As offshore wind turbine blades are getting larger, new methods to assess the integrity and remaining life time of the blades are needed. DNV has initiated a research and innovation project, and an associated Joint Industry Project (JIP), to develop best practices for composite blade integrity assessment, tailored to the needs of wind turbines operating in areas with extreme weather conditions. The industry consortium partners consist of Vestas, Energy Research Institute @ Nanyang Technological University and Instron.

The increasing length of offshore wind turbine blades has prompted the use of advanced composite materials, with positive operational experiences so far, but with a limited range of supporting analysis and testing methods that can be directly applied to large scale wind turbines. DNV initiated the innovation project to develop improved integrity assessment procedures for large scale offshore wind turbines in January 2011 and has joined the JIP industry consortium focusing on advanced composites for wind turbines. Leveraging the experience of Instron in bi-axial testing of composites with various flaws introduced, the expertise of DNV together with ERI@N in finite element analysis, and the knowledge of Vestas in this industry, the project aims to provide insight into composite failure in wind turbine blades. From this, DNV will develop integrity management procedures for advanced composite wind turbine blades.

Most offshore wind projects face the possibility of extreme weather conditions. This complicates key technical and operational issues such as material selection and blade manufacturing quality as well as the assessment of the remaining life of blades that have sustained damage due to extreme loading. The integrity management procedures developed by the DNV innovation project will utilize results from the Joint Industry Project to assess the integrity of advanced composite offshore wind turbine blades. The goal is to enable more accurate predictions of the remaining life of wind turbine blades however tough the environment.

Professor Subodh Mhaisalkar, Executive Director of ERI@N added, “In the first phase of this JIP, the research is addressing development of bi-axial testing methods and finite element analysis procedures that will enable development of test data for deriving and verifying models for flaw growth in the composites. This is required for remaining life predictions with regard to pre-existing manufacturing flaws or service induced damage. This project could be an important contribution to the wind industry, as the project can be extended to develop future standards, guidelines and procedures on the matter.”

“Vestas agrees that more work and data in this area would be valuable in helping the industry to develop better and more reliable products,” says Mr Peter Cheng, Vestas Vice President for Asia Innovation

“We are confident that this development of a set of integrity management procedures will benefit companies moving into the evolving offshore wind industry” says Mr. Markussen. “We therefore invite new participants from across the offshore wind industry to join the potential next phase of this Joint Industry Project.”

"As a natural consequence of the ambitious plans and targets set for renewable energy in many countries, we are seeing increasing projections on the amount of wind power being fed into the grid", says Managing Director, Bjorn Tore Markussen of DNV's Clean Technology Centre (CTC) in Singapore. "The increased expectations for wind power generation have led to growth in wind turbine size, particularly in offshore wind. The technical and potential quality issues faced in such a rapid growth phase can be overcome by cross-industry collaboration to develop best practices, such as this project".