearbox and converter. This analy turbine gearboxes seem to be achieving reliabilities similar to gearboxes outside the wind industry. However, win generators and converters are both achieving reliabilities considerably below that of other industries but the reli subassemblies improves with time. The paper also considers different wind turbine concepts. Then we conclude offshore wind turbines should be subject to more rigorous reliability improvement measures, such as more thor testing, to eliminate early failures. The early focus should be on converters and generators. Reliability of wind turbine subassemblies References (18) Cited By (214) Supplementary material (0) Keywords Related C Article

DOI to the publisher's website. • The final author version and the galley proof are versions of the publication after peer review. • The final published version features the final layout of the paper including the volume, issue and page numbers. Link to publication General rights Copyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright owners and it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights. • Users may download and print one copy of any publication from the public portal for the purpose of private study or research. • You may not further distribute the material or use it for any profit-making activity or commercial gain • You may freely distribute the URL identifying the publication in the public portal. If the publication is distributed under the terms of Article 25fa of the Dutch Copyright Act, indicated by the "Taverne" license above, please follow below link for the End User Agreement:

This study attempts to obtain more detailed knowledge of failures of wind turbines (WTs) by using the German “250MW Wind” test program database. Specific objectives are to show the reliability of some major components and to analyze how their design has advanced through time, what the main failures are, and which technologies have proven to work. Within the program, reports on operation and maintenance are analyzed with respect to WT type, size, and technologies used. This paper presents a comparison of component reliability through time, with respect to their technology. The results show significant differences in reliability for certain subcomponents depending on the size of the WT and especially on the type of power control. For instance, induction generators show half the annual failure rate compared to synchronous generators. The study also includes failures of other components that are affected or added due to the use of the components being analyzed. In general, the results show that failure rates of WTs decrease with time. Most of the data show a short period of “early failures” and later a long period of “random failures.” However, this is not the case for the megawatt class: As technology is introduced into the market, WTs show a longer early failure behavior, which has not yet become stable. Furthermore, large turbines, included in the database analyzed, show a significantly higher annual failure rate of components, per WT. This may be due to the immature technology of the WTs included in the database.

DOI to the publisher's website.• The final author version and the galley proof are versions of the publication after peer review.• The final published version features the final layout of the paper including the volume, issue and page numbers. Link to publication General rightsCopyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright owners and it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights.• Users may download and print one copy of any publication from the public portal for the purpose of private study or research. • You may not further distribute the material or use it for any profit-making activity or commercial gain • You may freely distribute the URL identifying the publication in the public portal.If the publication is distributed under the terms of Article 25fa of the Dutch Copyright Act, indicated by the "Taverne" license above, please follow below link for the End User Agreement:

In this article a reliability‐based approach to determine the extreme response distribution of offshore wind turbines is presented. Based on hindcast data, the statistical description of the offshore environment is formulated. The contour lines of different return periods can be determined. Simulations are carried out for a prototype design of a 3 MW offshore wind turbine. Statistical methods are applied to determine the distribution of the extreme responses. Three approaches are used here. In the MAX approach, only the maximum of each simulation is taken into account. The POT (peak over threshold) approach takes also local maxima into consideration. The process model uses the statistical properties of the process to predict the extremes. All three methods show similar results, but POT and the process model require fewer simulations. Comparison is made for the 100 year response between these reliability‐based models and a deterministic model. For this specific turbine the deterministic model underestimates the maximum flap moment but overestimates the maximum overturning moment of the support structure compared with the estimates of the reliability‐based methods. The application of the reliability‐based model can be extended to include other extreme load situations and achieve a more efficient structural design. Copyright © 2003 John Wiley & Sons, Ltd.