Current Energy Conversion Research Articles

Numerical study on ocean current energy converter by tandem cylinder with different diameter using flow-induced vibration

The use of bluff body, such as a circle cylinder in vortex-induced vibration (VIV) to convert current energy into electrical energy is a relatively under-utilized power generation technology with broad application prospects. To develop current energy on a 3 dimensional and enhance the synergy of the converter, the vortex-induced vibration power generation device needs to be composed of double cylinders or multiple cylinders. At present, experts and scholars have mainly studied the VIV characteristics of double cylinders in detail, but there are few studies on the energy conversion characteristics of them. To solve this problem, based on the vibration characteristics of double cylinders with equal diameters and unequal diameters, the energy conversion characteristics of them are compared and analyzed, in pursuing of the optimal parameter combination. The results show that the energy capture power of double cylinders with diameter ratio d/D = 0.6 is higher and more stable. Choosing a double cylinder with diameter ratio d/D = 0.6 and spacing ratio G/D = 3–5 can obtain more water flow energy. When the spacing ratio G/D < 3, the double cylinder with the diameter ratio d/D = 0.4 can obtain higher energy harvesting efficiency. When the spacing ratio G/D>3, the double cylinder with the diameter ratio d/D = 0.8, cylinders can obtain a higher energy harvesting efficiency. When the reduced velocity is set in the range of Ur ∈ (4, 7), the double cylinders’ energy harvesting efficiency is higher, and the water flow energy can be converted efficiently.

Dynamics analysis of the power train of 650 kW horizontal-axis tidal current turbine

Power trains are an important component of the tidal current energy conversion systems; however, the variable drive-torque and unbalanced moments produced by flow shear and turbulence cause power trains to vibrate. When the scale of the tidal current turbine increases, the vibration problem becomes prominent. The dynamic characteristics of power trains are complex. In this study, the power train of a 650 kW horizontal-axis tidal current turbine was studied. The power train adopted a low-speed-ratio semi-direct drive scheme proposed by Zhejiang University. A mathematical model of the power train was constructed. The influence of external excitations (including tidal current condition, unbalanced moments, and internal excitation) on dynamic characteristics was studied using simulations and sea trials. The simulation results showed that the radial and torsional vibrations of the low- and the high-speed shafts increased when the tidal current velocity increased. The fluctuation range of the bearing load increased under increases in the pitch and yaw moments. The meshing motion of the planetary gear plays a leading role in the vibration of low- and high-speed shafts. The power train model was validated by comparing the results of the experiment and simulation.

Underwater Noise Measurements around a Tidal Turbine in a Busy Port Setting

Acoustic emissions from current energy converters remain an environmental concern for regulators because of their potential effects on marine life and uncertainties about their effects stemming from a lack of sufficient observational data. Several recent opportunities to characterize tidal turbine sound emissions have begun to fill knowledge gaps and provide a context for future device deployments. In July 2021, a commercial-off-the-shelf hydrophone was deployed in a free-drifting configuration to measure underwater acoustic emissions and characterize a 25 kW-rated tidal turbine at the University of New Hampshire’s Living Bridge Project in Portsmouth, New Hampshire. Sampling methods and analysis were performed in alignment with the recently published IEC 62600-40 Technical Specification for acoustic characterization of marine energy converters. Results from this study indicate acoustic emissions from the turbine were below ambient sound levels and therefore did not have a significant impact on the underwater noise levels of the project site. As a component of Pacific Northwest National Laboratory’s Triton Field Trials (TFiT) described in this Special Issue, this effort provides a valuable use case for the IEC 62600-40 Technical Specification framework and further recommendations for cost-effective technologies and methods for measuring underwater noise at future current energy converter project sites.

Capabilities of an Acoustic Camera to Inform Fish Collision Risk with Current Energy Converter Turbines

A diversified energy portfolio may include marine energy in the form of current energy converters (CECs) such as tidal or in-river turbines. New technology development in the research stage typically requires monitoring for environmental effects. A significant environmental effect of concern for CECs is the risk of moving parts (e.g., turbine blades) colliding with animals such as fishes. CECs are installed in energetic locations in which it is difficult to operate sensors to fulfill monitoring requirements for informing collision risk. Collecting data (i.e., about blade strikes or near-misses) that inform interactions of fishes with CECs is usually attempted using active acoustic sensors or video cameras (VCs). Limitations of low-light conditions or water turbidity that preclude effective use of VCs are overcome by using high-resolution multibeam echosounders (or acoustic cameras (ACs)). We used an AC at two sites to test its ability to detect artificial and real fish targets and determine if strike, near-miss, and near-field behavior could be observed. Interactions with fish and artificial targets with turbines have been documented but strike confirmation with an AC is novel. The first site was in a tidal estuary with a 25 kW turbine and water clarity sufficient to allow VC data to be collected concurrently with AC data showing turbine blade strike on tethered artificial fish targets. The second site was a turbid, debris-laden river with a 5 kW turbine where only AC data were collected due to high water turbidity. Data collection at the second site coincided with downstream Pacific salmon (Oncorhynchus spp.) smolt migration. Physical fish capture downstream of the turbine was performed with an incline plane trap (IPT) to provide context for the AC observations, by comparing fish catches. Discrimination between debris and fishes in the AC data was not possible, because active movement of fishes was not discernable. Nineteen fishes were released upstream of the turbine to provide known times of possible fish/turbine interactions, but detection was difficult to confirm in the AC data. ACs have been used extensively in past studies to count large migratory fish such as Pacific salmon, but their application for small fish targets has been limited. The results from these two field campaigns demonstrate the ability of ACs to detect targets in turbid water and observe blade strikes, as well as their limitations such as the difficulty of distinguishing small fishes from debris in a high-energy turbid river. Recommendations are presented for future applications associated with CEC device testing.

Low‐Dimensional Electrocatalysts for Acidic Oxygen Evolution: Intrinsic Activity, High Current Density Operation, and Long‐Term Stability

AbstractProduction of green hydrogen (H2) by water electrolysis is important for achieving the global mission of carbon neutrality. For this, acidic water electrolysis with a higher current density operation and energy conversion efficiency compared with alkaline water electrolysis has attracted much attention. The four‐electron‐transfer oxygen evolution reaction (OER) limits the overall efficiency of water electrolysis devices. In recent years, low‐dimensional OER catalysts have been extensively explored to increase the overall efficiency of such devices, but most of them work well only at low current density and show unsatisfied long‐term stability. In this review, recent progress in acidic OER is discussed and three aspects including intrinsic activity, high current density operation, and long‐term stability are focused upon. Strategies to improve these aspects including surface chemistry engineering, constructing porous structure, and protecting the active sites’ are comprehensively reviewed. Finally, prospects for developing high‐performance catalysts with high current density operation and long‐term stability for industrial applications are proposed.

Time-delay closed-loop control of an infinitely variable transmission system for tidal current energy converters

This paper presents a nonlinear closed-loop control combined with an integral time-delay feedback control of an infinitely variable transmission (IVT) to adjust its speed ratios with respect to variable input speeds that are induced by variable tidal speeds. A speed ratio closed-loop control for the IVT system involves a forward speed controller and a crank-length controller for different operating conditions of a tidal current energy converter (TCEC). The time-delay feedback control is designed to reduce speed fluctuations of output speeds of the IVT to track a desired output speed. Experimental investigation for tidal current energy applications was carried out to test validity of the time-delay feedback control of the IVT system. Rotation speeds of the TCEC based on measured variable tidal current data are used as control inputs for control experiments of the IVT system. An instrumented rotation speed measurement system of the IVT system is deployed so that quantities needed for the time-delay control variable can be measured. Experimental results of variable tidal speeds show that speed ratios of the IVT with the proposed control strategy can achieve excellent tracking responses for the desired constant output speed and reduce speed fluctuations of output speeds of the IVT.

Performance Assessment of Two Horizontal Shroud Tidal Current Energy Converter using Hydraulic Experiment

In this study, the two horizontal shroud tidal current energy converter, which can generate power even under low flow speed conditions, was developed. In order to determine the shape of the shroud system, a three-dimensional numerical simulation test was conducted, and a 1/6 scale down model was made to perform a hydraulic model experiment. The hydraulic model experiment was performed under four flow conditions, and the flow speed, torque, and RPM were measured for each experimental case. As a result of the numerical simulation test, it was found that the flow speeds passing through the nozzle were increased by about 2~3 times in the cylinder, and when the extension ratio was 2:1, the highest flow speed was shown. In addition, it was found that the flow speeds increased 2.8 times when the diameter ratio between the nozzle and the cylinder was 1.5:1. Meanwhile, as a result of the hydraulic model experiment, it was found that when the tip speed ratio was between 1.75 and 2, the power coefficient was 0.32 to 0.34.

Optimization design of GaAs-based betavoltaic batteries with p–n junction and Schottky barrier structures

This paper presents the calculation model and the optimization design of the GaAs-based betavoltaic batteries with p–n junction and Schottky barrier structures. First of all, by using the Monte Carlo code, the transport process and energy deposition distribution of the source beta particles in the GaAs material are simulated. The relationships between the output parameters of batteries and the physical parameters of energy converter such as p–n junction depth, Schottky metal thickness, depletion region width and doping concentrations are discussed through the numerical calculation. For the GaAs p–n junction battery, the maximum output power density of 0.135 can be achieved when the junction depth is x j = 0.05 , the doping concentrations are and . Meanwhile, the short-circuit current density, open-circuit voltage, filling factor and energy conversion efficiency are 0.254 , 0.638 V, 83.3% and 2.63%, respectively. Among the selected metals of Au, Pd, Ni and Pt for the GaAs Schottky barrier diodes, the Pt-GaAs battery has the best output performance due to its large work function. The maximum output power density of 0.169 can be achieved when a 20 nm thick Schottky metal Pt is selected and the doping concentration is . The associated output parameters of the battery are 0.234 , 0.835 V, 86.5% and 3.29%, respectively.

Hydrodynamic and Morphodynamic Influences from Ocean Current Energy Conversion Sites in the South–Southeastern Brazilian Inner Shelf

As marine renewable resources begin to become a feasible energy source, it becomes crucial to investigate the nearshore impact of hydrodynamic and morphodynamic processes. As part of the implementation of turbines in the numerical modeling environment of Telemac-3D and Sisyphe modules, we conducted a 10-year run to evaluate nearshore impacts of turbines in the flow. We used five criteria to define viable locations. Turbines sites were added to a conversion energy model coupled into the hydrodynamic model in order to develop properly the flow changes towards the energy conversion process. The results revealed that in the three chosen spots, turbines were not converting equally the current energy within the site. In fact, the turbines located on the outer side of the farm developed greater conversion rates. This impacted the nearshore in the following ways: (1) the decrease in the currents intensity that generates strong adjustments in the water column, breaking the natural pattern of vertical circulation; (2) development of lateral flows that in time affects the bottom dynamics and results in changes in sediment deposition; and (3) increase in bedload transport rates around the turbine’s field due to divergence in the flow. The idealized turbines sites produced 1,775 GWh in 10 years, which could provide electricity to 54,181 residences during this period.

Ultra-low friction self-levitating nanomagnetic fluid bearing for highly efficient wind energy harvesting

Wind energy provides one of the most sustainable and cleanest forms of energy conversion to tackle the biggest global concern of CO2 emissions from the use of fossil fuels. It is also challenging to build an efficient energy harvester to minimize the losses at several levels during the electrical energy conversion. Herein, we have proposed a novel wind energy harvester that capitalizes on the self-levitation nanomagnetic fluid bearing. The magnetic fluid contains magnetic nanoparticles which sticks to the magnets forming bearing around the edges and providing magnets a passive levitation, which eventually results in an ultra-low frictional surface between the permanent magnet and bottom support surface. The motion of the magnets attached to the rotating fan-shaft assembly driven by the blades and input blowing wind relative to the fixed coils induces a current in the coil. The mechanism has been effectively utilized to develop a highly efficient prototype wind energy harvester, which runs at a very low wind speed of 2 m/s. The prototype wind energy harvester promises to generate 2.59Watt power with an efficiency of 26% at a gentle wind speed (4.5 m/s). Simulations are conducted to support the experimental results of the prototype and the simulation model is further extended to upscale the harvested power for more realistic applications. Our invention has a tremendous potential to produce highly efficient wind energy conversion at a large scale by solving the major problem in the current wind energy conversion systems.

Experimental implementation of voltage and frequency regulation in DFIG connected to a dc-link for marine current energy conversion system

Experimental implementation of voltage and frequency regulation in DFIG connected to a dc-link for marine current energy conversion system

A Review of Modeling Approaches for Understanding and Monitoring the Environmental Effects of Marine Renewable Energy

Understanding the environmental effects of marine energy (ME) devices is fundamental for their sustainable development and efficient regulation. However, measuring effects is difficult given the limited number of operational devices currently deployed. Numerical modeling is a powerful tool for estimating environmental effects and quantifying risks. It is most effective when informed by empirical data and coordinated with the development and implementation of monitoring protocols. We reviewed modeling techniques and information needs for six environmental stressor–receptor interactions related to ME: changes in oceanographic systems, underwater noise, electromagnetic fields (EMFs), changes in habitat, collision risk, and displacement of marine animals. This review considers the effects of tidal, wave, and ocean current energy converters. We summarized the availability and maturity of models for each stressor–receptor interaction and provide examples involving ME devices when available and analogous examples otherwise. Models for oceanographic systems and underwater noise were widely available and sometimes applied to ME, but need validation in real-world settings. Many methods are available for modeling habitat change and displacement of marine animals, but few examples related to ME exist. Models of collision risk and species response to EMFs are still in stages of theory development and need more observational data, particularly about species behavior near devices, to be effective. We conclude by synthesizing model status, commonalities between models, and overlapping monitoring needs that can be exploited to develop a coordinated and efficient set of protocols for predicting and monitoring the environmental effects of ME.

Energy-based fuzzy supervisory non integer control for performance improvement of PMSG-Based marine energy system under swell effect and parameter uncertainties

Permanent magnet synchronous generators (PMSG) based marine current system has gained much attention due to several advantages such as high predictability, rapid response and high-power density. The performance and power integration efficiency of the above-mentioned system greatly rely on the applied control system. However, system nonlinearities, parameter variations make the controller design process a challenging task. This paper introduces passivity based fuzzy fractional order proportional integral and derivative (PID) controller for PMSG based marine current energy conversion system under swell effect and parameter uncertainties. The proposed approach combines a new passivity-based current control (PBCC) with a fuzzy fractional order PID control (FFO-PID). The proposed method is tested under the swell effect and parameter uncertainties using MATLAB/Simulink. The proposed controller exhibits robustness against swell effect, parameter changes and shows fast convergence of the system states. Furthermore, the exponential stability and error convergence of the proposed controller is analytically justified.

Study and Design of a DC/AC Energy Converter for PV System Connected to the Grid Using Harmonic Selected Eliminated (HSE) Approach

Nowadays, distributing network-connected photovoltaic (PV) systems are expanded by merging a PV system and a Direct Current (DC)/Alternating Current (AC) energy converter. DC/AC conversion of PV energy is in great demand for AC applications. The supply of electrical machines and transfer energy to the distribution network is a typical case. In this work, we study and design a DC/AC energy converter using harmonic selective eliminated (HSE) method. To this end, we have combined two power stages connected in derivation. Each power stage is constituted of transistors and transformers. The connection by switching of the two rectangular waves, delivered by each of the stages, makes it possible to create a quasi-sinusoidal output voltage of the inverter. Mathematical equations based on the current-voltage characteristics of the inverter have been developed. The simulation model was validated using experimental data from a 25.2 kWp grid-coupled (PV) system, connected to Gridfit type inverters. The data were exported and implemented in programming software. A good agreement was observed and this shows all the robustness and the technical performances of the energy converter device. It emerges from this analysis that the inverter output voltage and the phase angle thus simulated are very important to control in order to orientate the transfer of the power flow from the continuous cell to cell to the alternating part. Simulated and field-testing results also show that increases in the value of the modulation factor (m) for low power output are highly significant. This study is an important tool for DC/AC inverter designers during initial planning stages. A short presentation of the design model of the inverter has been proposed in this article.

The Disk-Magnet Electromagnetic Induction Applied to Thermoelectric Energy Conversions

The thermoelectric energy conversion technique by employing the Disk-Magnet Electromagnetic Induction (DM-EMI) and improved DM-EMIs is shown, and possible applications to heat engines as one of the energy harvesting technologies are also discussed. The idea is induced by integrating irreversible thermodynamical mechanism of a water drinking bird with that of a Stirling engine, resulting in thermoelectric energy generation different from conventional heat engines. The current thermoelectric energy conversion with DM-EMI can be applied to wide ranges of temperature differences. The mechanism of DM-EMI energy converter is examined in terms of axial flux magnetic lines and categorized as the axial flux generator. It is useful for practical applications to macroscopic heat engines such as wind, geothermal, thermal and nuclear power turbines and heat-dissipation lines, for supporting thermoelectric energy conversions. The technique of DM-EMI will contribute to environmental problems to maintain clean and susceptible energy as one of the energy harvesting technologies.

Photovoltaic performance of novel Perovskite/organic integrated solar cells with high efficiency and high stability

Perovskite/organic integrated solar cell possesses the perovskite active layer with wide band gap that can absorb high energy photons, while the lower energy photons can pass through the perovskite layer and be absorbed by the organic active layer with narrow band gap. By introducing a Bulk heterojunction (BHJ) consisting of perovskite materials and near-infrared (NIR) organic semiconductor materials in the visible light region, the enhanced short-circuit current density of organic cells can be obtained while maintaining the high open-circuit voltage of perovskite-type devices. We prepare perovskite/organic integrated solar cells by directly deposing the narrow band gap organic active layer PC&lt;sub&gt;20&lt;/sub&gt;BDTDPP:PC&lt;sub&gt;71&lt;/sub&gt;BM on CH&lt;sub&gt;3&lt;/sub&gt;NH&lt;sub&gt;3&lt;/sub&gt;PbI&lt;sub&gt;3&lt;/sub&gt;. The CH&lt;sub&gt;3&lt;/sub&gt;NH&lt;sub&gt;3&lt;/sub&gt;PbI&lt;sub&gt;3&lt;/sub&gt;/PC&lt;sub&gt;20&lt;/sub&gt;BDTDPP:PC&lt;sub&gt;71&lt;/sub&gt;BM integrated solar cell can widen the perovskite absorption spectra, thereby increasing the near-infrared light absorption. The results show that the short-circuit current density of the integrated solar cell increases to 23.90 mA/cm&lt;sup&gt;2&lt;/sup&gt;, the optical response is widened to 920 nm, the external quantum efficiency reaches 85% in the visible region, and is close to 55% in the near infrared region (800–900 nm), and the energy conversion efficiency of the device increases up to 20.30%. The integrated current density, quantum efficiency, and energy conversion efficiency of the best device are the highest values ever reported in perovskite/organic integrated solar cells. At room temperature of 25 ℃ and humidity of 30%, the efficiency of the device decreases to 95% of the original efficiency after 350 h, showing excellent device stability. The results show that it is an effective method to improve the near-infrared absorption of perovskite solar cells and improve the performance of perovskite/organic integrated solar cells through material combination and device structure optimization. The present research provides theoretical guidance and experimental basis for the development of perovskite/ organic integrated cells with high efficiency and stability in the future.

A Study on the Impact of Energy Conversion Policy in Response to Climate Change in Ports

Purpose - With the government s energy conversion policy response to climate change, coal-fired power plants are scheduled to be closed. This study examines the impact of the closure of coal-fired power plants located in and around ports in terms of port of entry, port workers, cargo volume, and port industries. Design/Methodology/Approach - This study examines the current status of ports in terms of port entry, workers, and port volume based on the study of recent coal-fired power plants that are scheduled to be closed due to the government s energy conversion policy. Then, the impact of coal-fired power plant closure was estimated with regard to port volume and the employment of port workers. Findings - Ports which have a high proportion of bituminous coal including Taean port, Samcheonpo port, Hadong port, and Boryeong port are expected to see decreases in cargo volume up to 60%. As a result, a negative affect on ports specifically port workers, port loading/unloading business, and preliminary businesses is expected. To successfully respond to these changes, broadly-based countermeasures are required. Research Implications - This study examines the impact of coal-fired power plants on ports and provides policy suggestions for port authorities to change the perception of the current energy conversion policy. Port authorities need to establish a communication channel for proper conversion. In addition, the national and local governments must utilize sites created by the reclamation of public water surface to produce opportunities for proper conversion.

Polyketone Functionalization: New Ways to Anion Conducting Polymers

Ion-exchange membranes (IEMs) are at the core of many energy storage and conversion devices, such as fuel cells and redox flow batteries, being responsible for the migration of ionic species, separating the fuel stocks, and providing support to the electrode assemblies. For practical applications they are required to possess not only high ionic conductivity, but also specificity, thermal stability, long lifetime, and electrical insulation. The preparation of polymeric materials with such high-performance properties is still challenging and can lead to high prices, hindering their widespread use in energy conversion technologies. This is even more arduous when considering polymers to be used in anion conducting membranes, due to the need for the extra chemical stability and ability to withstand alkaline conditions at high temperatures for long periods of time [1].Polyketones are known to be high performance thermoplastic polymers with applications ranging from fire-retardants film coatings, packaging, and fibers, resulting from their high thermal and chemical stability. They can be obtained in high yields by copolymerization of inexpensive and readily available feedstocks such as ethylene and carbon monoxide. Our group proved that polyketones with alternating 1,4-dicarbonyl repeating units constitute an ideal starting point to access a wide class of modified polymers by simple Paal-Knorr cyclization, to gain pyrrole-N-bound functional groups stemming from the aliphatic backbone [2].This is a new account on our research on the ion conducting polymeric materials derived from polyketone, obtained by reaction with variously functionalized amines, and their easy conversion to anion exchange materials. The effect of reaction conditions on their thermal properties and chemical stability in alkaline media has been studied, and their conductivity in a wide range of frequencies assessed by broadband electric spectroscopy to shed light on the conduction mechanisms.The proposed conducting polymers combine the thermal stability of the aliphatic polyketone structure with the chemical flexibility given by the groups derived from functionalized amines branching out, proving to be highly tailorable, with possible applications in current energy conversion technologies. Acknowledgements: The authors wish to thank the Research Projects of Relevant National Interest (PRIN 2017) of the Italian Ministry of Education, University and Research “Novel Multilayered and Micro-Machined Electrode Nano-Architectures for Electrocatalytic Applications (Fuel Cells and Electrolyzers)” (Prot. 2017YH9MRK) and the SID2020 Project of the Department of Industrial Engineering, University of Padova “A New frontier in Hybrid Inorganic-Organic Membranes for Energy Conversion and Storage Devices” (Prot. BIRD201244) for funding.

Study the Effect of Doping Ratios the n-type Silicon SWCNTm / PLA on Solar Cell Efficiency

In this work, SWCNTm / PLA was employed as a fundamental compound, and nanofilms of SWCNTm / PLA were coated onto n-kind silicon substrates. The spin coated technique was used to determine the thickness in (SWCNTm / PLA). Various thicknesses in (SWCNTm / PLA) (162, 100, and 82) n.m are procured via at vary spin spades (1500, 3000, and 4500) r.pm.' light (100 mw/cm2) and dark (J-V) requirements were used to produce the current denisity-volt features. The characteristics of the photovoltaic models namely, open circuit voltage (Voc), short–circuit current density (Jsc), foll ratio (FF), and energy conversion efficiency (ɳ) were calculated. The better thickness of (SWCNTm / PLA) films for highest (ɳ), (Jsc) and greatest power point presentation' is 100 n m, according to our findings.

Bidirectional Impulse Turbine With Spiral Flow Collector for Tidal Energy Conversion

Abstract In order to make use of ocean renewable energy, a combination system of a bidirectional impulse turbine and a bidirectional flow collector for tidal current energy conversion is investigated in this paper. It is the advantage that this turbine system does not need an operation of orientation change according to the reversal of regular tidal orientation when fixed on the seabed. The experimental investigations by using both a circulating water tank and a towing tank showed that the turbine power output could be increased by adopting the flow collector proposed in this study. Then the flow collector with a fixed spiral vane named spiral flow collector was investigated by both a circulating water tank test and computational fluid dynamics (CFD) analysis. The experimental result of the spiral flow collector showed that the performance improvement was found on the increase of axial velocity in the turbine which contributed to the increase of the turbine power output. The results of CFD analysis showed that 180 deg of the skew angle of the fixed spiral vane was suitable in view of the angular moment at the turbine inlet in this case.