Evaluation of fatigue loads of horizontal up-scaled wind turbines

Wind turbines, especially for offshore applications, are continually being up-scaled on the basis that having fewer separate sites per installed MW will reduce balance of plant and O&M costs and hence may reduce cost of energy. Obviously the loads on a wind turbine increase with the size of the machine. However there is presently no generic, systematic study of how fatigue loads vary with wind turbine size. Both extreme and fatigue load evaluation is essential for the design of wind turbines. This paper however has its focus solely on fatigue loads.The aim is to investigate the dependency of fatigue loads (lifetime damage equivalent loads are employed to calculate the fatigue loads) on wind turbine scale and subsequently to develop generic fatigue load trends with scale, ideally in the form of simple power law curves.Seven wind turbine models were created from a reference model (Danish design) based on up-scaling with similarity. Such scaling does not accurately reflect commercial trends but is considered a best starting point to gain fundamental understanding. Fatigue loads in various design load cases (startups, power production, idling, and shutdowns) as specified in IEC standards are simulated and trend lines determined. This work is part of a much larger generic study of all the main influences on wind turbine loads.