Consistent direct-drive version of the NREL 5MW turbine

Access to relevant reference wind turbine models is important to the wind energy
community to advance turbine technology and lower the cost of wind energy. Multiple reference
turbines are available, which can be used to simulate their structural response using aero-elastic
codes. A common feature of current reference turbines is the utilization of a gearbox, and at
present no direct-drive reference model is publicly available. This does not reflect the trend in
the industry with direct-drive turbines becoming increasingly popular.
In this work we develop an onshore direct-drive version of the geared 5MW reference wind
turbine by NREL. The presented direct-drive model is a fully consistent conversion of the geared
design, intended to analyse the differences in structural loads between the two concepts.
By simulating the developed direct-drive turbine model we show that fatigue loads on the
drivetrain differ significantly for the gearless design, with approximately 10% lower loads for
design class IIB from the IEC 61400-1 design standard. The developed direct-drive turbine
model can be used in the wind energy community to improve the understanding of differences
in structural loads between geared and direct-drive designs of modern multi-megawatt wind
turbines.