A power performance test is a set of measurements that relates inflow wind conditions to the wind turbine power. Data from the test is often used to create wind turbine power curves, or used to validate computer models of wind turbine performance. Data can also be used to demonstrate the effect of turbine modifications on performance.
The state of the industry in power performance testing is the use of an upwind met tower to allow measurements of wind speed and direction, air temperature, and barometric pressure at hub height. This approach is codified in the international standard IEC 61400-12-1 (2005). The state of the art is starting to diverge from this approach. Instead, remote sensing devices (typically lidar) positioned in place of the met tower are now being used to measure the wind speed at the hub or at multiple heights in the rotor disk. When multiple heights are used this allows the calculation of a rotor-equivalent wind speed (REWS) . A met tower may be used to provide a cross-check on the remote sensing device, or allow scaling of lidar wind speeds to the met tower. The REWS approach was tested in the first phase of Task 32, and found to be more accurate than the traditional hub height measurements . As a result of Task 32 and other investigations, REWS will be included as a method in the forthcoming revision to IEC 61400-12-1. A new technique in power performance testing is the use of nacelle- or spinner- mounted, forward looking lidar that are used to quantify the incoming wind, and then used in the same way as upwind met towers or ground-based lidars.
Power performance testing using either upwind lidar or forward-looking lidar could be cheaper and more accurate than traditional met towers. However, barriers to the adoption of lidar for power performance testing exist additional to those for site assessment:
- A lack of standards. There is no well-publicized chain of recommended practices and standards that define how a lidar for power performance testing can be calibrated, deployed, and analyzed.
- A lack of transferability. In order to move to widespread power performance testing using lidar it is essential to demonstrate that the method is at least as accurate as met towers, or possibly better. However, the lack of open and rigorous studies by unbiased groups that allow comparison of the two methods prevents this comparison.
- Identify gaps in standards and transferability that may prevent widespread adoption.
- Explore if and how new standards for the use of ground-based lidar systems needs to be adapted for the use of nacelle or spinner-based or floating lidar systems.
- Wagner, M. Courtney, J. Gottschall, P. Lindelöw-Marsden, “Accounting for wind shear in wind turbine power performance measurement”, Wind Energy, vol. 14, issue 8, pp. 993-1004, 2011.
- R Wagner, B Cañadillas, A Clifton, S Feeney, N Nygaard, M Poodt, C St Martin, E Tüxen and J W Wagenaar, “Rotor equivalent wind speed for power curve measurement – comparative exercise for IEA Wind Annex 32”, Journal of Physics: Conference Series, vol. 524, no. 1, p. 012108, 2014.