Efficient development of offshore windfarms (ENDOW): Final report to the European Commission

Europe has large offshore wind energy potential that is poised for exploitation to make a significant contribution to the objective of providing a clean, renewable and secure energy supply. Offshore wind energy developments are underway in many European countries with planned projects of several thousand megawatts to be installed in addition to the 250 MW installed by the end of 2002. While experience gained through the demonstration projects currently operating is valuable, a major uncertainty in estimating power production lies in the prediction of the dynamic links between the at-mosphere and wind turbines in offshore regimes. The objective of the ENDOW project was to evaluate, enhance and interface wake and boundary-layer models for utilisation offshore. The project resulted in a significant advance in the state of the art in both wake and marine boundary layer models leading to improved prediction of wind speed and turbulence profiles within large offshore wind farms. Use of new databases from existing offshore wind farms and detailed wake profiles collected using a sodar provided a unique opportunity to undertake the first comprehensive evaluation of offshore wake model performances. The wake models evaluated vary in complexity from empirical solutions to the most advanced models based on solutions of the Navier-Stokes equations using eddy viscosity combined with a k-epsilon turbulence closure. Results of wake model performance in different wind speed, stability and roughness conditions provided criteria for their improvement. Mesoscale model simulations were used to evaluate the impact of thermal flows, roughness and orography on offshore wind speeds. The model hierarchy developed under ENDOW forms the basis of design tools for use by wind energy developers and turbine manufacturers to optimise power output from offshore wind farms through minimised wake effects and optimal grid connections. The design tools are being built onto existing regional scale models and wind farm design software which was developed with EU funding and is in use currently by wind energy developers. This maximises the expected impact of this project through efficient use of existing resources and ease of upgrade for end-users. The objective of the ENDOW project was to evaluate, enhance and interface wake and boundary-layer models for utilisation offshore. The project resulted in a significant advance in the state of the art in both wake and marine boundary layer models leading to improved prediction of wind speed and turbulence profiles within large offshore wind farms. Use of new databases from existing offshore wind farms and detailed wake profiles collected using a sodar provided a unique opportunity to undertake the first comprehensive evaluation of offshore wake model performances. The wake models evaluated vary in complexity from empirical solutions to the most advanced models based on solutions of the Navier-Stokes equations using eddy viscosity com- bined with a k-epsilon turbulence closure. Results of wake model performance in different wind speed, stability and roughness conditions provided criteria for their improvement. Mesoscale model simulations were used to evaluate the impact of thermal flows, roughness and orography on offshore wind speeds. The model hierarchy developed under ENDOW forms the basis of design tools for use by wind energy devel- opers and turbine manufacturers to optimise power output from offshore wind farms through minimised wake effects and optimal grid connections. The design tools are being built onto existing regional scale models and wind farm design software which was developed with EU funding and is in use currently by wind energy developers. This maximises the expected impact of this project through efficient use of existing resources and ease of upgrade for end-users.