Guaranteeing high availability of wind turbines

Modern wind turbines are relatively “immature” in the sense that they have not been fielded for a sufficient amount of time to assess their long-term viability. Availability, the ability of a system to function when it is required, is a major concern for alternative energy systems. Profits and environmental benefits will be lost if the costs and energy required to maintain a system outweigh the benefits obtained. Prognostics and system health management (PHM) methods can have a significant impact on the wind energy community. PHM enables the manufacturers and operators of complex systems to move from traditional timeor cyclebased maintenance to condition-based maintenance, which can significantly improve availability. This paper discusses the challenges in guaranteeing the high availability of wind turbines, and the use of PHM as a methodology to guarantee the high availability. A new sensor system for the health monitoring of turbine blades is proposed and a return on investment analysis for its use is presented. The work presented in this paper is structured as the following: Section 2 discusses the challenges for ensuring the availability of wind turbines. Section 3 introduces prognostics and health management as a method to ensure high availability of turbines. Section 4 discusses the state of health monitoring of wind turbines. Section 5 introduces a sensor system for the health management of blades and gearboxes, and includes a return on investment analysis, and Section 6 concludes the paper and provides directions for future research. 2 CHALLENGES IN AVAILABILITY OF WIND TURBINES The Wind Energy Operations & Maintenance Report was recently published (Asmus and Seitzler, 2010) and included a discussion highlighting the challenges with wind energy systems. Some of the most notable conclusions are that the operation and maintenance (O&M) costs for wind power are double or triple the figures originally projected, they are particularly high in the United States. Another interesting fact is that many gearboxes, designed for a 20-year life, are failing after 6 to 8 years of operation. These challenges indicate that reliability, maintainability, and availability stand among the key challenges to the economic viability of wind turbines and their ability to compete with traditional energy sources. This section summarizes these challenges.