Assessment of a rotor blade extension retrofit as a supplement to the lifetime extension of wind turbines

Abstract

Abstract. The potential lifetime of wind turbine components is usually not fully utilized as the site conditions are less severe than assumed in the turbine design. Operators of wind farms can make use of the excess fatigue budget to increase the energy yield and thus decrease the levelized cost of energy (LCoE). To achieve this, the lifetime of the turbine can be extended until the fatigue budget is exhausted. Alternatively, a rotor blade extension (RBE) is an option to increase the energy yield of a wind turbine. An RBE increases the blade length and thus the swept area and the energy yield. An RBE also increases the loads on the turbine, however. Higher fatigue loads in turn reduce the fatigue budget of a turbine. This study investigates whether the use of an RBE is advantageous compared with a sole lifetime extension (LTE). As the use case, a commercial 1.5 MW turbine located in northern Germany was investigated. Aeroservoelastic multibody load simulations and simplified static load simulations were verified with each other. These simulations revealed the loads to determine the fatigue budget of the turbine components. Since the blade became the critical component when a certain RBE length was exceeded, the blade was subjected to a structural fatigue analysis. The fatigue analysis focused on the trailing-edge bond line which became critical when lead–lag loads increased with blade length. Finally, the energy production gains due to LTE and RBE were assessed. For the use case turbine, this study revealed an LTE of 8.7 years after a design life of 20 years with an additional energy yield of 43.5 %. Moreover, the extension of the 34 m blade with an RBE length of 0.8 m further increased the yield by 2.3 %.

Impact of Site-Specific Thermal Residual Stress on the Fatigue of Wind-Turbine Blades

“…The trend in blade design tends toward a site-specific wind consideration in order to decrease the levelized cost of energy (LCOE), which means that a blade tip extension is fitted to a modular blade to obtain the optimum rotor diameter for an individual wind site; cf. Rosemeier and Saathoff [46] and Christenson et al [63]. Our research shows that, although the computational effort is greater, a sitespecific temperature consideration plus a more realistic degree-ofcure assumption yield a more critical design than is obtained with traditional temperature-independent modeling plus the assumption of an unrealistically high degree of cure.…”

“…The relatively computationally efficient quasi-static simulations have shown good agreement with aeroelastic simulations for the trailing-edge evaluation up to 40% blade length when a load factor of γ l 1.25 was multiplied with the amplitude load; see the work of Rosemeier and Saathoff [46].…”

“…Further details of the simulation method can be found in Refs. [5,45,46]. Euler-Bernoulli [47] beam theory was used to calculate the longitudinal strains and stresses along the trailing edge.…”

Validation of crack initiation model by means of cyclic full-scale blade test

“…The validated crack initiation model can be applied for design purposes taking into account the operating-temperature-dependent [31] and manufacture-induced multi-axial mean stress-states, and the multi-axial mean and amplitude stress-states due to field operating conditions, e.g., by using a simplified engineering approach as proposed in [7,32], i.e., a deterministic wind plus lead-lag gravity loads to predict the crack initiation in the field.…”

Improved Design of a Large Offshore Wind Farm by Using Biogeography based Optimization

“…WTs become brittle, which reduces performance and safety. The lifespan of a wind farm is estimated at 20 years [22,23].…”