Offshore wind energy is essential for expanding renewable energy generation and reducing global greenhouse gas emissions. However, as offshore wind turbines form new elements in the marine environment, the offshore wind infrastructure has implications for the physics of the atmosphere and ocean. In this study, we demonstrate the effects of surface wind speed reduction and structure-induced mixing, and illustrate the consequences for ocean dynamics in the southern North Sea. Using unstructured grid modeling, we present simplified parameterizations to account for wind speed reduction due to offshore wind farms and the underwater structure drag by offshore wind turbine foundations in hydrodynamic models. The simulations cover the seasonal cycle of the summer stratification, while taking into account the recent state of European offshore wind development in the southern North Sea. The modeling shows that offshore wind farm effects cause large-scale structural changes in ocean physics, systematically affecting the North Sea hydrodynamics. The wake effects at offshore wind farms lead to spatial redistributions of horizontal currents and, in particular, affect the seasonal stratification development on regional scales. Although these perturbations are on the order of natural variability, changes in regional stratification suggest potential consequences for biogeochemical processes and marine ecosystem dynamics. With our results, we provide new insights into the adaptation of coastal seas to offshore wind farm effects and raise awareness for potential changes in the future coastal ocean and the southern North Sea.

How to cite: Christiansen, N., Daewel, U., Djath, B., Carpenter, J., Suzuki, N., and Schrum, C.: Regional impacts of offshore wind farms on the North Sea hydrodynamics, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12169, https://doi.org/10.5194/egusphere-egu23-12169, 2023.

The drive to achieve net zero carbon has motivated the development of offshore wind into deeper waters further from shore. The relatively weak tidal currents and deep water of future development sites means that infrastructure will, for the first time, be deployed at scale in seasonally stratified waters.   Current designs for floating turbines have sub-structures which penetrate this stratification.  Flow past such substructures generates turbulent wakes which can regionally enhance the very low levels of internal mixing observed in the seasonal thermocline. 

These low natural mixing rates drive nutrient fluxes which sustain phytoplankton growth at the subsurface chlorophyl maximum through the summer months and are responsible for 50% of the primary production in shelf seas.  Since this production supports the marine food web, changes to the physical drivers will fundamentally impact the marine food web.  Therefore, an anthropogenic source of turbulent mixing at the seasonal thermocline, has the potential to cause fundamental biogeochemical changes, impacting ecosystems, and fisheries in shelf seas. 

We present new measurements of strongly elevated turbulence within wakes at a shallow water wind farm.  Strongly enhanced mixing is observed in the wake, and across the wider wind farm area and is associated with reduced stratification.    These observations and our estimates for deeper water wakes suggest that mixing from these structures can be significant, and further research is essential to quantify the impact of this new source of anthropogenic mixing.

How to cite: Lincoln, B. and Rippeth, T.: Enhanced mixing by floating wind farms in stratified shelf seas, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14622, https://doi.org/10.5194/egusphere-egu23-14622, 2023.

The whole world is urgently looking for alternative renewable energy resources to power its future economy with less carbon footprint. As one of the world’s largest energy consumers and CO₂ emitters, China is making all efforts to decarbonize its power systems (‘carbon neutrality by 2060’), with special attention to offshore wind power. However, the potential of offshore wind power generation and emissions mitigation is largely unknown, and the contribution to regional carbon neutrality needs to be further clarified. Here, we estimate the offshore wind resource, its generation potential, and the reduction of CO₂ emissions from offshore wind power to replace coal-fired power generation. We find that the abundant offshore wind energy resources in China can potentially generate enough electricity to fully power the country. However, current utilization of offshore wind energy is relatively limited, supplying less than 1% of local electricity needs. With the development of offshore wind farms, this share could be over 20 times higher in 2050 than that at present. The total emissions reduction would increase from 11.9 Tg CO₂-eq yr^–1 in 2019 to 294.3 Tg CO₂-eq yr^–1 in 2050 because of reduced coal use, significantly contributing to emissions mitigation along the coastal provinces. Our results highlight the important role of offshore wind power in upgrading the regional energy system and achieving carbon neutrality of China, and it will also give imputes to a cleaner electricity system worldwide. Future studies are encouraged to further explore the feasibility of offshore wind farm construction.

How to cite: Deng, X. and Qin, Z.: Offshore wind power in China contributing to regional power system upgrade and carbon neutrality, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10609, https://doi.org/10.5194/egusphere-egu23-10609, 2023.

How to cite: Suzuki, N. and Carpenter, J.: Eddy diffusivity and viscosity due to offshore wind turbine monopile foundations in tidal currents, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8817, https://doi.org/10.5194/egusphere-egu23-8817, 2023.

The continued expansion of offshore wind as a global energy technology represents a significant expansion of infrastructure into a range of coastal and oceanic regions. Effective design, operation and understanding physical impacts of turbines benefit from a detailed understanding of the wave conditions. In order to cover the spatial extent of offshore wind farms and to ensure high quality data, some combination of in-situ measurements and phase averaging wave modelling are commonly applied. These are used for monitoring current conditions and for short term forecasts that govern crucial operational decisions. Inaccuracies in this process lead to vessels missing suitable conditions to carry out an operation, or operations being aborted due to unsafe conditions. Both of these outcomes, cost money or affect safety.

This work reviews recent progress in using machine learning to develop surrogate wave modelling that can offer real-time spatial wave data leveraging a combination of in-situ measurements and model hindcasts, but without relying on continuous processing from traditional wave models. The outcomes show an improvement in accuracy of real-time wave predictions when compared to regional wave modelling, available at a fraction of the computational cost. This highlights the potential of this approach to change how wave data is provided for operational purposes, with immediate potential for reduced costs and improved safety for vessels working at offshore wind farms. The results also highlight the ongoing potential for research and development of surrogate models as part of the future of numerical wave modelling.

How to cite: Ashton, I., Chen, J., Steele, E., and Pillai, A.: Surrogate wave modelling to improve operational wave data for offshore wind farms, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15848, https://doi.org/10.5194/egusphere-egu23-15848, 2023.

The Canary Islands in the eastern North Atlantic has an abundant and diverse renewable energy resource but currently generates much of its electricity from imported diesel, at significant financial and environmental cost.  To address this, the government and electricity supplier are investing heavily in infrastructure to transform the islands’ energy mix to incorporate offshore wind and wave power. 

Economically and technically feasible offshore wave energy projects rely on understanding the regional distribution of wave properties (e.g. to optimize site selection), and how the wave power varies at inter- and intra-annual timescales.  We have constructed an 11-year wave hindcast model for a potential wave energy site at an energetic location in the north-west coast of Lanzarote, one of the largest of the Canary Islands, to investigate the spatial and temporal distribution of wave power. 

Due to a lack of a continental shelf, wave power is homogeneous until a few km from the coastline, and then begins to vary rapidly in space.  Temporal variation is relatively low due to the latitude.  The wave resource is heavily dominated by swell, with uninterrupted fetch across the Atlantic, and largely uncorrelated with local wind.  This makes co-location of wind and wave energy arrays particularly attractive from the perspective of reducing resource variability, as well as the other practical and financial benefits of sharing a grid location with more established offshore wind technology.

Finally, we demonstrate and validate a simple non-physics based process for extending the output timeseries beyond the hindcast duration, by correlating with parameters from global datasets.  This method also allows the possibility of power forecasting based on global operational models.

How to cite: Christie, D., Neill, S., and Arnold, P.: Wave Power in Lanzarote: Spatiotemporal Variability, Wind Co-location and Non-Physics based Modelling, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13905, https://doi.org/10.5194/egusphere-egu23-13905, 2023.

Ocean renewable energy has strong potential for substituting power plants that rely on the combustion of fossil fuels. Due to maturity, offshore wind farms  are one of the most promising forms of ocean renewable energy. There are several windfarms around the world located in nearshore/beach regions (e.g. Bangui Wind Farm, Philippines). Scour around the foundation of nearshore windfarm structures is one of the important technical aspects to be addressed. In this study, field  investigations on the development of scour around scaled model piles  are carried out in two regions of wave breaking, viz.,  i) Uthandi beach, South Chennai, India, open coast having no structures and (ii) Muttukadu beach, South Chennai, India, which is 8 km south of Uthandi beach, having two breakwaters at Muttkadu lake mouth with eight groins in varying lengths with spacing of 50-200m.  Field investigations show rapid increases of the scour depth during swash due to wave uprush around piles and the scour depth reduces significantly during back wash. The field measurements on scour depth (S) around piles of various diameters (D) are well matching with previous published results of scour analysis (Sumer et al..2001).  The relative scour depth (S/D) increases with increase of upstream water run up heights, flow velocities, Froude number and pile positions relating to the location of wave breaking. The comparison of observed scour depths around piles in plunging and spilling wave breaker region indicates that the relative scour depth in plunging wave breaker is higher by around a factor of 1.3 times than that of the scour depth observed in the spilling breaker region.  The present study indicates that, to determine the foundation design depth of the piles for construction of pile supported structure in the region of wave breaking or in the surf zone, the scour depth must be estimated by considering additional depth variation on the beach profile for different monsoon season.  It is observed that the maximum relative scour depth (S_max / D) and width of scour hole are reduced significantly about 50% to 75% with presence of cotton cloths around piles.  However, for a full-scale wind turbine, a suitable geotextile material should be used. This presentation details the various aspects of hydrodynamic field measurements on scaled pile models, which serve as design parameters for designing the pile supported coastal structures including wind energy farms in nearshore regions.

Key Words:  Ocean Renewable Energy, near offshore wind farms, hydrodynamics, scour measurements, swash region, offshore piles

Reference:

• Mohamed Rajab. P.(2019), Hydrodynamic Analysis of Scour Around Offshore Piles.

             Ph.D. Thesis., AMET University, India.

• Sumer, B.M., Whitehouse, R.J.S. and Tørum, A.,(2001). Scour around coastal structures: a summary of recent research. Coastal Engineering, Vol.44:153-190.

How to cite: Kannapiran, T. and Neill, S.: Field Investigations of Scour Around Scaled Piles in a Region of Wave Breaking, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16285, https://doi.org/10.5194/egusphere-egu23-16285, 2023.

The predictability and opportunity to provide baseload power has made tidal energy one of the most attractive marine renewable energy resources to help fight anthropogenic climate change. This has led to extensive research regarding the overall resource and methods of extraction. However, with differing designs found in today’s tidal turbine market, it is clear that there remains an ongoing debate as to where a tidal turbine should sit within the water column. In this study, a floating turbine and bottom mounted turbine, both based on current designs found in the market, were analysed over a tidal cycle in a 3D hydrodynamic model of the Morlais tidal test zone. The model was validated from ADCP measurements from the same area and recorded over the same tidal cycle. The aim was to establish the most efficient design and its effect on the surrounding water column. The results showed significant differences in the near-field effects of each turbine, but negligible effects were found further afield. Over the established tidal cycle, the floating turbine was found to be more efficient.

How to cite: Lewis, J., Neill, S., and Poovadiyil, S.: Comparison Of a Floating and a Bottom Fixed Tidal Turbine in a Coastal Marine Environment, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7277, https://doi.org/10.5194/egusphere-egu23-7277, 2023.

How to cite: Guo, B., Ahmadian, R., and Falconer, R.: The influence of open boundary location on tidal lagoon modelling, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17174, https://doi.org/10.5194/egusphere-egu23-17174, 2023.

Accurate ocean data (i.e., tide, current velocity and direction, wave) are essential for numerous environmental studies: 1) development of marine renewable energy (e.g., maximize the efficiency of energy conversion); 2) aquaculture (e.g., offshore development); 3) anthropic pollution (e.g., plastic/pollutant dispersal); and 4) ecology (e.g., spread of invasive species).

The exponential increase of computational power has made numerical models, such as Eularian hydrodynamic models and Lagrangian particle tracking models (PTM) useful tools to characterize physical oceanographic parameters. However, methods to validate PTMs appear less developed due the complexity of biophysical process interactions; for example, uncertainty remains on the impact of wind on surface currents and how the effects of wind are propagated through the water column

Here, we use a novel set of data representing the travel of drifters in the Irish Sea during two consecutive years (summer 2021 and 2022). The experiment aim is to reduce the near surface flow uncertainty influencing particle dispersal. Data were collecting using a range of drifters released in coastal and offshore locations of a tidally dominate shelf-sea (Irish Sea): 1) variation of drogue depth between 1m and 5m; 2) variation of period from tidal cycles to spring-neap cycles; and 3) some with reduced “windage” designs (no drogue and minimal exposure above surface).

Preliminary results show the importance of wind driven current between the surface and 5 m depth, which should be take into account when considering the development of PTM. Furthermore, we find some scales of oceanographic processes that affect transport, such as turbulent eddies and waves, were not resolved - and yet our predictions broadly matched observations.

How to cite: Demmer, J. and Neill, S.: Characterization of surface flow using Lagrangian drifter for particle tracking model applications., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2296, https://doi.org/10.5194/egusphere-egu23-2296, 2023.