Wind turbines harvest the kinetic energy of the winds in the lower atmosphere to generate electricity, thereby reducing the wind speed locally.  Over oceans, this can have direct consequences for the wind energy input into the oceanic mixed layer, as well as associated wave dynamics, ocean mixing, and the wind-driven circulation.  To estimate the potential relevance of these effects, we consider a scenario of 150 GW of installed capacity, as formulated by the Esbjerg declaration, which we distribute over a hypothetical area of 100 000 km² in the North sea.  To do so, we budget kinetic energy fluxes within the lower atmosphere to estimate the impacts of wind energy use on frictional dissipation near the surface, and then use relationships inferred from the ERA-5 reanalysis to link frictional dissipation to different aspects of ocean dynamics.  Our first-order estimates show that the mean wind speed is reduced by 12% in this scenario.  Using the mean wind speed as an example case, such a reduction is associated with a more substantial reduction of surface friction by about 33%.  In this case, the ocean impacts are reflected in reduced wave heights by 14%, reductions in Stokes drift velocities at the ocean surface by 18%, wave power by 27%, and ocean mixing by 35%.  These basic energetic arguments highlight the need to assess and quantify the extent of impacts large-scale offshore wind power use is likely to have on ocean dynamics that need to be considered with the anticipated expansion in the coming decades.  This is necessary in order to mitigate potentially substantial and detrimental impacts on marine ecosystems.

How to cite: Kleidon, A. and Badger, J.: Follow the energy: Why using more offshore wind power weakens ocean dynamics and impacts marine ecosystems, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6212, https://doi.org/10.5194/egusphere-egu24-6212, 2024.

In the southern North Sea, a relatively shallow shelf sea, offshore wind farms are being constructed and planned on an extensive scale. To assess the possible ecosystem effects of these upscaling efforts (from 20GW in 2020 to more than 300 GW in 2050), we need to quantify the effect of turbines on local hydrodynamics and suspended matter dynamics. In this study, we present the results of a field campaign aiming at quantifying these effects.

The campaign was undertaken in June 2022 in the Belgian Coastal Zone. We measured a set of hydrographic parameters at various locations around a single turbine, supplemented with water and sediment samples.

The data reveal how the turbine enhances the local hydrodynamics and hydrographic parameters. In the turbine wake, we observe an increase in turbulent kinetic energy. This leads to a more well-mixed water column. At the water surface, this leads to colder and more saline water, while the water near the seabed becomes warmer and less saline. These effects are closely linked to the direction of the tidal current, as the turbine-induced wake is only several turbine diameters wide. The wake length is much longer, extending for several hundreds of meters behind the turbine.

This presentation discusses the study setup and the steps required to quantify the impact of turbines on local hydrodynamics. Furthermore, we will discuss how this knowledge is implemented in large-scale models, as this step is crucial for assessing the ecosystem impact of upscaled offshore wind.

How to cite: Hendriks, E., Langedock, K., van Duren, L., Vanaverbeke, J., Boone, W., and Soetaert, K.: Near-field measurements around offshore wind turbines show how they enhance hydrodynamics in their direct environment, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20440, https://doi.org/10.5194/egusphere-egu24-20440, 2024.

This study presents a detailed analysis of weather window accessibility for Marine Renewable Energy (MRE) sites along Ireland's coast, utilizing a robust 12-year met-ocean dataset. The research focuses on key test sites - the Atlantic Marine Energy Test Site (AMETS), the Galway Bay Test Site (GBTS), and the Westwave Demonstration Site - and expands to a broader spatial analysis of Irish coastal waters. By integrating significant wave height and wind data, the study evaluates site accessibility, emphasizing the paramount role of wave height in determining access. Findings reveal substantial spatial variability in accessibility, with high-resource areas like AMETS facing greater access challenges due to harsher conditions, as opposed to the more accessible GBTS. The study underscores the need for a nuanced, region-specific approach to MRE development in Ireland, highlighting how strategic planning and technological advancements are crucial in exploiting the country's significant MRE potential. The results also stress the importance of long-term data for accurate environmental variability assessment, offering vital insights for future MRE site viability and strategy development.

How to cite: Eftekhari, A., Moore, D., and Nash, S.: Optimizing Weather Windows for the Deployment, Operation, and Maintenance of Marine Renewable Energy Devices in Irish Coastal Waters, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10270, https://doi.org/10.5194/egusphere-egu24-10270, 2024.

The global shift towards sustainable energy underscores the increasing importance of wind power in the energy transition. However, there is a scarcity of studies focusing on diurnal variations in wind energy potential across different sites, leading to potential inaccuracies in energy generation estimates. This study addresses this gap by conducting a thorough investigation into the diurnal patterns of wind power density (WPD) at 30 m and 60 m hub heights for six coastal Indian sites spanning the period 1969-2007.

Hourly wind speed data obtained from the Indian Meteorological Department (IMD) for these locations formed the basis for a detailed analysis using the Weibull distribution model. The study highlights the crucial need to account for diurnal fluctuations in wind speed, as overlooking them may result in overestimating night-time and underestimating daytime WPD.

Key findings include the identification of Tuticorin as exhibiting the highest diurnal WPD, reaching a peak of 714.53 W/m2 in July at the 60 m hub height, while Mormugao experienced the lowest diurnal WPD during December. Substantial variations in WPD were observed between day and night, emphasizing the necessity of considering diurnal wind speed fluctuations for accurate energy generation predictions.

The implications of this study extend beyond mere data analysis. The results have practical significance for designing and sizing energy storage systems to ensure uninterrupted energy supply throughout the day and night. Additionally, the findings can guide the installation of hybrid energy storage systems, contributing to reduced operational costs and environmental impacts.

The study concludes with recommendations for further research, suggesting the implementation of energy storage systems and hybrid systems for selected locations studied. Energy storage systems are deemed essential for balancing intermittent wind energy generation, while the integration of wind and solar resources in hybrid systems could optimize overall renewable energy generation. The insights gained from this study provide a foundation for developing region-specific renewable energy systems tailored to unique wind characteristics, emphasizing the importance of energy storage and hybrid solutions for a reliable and uninterrupted power supply.

In summary, this study contributes valuable insights into the diurnal variations of wind power density in coastal regions of India, offering a comprehensive understanding of the wind energy potential in these areas. These insights serve as a basis for the development of sustainable and efficient renewable energy systems, highlighting the critical role of energy storage and hybrid solutions in ensuring a consistent and reliable power supply.

How to cite: Yadav, S., Sarkar, A., and Singal, S. K.: Comprehensive Analysis of Diurnal Wind Power Density Variations for Optimizing Wind Energy Integration in Coastal Regions of India, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4591, https://doi.org/10.5194/egusphere-egu24-4591, 2024.

Over the last three decades the offshore wind energy sector in the UK and globally has grown rapidly and the recent COP28 climate summit reinforced the North Sea Collaboration (NSEC) on the development of offshore wind which targets an installed capacity of at least 260 GW of offshore wind energy by 2050. Due to this accelerated demand for offshore wind there has been increased demand for research on scour around subsurface structures in the offshore environment. It is also beneficial to minimise the influence of subsurface foundations on the marine ecosystem and therefore scour mitigation methods that enhance marine habitats would be advantageous. This study uses experimental modelling to explore the impact of scour mitigation around monopile foundations and evaluate successful methods whilst considering the habitats living around the offshore structures.

Currently rock armour is most commonly used as an optimised scour protection layer for creating biodiversity enhancements. In this study four different scour mitigation techniques were assessed to analyse their effectiveness for scour mitigation; Textured Collars, Rock Dumping, Textured Piles and Rock Bags. All four scour mitigation techniques investigated have additional bio-enhancement capabilities and can be classed as a ‘Nature Inclusive Designs’ used to promote marine biodiversity and seaweed planting.  These scour mitigation methods include both dynamic and flow altering strategies using both the sea floor area around the monopile foundation and the foundation surface itself.  The experiments measured scour development under two different flow conditions until an equilibrium bed state developed. In some experiments, a novel Mylar Film technique was used to enable continuous measurement of scour development through structures being tested whilst simultaneously preventing water and sediment transfer. The results shown in Figure 1 suggest that under low flow conditions rock dumps and textured collars are the most effective scour mitigation technique to reduce scour depth. Textured collars prove to be the most successful for reducing scour depth under both flow conditions tested in these experiments.

How to cite: Bradbury, M., McLelland, S., Dorell, R., Marten, K., and Whitehouse, R.: Understanding the Effectiveness of Scour Mitigation Techniques at Offshore Windfarms Using Experimental Modelling, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17966, https://doi.org/10.5194/egusphere-egu24-17966, 2024.

Offshore wind energy has been widely accepted as a major component of renewable electricity to support Net Zero objectives and tackle climate change. This acceptance has led to an accelerated deployment of the offshore wind industry in the North Sea, with larger wind farm areas and bigger structures to support longer blades and more powerful turbines. As water flow encounters the foundations of structures, turbulence is generated, leading to the creation of visible downstream wakes. This redistribution of sediment may have an impact on water column processes, and near-field benthic communities.  Sediment wakes within the wind farm may also influence predator/prey interactions and could indicate areas to target or avoid for the location of aquaculture lines or other collocated activities.

The use of remote sensing techniques allows regular monitoring of turbidity in wind farm areas. A virtual constellation composed of Sentinel-2 (European Space Agency) and Landsat-8/9 (NASA) makes it possible to study sediment wake movements at high spatial and temporal resolution while considering tidal influence. Satellite images combined with current velocity, wave models, oceanography data and inherent properties of each turbine allow a better understanding of the parameters regulating the intensity of wakes.

Six offshore wind farms have been studied in two different sites: one in the UK (Lincolnshire) and the other in Belgium (Belgian EEZ) for a total of 269 turbines. A new method of pixel extraction has been developed to automatically extract turbid wakes around every turbine depending on the current direction. This was used to study the changes in suspended particulate matter (SPM) concentration within the wake. The British site, containing 3 wind farms, showed a strong turbine effect, whose intensity varied from 0 (absence of wake) up to 6 g.m^-3 of SPM concentration compared to the concentration upstream of the turbines, while the Belgian site, containing 3 wind farms, showed less variability and less intense wakes. As a preliminary result, and without isolating each parameter from the others, the type of foundation seems decisive for wake formation and SPM concentration at the surface: jacket foundations showed less intense wakes than monopiles and gravity-based structures (Mann-Whitney, p<0.001), showing that the shape and size of the foundation affect sediment resuspension. Also, and especially within the Belgian wind farms, wakes were more intense in winter/spring than during summer/autumn as storm events may create even more turbulence and enhance sediment resuspension (Mann-Whitney, p<0.01 and p<0.001).

A Generalised Linear Model incorporating current velocity, wind wave height, swell period and height, type of foundation, seabed morphology and seasonality was generated to explain the influence of physical and environmental parameters on sediment wake in wind farms and can help predict the SPM increase downstream of a structure.

How to cite: Lecordier, E., Forster, R., Mazik, K., Gernez, P., and York, K.: Sediment Wakes Within Offshore Wind Farms Using Sentinel-2 and Landsat-8/9, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6132, https://doi.org/10.5194/egusphere-egu24-6132, 2024.

An energy transition from fossil fuel energy to renewable energy is needed to alleviate global climate change and achieve the Net Zero emission target. While focus has been put on wind and solar energies, they are intermittent and non-dispatchable. Consequently, there will be a significant need for filling the gap between renewable energy supply and energy demand. Tidal energy is potentially capable of contributing to balancing this gap because of its predictability and dispatchability. Tidal range schemes (TRSs) utilise the tidal range to create artificial head differences across the structures. The head differences then drive the turbines to generate electricity. TRSs can also be used as energy storage by controlling the turbine operation and even pumping water into or out of the impoundment. The UK has vast tidal energy resources which are mainly unutilized. While several TRSs have been proposed, there are currently no TRSs developed in the country because of their large initial investment cost and significant impacts on their adjacent coastal areas. Approaches to determine the optimal design and operation of TRSs are needed to improve their cost-effectiveness.

            This research studies the optimal number of turbines for TRSs. There have been discrepancies concerning whether an optimal number of turbines exists for any given TRS by merely optimising its annual energy production (AEP).  Several published works (Aggidis and Feather, 2012; Petley and Aggidis, 2016; Vandercruyssen et al., 2022) showed that the AEP increases as more turbines are used until the turbines fully utilise the available tidal energy. Once the tidal energy is fully utilised, adding more turbines does not increase or decrease the AEP. However, other published works (Xue et al., 2021; Hanousek et al., 2023) showed that there is an optimal number of turbines for a given TRS that produces the maximum AEP and using turbines more than the optimal number reduces AEP. This research reconciles the two aforementioned statements by optimising the AEP of a proposed TRS at an unused dock with a 0D model with and without constraining the maximum starting head to 7.5 m, which is lower than the tidal range at the TRS site. Such a constraint would be necessary if the TRS is used as a flood protection measure as well as an energy source. Results showed that AEP increased with an increase in the number of turbines until the entire tidal range was utilised if the constraint was not applied. With the starting head constraint applied, there was an optimal number of turbines beyond which the AEP decreased. The absence of the optimal number of turbines in the unconstrained condition demonstrates the importance of cost models in selecting the optimal number of turbines. Reference: (i) Aggidis and Feather (2012). 10.1016/j.renene.2011.11.045; (ii) Hanousek et al. (2023). 10.1016/j.renene.2023.119149; (iii) Petley and Aggidis (2016).  10.1016/j.oceaneng.2015.11.022; (iv) Vandercruyssen et al. (2022). 10.1016/j.heliyon.2022.e11381; (v) Xue et al. (2021). 10.1016/j.apenergy.2021.116506

Figure 1. The annual energy production for Barry Dock Lagoon with an increasing number of turbines with and without the maximum starting head constraint (≤ 7.5m).

How to cite: Lam, M.-Y., Qadrdan, M., and Ahmadian, R.: Optimising the number of turbines in Tidal Range Schemes, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11584, https://doi.org/10.5194/egusphere-egu24-11584, 2024.

How to cite: Dhar, N., Dorrell, R. M., Lloyd, C. J., McLelland, S. J., and Walker, J.: Effect of Increased Geometric Complexity on LoadActing on Floating Offshore Wind Turbine Platforms, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16226, https://doi.org/10.5194/egusphere-egu24-16226, 2024.

Tidal and ocean current energy represent continuous and reliable renewable sources that can offer valuable electricity to remote communities located near ocean shores. Ocean currents result from various factors such as tidal forces, wind shear at the water surface, temperature gradients due to inflow from melting water, salinity gradients caused by incoming freshwater, the Coriolis effect, and underwater topography. In the Faeroe Islands, ocean currents have been harnessed to produce power exceeding 1 MW (https://minesto.com/), providing an essential energy source for the ongoing energy transition.

Especially in the Arctic, temperature and salinity gradients can enhance water velocity within a stratified water column in coastal areas. Therefore, comprehensive monitoring, accounting for the vertical stratification of the water column, becomes imperative to accurately assess the full potential of ocean currents. To accomplish this, we intend to employ an Acoustic Doppler Current Profiler (ADCP) (Xylem, Inc, 2015) to evaluate the three-dimensional velocity field at various locations in Iceland, aiming to comprehend the complete potential of ocean current energy.

We will start our investigation with preliminary monitoring in Fossvogur, a two-kilometer-long fjord situated in front of Reykjavik University in Reykjavik, Iceland. We will combine in-situ ADCP data with remotely sensed surface temperature and vertical CTD proofing of the water column. Once our data collection and processing methods are standardized, we plan to extend our approach to locations with stronger ocean currents, such as Hvammsfjördur just south of the Wastfjords. Our initial findings suggest that tidal currents, temperature and salinity gradients, and wind shear significantly contribute to increasing ocean currents, challenging the assumption that the energy potential of these currents might have been underestimated in the past. This revelation could substantially aid in the energy transition of remote coastal communities by providing them with clean, cost-efficient, and environmentally friendly energy sources.

Moreover, our methodology holds promise for application in any coastal region, potentially offering a renewable energy solution for various coastal communities.

How to cite: Finger, D. C. and Audunsson, H.: Assessing the potential of tidal and ocean current energy for remote Arctic communities, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8558, https://doi.org/10.5194/egusphere-egu24-8558, 2024.