A straightforward approach to site-wide assessment of wind turbine tower lifetime extension potential

This contribution presents a novel methodology to evaluate the lifetime extension potential of wind turbines—taking towers as the key component that preserves onshore turbines' structural integrity—as a consequence of the difference between design and site-specific loads. Specifically, attention is drawn to the site-specific wind direction distribution, which provides an additional source of lifetime extension potential. For this purpose, variants of closed-form solutions (based on the tower section’s normal stress) are developed to enable fatigue damage accumulation due to fore-aft and side-to-side bending moments at any point on the tower circumference without the need for further information on tower section geometry or material properties. Based on the degree of data availability, different scenarios are defined to estimate lifetime extension potential from the accurate tower's normal stress and approximations using resultant bending moment, fore-aft bending moment, and finally, wind rose data only. The methodology is applied to a wind farm case study using the actual SCADA data with a partially validated turbine’s aeroelastic model to obtain operational loads. The results indicate that this quick and fairly accurate approach can be used as an initial stage in identifying wind turbines across large farms, which have the largest lifetime extension potential.