State-of-the-art efficiency determination of a wind turbine drivetrain on a nacelle test bench

Abstract. The efficiency of wind turbine drivetrains is a topic of great interest for both the wind energy industry and the academic community. With the developing maturity of this technology and the increasing pressures to reduce costs, the importance of drivetrain efficiency has grown. However, insufficient accuracy in torque measurement makes actually determining the efficiency of wind turbine drivetrains a very challenging task. In the project known as WindEFCY, state-of-the-art measurement and calibration instruments are used to determine the drivetrain efficiency of a direct drive wind turbine on the nacelle test bench called the DyNaLab. This paper discusses the test configuration applied for this work as well as the instrumentation of the measurement systems used. It further presents the results from two tests of different types to demonstrate the process of efficiency determination and the analysis of uncertainty. Within the paper’s scope of study, an uncertainty level of approximately 0.7 % is achievable when measuring drivetrain efficiency. Details and recommendations concerning data processing and uncertainty analysis are also given in the paper.