Acoustic techniques for wind turbine blade monitoring

The total electrical generation capacity from wind sources in the International Energy Agency (IEA) Wind Member Countries has increased from 4 GW in 1995 to more than 51 GW in 2005 thus underlining the strategic importance of the resource. In the last year alone the UK increased its wind generation by 447 MW, an increase of 85% over that for the previous year. In 2004, wind generation formed just 0.5% of the national electric demand; this contribution is set to rise over the next few years with some predictions that wind energy will rise to 8% of the total UK demand by 2010. The rotor blades of a wind turbine system are a significant structural component of the overall system, and typically account for 30% of lifecycle costs, and contribute 34% to overall system downtime. Despite their importance, there is currently very little monitoring of the structural integrity of rotor components, and what does exist is limited. We perceive that especially with the current political and technological emphasis on offshore installations, there will be an increase in the perceived need for remote structural monitoring, and there is indeed currently great interest in this area from the wind turbine industry. This work focuses on the applications of acoustic techniques to assess the integrity of typical rotor blade structures. Preliminary results discuss the limiting aspects of acoustic based techniques based on the physics of acoustic wave propagation in typical structural components. Comparisons between acoustic emission approaches and conventional active ultrasound will be considered.