Figure 1: Under Performance Tab

The under-performance tab can be used to create a performance loss by shifting the power curve to the right. The nice thing about this is that the performance loss is encountered below rated. The difficult part of this is that it is hard to specify a shift in m/s that will give a definite value of energy loss. However, the latest version of Openwind incorporates a post-processing step in which the wind speed shift can be iterated in order to give a user-specified loss which is the second option in figure 1 above. If bin-averaged power curve test results are available for a turbine then this can be input into the table as a list of power scaling factors which are then applied to the published power curve.

The iterative method referred to above is also used to group together a number of other performance losses which are specified in the energy loss settings