Ocean Energy Resources Research Articles

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).

Analysis of the Development of Ocean Energy Industry in China

The global ocean energy resource is abundant. The ocean energy is a kind of emerging renewable energy. Climate change is the focus for international society. For the independence and the safety of energy, many countries take renewable energy into consideration. The emerging ocean energy industry is an important choice for marine economy recovery. The ocean energy resource is rich in China. Fostering ocean energy industry in China is very important for implementation of Carbon Peak and Carbon Neutral strategy, diversifying the energy structure and developing marine economy. In the critical period of ocean energy industrialization in China, it’s necessary to summarize the status of ocean energy technology and industry and to analyze the developing trend and application scenarios.

Ocean energy

This article presents the principles and technologies for converting the main renewable ocean energy resources (ocean thermal energy, wave energy and tidal energy) into electricity. Their energy production potential is put into perspective in terms of the challenges of the energy transition.

The global techno-economic potential of floating, closed-cycle ocean thermal energy conversion

Ocean Thermal Energy Conversion (OTEC) is an emerging renewable energy technology using the ocean’s heat to produce electricity. Given its early development stage, OTEC’s economics are still uncertain and there is no global assessment of its economic potential, yet. Here, we present the model pyOTEC that designs OTEC plants for best economic performance considering the spatiotemporally specific availability and seasonality of ocean thermal energy resources. We apply pyOTEC to more than 100 regions with technically feasible sites to obtain an order-of-magnitude estimation of OTEC’s global technical and economic potential. We find that OTEC’s global technical potential of 107 PWh/year could cover 11 PWh of 2019 electricity demand. At ≥ 120 MWgross, there are OTEC plants with Levelised Cost of Electricity (LCOE) below 15 US¢(2021)/kWh in 15 regions, including China, Brazil, and Indonesia. In the short-to-medium term, however, small island developing states are OTEC’s most relevant niche. Systems below 10 MWgross could fully and cost-effectively substitute Diesel generators on islands where that is more challenging with other renewables. With the global analysis, we also corroborate that most OTEC plants return the best economic performance if designed for worst-case surface and deep-sea water temperatures, which we further back up with a sensitivity analysis. We lay out pyOTEC’s limitations and fields for development to expand and refine our findings. The model as well as key data per region are publically accessible online.

Study on Wave Energy Conversion Problem of Turbine-Integrated OWC Chamber

An oscillating water column (OWC) device is a promising wave energy converter (WEC) to utilize ocean wave energy resources. The OWC chamber absorbs the kinetic energy of ocean waves and converts the water column motion to reciprocating airflow. A power take-off system (PTO-system) of the OWC-WEC consists of an air turbine, generator, and power control system. An airflow drives an air turbine, which rotates a generator to produce electricity. The air turbine induces a pressure fluctuation due to its aerodynamic characteristics, which directly affects the fluid motion inside the chamber. In this study, the wave energy conversion problem of the OWC-WEC was discussed based on the experimental and numerical simulation results, considering the turbine-chamber interaction. The wave energy conversion problem from wave to power was solved using the finite element method (FEM)-based numerical wave tank in the time domain. The air turbine was numerically modeled based on aerodynamic coefficients and inertia properties. The validity of the present numerical method was examined by comparing it with the experimental results conducted in a two-dimensional wave flume at the Korea Research Institute of Ships and Ocean Engineering (KRISO). The effect of the turbine-chamber interaction on the energy conversion performance was investigated regarding the various rotational speeds of the air turbine based on experimental and numerical analysis. It was observed that the rotational speed conditions of the turbine, where the hydrodynamic performance of the OWC chamber and the aerodynamic performance of the turbine could be maximized, were different from each other. Therefore, it can be seen that a control technology considering the combined performance of the chamber and air turbine is required to maximize the energy conversion performance of the OWC-WEC.

Optimal Design of a Submerged Tidal Device for Low Current Environment

The tidal current power is one of the reliable renewable ocean energy resources that can be deployed at the region having ocean current. The feasible current speed for the application of tidal device is known to be more than 2m/s. As there are many islands in Asia where the current speed is below than the feasible speed, the submerged device that can produce the power at lower current speed with easy deployment and retrieve is introduce. To simplify the installation and O&M operations, the 4-point taut mooring system is applied that can also secure the designated position. In this study, a HAT (horizontal axis turbine) of 5-kW submerged tidal device is designed and analyzed for a low current region that consist of two buoyancy tanks, a yaw control strut, and a diffuser-type brimmed duct. To analyze the most stable condition, 9 different cases of width and height of the device and 8 different mooring arrangements (total 72 different cases) are investigated both by frequency and time domains. The results show that the dynamic behavior that mainly affects the turbine performance decreases with lower strut height. However, it was observed that the device width has little effect on the dynamic response of the device. The device dynamic motion decreases with decreasing azimuth angle and increasing hang-off angle of the mooring configuration. The optimal design configuration that can produce the maximum power is found that of 4.42 m width, 2 m height, 30° azimuth angle and 60° hang-off angle. According to API RP 2K code, the mooring system is also designed in both intact and damaged conditions. The proposed tidal device could be applied for the low current speed areas with easy implementation and maintenance.

Investigation of Dynamic Behavior of Ultra-Large Cold-Water Pipes for Ocean Thermal Energy Conversion

Ocean Thermal Energy Conversion (OTEC) is a process that can produce electricity by utilizing the temperature difference between deep cold water and surface warm water. The cold-water pipe (CWP) is a key component of OTEC systems, which transports deep cold water to the floating platform. The CWP is subjected to various environmental and operational loads, such as waves, currents, internal flow, and platform motion, which can affect its dynamic response and stability. In this paper, we establish a computational model of the mechanical performance of the CWP based on the Euler–Bernoulli beam theory and the Morrison equation, considering the effects of internal flow, sea current, and wave excitation. We use the differential quadrature method (DQM) to obtain a semi-analytical solution of the lateral displacement and bending moment of the CWP. We verify the correctness and validity of our model by comparing it with the finite element simulation results using OrcaFlex software. We also analyze the effects of operating conditions—such as wave intensity, clump weight at the bottom, and internal flow velocity—on the dynamic response of the CWP using numerical simulation and the orthogonal experimental method. The results show that changing the wave strength and internal flow velocity has little effect on the lateral displacement of the CWP but increasing the current velocity can significantly increase the lateral displacement of the CWP, which can lead to instability. The effects of waves, clump weight, internal flow, and sea current on the maximum bending moment of the CWP are similar; all of them increase sharply at first and then decrease gradually until they level off. The differences in the effects are mainly reflected in the different locations of the pipe sections. This paper suggests some design guidance for CWP in terms of dynamic responses depending on the operating conditions. This paper contributes to the journal’s scope by providing a novel and efficient method for analyzing the mechanical performance of CWP for OTEC systems, which is an important ocean energy resource.

Experimental study on hydrodynamic behavior and energy conversion of multiple oscillating-water-column chamber in regular waves

An oscillating water column (OWC) device is a promising wave energy converter that uses ocean wave energy resources. The OWC chamber absorbs the energy of ocean waves and significantly affects energy conversion performance. In this study, the hydrodynamic performance of a multiple OWC chamber was investigated experimentally, emphasizing its hydrodynamic behavior and energy conversion characteristics. A series of regular wave tests were conducted for single-, triple-, and asymmetric triple OWC chambers in a two-dimensional wave tank. The same orifice ratio was applied to the single and triple chambers to induce an equivalent turbine-chamber interaction owing to the pressure drop. It was found that the triple OWC chamber contributes to an increase in the converted pneumatic power compared to the single OWC chamber due to reducing the sloshing motion of the internal fluid. Moreover, the temporal fluctuation of the overall output power was reduced because of the water column motion of each triple OWC chamber with a phase difference. The rear chamber of the asymmetric triple chamber traps the wave energy and contributes to not only increasing the output power but also the variability. Therefore, it can be observed that multiple OWC chambers improve energy conversion performance by increasing the mean power output and reducing temporal fluctuation.

Development and Application of a GIS for Identifying Areas for Ocean Energy Deployment in Irish and Western UK Waters

Ireland and the UK possess vast ocean energy resources within their respective maritime areas. However, not all offshore areas are suitable for deployment of ocean energy devices. This article describes the development of a multitude of geospatial data relating to ocean energy site suitability, as well as a Web-GIS tool for hosting and performing analysis on this data. A validation of wave, water depth and seabed character data used in the study revealed good correlation between modelled and in situ data. The data is mapped, and the spatial patterns are discussed with relevance to ORE sector implications. A site selection model, which included much of this data, was developed for this study and the Web-GIS tool. A survey conducted with ocean energy technology developers revealed their desired site criteria. The responses were applied in a case study using the site selection model to uncover potential and optimum areas for deployment of both wave and tidal energy devices. The results reveal extensive areas of the Atlantic Ocean and Celtic Sea appropriate for wave energy deployment and less extensive areas for tidal energy deployment, in the Irish Sea and Inner Seas off the West Coast of Scotland.

Numerical investigation on hydrodynamic energy conversion performance of breakwater-integrated oscillating water column-wave energy converters

Various wave energy converters (WECs) have been developed to utilize ocean wave energy resources. Among them, an oscillating water column (OWC) device is a promising wave energy converter that has undergone several pilot tests in the ocean with various prototype devices. Recently, a breakwater-integrated OWC-WEC system was proposed to improve the economic feasibility by reducing the construction and installation costs of the OWC chamber structure. In this study, a numerical investigation was conducted to simulate the hydrodynamic energy conversion problem for a breakwater-integrated OWC-WEC. The boundary value problem with the Laplace equation was solved directly by using a three-dimensional numerical wave tank based on a finite element method in the time domain. In the present numerical method, an efficient numerical model for the tetrapod (TTP), which is used to protect a rubble mound breakwater, was introduced using multiple blocks and numerical damping zone. Further, numerical investigations were performed on the effects of breakwater integration, TTP layer modeling, and the application of the numerical damping zone, and their features in terms of the wavefield and the OWC chamber responses were analyzed. Finally, the validity of the present numerical method was examined by comparing it with the experimental data.

Ocean Energy Development under the Background of Carbon Emissions Peak and Carbon Neutrality in China

The ocean energy resources are abundant in China. The technical potential in Chinese coastal area is more than 70 GW. Thus, the utilization of ocean energy resources is very important for the energy saving and the mitigation of climate change. The Renewable Energy Law implemented since 2010 and the special fund program for ocean energy established in 2011 has advanced great progress of ocean energy technology research, development and demonstration in recent years in China. The ocean energy technologies in China have achieved rapid development under the support of the Ministry of Finance, the Ministry of Natural Resources, the Ministry of Science and Technology and so on. The accumulated capacity of ocean energy is in the international advanced level, but the ocean energy industry is still in early stage. The carbon emissions peak and carbon neutrality strategy put forward in China requires the transition to green energy and electricity, which also provides crucial opportunity for the development of the utilization of ocean energy resources in China. The paper introduces the status of ocean energy technology and industry in China firstly. Then the problems in the development of ocean energy are analysed. The potential of utilization of ocean energy is estimated to support the carbon emission reduction. Finally, the vision and main tasks are given.

Evaluation of a novel ammonia-water based combined cooling, desalination and power system based on thermodynamic and exergoeconomic analyses

It is of great significance and development potential to make full use of ocean thermal energy and seawater resources to solve the problem of energy and fresh water supply in tropical coastal areas. In the present article, an innovative ammonia-water (NH3-H2O) based combined cooling, desalination and power (CCDP) system is proposed, consisting of Kalina cycle-based ocean thermal energy conversion (OTEC), ejector refrigeration cycle (ERC) and spray flash evaporation (SFE) desalination unit. An ejector is introduced for coupling the Kalina cycle and ERC, which creates a larger pressure difference across the turbine in favor of higher power output. Besides, a multi-stage SFE desalination system is integrated into the proposed system for making full use of seawater resources and providing fresh water output. Mathematical model is established for simulating steady operation of the proposed system, and parametric analysis is performed to determine the influences of operational parameters including vapor generation pressure and temperature, ammonia concentration of basic solution and condensation pressure on the system thermodynamic and exergoeconomic performances. Results show that by comparison with the stand-alone Kalina cycle and the organic Rankine cycle (ORC) based multi-generation system, the proposed CCDP system is more advantageous with regard to the effective efficiency, exergy efficiency and net power output. Over 70% of the total exergy destruction occurs in the three components of SFE, condenser and turbine. The improvement of both effective efficiency and exergy efficiency can be accomplished by reducing the condensation pressure and raising the basic ammonia concentration, while not greatly affected by vapor generation temperature.

Multi-Energy System Based on Ocean Thermal Energy Conversion

The ocean thermal energy is abundant. The global total is about 40 billion kW. The ocean thermal energy conversion (OTEC) is clean and renewable, the power generation is stable, and the energy storage has high capacity. Active exploitation of ocean thermal energy resources is of great significance to realize the strategy of maritime power. In view of the efficiency limit of a traditional OTEC, authors propose an approach of a multi-energy complementary OTEC system that they can improve the efficiency of this system. The approach sets parameters at the system level and integrates solar energy, wind energy, energy storage and OTEC. For example, a 1MW integrated power generation system is designed and simulated by means of computer aided design and of conducting a model-based simulation, respectively. The efficiency of the complementary OTEC system with solar heating can reach 13.12%. In this article, the basic principle and working process of the approach are analyzed, and the system efficiency is calculated. The results show that, in comparison to the traditional OTEC, the complementary system of OTEC can improve the ratio of power generation output efficiency, stability and ocean energy utilization.

Numerical Investigation on Hydrodynamic Energy Conversion Performance of Breakwater-Integrated Oscillating Water Column-Wave Energy Converters

Various wave energy converters (WECs) have been developed to utilize ocean wave energy resources. Among them, an oscillating water column (OWC) device is a promising wave energy converter that has undergone several pilot tests in the ocean with various prototype devices. Recently, a breakwater-integrated OWC-WEC system was proposed to improve the economic feasibility by reducing the construction and installation costs of the OWC chamber structure. In this study, a numerical investigation was conducted to simulate the hydrodynamic energy conversion problem for a breakwater-integrated OWC-WEC. The boundary value problem with the Laplace equation was solved directly by using a three-dimensional numerical wave tank based on a finite element method in the time domain. In the present numerical method, an efficient numerical model for the tetrapod (TTP), which is an armored rubble mound breakwater, was introduced using multiple blocks and numerical damping zone. Further, numerical investigations were performed on the effects of breakwater integration, TTP layer modeling, and the application of the numerical damping zone, and their features in terms of the wavefield and the OWC chamber responses were analyzed. Finally, the validity of the present numerical method was examined by comparing it with the experimental data.

Experimental and Numerical Studies on the Focused Waves Generated by Double Wave Groups

From the experiment of Li et al. (2015) it was observed that the generation of freak waves in random wave trains may be attributed to the focusing of double wave groups with different peak frequencies. In order to investigate this generation process, a modified wave focusing experiment is carried out, in which the focused waves are generated by two wave groups with different peak frequency differences, assumed to focus at the same point and time. By analyzing the evolutions of the free surface elevation and wavelet spectra of the experimental data, it can be verified that the focusing of double wave groups can reproduce the generation process of the freak waves in random wave trains well. Phase lags of the double wave groups focusing relative to the linear superposition of the corresponding single wave group and changes in the amplitude spectra during the focusing process are obviously observed. The method for the symmetry-based separation of harmonics illustrates that the phase shifts are mainly caused by the third-order nonlinearity due to interactions between the two wave groups, rather than the even-order nonlinearity. Third-order nonlinearity makes the amplitude of waves small in the high-frequency region, resulting in a shift of the actual focusing location from the target location. Further investigations are conducted with the numerical simulation based on the High Order Spectral (HOS) method. The wavenumber-frequency spectra explain the evolution of the amplitude spectra and changes in the dispersive properties both in time and space, demonstrating that the third-order nonlinearity changes the dispersion relationship of the wave components more intuitively. The above phenomena become obvious for the cases with smaller peak frequency differences wave spectra. All these observations will lead to a better understanding of the mechanism of freak wave generation and lay an important foundation for the low-cost and large-scale development and utilization of ocean wave energy resources.

Working Fluid Candidates Selection for 100kW Ocean Thermal Power Generation Based on Environmental, Safety, and Thermodynamic Constrains

Due to its equatorial location, Indonesia has a huge amount of ocean thermal energy resource. However, this alternative renewable energy resource is still not well developed yet. In this paper, a selection procedure of working fluid for a 100 kW ocean thermal power generation is presented. The screening process was based on environmental, safety and thermodynamic constrains to obtain the best working fluid for this application. Five working fluid candidates are analyzed i.e. ammonia, butane, butene, isobutane, and isobutene. In term of environmental and safety aspects, ammonia is the best solution. But in thermodynamic point of view, isobutane shows the highest power conversion efficiency of 6.13%, whereas ammonia’s efficiency is only 1.87% for the same power output.

Ocean Renewable Energy Potential, Technology, and Deployments: A Case Study of Brazil

This study, firstly, provides an up-to-date global review of the potential, technologies, prototypes, installed capacities, and projects related to ocean renewable energy including wave, tidal, and thermal, and salinity gradient sources. Secondly, as a case study, we present a preliminary assessment of the wave, ocean current, and thermal gradient sources along the Brazilian coastline. The global status of the technological maturity of the projects, their different stages of development, and the current global installed capacity for different sources indicate the most promising technologies considering the trend of global interest. In Brazil, despite the extensive coastline and the fact that almost 82% of the Brazilian electricity matrix is renewable, ocean renewable energy resources are still unexplored. The results, using oceanographic fields produced by numerical models, show the significant potential of ocean thermal and wave energy sources in the northern and southern regions of the Brazilian coast, which could contribute as complementary supply sources in the national electricity matrix.

The development of the IHL wave-current turbine to convert the ocean energy from both wave and current

Indonesia has abundant of renewable sources of energy, among others: geothermal, solar, water, wind and marine therefore the promotion of the utilization of the renewable and sustainable energy is urgent. Since 2006 Indonesian Hydrodynamic Laboratory (IHL) BPPT has conducted research and developed a technology converts the ocean energy resources into electricity, the kinetic energy of marine current and the potential energy of wave. The prototype of marine current turbine, 2 kW and 10 kW respectively, had been installed in Larantuka Strait in 2010 and 2011 (http://www.youtube.com/user/erw4ndi). Since mostly the maximum speed of the marine current of many straits in Indonesia are in order 1.0 - 2.0 m/s, we developed the turbine prototype that can convert not only the kinetic energy of marine current but also the potential energy of the wave, called as wave-current rotor turbine, in 2013. The current usually mixes with wave height with order 0.4 - 0.8 m. A 2 kW prototype was installed under Suramadu (Surabaya - Madura) Bridge close to pier no. 56. The prototype showed a good performance especially in converting the kinetic energy of marine current. The research was continued in 2014-2016 under Ministry of Research and Technology (INSINAS RISTEK) budget scheme. Some innovations have been done to improve the performance of turbines.

On the Marine Energy Resources of Mexico

The Atlantic and Pacific coasts of Mexico offer a variety of marine energy sources for exploitation. Although the Mexican government has made important efforts to reduce its dependence on fossil fuels, national participation in clean energies is still limited in terms of electricity production. This paper presents a practical theoretical assessment of marine energy sources around Mexico, with the aim of identifying potential zones for subsequent, more detailed, technical evaluations and project implementations. The energy sources considered are ocean currents, waves, salinity, and thermal gradients. Using global databases, the percentages of energy availability for the defined thresholds were computed to establish the prospective regions with the most persistent power availability. This approach proved to offer more meaningful information than simple averaged values. Moreover, some environmental and socio-economic factors to be considered for future ocean energy resource assessments in Mexico were also discussed. The results show that the wave energy potential is highest in the northwest of Mexico (~2–10 kW/m for more than 50% of the time), and that there is a constant source of ocean current energy off Quintana Roo state (~32–215 W/m2 for more than 50% of the time). The thermal gradient power is more persistent in the southwest and southeast of the country, where ~100–200 MW can be found 70% of the time. The salinity gradient energy is strongest in the southeast of Mexico. The practical approach presented here can be extended to perform preliminary resources assessments in regions where information is scarce.

Preliminary Estimation of Tidal Current Energy for Three Straits in the Vicinity of Bali and Lombok Islands

Indonesia is an archipelago country which has a great potential of ocean energy resources including tidal current and wave power. In this present work, tidal power in three different straits, namely Alas strait, Bali strait and Lombok strait will be estimated. In order to achieve our goal, a two-dimensional, depth-integrated Advanced Circulation (ADCIRC-2DDI) model was employed. Eight tidal constituents were imposed along the ocean open boundaries. Two different sources of tidal constituents namely Le Provost and OTIS (OSU Tidal Inversion Software) were used. Tidal elevations have been validated and calibrated against tide gauge data in which at least six tide gauges are available in the study location. We found that, tidal constituents from high resolution database that is OTIS give better results. Open boundary conditions have been improved using Green’s function approach. As a result, significant reduction of the root-mean-square error (RMSE) has been obtained. This indicates that the method is powerful.  Furthermore, tidal current energy was estimated. Since there is no tidal current observation available in the area, tidal velocities were compared with the tidal current obtained from finite element solutions 2014 (FES2014). We found that tidal current obtained from ADCIRC model has a very good agreement with FES2014. Moreover, tidal current speed in the vicinity of Bali and Lombok islands could reach up to 3.8 m/s. As a consequence, tidal current power could exceed 10.98 kW / m 2 with assuming that turbine efficiency is about 0.39.