Re-purposing of shallow wind turbine foundations for power capacity increase

Re-purposing the foundations of older wind turbines to install new and larger wind turbines can reduce the investment costs and carbon emissions of wind energy development projects. In this paper, detailed numerical modeling is used to assess the behavior of a shallow foundation designed for a 5 MW wind turbine under the aerodynamic loads and seismic motions of larger replacement wind turbines. The finite element modeling scheme used for the soil under rocking foundations is validated based on experimental data. Results of this study indicate that maximum gapping and maximum tilting have similar trends of increase with increasing turbine power. Relaxing the no-uplift rule for normal operation conditions allows for installing an 8 MW wind turbine on the foundation designed for 5 MW, without compromising the foundation safety or serviceability requirements. However, the foundation does not perform satisfactorily with the 10 MW wind turbine. The no-uplift rule of design regulations for operational conditions is overly conservative. The limits of capacity increase for individual projects can be determined using the procedure presented in this paper.