A wind turbine that has reached the end of its designed service life does not necessarily have to be shut down and dismantled. Using suitable methods and tools as well as the necessary competence and experience, independent experts today are able to assess whether a plant has service life reserves after the designed service life has expired. TÜV SÜD summarises what is important for the evaluation and assessment of the further operation of wind turbines (EAW) and in which cases an analysis could be worthwhile.
The components and parts of a wind turbine that absorb forces and transfer loads as well as the plant’s operational management and safety system are designed by the manufacturer for a specific wind class and a defined operating period. The developers and designers conservatively determine the loads to be expected under standard conditions, considering the intended safety factors. In many countries including Germany, the calculations for onshore wind turbines are verified by a type or individual test carried out for the structural stability of wind turbines as part of the building permit by recognised testing authorities. This ensures that components such as rotor blades, tower, foundation, mechanical components as well as the other load-bearing elements are adequately protected against material fatigue during the designed service life.
Generally, wind turbines are designed for an operating life of 20 years – 25. Within this period, the operator can rely on the machines structural and system safety, subject to the facility being operated according to the correct procedures and original design, such as maintenance works and prescribed periodic inspection.
Once the designed service life has been reached, however, it can no longer be assumed that all safety-relevant and load-bearing parts will reliably continue to fulfil their function. At this time, compared to the very low level during the designed service life, the probability of fatigue cracks in the load-bearing structure, in connecting elements, in the drive train or in load-bearing elements of the nacelle, for example, can increase.
