With the European Commission’s ambitious goals for reducing greenhouse gas emissions and increasing renewable energy usage, marine renewables, including wave energy, have gained attention as a promising source of clean and predictable energy. Despite its potential, wave energy has lagged behind other renewable technologies like wind and solar, primarily due to higher costs and slower commercialization. This thesis investigates the impact of power output capping on the levelized cost of electricity (LCOE) of wave energy converters (WECs), a crucial metric for assessing their commercial viability. The research uses numerical modeling to calculate the theoretical LCOE/kg, considering both uncapped and capped power outputs. Using a cylindrical point absorber WEC, the study employs a boundary element method (BEM) solver to model hydrodynamic parameters, such as response amplitude operators and excitation forces. By constructing power matrices, the research analyzes the effects of two capping strategies on the AEP and capacity factor in both medium and high energy regions.
Results indicate that capping significantly influences the LCOE, with small variations observed between medium- and high-energy regions. The study highlights that specifically PTO damping capping has the most negative economic implication, with similar changes in LCOE in terms of percentage observed in high-energy regions and medium-energy regions. These findings contribute to the broader goal of advancing the commercialization of wave energy, supporting the transition towards a more sustainable and climate-neutral energy future.

In recent years, there has been growing interest in exploring the deployment of wave energy converters (WECs) in remote and harsh environments. However, research in this area remains limited, particularly concerning offshore environments with sea ice. This study focuses on investigating the energy production and economic feasibility of a point absorber in the Baltic Sea, specifically off the coast of Åland, which experiences seasonal ice cover. Four winter seasons with varying ice conditions are examined, ranging from ice-free to severe ice conditions. Additionally, the study aims to assess the survivability of the WEC under extreme level ice action and extreme wave conditions.

Based on literature review, a hexagonal slope-shaped buoy has shown promise in withstanding ice conditions up to 15 cm thickness in the Baltic Sea and is selected as the WEC design in this study. Metocean and sea ice data spanning from 2006 to 2021 are analysed from the NORA3 database. Through extreme value analysis, key parameters such as wave height, period, and ice thickness are determined. Survivability analysis is conducted to understand the forces exerted on the WEC during extreme ice load cases and extreme sea states. To evaluate energy production, hydrodynamic coefficients are computed using the Boundary Element Method solver Capytaine in the frequency domain. Subsequently, simulations are conducted using WEC-Sim to derive the power output of the WEC under varying sea states. Optimisation of the Power Take-Off (PTO) damping is performed to enhance performance for the specific site conditions. A comparison of power output is made among different WEC configurations with varying translator sizes.

The survivability analysis reveals important design considerations, especially regarding extreme ice conditions. When subjected to an extreme level ice thickness of 60 cm this results in calculated horizontal and vertical forces of 615 kN and 315 kN, respectively. In extreme sea states, simulations in WEC-Sim shows a maximum heave response of 4.16 m and a maximum heave force of 133 kN. Additionally, the investigation reveals significant fluctuations in wave energy converter (WEC) power production across the analysed winter seasons, characterised by varying ice conditions. During severe ice conditions (2009-2010), energy output decreased by nearly 50% compared to ice-free periods (2019-2020), potentially leading to a 95% increase in the levelised cost of energy (LCOE) if solely derived from that single season. These findings give valuable insights into the optimal WEC configuration, the maximising of power output and offer important considerations to WEC survivability for deployment in ice-covered regions.

The European energy transition policies aim to mitigate the effects of climate change by moving away from fossils and promoting both onshore and offshore renewable energy technologies. Although onshore renewables are driving the transition so far, policymakers believe that in order to achieve the targets, the power grid must have access to the theoretically abundant energy present in the oceans. More specifically, these targets suggest that by 2050, around the continent there should be at least 340 GW of marine and offshore renewables for EU member-states, in addition with 125 GW for the UK.

The present study investigates the role of marine and offshore renewable technologies in 100\% renewable energy scenarios, inspired by the European targets of 2030, 2040 and 2050. The assessment of their role is based on he upgraded version of the open-source PyPSA-Eur (Python for Power System Analysis - European Sector, v0.25.1) energy system modelling tool developed within the Marine Renewable Energies Lab (MREL) of TU Delft, the PyPSA-MREL-TUD. This version is designed to have access on wave and farshore wind resources. The PyPSA framework utilizes an extract of the entire ENTSO-e transmission network and ERA5 climate data. By using time-series of 2018 for both the energy demand and weather data, this energy system model attempts to find cost-optimal solutions for the configuration of the different components of the power system. The developments include the addition of three wave energy converters and two types of floating offshore wind turbines to the existing generators and their associated costs, as well as the upgrade of the spatial resolution of the GEBCO bathymetry dataset of the model. For wave power, the model can access shallow water, nearshore and farshore wave resources, while for wind power both bottom fixed and floating generators are sub-categorized according to their distance from shore. Two significant constraints of the model include minimum generator capacity constraints for wind and wave power, and 70 \% energy equity per country.

The analysis of the results focuses mainly on the generator and storage system configuration of the system. An emphasis was also given on the required expansion of the transmission grid, and the objective's investment and operational costs. What is initially observed is the impact of the spatial resolution of the ERA5 dataset on wave energy converter installations, which underestimated the energy potential profiles. Capacity constrained versions of the scenarios showed that wave energy has a higher average hourly market value, but is highly susceptible to seasonal patterns. Although the performance is better during colder periods, wave converters suffer the most during the warmer periods and are also the first generator type to be curtailed. While offshore wind turbines were installed all around the continent, with the best candidates being France, Baltic and Scandinavian countries, Greece and Romania, wave converters were installed mostly in Portugal, Ireland and Italy. However, the accessibility of every country to the sea basins varies. Country-specific analysis of the model implies that, for the 2050 horizon scenario, there is still a high level of dependability of landlocked countries on solar energy, on their neighbours and on storage systems. The overall line capacity must increase by a factor of two.

The current trend in the offshore renewable energy industry is to install ever larger offshore wind tur- bines (OWT) in ever deeper waters. This results in an increased capacity requirement of the substruc- ture which results in increased dimensions and thus higher hydrodynamic loads.
For the design of OWT the fatigue limit state is next to the ultimate limit state a crucial design loading condition to consider. In the current engineering practice, wave spectra are mostly reconstructed with the JONSWAP spectral parametrization which gives a simplified representation of the actual sea surface based on bulk wave parameters for wave components, such as wind-sea and swell. By using realistic frequency-directional (2D)-wave spectra instead of the JONSWAP spectral model, the wave spectral density distribution can be showed in its most authentic form.
This study investigates the influence of 2D-wave spectra on the wave-induced fatigue loads on OWT’s, as a comparison to the commonly used JONSWAP spectral parametrization. Therefore the relation of different wind and wave parameter as well as of the wave spectral characteristics on the wave-induced loads and the load differences between both spectra are investigated. Wave spectral data as well as bulk wave parameters for a wind-sea and swell wave component were obtained from the DHI MetOcean database for the Dutch North Sea. Based on those the fatigue loads were calculated in the frequency domain using Dirlik’s method.
Results show that the JONSWAP spectral parametrization leads to an overall overestimation in the range of ∼ 12 - 15 % of the total wave-induced fatigue loads compared to those obtained from 2D-wave spectra. The highest fatigue load differences and DEL overestimation between the JONSWAP and 2D- wave spectra were observed for significant wave heights between 2 and 3.8 m (14.70 % overestimation), peak periods between 8 and 15 s (13.63 % overestimation) and wind speeds between 10 and 20 m/s (15.04 % overestimation).
Furthermore, it was observed that narrow frequency and directional width, between 0.1 - 0.3 Hz and 20 and 30 deg, lead to the highest discrepancies for the calculated fatigue loads between the JONSWAP and 2D-wave spectra (∼ 13 % overestimation). For extreme sea states, that correspond to the upper 5 % of the observed data it appears that the JONSWAP spectral parametrization leads mostly to an underestimation of the calculated fatigue loads.
With the distance correlation calculation the dependencies between the wave characteristics, such as the frequency width, directional width and the peakedness parameter, and the fatigue load differences was quantified. But this analysis did not result in additional research insights since the obtained corre- lation coefficients were almost identical and only exhibiting weak dependencies.
Still, it can be concluded that using 2D-wave spectra in the engineering practice and for the fatigue load calculation on OWT’s with monopiles as substructures, physically more representative loads can be obtained compared to those computed with the simplified JONSWAP spectral model. This more realistic load estimation could finally lead to an improved design of OWT’s.

Array design of a wave farm composed of multiple WECs is an essential issue during the design phase of an offshore wave energy farm. Although various research has looked into the optimal array design, the optimization process usually takes a lot of time.

The objective of this thesis is to reduce the time required during the WEC design phase. The study focuses on performing a hydrodynamic analysis of a wave farm consisting of four single-point absorbers, examining the relationship between excitation force and array spacing, and determining the average total power production of the wave farm.

This thesis employs the Boundary Element Method (BEM) to analyze the hydrodynamic interactions of waves and oscillatory motions in WECs. Using the open-source software Capytaine, it estimates key hydrodynamic coefficients and solves the system of equations via Green's theorem to evaluate added mass and excitation forces. By selecting excitation force as a design parameter, a linear regression model is established. Furthermore, a machine learning model based on the Random Forest algorithm is developed to capture the complex relationship between total power output and the design parameter. After the machine learning model is created, the optimal array spacing for a specific site can be estimated quickly by combining results with a wave scatter diagram.

These findings aim to contribute to wave energy systems design by providing a reliable link between hydrodynamic results and design parameters and accelerating development in the wave energy sector.

In response to the escalating demand for renewable energy, wind turbines and their support structures have witnessed exponential growth in size in recent decades. However, this expansion presents substantial challenges, particularly in the face of severe storms and large waves, raising concerns about resonance-related issues. Accurate modeling of asymmetrical, non-linear waves generated during storms becomes crucial for safe and cost-effective wind turbine design. The prevalent approach embeds higher-order non-linear waves into linear theory, but recent studies have unveiled uncertainties in this method, necessitating innovative techniques for simulating non-linear waves. Some studies propose numerical wave models (NWMs) like SWASH and OceanWave3D, treated as numerical wave tanks (NWTs), as alternatives for predicting wave loads on offshore wind turbines. A comparative analysis between SWASH and OW3D reveals significant discrepancies, particularly in OW3D results, prompting further investigation into potential setup issues. Both non-linear models consistently report higher loads than the stream function method due to increased local accelerations, and differences in wave spectra underscore their ability to account for non-linear wave interactions. The study underscores the stream function's underestimation of loads, emphasizing the necessity of accurate non-linear wave modeling for predicting extreme loads. Recommendations for future research include extended convergence studies, user experience considerations, and a closer examination of non-linear effects on fatigue load predictions.

Global warming represents the most significant threat to humankind, making the need for renewable energy more crucial than ever. However, in densely populated areas near the coast, electricity production faces competition from various sectors such as agriculture, housing, and tourism. To address this challenge, one viable solution is to explore offshore electricity production.

Building upon this context, this research delves into investigating the wave-induced effect on power mismatch losses along a PV string in offshore floating photovoltaic (OFPV) systems. OFPV offers a promising solution for generating electricity in unused marine areas, complementing offshore wind energy. Although OFPV holds great potential, our understanding of its complexities remains limited, particularly regarding the impact of wave-induced power mismatch losses. To bridge this knowledge gap, a comprehensive approach is taken. A floating structure is modeled using the Bernoulli-Euler beam theory, while the fluid domain is analyzed using potential flow/linear wave theory. Structural behavior is examined in the frequency domain through the application of a FEM with the package Gridap in Julia. The wave amplitude spectra are determined using the Jonswap sea spectrum, with consideration given to four distinct sea states based on the Douglas sea scale: slight, moderate, rough and very rough. The optoelectrical modeling is conducted in pvlib in Python.

The results reveal that monthly energy losses due to power mismatch are negligible during summer months for all sea states studied. However, in winter months, monthly energy losses exceed 1%, with daily losses reaching up to 6%. Additionally, the orientation of the PV string is identified as a crucial parameter for minimizing losses. Finally, the findings indicate that using either a thick structure with a stiff and dense or a thin structure with a flexible and lightweight material can help reduce energy losses caused by power mismatch.

Ocean waves being considered to have huge potential on providing renewable energy resources. While significant research and application of wave energy converters have been conducted in many seas, exploration on low-energy seas is still an ongoing endeavour. In this study, a point absorber array is being studied in the scenario of implementing at low-energy site within Caspian Sea.
The primary objective of this study is to give an optimal layout for a point absorber array with five devices. Firstly, hydrodynamic analysis is conducted by Boundary Element Method using a frequency domain model in NEMOH and WEC-Sim. Layouts with different spacing factor are examined to obtain the power matrices for each case. The q-factor, a measure that quantifies the WEC array’s power absorption efficiency, and annual power production are readily calculated. Furthermore, given the annual energy production, an economic model is built to assess the CapEx, OpEx and LCOE, the Levelized Cost of Energy of the WEC array with different layouts. The final optimization phase finds a solution that simultaneously maximizes the q-factor and minimizes the LCOE by executing a multi-objective algorithm. The best layout configuration for the point absorbers array in the Caspian Sea site is determined, taking into account both high energy output and economic viability.

Offshore wind energy is poised for significant growth, with three major trends emerging: larger wind turbines, offshore wind farm sites in deeper waters further from the coast, and a shift towards floating offshore wind energy. While current floating wind turbines are installed using a tow-to-site strategy, the increasing size of turbines and foreseen implementation scale raises the question if on-site installation will be more a viable option. This research investigates the operational feasibility of on-site installation of the NREL 15 MW wind turbine blade on a semi-submersible floating wind turbine using a floating monohull crane vessel. This study uses a simplified frequency-domain multi-body model to assess the workability of installing blades on the GustoMSC Tri-floater using a floating monohull crane vessel. The model assumed first order potential flow, rigid body motions for the Tri-floater and the crane vessel, and neglected wind and current loads. The comparison of the multibody and single-body models revealed that positioning the crane vessel next to the Tri-floater resulted in shielding, diffraction, radiation and reflection effects, which were also observed vice versa for the crane vessel but to a lesser degree. Results show that the workability for floating-to-floating operations is 31%, compared to a workability for a fixed-to-fixed operation of 87%. The relative surge was limiting, caused by the crane vessel roll angle. A sensitivity analysis on wave direction showed that the wave direction has significant impact on the relative motion and the workability. This optimal wave orientation resulted in a floating-to-floating workability of 51%. The workability of a floating-to-fixed operation was found comparable to that of a floating-to-floating operation. The preliminary findings indicate that on-site installation for floating-to-floating operations is more challenging than fixed-to-fixed operations. However, workability is comparable to floating-to-fixed operations, suggesting little impact from floating wind turbines. Further research, including wind loads, is recommended to understand the difference between installations. Another area for study is the development of a specialized blade installation tool to aid floating wind turbine installation.

Tidal energy has the potential to be an important and necessary addition to the available sources of energy in the coming energy transition. While there is an extensive body of research on the topic of high tidal resource locations, little research exists on low tidal resource locations such as The Netherlands. The thesis aims to reduce this gap by designing the optimal Dutch tidal farm and determining its economic viability. Using Delft 3D and Telemac, 2D models are created to simulate the tidal resources based on shallow water equations. The models are used to determine the best location for the Dutch tidal stream farm through a multi-criteria decision making analysis using the analytic hierarchy process model. For the optimal location, a tidal cycle is extracted from delft dashboard data and the optimal configuration is designed. In the design stage of a tidal farm in low current velocities, the simulation shows the wake effect positively influences the production. The power production of such a tidal farm over a tidal cycle is calculated using various economic metrics. The results show that currently a tidal farm cannot be economically viable without substantial governmental support. However, this paper argues that tidal energy comes with a number of important benefits that cannot be neglected, such as sustainability, output consistency/predictability and potential future energy independency.
Therefore, tidal farms in low resource areas show potential, but further technological-, economical-, and (geo) political developments are needed in the coming years for them to become sufficiently beneficial in the Dutch energy transition to a sustainable energy mix.

In recent years, the demand for renewable energy has increased significantly because of its lower environmental impact than conventional energy technologies. As a result, wind power is one of the most important renewable energy sources. As land-based turbines have reached their maximum potential, recent market trends are moving into deeper waters with higher capacity turbines. The design of a floating offshore wind turbine (FOWT) foundation poses technical challenges. Mooring design, installation operations and the fact that it is a new engineering field, to name a few. Moreover, as mooring design for FOWT is still at an early stage of development, cost-effective installation remains one of the critical issues. After the FOWT is towed to the site, the mooring lines are hooked up, and one line is usually shortened. This can be performed in three ways: By seabed tensioning, inline tensioning or tensioning at the fairlead. In this investigation, details about mooring installation processes are collected from interviews, academic papers, manuals and videos to investigate differences between mooring system installations and ultimately figure out how pre-tensioning of these systems can be carried out most effectively. This work presents a comparison between these three existing methods for the final phase of mooring installation. To perform a quantitative study, the Umaine VolturnUS-S 15MW floater is considered. Current modelling techniques are expanded to allow for the static simulation of the rotations or sliding at the tensioning device. The model framework is used to find the static equilibrium and tensions at different phases in the installation operations. Additionally, an alternative mooring configuration is proposed with synthetic inserts to verify whether the tension is dependent on the mooring configuration. Finally, the dynamics between the anchor handling vessel(AHV), the FOWT and the mooring chains are modelled as a linear mass-spring system. Vessel responses and work wire tensions are compared against each other for identical environmental conditions and equipment specifications. Based on simulation results, it is found that the seabed tensioner causes little dynamic relation between the AHV and the floater and was not further investigated. Inline tensioning showed to be the method that requires the lowest tensions in the AHV work wire. Fairlead tensioning was found to be discouraged since the high required bollard pull forces. This issue is mitigated by a proposed new concept of fairlead tensioning. When the chain is hauled in from above the fairlead by a vessel crane or A-frame, it is possible to tension effectively without fuel-intense bollard pull.

Multi-renewable energy systems, which must consider emerging technologies that exploit other available renewable energy resources, have the potential to reduce the variability of current mature renewable technologies such as solar and wind, increase power availability, diversify the electricity supply, and ultimately accelerate the substitution of fossil fuels. Ocean energy technologies can represent an important part of these multi-renewable generation low-carbon energy systems, given their vast and yet untapped source of renewable energy medium. They are increasingly being perceived as an important piece of future energy systems, given they are characterized by stable generation profiles, predictability, and high energy density. Among the different ocean energy technologies, wave energy shows strong potential to support carbon reduction targets and meet expected increases in electricity demand. It is considered one of the most dense, predictable, and persistent energy sources, with multiple regions exposed to the wave energy resource.
This researched performed an exploratory investigation of the impacts and interactions of wave energy in a wider context under future cost-optimal and multi-renewable configurations of the European transmission network. This was achieved, first, by expanding the renewable energy capabilities of the existing open-source PyPSA-Eur, energy system model and dataset of the European power system at the transmission level covering the full ENTSO-E area, to include the wave energy resource. And second, by simulating a set of future, cost-optimal, and multi-renewable European power systems at 2030, 2040, and 2050 horizons employing a greenfield optimization approach and considering cost-reduction potentials of wave energy and other generating technologies.