OWEA

Verification of offshore wind turbines

Project coordinator: ForWind – Center for Wind Energy Research, Carl von Ossietzky University of Oldenburg

Offshore wind energy converters are subjected to harsher environmental conditions than those an onshore wind turbine typically undergoes: this clearly leads to new challenges for the design of a next generation of larger wind turbines. In order to allow for the design of more reliable offshore wind turbines, the valuable and extensive experience gathered in Germany in the area of onshore wind energy are to be extended and further developed.

The verification of the key parameters employed for the design and the operation of an offshore wind energy converter were the main subject of the joined research project „Verification of offshore wind turbines“ (OWEA), conducted within the time frame 01.11.2007 – 30.09.2012 at the test site “Alpha Ventus”. The main objective of the project was to improve the utilization of the offshore wind energy in Germany, by making it more economical, safer and easier to organize. The most relevant research themes comprised the verification of the power curve for a single wind turbine and of the flow and performance conditions of the entire wind farm, under a set of well-described offshore environmental conditions. Further tasks encompassed the validation of the dynamic behaviour typically for an offshore wind energy converter (including load conditions derived from the concurrent action of wind, waves and the wind farm itself) as well as the development of a monitoring system, capable of supervising the operation state of the offshore wind turbine.

Principal partners of the OWEA project were the University of Stuttgart, the Carl von Ossietzy University of Oldenburg (ForWind), the Leibniz University of Hannover and UL International GmbH (DEWI). Integrated within the OWEA project were also contributions coming from further partners, such as the Karlsruhe Institute of Technology (KIT), Adwen GmbH and Senvion SE.

Prof. Martin Kühn led the OWEA project, first affiliated with the University of Stuttgart and from April 2010 on with the Carl von Ossietzky University of Oldenburg.

Main achievements of the OWEA project comprise a better understanding of the effects of the atmospheric inflow on the power output of an offshore wind turbine as well as of the overall wind farm. Several nacelle-based LIDAR measurement procedures were developed to validate the power curve as well to analyze the inflow conditions in an offshore environment. An improvement in the modelling of the offshore conditions was achieved by a complex three-dimensional and by a strongly parameterized one-dimensional wind field model. A novel stochastic model suited for the description of the offshore wind conditions was also developed, as well as CFD models capable to describe and analyze short- and far-field wake effects, wind farm inflow conditions and wake effects driven by the whole wind farm. Moreover, new calculation tools for the design of an offshore wind turbine, installed on complex braced substructures, such as tripods and jackets, have been developed and successfully validated. It was also possible to transfer and apply such tools from research to industry. Finally, studies were conducted to ascertain the feasibility and potential of a load monitoring system; results proved the efficiency and applicability of such a system, built employing a so-called neural network approach and capable on the processing standard SCADA signals.

Research questions related to the project

  1. What effects do particular environmental conditions have on the performances shown by an offshore wind energy converter? Is it possible to investigate these performance curves offshore, with a sufficiently large degree of accuracy by employing LIDAR technology?

  2. What loading conditions will an offshore wind turbine undergo, when subjected to the combination of low turbulent intensities and wake effects?

  3. How reliable and robust are the already available simulation tools typically employed for the loads and performance analysis of an offshore wind turbine? Is it possible to improve the results by means of an integrated simulation environment, where highly-complex support structures are represented?

  4. How can an efficient and robust load monitoring system be implemented and how can such a system be decently used in order to improve the operational behaviour of the wind turbine?

  5. Is it possible to improve the turbulent wind field models in order to represent the turbulent conditions typical of an offshore area more efficiently? Moreover, how can the estimation of vertical wind shear and the turbulent intensities be improved?

Partners

ForWind – Center for Wind Energy Research, Carl von Ossietzky Universität Oldenburg
Institute of Physics

ForWind - Center for Wind Energy Research, Leibniz-Universität Hannover
Institute of Civil Engineering (www.stahlbau.uni-hannover.de)

  • Prof. Dr.-Ing. Peter Schaumann (schaumann(at)stahl.uni-hannover.de)

University Stuttgart
Stuttgart Wind Energy (www.uni-stuttgart.de/windenergie)

  • Prof. Dr. Po Wen Cheng (cheng(at)ifb.uni-stuttgart.de)

Institute for Aerodynamics and Gasdynamics (www.iag.uni-stuttgart.de/IAG)

  • Dr.-Ing. Thorsten Lutz (lutz(at)iag.uni-stuttgart.de)

UL International GmbH (DEWI) (www.dewi.de)

  • Dr. Tom Neumann (t.neumann(at)dewi.de)

Karlsruhe Institute of Technology (KIT)
Institute of Meteorology and Climatic Research – Atmospheric Environmental Research

  • Prof. Dr. Stefan Emeis (Stefan.Emeis(at)imk.fzk.de)

Senvion SE (www.senvion.com)

  • Dr. Jan Kruse (jan.kruse(at)senvion.com)

Adwen GmbH (www.adwenoffshore.com)

  • Björn Siegmeier (bjoern.siegmeier(at)de.adwenoffshore.com)

Subcontractors

DEWI-OCC Offshore and Certification Centre GmbH (www.dewi-occ.de)

Fördergesellschaft Windenergie e.V. (www.wind-fgw.de)

DNV GL (www.dnvgl.com)

Fraunhofer IWES (www.iwes.fraunhofer.de)