Nearshore Wave Damping Due to the Effect on Winds in Response to Offshore Wind Farms

Abstract

Despite the progress that has been made in modeling wind wake interaction between turbines in offshore wind farms, only a handful of studies have quantified the impact of wind turbines or wave farms upon surface waves, and there are even less articles about the wave blockage induced by the whole array of turbines upon wind waves. This hypothetical case study proposes a methodology that takes into account the combined effect of wind wake and wave blockage on wind waves when transforming offshore waves to nearshore in an offshore wind farm scenario.Keywords: offshore wind farm; wind wake modelling; wave blockage modelling; wind farm footprint. MOTIVATIONThe wind provides a rich energy source, which can be exploited to achieve a sustainable energy supply for years to come and to meet the increasing demand for energy world-wide. The recent construction of large wind farms offshore makes the implementation of wind energy highly realizable. In addition, energy production increases because larger turbines can be deployed offshore. Current offshore wind farms are often installed in near-shore areas where water depths are less than 20 m and where connection to the electrical grid is convenient.One of the most important environmental issues associated with offshore wind turbines (along with the visual impact and, to a lesser extent, ambient noise levels) is that the supporting structures are likely to affect the wave and circulation regime, as well as sediment transport, due to the blockage and scattering of wave energy due to the piles. In addition, the activity induced by the rotating blades generates a downwind turbulent wake, within which the wind speeds are lower than the far field (i.e free stream) value. This is likely to have an impact on locally generated wind waves, both within and downwind of the wind farm.Only a few published studies analyse the impact of wind turbines or offshore wave farms upon surface waves near the coast (CEFAS, 2005;Millar, Smith, and Reeve, 2007). The former investigates the wave blockage effect induced by wind turbines upon surface waves by means of a wave agitation model based on the mild slope equation. The latter estimates the changes in the shoreline wave climate associated with the development of arrays of wave energy converters (WECs) by making use of the SWAN wave transformation model (Booij et al., 1999), along with a set of empirical transmission percentages in order to represent the wave energy damping.Regarding the wind wake, there is a wide range of publications discussing the modelling of either the vertical wind profile (Lange, Larsen, Højstrup and Barthelmie, 2002) or the wake development at hub height downwind of the wind farm (Barthelmie, Pryor, Frandsen and Larsen, 2004).However, no studies are published that assess the importance of the whole array of wind turbines upon wind waves when considering the effects of wind wake and wave blockage together. The purpose of this study is to quantify the effect of these structures on wind waves, which propagate toward the coast....

Assessment of the impact of offshore wind farm foundations in the English Channel on larval dispersal and connectivity using numerical modeling

“…Regarding the effects of wind, our model currently incorporates them as a surface stress representing pressure. Previous research underscores the importance of a more accurate consideration of wind turbine motions, which can significantly alter the surrounding wind field because they change the atmospheric turbulence and therefore modify the air-sea fluxes [69,70]. Incorporating such modifications using for example an existing coupled ocean-atmosphere model is promising way and the next step.…”