On the effects of bat protection strategies on energy production and structural loads of wind farms

Abstract. As wind energy deployment expands, bat protection curtailment is increasingly required for ecological and regulatory reasons. Operators typically implement static, also called 'blanket', schedules based on environmental thresholds for predefined periods, while dynamic approaches based on real-time sensing have emerged as an alternative that can reduce unnecessary curtailment. To date, these strategies have been primarily evaluated using production-based metrics, although frequent curtailment-induced start-ups and shutdowns may affect structural loading and long-term fatigue accumulation. This study proposes an evaluation methodology to quantify impacts on both energy production and structural fatigue accumulation under different bat protection operational strategies. The methodology combines long-term environmental and bat activity data with wind farm flow modeling, mode-dependent surrogate models to represent aeroelastic fatigue response in normal and curtailment-related operating states, and consistent aggregation of energy and fatigue metrics over long time horizons. The approach is demonstrated in a case study of an onshore wind farm in France by comparing representative static and dynamic bat protection strategies with a baseline in which no bat protection strategy is implemented. The results show that energy losses are lower for the evaluated dynamic strategies compared to all considered static schedules. Cumulative fatigue impacts are channel-dependent and are small for most responses and bat protection strategies. However, some loads showed sensitivity to curtailment, indicating that bat activity frequency and its combination with the local climate can lead to increased fatigue loading. The operational, energy, and fatigue cumulative impacts are analyzed, along with the effects of interannual variability, and the main drivers and sensitivities are identified. Based on these, implications for decision-making when selecting an operational strategy are discussed, and the need for site-specific evaluation of both energy and fatigue is highlighted. Moreover, key assumptions are explained and research gaps are identified, especially regarding how fatigue contributions from transient events should be modelled and accounted for in long-term evaluations. Finally, based on the findings, pathways to optimize bat protection strategies are suggested, aiming to achieve the targeted bat protection levels while minimizing energy losses and supporting asset reliability.