Showing papers on "Marine energy published in 2021"

Nodding Duck Structure Multi-track Directional Freestanding Triboelectric Nanogenerator toward Low-Frequency Ocean Wave Energy Harvesting

Abstract: Development of ocean energy conversion technique is a strategic requirement to optimize the energy structure and expand the "blue economic" space. Triboelectric nanogenerator (TENG) provides a potential approach for efficiently capturing wave energy with its unique advantages. Herein, a nodding duck structure multi-track freestanding triboelectric-layer nanogenerator (NDM-FTENG) is developed for ocean wave energy harvesting at a low-frequency range. Configuration parameters including track numbers, connection approach, oscillation frequency, and swing amplitude on electrical output performances of NDM-FTENG are systematically investigated and optimized; the maximum instantaneous power density of 4 W/m3 is obtained by one NDM-FTENG block with 320 LEDs lighted up simultaneously. Overall, NDM-FTENG is proved to be an efficient device for driving small electronics with excellent stability and durability in a real water wave environment, and the power potential can be further magnified by combining more NDM-FTENG devices in parallel to form a network toward large-scale blue energy harvesting.

Scour protections for offshore foundations of marine energy harvesting technologies: A review

Abstract: The offshore wind is the sector of marine renewable energy with the highest commercial development at present. The margin to optimise offshore wind foundations is considerable, thus attracting both the scientific and the industrial community. Due to the complexity of the marine environment, the foundation of an offshore wind turbine represents a considerable portion of the overall investment. An important part of the foundation’s costs relates to the scour protections, which prevent scour effects that can lead the structure to reach the ultimate and service limit states. Presently, the advances in scour protections design and its optimisation for marine environments face many challenges, and the latest findings are often bounded by stakeholder’s strict confidential policies. Therefore, this paper provides a broad overview of the latest improvements acquired on this topic, which would otherwise be difficult to obtain by the scientific and general professional community. In addition, this paper summarises the key challenges and recent advances related to offshore wind turbine scour protections. Knowledge gaps, recent findings and prospective research goals are critically analysed, including the study of potential synergies with other marine renewable energy technologies, as wave and tidal energy. This research shows that scour protections are a field of study quite challenging and still with numerous questions to be answered. Thus, optimisation of scour protections in the marine environment represents a meaningful opportunity to further increase the competitiveness of marine renewable energies.

Ocean Thermal Energy Conversion and Other Uses of Deep Sea Water: A Review

Abstract: Research into renewable energy is an active field of research, with photovoltaic and wind being the most representative technologies. A promising renewable energy source is Ocean Thermal Energy Conversion (OTEC), based on the temperature gradient of seawater. This technology has two contradictory features, as its efficiency is relatively low while, on the other hand, its energy source is almost unlimited. OTEC research has focused on optimizing energy extraction, with different techniques having been used for this purpose. This article presents a review of the advances and applications of OTEC technology around the world. Throughout the document, the different uses of deep seawater are analyzed; further, the current systems which generate energy through the marine temperature gradient are reviewed, and the main advantages and disadvantages of each method are highlighted. The technical operations, construction variations, and the projects that have been developed around the world and those which are in the planning phase are also detailed. The two main conclusions are that this technology is still under development, but it is quite promising, especially for regions with little access to drinking water. Second, given the high implementation costs and low conversion efficiency, the development of this technology must be sponsored by governments.

Towards large-scale electrochemical energy storage in the marine environment with a highly-extensible “paper-like” seawater supercapacitor device

Abstract: Harvesting energy from natural resources is of significant interest because of their abundance and sustainability. In particular, large-scale marine energy storage shows promising prospects because of the massive and diverse energy forms such as waves, tide and currents; however it is greatly hindered due to its complicated circumstances and intermittent nature. Storing and transporting locally generated energy has become a vital step for future sustainable energy supplies. Here, we proposed a highly-extensible “paper-like” all-in-one seawater supercapacitor constructed from a nanofiber-based film in operando towards electrochemical energy storage in the marine environment, which features lightweight and excellent mechanical properties with a typical thickness of about 100 μm. The single supercapacitor cell shows a remarkable performance with an energy density of 6.6 mW h cm−3 at a power density of 99.0 mW cm−3, and exhibits a capacitance retention of 100% under different bending operations. Moreover, the large-scale extensibility of the all-in-one seawater supercapacitor cell was fully demonstrated with an optimized circuit design. The integrated device connected with multiple cells in series and parallel can successfully drive a motor with a voltage of 12 V and a power of 2.5 W for operation. It shows prospective applications for future large-scale distributed energy storage systems in the marine environment.

Using machine learning to derive spatial wave data: A case study for a marine energy site

Abstract: Ocean waves are widely estimated using physics-based computational models, which predict how energy is transferred from the wind, dissipated, and transferred spatially across the ocean. Machine learning methods offer an opportunity to predict these data with significantly reduced data input and computational power. This paper describes a novel surrogate model developed using the random forest method, which replicates the spatial nearshore wave data estimated by a Simulating WAves Nearshore (SWAN) numerical model. By incorporating in-situ buoy observations, outputs were found to match observations at a test location more closely than the corresponding SWAN model. Furthermore, the required computational time reduced by a factor of 100. This methodology can provide accurate spatial wave data in situations where computational power and transmission are limited, such as autonomous marine vehicles or during coastal and offshore operations in remote areas. This represents a significant supplementary service to existing physics-based wave models.

An extensive thermo-economic evaluation and optimization of an integrated system empowered by solar-wind-ocean energy converter for electricity generation – Case study: Bandar Abas, Iran

Abstract: In parallel with efforts to shift human societies' reliance from fossil fuel to renewable resources, in this paper, three green-based energy generation configurations were proposed and examined thermoeconomically. Afterwards, the one with the highest performance was selected for further investigation. The chosen system was empowered by an ocean thermal energy convertor (OTEC), a wind turbine, and a solar flat plate panel. The system was modeled by Engineering Equation Solver (EES) software to conduct sensitivity analysis by assessing the impact of changes in objective parameters on the net power output, thermoelectric generator (TEG) power output, exergy efficiency, and cost ratio. In the following steps, EES was coupled with MATLAB through Dynamic Data Exchange (DDE), and a non-dominated sorting genetic algorithm (NSGA-II) was employed for optimizing design parameters including solar panels' area, organic Rankine cycle (ORC) turbine inlet temperature, condenser outlet temperature, ORC pump and turbine efficiency, TEG figure of merit, and evaporator pinch point to reach the highest possible exergy efficiency and the least amount for cost ratio. The system performed with 13.88% exergy efficiency. The exergy destruction analysis showed wind turbine was the most exergy destructor in the system. The configuration is able to generate 448 kW power at its optimal point. Eventually, a case study for Bandar Abbas city, a coastal town in the south of Iran, is carried out to investigate the system's performance concerning the region's potential throughout a year. The results indicate that the system can potentially supply 38 Iranian households with electricity all year-round.

Recent developments in energy storage systems for marine environment

Abstract: Marine batteries are designed specifically for marine vehicles with heavier plates and robust construction to withstand the vibration and pounding that can occur on board any powerboat. These batteries are specially developed to meet the potential and futuristic needs of sea vehicle applications. This paper reviews several types of energy storage systems for marine environments, which have been extensively used to improve the overall performance of marine vehicles. Key technological developments and scientific challenges are considered for a broad range of marine batteries. The primary and secondary marine battery technologies are discussed, and the corresponding outputs are reported in terms of energy capacity, charging–discharging rates, cycle life, energy and power density, shelf life, and their environmental impact. The performance comparison is analyzed for various batteries such as lead-acid, lithium-ion, nickel–cadmium, silver–zinc, and open water-powered batteries for marine applications. After a brief discussion on these technologies, the global scenario of the marine battery market is reported, which is segmented by regions, applications, and ship types. Further, we summarize the eco-marine power system, and the future directions of marine energy storage systems are highlighted, followed by advanced Al-battery technology and marine energy storage industry outlooks up to 2025.

The possibilities to improve ship's energy efficiency through the application of PV installation including cooled modules

Abstract: The sea environment protection requirements getting stricter with time have caused nowadays growing interest in the application of the renewable energy sources in the marine power systems. This allows to reduce the CO2 emission and therefore to achieve more advantageous value of ship's energy efficiency index. One of the more preferably applied arrangements, regardless of the ship's size, are the photovoltaic systems (PV systems). Their contribution to the electricity production on ships can be increased through the application of PV panels water cooling which results in the increase of their efficiency. This article presents the calculation methods allowing to determine the energy profits obtainable owing to the application of the PV modules cooling system using the water taken from the ship's power plant cooling system. The results of calculations for PV installation of a selected ro-pax vessel planned for the operation on the Świnoujście –Ystad line have been used and presented in this article.

Analysis of the Effects of the Location of Passive Control Devices on the Platform of a Floating Wind Turbine

Abstract: Floating offshore wind turbines (FOWT) are subjected to strong loads, mainly due to wind and waves. These disturbances cause undesirable vibrations that affect the structure of these devices, increasing the fatigue and reducing its energy efficiency. Among others, a possible way to enhance the performance of these wind energy devices installed in deep waters is to combine them with other marine energy systems, which may, in addition, improve its stability. The purpose of this work is to analyze the effects that installing some devices on the platform of a barge-type wind turbine have on the vibrations of the structure. To do so, two passive control devices, TMD (Tuned Mass Damper), have been installed on the platform of the floating device, with different positions and orientations. TMDs are usually installed in the nacelle or in the tower, which imposes space, weight, and size hard constraints. An analysis has been carried out, using the FAST software model of the NREL-5MW FOWT. The results of the suppression rate of the tower top displacement and the platform pitch have been obtained for different locations of the structural control devices. They have been compared with the system without TMD. As a conclusion, it is possible to say that these passive devices can improve the stability of the FOWT and reduce the vibrations of the marine turbine. However, it is indispensable to carry out a previous analysis to find the optimal orientation and position of the TMDs on the platform.

Electrical control strategy for an ocean energy conversion system

Abstract: Globally abundant wave energy for power generation attracts ever increasing attention. Because of non-linear dynamics and potential uncertainties in ocean energy conversion systems, generation productivity needs to be increased by applying robust control algorithms. This paper focuses on control strategies for a small ocean energy conversion system based on a direct driven permanent magnet synchronous generator (PMSG). It evaluates the performance of two kinds of control strategies, i.e., traditional field-oriented control (FOC) and robust adaptive control. The proposed adaptive control successfully achieves maximum velocity and stable power production, with reduced speed tracking error and system response time. The adaptive control also guarantees global system stability and its superiority over FOC by using a non-linear back-stepping control technique offering a better optimization solution. The robustness of the ocean energy conversion system is further enhanced by investigating the Lyapunov method and the use of a DC-DC boost converter. To overcome system complexity, turbine-generator based power take-off (PTO) is considered. A Matlab/Simulink study verifies the advantages of a non-linear control strategy for an Oscillating Water Column (OWC) based power generation system.

An Oscillating Water Column (OWC): The Wave Energy Converter

Abstract: Ocean waves are a valuable resource of renewable energy that can make a significant contribution to the supply of electricity to countries situated offshore when used in great measure. An extensive range of innovations was proposed, investigated, and assessed in some cases under actual ocean conditions. OWC devices are an important class of wave energy method. The majority of designs used in the conversion of wave energy into the sea are OWC. There is a fixed or floating hollow structure in an OWC under the water surface, which pits the air over the inner free zone. The wave action alternately compresses and separates the air that is forced to flow into a turbine together with a generator. A detailed analysis of OWC technologies is discussed in this paper.

Ocean Energy Systems Wave Energy Modeling Task 10.4: Numerical Modeling of a Fixed Oscillating Water Column

Abstract: This paper reports on an ongoing international effort to establish guidelines for numerical modeling of wave energy converters, initiated by the International Energy Agency Technology Collaboration Program for Ocean Energy Systems. Initial results for point absorbers were presented in previous work, and here we present results for a breakwater-mounted Oscillating Water Column (OWC) device. The experimental model is at scale 1:4 relative to a full-scale installation in a water depth of 12.8 m. The power-extracting air turbine is modeled by an orifice plate of 1–2% of the internal chamber surface area. Measurements of chamber surface elevation, air flow through the orifice, and pressure difference across the orifice are compared with numerical calculations using both weakly-nonlinear potential flow theory and computational fluid dynamics. Both compressible- and incompressible-flow models are considered, and the effects of air compressibility are found to have a significant influence on the motion of the internal chamber surface. Recommendations are made for reducing uncertainties in future experimental campaigns, which are critical to enable firm conclusions to be drawn about the relative accuracy of the numerical models. It is well-known that boundary element method solutions of the linear potential flow problem (e.g., WAMIT) are singular at infinite frequency when panels are placed directly on the free surface. This is problematic for time-domain solutions where the value of the added mass matrix at infinite frequency is critical, especially for OWC chambers, which are modeled by zero-mass elements on the free surface. A straightforward rational procedure is described to replace ad-hoc solutions to this problem that have been proposed in the literature.

A comprehensive study of the tides around the Welsh coastal waters

Abstract: A computational model has been used to explore characteristics of the barotropic tide around the Welsh coast in detail for the first time. Proper understanding of tidal characteristics is vital for the sustainable use of marine resources; particularly for industries such as marine energy extraction, aggregate mining, aquaculture, as well as regulators and agencies with responsibilities for the resource management and public safety. In shallow water areas, the influence of bathymetry and energy dissipation leads to the generation of higher harmonics that cause complex tidal phenomena. The Celtic and Irish seas, which enclose the Welsh coast (UK), are heavily industrialised shallow water seas with macro-to mega-tidal semi-diurnal tides. It is shown that tidal distortion is significant in the Bristol Channel (S. Wales) and in the large shallow estuaries of the N. Wales coast; for much of the west coast this is only significant in localised areas around headlands and islands. Tidal dominance switches from flood dominant in the south and north to ebb dominant on the west coast. Highly complex patterns of vorticity in the tidal residual flow are noted. All these factors mean that careful siting of industry and coastal management interventions is required to avoid disruption of the natural system.

Tidal Energy Round Robin Tests: A Comparison of Flow Measurements and Turbine Loading

Abstract: A Round Robin Tests program is being undertaken within the EC MaRINET2 initiative. This programme studies the used facility influence can have on the performance evaluation of a horizontal axis tidal turbine prototype when it is operated under wave and current conditions. In this paper, we present the design of experiments that is used throughout the work programme and the results related to the flow characterisation obtained at the Ifremer wave and current circulating tank, the Cnr-Inm wave towing tank and the ocean research facility FloWave. These facilities have been identified to provide adequate geometric conditions to accommodate a 0.724 m diameter turbine operating at flow velocities of 0.8 and 1.0 m/s. The set-up is replicated in each of the facilities with exemption of the amount of flow measuring instruments. Intrinsic differences in creating wave and currents between facilities are found. Flow velocities are up to 10% higher than the nominal values and wave amplitudes higher than the target values by up to a factor of 2. These discrepancies are related to the flow and wave generation methods used at each facility. When the flow velocity is measured besides the rotor, the velocity presents an increase of 8% compared to the upstream measurements.

A Twenty-Year Analysis of Winds in California for Offshore WindEnergy Production Using WRF v4.1.2

Abstract: . Offshore wind resource characterization in the United States relies heavily on simulated winds from numerical weather prediction (NWP) models, given the lack of hub-height observations offshore. One such NWP data set used extensively by U.S. stakeholders is the Wind Integration National Dataset (WIND) Toolkit, a 7-year time-series data set produced in 2013 by the National Renewable Energy Laboratory. In this study, we present an update to that data set for offshore California that leverages recent advancements in NWP modeling capabilities and extends the period of record to a full 20 years. The data set predicts a significantly larger wind resource (0.25–1.75 m s−1 stronger), including in three Call Areas that the Bureau of Ocean Energy Management is considering for commercial activity. We conduct a set of yearlong simulations to study factors that contribute to this increase in the modeled wind resource. The largest impact arises from a change in the planetary boundary layer parameterization from the Yonsei University scheme to the Mellor-Yamada-Nakanishi-Niino scheme and their diverging wind profiles under stable stratification. Additionally, we conduct a refined wind resource assessment at the three Call Areas, characterizing distributions of wind speed, shear, veer, stability, frequency of wind droughts, and power production. We find that, depending on the attribute, the new data set can show substantial disagreement with the WIND Toolkit, thereby driving important changes in predicted power.