Over the years, we have witnessed rapid growth in both onshore and offshore wind turbine systems. At the same time, the entire wind industry has become even more competitive, as wind turbine manufacturers aim to launch their product on the market in the shortest time possible. Successful and rapid prototype testing plays a crucial role here. Why? Well, it ensures the required product reliability is achieved and helps in bringing the product to market in the shortest time possible.
Improving the way things are done!
Field testing is the conventional way of testing full wind turbine systems and is a mandatory requirement for obtaining type certification. The complete certification campaign usually takes several years. This lengthy duration is a significant cost factor in turbine development and decisively determines the time to market. Consequently, we have seen significant advances toward finding alternatives to conventional testing methods in recent years, leading to the development of several ground-based nacelle testing facilities around the world. These facilities offer system-level testing capabilities for the complete nacelle, one goal being the application of realistic loads in multiple degrees of freedom like those that the drivetrain components will be subjected to in field operation. No more waiting for ideal wind conditions, the laboratory can recreate the desired wind conditions as needed!
Change is good!
Nacelle testing is a fairly new approach compared with other aspects of wind turbine validation. Apart from their primary use, nacelle test benches have been employed to develop novel methods for torque measurement and drivetrain efficiency evaluation   and have also been used to develop and test new drivetrain and generator technologies . Although nacelle test benches cannot fully replace field testing due to their physical limitations, they do represent an alternative for performing certification-relevant tests, which may help to reduce the number of field tests required. The IEC Technical Committee 88 is aiming to specify uniform testing procedures for nacelle test benches and is addressing the definition of a nacelle test bench, system requirements, and test and measurement procedures. It can be expected that nacelle test benches with Hardware-in-the-Loop (HiL) systems will contribute significantly towards the electrical certification of wind turbines in the near future.
Keep making them bigger?
The fast-growing trend of increasing wind turbine size and operational capacity has increased the demands on the existing nacelle testing facilities. Many of them are already (or will soon be) too small to cope with the higher demands associated with the testing of larger wind turbines. There has been a trend toward constructing bigger test benches to accommodate the requirements of larger wind turbines. However, this continuous trend of constructing bigger nacelle test benches for larger wind turbines might not be a sustainable solution. Some of the foreseeable challenges for future nacelle test benches include:
- Acceptable testing costs
- Application of highly dynamic loads and torque in the range of several MNm with high accuracy and controllable bandwidth
- Maintaining test run and control stability for the integrated system of mechanical components and the complex electrical controller system during HiL testing.
Making the most of what we already have
In our opinion, smart solutions are required to enhance the capabilities of existing nacelle test benches and maximize their use for testing future wind turbines: for example, improving and optimizing the infrastructures that already exist instead of constructing new ones from scratch. The latest developments and the successful demonstration of the combined use of physical tests and simulations in the automotive, railroad, and aerospace sectors have already shown great potential. Learning from other industrial sectors and experimenting with the combined use of physical and simulative testing methods might help to discover solutions to some of the challenges of nacelle testing. We believe that a possible solution lies in combining the physical and virtual testing paradigms in a manner which complements the capabilities of the test bench. This form of ‘hybrid testing’ could also potentially reduce the cost of testing. In our next blog article, we will present the concept of hybrid testing in further detail.
 H. Zhang and M. Neshati, “An effective method of determining the drive-train efficiency of wind turbines with high accuracy,” Journal of Physics: Conference Series, 2018.
 H. Zhang, J. Wenske, A. Reuter and M. Neshati, “Proposals for a practical calibration method for mechanical torque measurement on the wind turbine drive train under test on a test bench,” Wind Energy, vol. 23, no. 4, pp. 1048-1062, 2020.
 H. Kyling, N. Eich and P. Feja, “Measuring MNm torques as part of a prototype testing campaign of a high-temperature superconducting generator for wind turbine application in the scope of the Ecoswing project,” Journal of Physics: Conference Series, vol. 1222, 2019.
 M. O. Siddiqui, P. R. Feja, P. Borowski, H. Kyling, A. R. Nejad and J. Wenske, “Wind Turbine Nacelle Testing: State-of-the-Art and Development Trends,” [Manuscript submitted for publication], 2023.
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