Ørsted has announced recently that it had revised its estimates for future energy production of its offshore wind farms as a result of improving its methodology for calculating turbine interaction loss. The announced change appears to be, in part, related to a DNV GL paper published in the scientific journal Energies in June 2018.
Using field measurements and simulation results, the paper showed that blockage effects cause wind speed reductions upstream of a wind farm that are more pronounced and far-reaching than commonly assumed. It also found that front row turbines, contrary to long-held assumptions, will generally produce less energy than they would operating in isolation, constituting a material turbine interaction loss.
This wind-farm-scale blockage effect impacts all wind farm projects, both onshore and offshore. The magnitude of the effect will depend on several factors, including the turbine characteristics, the turbine layout/locations, and site-specific atmospheric conditions. It is the combination of these parameters rather than the onshore/offshore distinction that determines the magnitude of the effect. According to DNV GL’s current state of knowledge and depending on project-specific factors, previously unaccounted for turbine interaction losses related to blockage represent 0% to 4% of mean annual energy yield.