Beyond wind-sector management: optimal wind farm operational planning for balancing fatigue damage and extending lifetime

Abstract. We present an optimization framework for long‑term wind farm operation that balances fatigue loads and energy yield to extend turbine and farm lifetime. The approach plans per‑turbine derating setpoints for discrete wind conditions using an engineering wake model and surrogate models for power and damage. We formulate the problem as a nonlinear program and solve it either for the full farm in a single run or iteratively per turbine. The method is demonstrated on a 9‑turbine farm under onshore and offshore turbulence conditions and across multiple failure modes. For tower bottom bending, modest lifetime extensions of 2–5 years increase net present value (NPV) between (5 % and more than 100 %) with small losses of annual energy production (AEP) of 1–4 % onshore and less than 0.2 % offshore. The per‑turbine optimization achieves similar results as the full farm approach in most cases. Under offshore turbulence, upstream derating more effectively reduces wake‑induced turbulence and the coordinated farm optimization yields additional benefits. When blade edgewise loads are included, lifetime gains require stronger derating due to rotational‑speed sensitivity and reduce economic benefits. The framework produces implementable lookup tables that can be integrated into wind farm planning and control. While results rely on steady wake models and design‑style damage estimation and thus represent first‑order comparisons, they show that targeted derating can redistribute damage and extend lifetime with limited impact on energy.