One important environmental concern in operating wind farms is the bat risk of collision with wind turbines’ rotating blade. To avoid this, the bat curtailment practise is implemented, in which the turbines are shutdown during bat activity periods. This, however, leads to a decrease in the annual energy production (AEP). A proper assessment of the energy loss due to bats is key to correctly estimate the wind farm AEP. Following the manufacturer strategy, the industry standard provides a model to estimate the annual energy efficiency due to bat curtailment in wind farms. This is a time domain efficiency model that works with setting the power generation time stamps to zero into the reconstructed hub height power time series used to alculate the AEP, according to temperature, wind speed and time limits that are recognised to be sensitive to the bat activity. The exact values of these limits depend on the turbine control system design choice of the specific turbine model.
However, after analysing the post-construction operational data of wind farms, the annual bat energy efficiency evaluated according to the industry standards is observed to underestimate the real efficiency seen in operation.
In this work, the aim is to explain and evaluate the discrepancies seen between the bat curtailment losses in operation and the bat efficiencies modelled using the industry standard. To achieve this, the operational data of different wind farms are analysed and the resulting differences in losses are broken
down into multiple categories including yearly windiness, error in the control strategy implementation, inaccuracy of nacelle instrument readings of the ambient parameters (including the wind speed), inertia in the control of the turbine.
The content of this work is organised as follows: in Chapter 4 the theoretical content and tools supporting the research are given, in Chapter 5 the research question is explained in detail, in Chapter 6 the methodology applied to analyse the operational data is described, then, the behavior of three wind farms is investigated during bat curtailment, in Chapter 7 the three wind farms are analysed in pre-construction and the bat curtailment energy losses are evaluated according to the industry methodology, in Chapter 8 the post and pre-construction results are compared and the gaps between the two are investigated, in Chapter 9 a sensitivity analysis over the parameters seen as sensitive to bat curtailment is carried out to understand the influence these have in the bat losses, in Chapter 10, an alternative methodology to correct for the nacelle anemometer reading is proposed and, finally, in Chapter 11 the conclusion is drawn.