8.5_Skrzypiński: Blade erosion in wind farm layout and/or control optimization

Present work is an exploratory study of the effect of including blade erosion of wind turbine blades on the layout and/or control optimization of wind farms. On the one hand, an extensive study of different aspects of rain-induced blade erosion is being carried out in an ongoing project EROSION (http://www.rain-erosion.dk) led by DTU. Among other aspects, the project includes: (1) accelerated experimental study of the relation between rainfall parameters, blade tip speed and the pace of erosion (2) engineering modelling of the effect of erosion on energy production (3) inclusion of erosion in innovative turbine control with the scope on maximizing long-term profit, i.e. Erosion Safe Mode (ESM) (4) full-scale shoulder-to-shoulder validation of the ESM. On the other hand, for many years DTU together with its industrial partners has been developing the OpenMDAO-based open source (MIT license) wind farm layout and control optimization platform TOPFARM (www.topfarm.dtu.dk). Then, given the increasing interest of the wind energy industry, especially farm operators, in the problem of erosion, and the demand to decrease the ever-increasing erosion-related costs, especially offshore, it is a rational next step to open the process of including the research outputs of EROSION published by Bech et al. [1] in the TOPFARM framework. The first step is inclusion of the effect of rain intensity and turbine tip speed on the pace of erosion. The second step is inclusion of the effect of erosion on the energy production. Regarding the erosion-induced drop in the AEP, it depends on many factors, e.g. turbine characteristics, the level and type of erosion or how frequently maintenance is carried out. With this respect, different industrial sources report different values of average AEP drop, most falling within the 2-5% range. Hence, it is natural to account for such gradual drop in codes that, among other features, compute wind farm energy production, e.g. TOPFARM. In the light of uncertainty in exact values, the initial approach may be a conservative one. The third step is to include the erosion-safe control proposed by Bech et al. [1] in a wind farm context. The method assumes a temporary decrease in tip speed during heavy precipitation events in order to decrease the pace of erosion. In such operation, the short-term decrease in energy production due to decreased tip speed may by outbalanced by a long-term increase caused by a better overall condition of blades and reduced cost of maintenance and repair operations. The latter are especially expensive offshore due to the cost of vessels and limited weather windows. Inclusion of such control in wind farm context may provide information about its potential effect on interaction between turbines in a farm, e.g. through wakes. Consequently, it may affect the optimal layout of the farm, which is to be investigated in present work.

[1] Bech et al., Wind Energy Science. 3, 729 (2018)