Offshore wind energy is becoming a key contributor to the renewable energy mix in Europe. In recent years we have seen a disruptive growth in the size of wind turbines, implying an increased weight and lowered resonance frequency. More than ever the design of the substructures/foundations is (metal) fatigue driven. At VUB we develop(ed) techniques that allow to assess the fatigue age of existing wind turbines offshore. These provide essential information for maintenance and possible life time extension.It is key to realize that fatigue is the result of the interaction between structural dynamics and periodic loads, e.g. waves. It therefore is essential that the structural dynamics are predicted correctly in design and factored in during any fatigue assessment. To improve the accuracy of future of fatigue assessments and optimize future designs this project will target to develop methodologies to use monitoring data to update structural properties of wind turbines (Model-in-the-loop-monitoring). From the updated models on the fleet leaders, we will update the structural properties of the entire fleet through an intelligent measurement strategy. In a final step the updated models are combined with the previously developed tools for load extrapolation and fatigue life assessment to obtain the true fatigue age of the farm and ultimately bring down the cost of renewable energy offshore