Ocean Energy Research Articles

Experimental insights on biofouling growth in marine renewable structures.

Marine biofouling is a threat to industries working in the marine environment, representing significant costs associated with equipment impairment and loss of performance. In the Marine Renewable Energy (MRE) and other maritime sectors which operate at sea for long periods, an important aspect of biofouling is related to the type and frequency of inspections and biofouling removal procedures. This study investigated important parameters of macrofouling ( e.g. composition, including the presence of non-indigenous species, thickness, and weight) from communities growing on samples that emulate tubular components of marine renewable devices. The trials were performed during short periods of submersion (one to eight weeks) in the seasons when the colonisation process should be most intensive (spring, summer, and autumn). Furthermore, the frictional resistance forces generated during the scraping of biofouling from those components were investigated. Overall, results provide insights on the growth rates and removal requirements of biofouling in marine components. The results show that, while biofouling growth in early colonization stages might not present great detrimental effects to wave energy components, the consequent marine corrosion (fostered by biofouling) and the settlement of non-indigenous species (NIS) should be factors of concern. Performing biofouling-related maintenance activities after the peak of maximum growth and reproduction (during the warmer seasons in temperate to cold environments) is suggested to reduce the number and frequency of activities. NIS can be detected at very early stages in the colonization process, highlighting the importance of biofouling monitoring and the implementation of biosecurity risk assessment plans early in the operational stage of MRE projects.

A Triboelectric-Electromagnetic Hybrid Nanogenerator with Magnetic Coupling Assisted Waterproof Encapsulation for Long-Lasting Energy Harvesting.

Ocean energy harvesting based on a triboelectric nanogenerator (TENG) has great application potential, while the encapsulation of triboelectric devices in water poses a critical issue. Herein, a triboelectric-electromagnetic hybrid nanogenerator (TE-HNG) consisting of TENGs and electromagnetic generators (EMGs) is proposed to harvest water flow energy. A magnetic coupling transmission component is applied to replace traditional bearing structures, which can realize the fully enclosed packaging of the TENG devices and achieve long-lasting energy harvesting from water flow. Under the intense water impact, magnetic coupling reduces the possibility of internal gear damage due to excessive torque, indicating superior stability and robustness compared to conventional TENG. At the waterwheel rotates speed of 75rpm, the TE-HNG can generate an output peak power of 114.83mW, corresponding to a peak power density of 37.105Wm-3. After 5h of continuous operation, the electrical output attenuation of TENG is less than 3%, demonstrating excellent device durability. Moreover, a self-powered temperature sensing system and a self-powered cathodic protection system based on the TE-HNG are developed and illustrated. This work provides a prospective strategy for improving the output stability of TENGs, which benefits the practical applications of the TENGs in large-scale blue energy harvesting.

Systematic Analysis of Potential Marine Renewable Energy for Coastal Ecological Balance on Bawean Island: A Review

Systematic Analysis of Potential Marine Renewable Energy for Coastal Ecological Balance on Bawean Island: A Review

StraitFlux – precise computations of water strait fluxes on various modeling grids

Abstract. Oceanic transports shape the global climate, but the evaluation and validation of this key quantity based on reanalysis and model data are complicated by the distortion of the used curvilinear ocean model grids towards their displaced north poles. Combined with the large number of different grid types, this has made the exact calculation of oceanic transports a challenging and time-consuming task. Use of data interpolated to standard latitude/longitude grids is not an option, since transports computed from interpolated velocity fields are not mass-consistent. We present two methods for transport calculations on grids with variously shifted north poles, different orientations, and different Arakawa partitions. The first method calculates net transports through arbitrary sections using line integrals, while the second method generates cross sections of the vertical–horizontal planes of these sections using vector projection algorithms. Apart from the input data on the original model grids, the user only needs to specify the start and endpoints of the required section to get the net transports (for the first method) and their cross sections (for the second method). Integration of the cross sections along their depth and horizontal extent yields net transports in very good quantitative agreement with the line integration method. This allows us to calculate oceanic fluxes through almost arbitrary sections to compare them with observed oceanic volume and energy transports at available sections, such as the RAPID array or at Fram Strait and other Arctic gateways, or to compare them amongst reanalyses and to model integrations from the Coupled Model Intercomparison Projects (CMIPs). We implemented our methods in a Python package called StraitFlux. This paper represents its scientific documentation and demonstrates its application on outputs of multiple CMIP6 models and several ocean reanalyses. We also analyze the robustness and computational performance of the tools, as well as the uncertainties in the results. The package is available on GitHub and Zenodo and can be installed using pypi.

Design comparison and effects of a chamber structure on wave dissipation

ABSTRACT Among all the ocean energy sources that have been widely studied, chamber structures such as oscillating water column (OWC) technologies are effective and low-cost methods to develop hundreds of wave power generation devices as the disadvantage is its lack of efficiency. Even if the OWC system does not perform any power generation operations, it is a wave-absorbing structure. A large part of the wave energy may be blocked by the structure’s acting chamber or could be dissipated during the interaction of the waves in the air chamber, which affects the actual power generation benefit evaluation. Nevertheless, a better wave attenuation structure may present a relatively poor design of the OWC generator chamber. A series of experiments were conducted with regular and irregular wave conditions to study the effects of energy dissipation caused by a chamber structure under varied barrier and orifice designs.

Spatiotemporal variation in phenology of the invasive brown macroalga Sargassum muticum (Yendo) Fensholt and the environmental parameters relationships along four different sites on the Atlantic coast of Morocco

The alien brown seaweed Sargassum muticum (Yendo) Fensholt is currently observed along the coasts of Morocco. The present study aimed to evaluate the impact of physicochemical parameters on the distribution of S. muticum at four sites on the Atlantic coast of Morocco harvested between 2019 and 2020. This study showed that the highest biomass, thalli length, and fertility values were recorded in sampling sites characterized by optimal physicochemical (temperature, pH, and salinity) and nutrient H₃PO₄ during summer. The highest biomass values were recorded in August for Sidi Bouzid and Moulay Abdellah sites, conversely, in Saada and Jorf Lasfar sites the highest values were observed in February and March respectively. The thallus length was slightly larger in Moulay Abdellah site with 77.30 ± 14.09 cm compared with the three other sites during the summer/spring periods. Minimum thalli length was recorded in September for all studied sites. The thalli of S. muticum were fertile earlier in Sidi Bouzid and Saada during spring and peaked during the summer season for all studied sites showing a positive correlation with increasing temperature.Finally, the collected data shows that indeed physicochemical parameters influence bioecological parameters. Thus, contributed to a better understanding of the temporal variation of S. muticum phenology on the Moroccan Atlantic coast, these data provide the necessary information for coastal marine management and biomonitoring program as well as sustainable utilization of this renewable marine resource.

High-Coupled Magnetic-Levitation Hybrid Nanogenerator with Frequency Multiplication Effect for Wireless Water Level Alarm.

Hybrid nanogenerators (HNGs) represent a promising avenue for water energy harvesting, yet their commercial viability faces hurdles such as limited power output, poor coupling, and constrained operational lifespans. Here, a highly coupled triboelectric-electromagnetic magnetic-levitation hybrid nanogenerator (ML-HNG) is introduced that shows great potential for water energy harvesting. The ML-HNG fulfills the challenges of high power output, strong coupling, and long operational lifespans. During the contact-separation process of the triboelectric nanogenerator (TENG), the changing magnetic flux in the electromagnetic generator's coils generates a potential difference between the coils and Cu electrodes. The unique design of the ML-HNG employs a shared coil electrode configuration, which enhances the coupling without adding extra volume. This integration allows the ML-HNG to achieve multi-frequency vibrations and multiple output cycles per external longitudinal movement, a phenomenon known as the frequency multiplication effect. With an average power density of 1.69W m-3 in water, the ML-HNG provides continuous power for a thermo-hygrometer and can quickly drive a wireless water level alarm system within a minute. This groundbreaking hybrid nanogenerator design holds significant promise for the efficient and consistent harvesting of low-frequency ocean wave energy, marking a substantial advancement in blue energy technology.

Techno-economic analysis and optimization of a multiple green energy generation system using hybrid wind, solar, ocean and thermoelectric energy

Techno-economic analysis and optimization of a multiple green energy generation system using hybrid wind, solar, ocean and thermoelectric energy

Evaluation of Different Methodologies for Wave Energy Conversion Systems Integration into the Power Grid Using Power Hardware-in-Loop Emulation

The ocean energy resources hold the promise of a sustainable solution within global efforts to diversify energy sources and mitigate climate change. Wave energy conversion (WEC) systems, as emerging technologies, offer adaptability and the potential to harness predictable wave energy. However, integration of WEC systems into a power grid brings challenges for system operators due to their nature of operation. Addressing these demands is a multilayered process that involves highly efficient power electronic devices, control systems, and efficient energy storage solutions. This paper specifically focuses on the methodologies of the grid integration of a specific wave energy conversion system—a point absorber developed by the company Sigma Energy. Proposed methodologies are experimentally tested using power hardware-in-loop (PHIL) emulation of a fully monitored and controlled small-scale microgrid equipped with a battery energy storage system (BESS), different emulators of loads, and distributed generators (DG).

Energy-efficient frontal polymerization of poly(DCPD-co-TCPD) with improving thermomechanical properties and chemical resistance

Polydicyclopentadiene (PDCPD) was attractive in marine, automotive and new energy fields, but limited by its lower rigidity. Herein, poly(dicyclopentadiene-co-tricyclopentadiene) (poly(DCPD-co-TCPD)), was prepared by rapid and energy-efficient frontal polymerization (FP). The flexural properties of copolymers prepared via FP were comparable to those prepared by long-term oven curing. Furthermore, the study explored the cis-trans isomerization of double bond, molecular weight between cross-links, density, swelling degree and monomer conversion to systematically analyze the influence of tricyclopentadiene (TCPD) incorporation. Notably, the selected comonomer TCPD was relatively simple in synthesis, and its incorporation resulted in remarkable enhancement of the thermomechanical properties and acid-base resistance of neat PDCPD. At an 80 wt% TCPD incorporation, the flexural modulus increased significantly from 1865 MPa to 2703 MPa, and the Tg elevated from 147 ℃ to 210 ℃. Compared to other widely used thermosets, poly(DCPD-co-TCPD) exhibited significant advantages in terms of being lightweight and heat-resistant. The resulting thermosets demonstrated considerable potential for applications as high-performance thermosets and in composites with adjustable thermomechanical properties.

Auxiliary Heat System Design and Off-Design Performance Optimization of OTEC Radial Inflow Turbine

In this paper, solar energy is used as the auxiliary heat source of the ocean thermal energy radial inflow turbine, and the thermodynamic model of the circulation system is established. In addition, the ejector is introduced into the ocean thermal power generation system, and the process simulation is carried out using Aspen Plus V12. To address performance attenuation of the radial turbine under varying working conditions, shape optimization of a 30 kW OTEC radial turbine was conducted. Finally, the off-design performance variation in the radial inflow turbine is analyzed in the presence of a solar auxiliary heat source. The results show that the use of an auxiliary heat source can effectively improve the cycle efficiency of the system and is also conducive to the stable operation of the radial turbine. Under the condition of auxiliary heat source, the system cycle efficiency is increased by 2.269%.

Modelling environmental life cycle performance of alternative marine power configurations with an integrated experimental assessment approach: A case study of an inland passenger barge

There is pressure on the global shipping industry to move towards greener propulsion and fuel technologies to reduce greenhouse gas emissions. Hydrogen and electricity are both recognised as pathways to achieve a net-zero. However, in the evaluation of the environmental performance of these alternative marine power configurations, conventional life cycle assessment (LCA) methods have limitations reflecting the varied nature of ship design and operational modes. The integration of LCA with experimental assessment could remedy the shortcoming of conventional approaches to data generation. The system energy demand data in this study was generated based on specific ship design and directly fed into life cycle assessment. To demonstrate the effectiveness and potential the approach was applied to a case study of inland waterway vessel. Suitable hybrid PV/electricity/diesel and hydrogen powered fuel cell systems for the case vessel were modelled; and hydrodynamic testing and dynamic system simulation was undertaken to provide ship performance data under various operational/environmental profiles. Lifecycle assessment (LCA) indicated hydrogen and electrical propulsion technologies have the potential for 85.7 % and 56.2 % emissions reduction against an MGO base case, respectively. The results highlight that implementation of both technologies is highly dependent on energy production pathways. Hydrogen systems reliant on fossil feedstocks risk an increase in emissions of up to 6.3 % against the MGO base case. Sensitivity analysis indicated an electrical system with electricity production from 79.5 % renewables could achieve savings of 82.2 % in GHG emissions compared to the MGO base case. Crucially, the results demonstrate a further development of the LCA approach which can enable a more accurate environmental performance evaluation of alternative marine power configurations considering specific ship design and operational characteristics. Ultimately this addition makes the results more meaningful for commercial operations and decision making in the selection of alternative marine power systems to support the transition to net-zero.

International alliances and technology diffusion: A worldwide analysis of adoption of energy, railway and satellite technologies

This study analyzes the role of international alliances in the adoption of new technology at the national level. We look at the worldwide diffusion of six key infrastructure technologies during the past six decades among 161 countries: nuclear power, solar power, wind power, marine power, high-speed rail, and telecommunication satellites. Acknowledging that international relations are not solely structured by formal alliances, we further investigate the impact of neighboring states on technology diffusion, as neighbors tend to maintain strong economic and cultural ties. We further look at simple imitation effects between states with similar political systems. With our focus on international alliances as drivers of international technology diffusion, our study complements economic studies on technology diffusion. For most of the technologies, we find evidence for spillovers between allied states as well as between neighboring states, while no such evidence was found for institutionally similar states. These results confirm the important role that international alliances may play in technology diffusion.

Semi-submersible non-axial current generators based on improving current energy conversion efficiency

Abstract With the development and utilization of ocean current energy, how to improve the efficiency of ocean current energy utilization has become the focus of attention in many countries. In this paper, the optimal design of the structure of the ocean current generator is mainly used to improve the energy capture power and the conversion efficiency of the ocean current energy unit under the condition of low flow rate. The effect of peripheral fluid growth on the generator is analyzed using finite element analysis. The three-dimensional finite element model of the semi-submersible axial-current generator is established by using the ANSYS finite element method, and the calculation and analysis of the peripheral fairing are simplified. Through finite element calculation and analysis, the velocity cloud diagram and velocity linear vector diagram are obtained, respectively. The results show that the semi-submersible axial current generator has the ability to start and generate electricity at low velocity and can use the current resources for power supply in situ. Its application can maximize the current capture and greatly improve the utilization rate of current energy.

Analysis of Power-Maximizing Region 2 Controllers for Wind and Marine Turbines

Wind and marine energy are rapidly growing and complementary technologies that share some techniques for simplified modeling and control, particularly in below-rated flow speeds. A turbine operator has several choices of controller for maximizing power in Region 2. The simple and ubiquitous KΩ2 control law is often effective but limited in its flexibility. Alternative controllers use reference tracking to split the control objectives into a low-bandwidth optimal tip-speed ratio tracking loop to maximize steady-state power and a higher-bandwidth proportional-integral control loop to reject inflow turbulence. Several options exist for identifying the slowly varying optimal set point during operation, based on estimating the inflow velocity or filtering the power or torque signals. This study compares the trade-offs between performance and other design priorities for a few choices of reference-tracking controller in the literature for reference wind and marine turbines. Analysis is performed in the frequency domain using the linearization of each controller, and the impact of turbulent disturbances on the closed-loop system is described. The controllers are simulated in OpenFAST to analyze their performance with higher-order nonlinear turbine dynamics.

Strong Eddy Kinetic Energy Anomalies Induced by Baroclinic Instability in the Southwest Region of the Kerguelen Plateau, East Antarctica

AbstractEddy activity is particularly prominent in the Southern Ocean due to the instabilities of the Antarctic Circumpolar Current, which plays a critical role in energy transport of the global ocean. In this study, a systematic energetics analysis framework is employed to investigate notable anomalies of an intensified Eddy Kinetic Energy (EKE) event observed in the southwest region of the Kerguelen Plateau in the Indian sector of the Southern Ocean in 2017, utilizing a reanalysis product. The EKE anomalies, presenting across all depths, emerged in April, peaked during the austral winter, and persisted into the subsequent summer. Energetics analysis indicates that the pronounced EKE anomalies are primarily determined by baroclinic instability, with distinct governing mechanisms at the surface and in the internal ocean. The anomalous intrusion of warm Circumpolar Deep Water intensified the baroclinic energy conversion in the subsurface, contributing significantly to the EKE anomalies. Moreover, strong anomalous wind‐induced Ekman pumping served to amplify the lifting of isopycnals, which enhanced the baroclinic instability and subsequently intensified the EKE anomalies. This study sheds new light on underlying mechanisms governing local polar dynamics and provides insights into the intricate interaction between ocean dynamics and energy distribution in the Antarctic region.

Analysis of OWC impulse turbine flow characteristics considering the blade tip clearance

Abstract Oscillating water column (OWC) ocean wave energy recovery device is a popular technology in current wave energy research, which possesses the advantages of a sturdy structure and low-maintenance requirements. The device recovers energy by unidirectional rotation in the reciprocating airflow generated by an impulse turbine. Its operational performance depends on the flow efficiency of the core component, the air turbine. In this paper, a prototype impulse turbine with blades tip clearance of 1 mm was considered, and the SST k-ω turbulence model is used to calculate the operating performance of the air turbine at different operating points. The calculation result shows that the efficiency of the turbine under the optimal operating conditions is about 51.41%. When the flow coefficient is less than 0.8, the primary focus of energy loss in the rotor occurs at the blade tip. The low flow rate leads to a high inlet angle causing fluid friction. In these small flow conditions, the pressure drop at the leaf top gap is cantered on the inlet, and the speed in the gap flow field is significantly reduced. When the flow coefficient is greater than 1.4, the concentration of energy loss in the rotor primarily occurs within the flow channel, where the high-velocity air causing a local high-speed zone.

A triboelectric nanogenerator based on a spiral rotating shaft for efficient marine energy harvesting of the hydrostatic pressure differential

Equipment used in underwater sensing and exploration typically relies on cables or batteries for energy supply, resulting in a limited and inconvenient energy supply and marine environmental pollution that hinder the sustainable development of distributed ocean sensing networks. Here, we design a deep-sea differential-pressure triboelectric nanogenerator (DP-TENG) based on a spiral shaft drive using modified polymer materials to harness the hydrostatic pressure gradient energy at varying ocean depths to power underwater equipment. The spiral shaft structure converts a single compression into multiple rotations of the TENG rotor, achieving efficient conversion of differential pressure energy. The multi-pair electrode design enables the DP-TENG to generate a peak current of 61.7 μA, the instantaneous current density can reach 0.69 μA cm−2, and the output performance can be improved by optimizing the spiral angle of the shaft. The DP-TENG can charge a 33 μF capacitor to 17.5 V within five working cycles. It can also power a digital calculator and light up 116 commercial power light-emitting diodes, demonstrating excellent output capability. With its simple structure, low production cost, and small form factor, the DP-TENG can be seamlessly integrated with underwater vehicles. The results hold broad prospects for underwater blue energy harvesting and are expected to contribute to the development of self-powered equipment toward emerging “smart ocean” and blue economy applications.

Second Version of Marine Energy Technologies Online Conference [Chapter News]

Second Version of Marine Energy Technologies Online Conference [Chapter News]

Regulating the redox cycle of nickel species for efficient seawater electrolysis

Promoting the self-reconstruction of NiFe-based catalysts represents a promising approach to facilitate seawater splitting, albeit with significant challenges. Herein, the redox cycle of Ni species is subtly regulated by decorating NiFe hydroxides with vanadium. Both experimental and theoretical studies demonstrate that the incorporation of V boosts the self-reconstruction of NiFe hydroxides and allows a superior OER performance on account of diminished propensity for chlorine adsorption and optimized binding energy of oxygen-containing intermediates. Consequently, the NiFeV/NF catalyst delivers 2.0 A cm−2 at an ultralow overpotential of 369 mV in 1.0 M KOH and exhibits exceptional stability for 720 h at 20 A in an alkaline membrane electrode assembly (MEA) electrolyzer. In alkaline seawater, it achieves prolonged stability, surpassing 240 h at 500 mA cm−2 with OER selectivity of 99 %. This work significantly advances the field of seawater electrolysis powered by marine renewables, paving the way for on-site hydrogen production.