Primary Conversion Efficiency Research Articles

Finding the best shape of floating wave energy converters for different primary geometries: Experimental and numerical investigations

This research aimed to identify the optimal geometry for maximizing wave energy extraction from wave energy converters (WECs) by employing different primary geometries of floating bodies (specifically, cube, cylinder, and sphere). Laboratory experiments were conducted using a wave tank to generate waves with varying characteristics. The floats were subjected to waves of different wave conditions, including height (4 cm, 6 cm, and 9 cm) and frequency (0.9 Hz and 0.83 Hz). Multiple probes and sensors were used to collect experimental data. The results revealed that when hit by a wave with a height of 9 cm and a frequency of 0.9 Hz, the rectangular cube experienced an average displacement of 12 cm and 14 cm along its length, with the same weight and draft, respectively. Furthermore, comparisons of the experimental data across different scenarios indicated that the rectangular cube, elongated perpendicular to the incident waves, performed well in most of the test cases. The efficiency of primary wave energy conversion was evaluated for all floated bodies and wave conditions, encompassing a range of values from 0.02 to 0.34. Additionally, numerical simulations of wave and float displacement demonstrated good agreement with the experimental observations.

Hybrid geothermal-fossil power cycle analysis in a Polish setting with a focus on off-design performance and CO2 emissions reductions

Growing demand for electricity due to economic development contributes to increased greenhouse gas production, especially CO2. However, emissions can be limited by enhancing the efficiency of primary energy conversion, such as integrating geothermal energy into coal-fired power plants. Therefore, this paper proposes replacing conventional feed-water heaters with geothermal preheaters to create a hybridized system. This study was based on a numerical model validated at a selected Polish power unit. The model was subsequently calibrated for off-design conditions to facilitate partial load analysis. The obtained characteristics outperformed those of the non-hybrid unit, generating over 18 MW of electric power output. Such an improvement could potentially boost the unit's net efficiency by more than 2.6 %. This enhancement is significant as power units typically operate under part load for approximately 90 % of the time, hence the need to evaluate the performance characteristics of hybridized units in those states. Furthermore, the research outlines the potential decrease in the plant's CO2 emission factor, with reductions reaching up to 6.5 % under off-design conditions. Based on a gap analysis of the existing literature, this paper's comprehensive partial load evaluation serves as a new addition to research on hybridized systems.

Effects of Exogenous Melatonin on the Growth and Physiological Characteristics of Ginkgo biloba L. under Salinity Stress Conditions

Ginkgo (Ginkgo biloba L.) is a cherished relic among plants, commonly planted as a street tree. However, it faces cultivation challenges due to escalating soil salinization and widespread snowmelt application. Therefore, this study used 4-year-old Ginkgo seedlings to investigate how exogenous melatonin at varying concentrations affects seedling growth and physiology under salinity stress. The results revealed that appropriate melatonin concentrations (0.02, 0.1 mmol·L−1) significantly mitigated leaf yellowing under different NaCl stress levels. Furthermore, they increased ground diameter, current-year branch growth, relative water concentration, free proline, and soluble sugars in leaves. Melatonin also reduced electrolyte exudation rates, flavonoids, and malonic dialdehyde concentration, while enhancing peroxidase and superoxide dismutase activities. This led to reduced chlorophyll content, photosynthetic rate, stomatal conductance, and transpiration rate, stabilizing intercellular CO2 concentration, preserving photosynthetic structures, and enhancing photosynthetic rates. Additionally, the decline in the photosynthetic electron transport rate, the effective photochemical quantum yield of PSII, and the potential efficiency of primary conversion of light energy of PSII was alleviated. Minimal fluorescence and the non-photochemical quenching coefficient also improved. However, high melatonin concentration (0.5 mmol·L−1) exacerbated salinity stress. After analyzing composite scores, the 0.02 mmol·L−1 melatonin treatment was most effective in alleviating NaCl stress, while the 0.5 mmol·L−1 treatment intensified physiological stress under 200 mmol·L−1 NaCl stress. Principal component analysis and correlation analysis identified seven physiological indicators (photosynthetic rate, transpiration rate, photosynthetic electron transport rate, minimal fluorescence, superoxide dismutase, free proline, and chlorophyll a) and three growth indicators (ground diameter, branch length, and current-year branch thickness) as key markers for rapid salinity stress assessment in Ginkgo. These findings are crucial for addressing challenges associated with snowmelt’s impact on roadside Ginkgo trees, expanding planting areas, and breeding exceptional salt-tolerant Ginkgo varieties.

Experimental Proof-of-Concept of a Hybrid Wave Energy Converter Based on Oscillating Water Column and Overtopping Mechanisms

This paper presents the results of laboratory tests on a hybrid wave energy converter concept, the O2WC (Oscillating-Overtopping Water Column) device. The proposed device aims at providing an alternative to the classical OWC concept, storing part of the wave energy of the highly energetic sea states in a second chamber at atmospheric pressure, through overtopping phenomena. In this way, the maximum airflow rate and air pressure in the OWC chamber are reduced, possibly aiding the safe functioning of the air turbine, and allowing to exploit the excess of energy instead of dissipating it through by-pass valves. The performance of the device is investigated under different incident wave conditions, for different design parameters. The height of the overtopping threshold from the second chamber of the device which allows to maximize the performance has been selected. Results show that the decrease of the primary conversion efficiency of the OWC component of the device caused by the decreased air pressure in the OWC chamber can be partially compensated by the additional energy stored in the overtopping chamber of the O2WC device. Overall, the studied O2WC device has capture width ratio values ranging between 0.3 and 0.7.

Evaluation of the effects of optimization of gas boiler burner control by means of an innovative method of Fuel Input Factor

In the course of the research, the authors diagnosed the necessity to constantly search for solutions increasing the efficiency of converting primary energy into useful energy, in particular in heat sources equipped with systems powered by gaseous fuel. This is especially important in the EU countries, where on average approx. 46% of heat is produced by means of natural gas. This problem is particularly important in the context of the growing requirements to reduce greenhouse gas emissions and the guidelines related to the decarbonization plan for all European Union countries. Therefore, the authors conducted operational tests of the existing heat sources based on low-temperature gas boilers, the purpose of which was to identify and analyze the possibility of their optimization, with particular emphasis on increasing the efficiency of primary energy conversion and reducing emissions of such pollutants as greenhouse gases. The work uses a method of practical optimization, which makes use of measurement data in order to identify the parameters of gas boilers which are susceptible to improvement, and then improves these parameters. The several-year-long research was carried out with various configurations of energy sources in various technological systems, while the final analysis covered operating data from two gas boiler houses collected over 200 full days, in which measurements were carried out continuously to ensure high quality of measurement data. The article presents an assessment of the efficiency of gas boiler houses conducted by means of a fuel input coefficient (FIF) developed by the authors. The influence of selected factors on the efficiency of heat generation processes was also analyzed, including: external temperature, the amount of domestic hot water consumption, and above all, methods of controlling heat source devices. The effects were assessed using the FIF. It has been shown that the method of comparing the operation of heat sources based on the fuel input coefficient (FIF) is an effective diagnostic tool to verify the correctness of boiler room operation, and that appropriate settings in boiler operation can significantly affect the energy efficiency of sources and reduce greenhouse gas emissions.

Effects of air chamber and curtain wall geometries on energy conversion performance in a fixed oscillating water column-type wave energy converter

Abstract An oscillating water column-type wave energy extractor is composed of an air chamber, an air turbine and a generator. The energy conversion process is compounded of the primary conversion in an air chamber and the secondary conversion of an air turbine. The oscillating water column-type wave energy extractor is considered to be safe even under dirty weather conditions. For societal implementation, there is a need to make a design method which can consider the water surface motion, the pressure fluctuation in an air chamber, the rotations of an air turbine and a generator. At here, the authors carried out the 2-dimensional wave tank tests using the model oscillating water column equipped with the impulse turbine and a generator to obtain the experimental data needed to make this design method. In the experiments, the effects of the air chamber and curtain wall geometries on energy conversion performance in regular wave conditions were investigated. As the results, it is noticed that the geometry of the curtain wall and the vortex shedding from the corners of curtain wall affect the primary conversion efficiency.

Efekti primjene prirodnog gasa pri sagorijevanju čvrstih goriva u letu – reburning tehnologija

The energy transition basically implies a phased and significant reduction in the use of fossil fuels, until the final cessation of use in the near future. Renewable energy sources and alternative fuels are an increasingly important part of the energy transition. At the same time, it is necessary that energy systems increase energy efficiency and environmental acceptability. In this regard, great efforts are being made to expand the portfolio of primary fuels in existing large energy systems, e.g. thermal power plants. Therefore, today in large boilers, in order to reduce NOx emission, staged air supply for combustion is inevitably used as the primary measure in the furnace (air staging). In addition to the previous measure, there are many examples of staged fuel supply to the combustion zone (fuel staging), and still a small number of examples of the use of third or additional fuel, e.g. application of biogas or natural gas in combustion of pulverized solid fuels (reburning technology). General, these measures simultaneously increase the efficiency of primary energy conversion from fuel and reduce the emission of undesirable components into the environment. The results of this paper show the extent to which the effects of the use of natural gas in the co-firing of Bosnian coal and waste wood biomass are expressed. In this process there is an additional reduction of NOx in proportion to the share of gas - at a process temperature of 1350 °C and at 10% of the energy content of gas in combustion with coal, compared to emissions without additional fuel, recorded reduction of NOx emissions by more than 250 mg/mn 3.

Experimental study on a bottom corner of the floating WEC

The study is investigating the effects of various back bottom corner geometries of the Backward Bent Duct Buoy floating oscillating water column at different wave height conditions. Three BBDB with different geometries of the back bottom corner, namely curved, square, and inclined were used. The 3-dimensional wave basin was used to generate the regular wave spectrum with wave heights of 0.05 m–0.15 m and wave periods of 1 s–5 s. It demonstrated the characteristics inside the air column of each BBDB were significantly influenced by the back bottom corner geometry. The results showed that the curved bottom corner produced the highest water elevation, water column chamber pressure, and outlet air flow rate. This observation was due to the curved geometry that reduced the viscous energy loss from the body surface and water. Moreover, it was found that the curved bottom corner produced the higher primary conversion efficiency compared to the square and inclined bottom corner. Despite the characteristics inside air column, it was found that the resonance frequency contributed to the maximum value of the primary conversion efficiency regardless of the various geometries of the back bottom corner.

Melatonin alleviates imidacloprid phytotoxicity to cucumber (Cucumis sativus L.) through modulating redox homeostasis in plants and promoting its metabolism by enhancing glutathione dependent detoxification

Melatonin (Mel), a powerful antioxidant that has the ability to regulate physiological and biochemical processes in plants under abiotic stresses. However, its roles in pesticide detoxification is poorly understood. Herein, selecting leaf spraying insecticide imidacloprid (IMD) as the model, we demonstrated the detoxification mechanism underlying root pretreatment of Mel on IMD in cucumber. IMD treatment affected the primary light conversion efficiency of photosystem II (Fv/Fm), reduced the quantum yield, and increased hydrogen peroxide and superoxide anions contents as well as the levels of membrane lipid peroxidation, indicating that excessive IMD treatment induces oxidative stress. Nonetheless, by increasing the appropriate levels of exogenous Mel, the photosynthesis of cucumber under IMD treatment reached the control levels, effectively removing reactive oxygen species. Furthermore, the content and ratio of ascorbate (AsA) and glutathione (GSH) were decreased under IMD treatment; Mel treatment enhanced the AsA/DHA and GSH/GSSG ratios, as well as the activities of MDHAR, DHAR and GR, suggesting that Mel could alleviate oxidative stress of cucumber treated with IMD by regulating the ascorbic acid-glutathione cycle. Importantly, IMD degradation rate and glutathione S-transferase (GST) activity increased after Mel treatment. The levels of transcripts encoding antioxidant enzymes GPX and GST (GST1,2 and 3) were also increased, indicating that Mel accelerated IMD degradation. These results suggest that Mel plays an important role in the detoxification of IMD by promoting GST activity and transcription and the AsA-GSH cycle, thus providing an approach for plants to reduce IMD residue through the plant's own detoxification mechanism.

Use of the Mps method to estimate the energy conversion efficiency of the owc-wec (first report)

In recent years, ocean renewable energy has been increasingly in the spotlight due to global warming and energy issues etc. Research on ocean renewable energy devices is being carried out by many researchers, companies and countries. Additionally, many sea tests are being carried out by countries with real sea test sites. Ocean renewable energy devices still need to research about a power generation method, an energy conversion efficiency and costs etc. In this paper, Authors focus on the oscillating water column type wave energy converter (called below OWC-WEC). It is considered that the OWC-WEC is useful because a movable part which becomes a cause of trouble is few and can also be used as a breakwater device. In this study, the MPS (Moving Particle Semi-implicit) method is applied to the performance analysis of the OWC-WEC. It is because the performance analysis by various parameters and the reduction of an experimental cost is needed. In this paper, these following items are shown; 1) the development of analysis program code which can simulate the multiphase flow by three phases of gas, liquid and solid, 2) the development of air duct model, 3) verification of the usefulness of the improved MPS program code and 4) verification of the applicability to the performance analysis of the OWC-WEC. This program code was applied to the simulation of the fixed type OWC-WEC. Following this, the reproducibility of the primary conversion efficiency of the fixed type OWC-WEC by this program code was verified and discussed. Finally, the usefulness and applicability of this program code were discussed and recommendations for future work were made.

Procedure to select combined heating and hot water systems: An expeditious cost optimality approach

The European Union has proposed a common methodology to identify energy-efficient measures with the minimum global cost throughout the lifecycle. It is known that the energy impact of a specific measure is influenced by other measures in the same package, which affect its profitability. For this reason, the cost-optimal package cannot be a simple combination of individual cost-optimal retrofitting measures. Thus, to define a cost optimal solution, the energy performance and the global cost of a large number of packages need to be calculated and analysed.To overcome the expensive computational effort of this type of study, this work proposes an expeditious procedure for selecting the optimal energy source for heating and domestic hot water (DHW) service generation as a function of the following variables: energy needs and costs, initial investment, primary energy conversion factors and efficiency of energy systems. The method was applied to a reference dwelling in the Portuguese building stock. With the expeditious cost optimality approach, once an energy system configuration has been determined, an estimation of the cost-optimal package can be established as the sum of the most profitable options for each element.

Flow Field Analysis around the Forced Oscillating Plate under the Free Surface by Vortex Method — 2D Viscous Fluid Analysis Based on Fundamental Equations Using Velocity and Vorticity as Unknown Quantities —

Fins are often installed on submerged parts of a floating structure to reduce its motion in waves. It is expected that its kinetic energy is reduced by vortex generated from fins because its energy is converted into vortex energy around fins. To utilize this method, numerical analysis method for viscous fluid is required to decide the optimum shape and installation position of these fins. For this problem, authors proposed 2D numerical analysis method in time domain, using vortex method that can consider the fluid viscosity and calculated motions and primary conversion efficiency of a floating OWC-type wave energy converter in waves. In this method, unknown quantities are vorticity and stream function. As a next step, vortex method should be expanded to 3D problem so that it will be applied to actual design for floating structure, however its method can't be applied because stream function isn't defined in 3D problem. Therefore, development of vortex method using vorticity and velocity as unknown quantities is required. In this paper, by restricting to 2D problem, the vortex method using these unknown quantities is applied to flow field around a 2D cylinder in uniform flow and a forced oscillation problem of a submerged plate under the free surface. We carry out the comparison between calculation and experimental results, confirming its effectivity and reliability.

MODEL EXPERIMENT AND FIELD TEST OF PW-OWC TYPE WAVE POWER EXTRACTING BREAKWATER

Many research studies on wave power conversion have been conducted in Japan over the past 30 years, but the outgrowth of these studies have yet to be put to practical use. In this study, medium-scale and large-scale hydraulic model experiments as well as prototype field test on a new oscillating water column with a projecting wall (PW-OWC) wave power extracting breakwater were carried out in order to investigate the efficiency of energy conversion. The primary energy conversion efficiency of the PW-OWC converter is about 10% larger than that of the standard OWC type used in the medium-scale experiments. The primary energy conversion efficiency of the large scale experiments is about 20-30-% smaller than that of the medium scale experiments. The secondary energy conversion efficiency ranges from 0.20 to 0.42 and becomes small when the wave period is short and the wave height is large.

Dynamic behavior of a wave power buoy with interior on-board linear generator

Wave energy conversion is attractive from the viewpoint of the size of the renewable resource, but prototypes continue to suffer from high costs, leading to the idea of combining a wave energy conversion function with a conventional function of another ocean or coastal infrastructure to achieve cost-sharing between functions. Here, a wave power device in which a linear generator is installed inside a sealed floating horizontal circular cylindrical buoy is studied, which has dual functions of a wave power converter and a floating breakwater. A two-dimensional Navier Stokes numerical wave tank is used, together with a Volume of Fluid method to model the detail of the buoy-wave interaction. After model validation, the primary conversion efficiency of the device, and the wave transmission and reflection coefficients are explored. It is found that the maximum primary conversion efficiency is close to 25%. In resonant state, the amplitude of the translator's relative oscillation could be much larger than that of incident wave. When the incident wave frequency departs from the natural frequency of the linear generator, the energy conversion efficiency deteriorates rapidly. When wave energy conversion reaches maximum efficiency, the corresponding wave transmission coefficients are in the range of 0.7–0.75, and the corresponding wave reflection coefficients are in the range of 0.2–0.3.

Wave energy extraction by horizontal floating cylinders perpendicular to wave propagation

A two-dimensional numerical wave flume is established based on finite element and Volume of Fluid (VOF) methods for incompressible viscous flow. The numerical model is used to simulate waves interacting with single and double horizontal floating cylinders perpendicular to the direction of wave propagation. In the simulations, motion of the floating cylinders, wave forces and wave surface elevations in front of and behind the cylinders are calculated. By applying a damping force on the cylinders to simulate the electrical load, the primary conversion efficiency of wave power is derived. The effect of the cylinders’ cross-sectional size, the normalized damping coefficient for the cylinders’ heave motion, the primary conversion efficiency and the wave transmission coefficient are discussed. This investigation reveals that: larger cylinders are capable of extracting more wave power than smaller ones and also lowering wave transmission; an optimum normalized damping coefficient exists for wave power conversion; when this coefficient increases, heave motions of the cylinders decrease whilst the relative vertical wave force on the cylinders increases; total primary conversion efficiency for double cylinders is higher than that of two separately deployed cylinders due to cylinder-wise interaction.

Experimental Study on Performance of Wave Energy Converter System with Counterweight

In order to convert wave energy into large quantities of high-efficiency power, it is necessary to study the optimal converter system appropriate for the environment of a specific open ocean area. A wave energy converter system with a counterweight converts the translation energy induced from the heave motion of a buoy into rotary energy. This experimental study evaluated the primary energy conversion efficiency of the system, which was installed on an ocean generating basin with a power take-off system. Moreover, this study analyzed the energy conversion performance according to the weight condition of the buoy, counter-weight, and flywheel by changing the load torque and wave period. Therefore, these results could be useful as basic data such as for the optimal design of a wave energy converter with a counterweight and improved energy conversion efficiency.

Improvement of Performance of Wave Power Conversion Due to the Projecting Walls for Oscillating Water Column Type Wave Energy Converter

This paper describes a method to improve the performance of primary conversion of wave power takeoff. The wave energy converter (WEC) used here was of oscillating water column (OWC) type. This method for improvement has been already proposed in past research and its usefulness has been confirmed. It involves projecting walls (PWs) being attached to the front of the inlet–outlet of the OWC. The prediction method of hydrodynamic behaviors for the OWC type WEC with PWs installed is explained in this paper. The boundary element method with the Green's function is applied, and influence of air pressure and free surface within every air-chamber was directly taken into consideration in the prediction method based on linear potential theory. Validity of the prediction method was proved by comparing the results with the results of model experiments. Series calculations are performed with the prediction method. Behaviors of air pressure, water elevation, and the efficiency of primary conversion of wave power were investigated. From the calculations, length of the PWs was shown to affect the efficiency of primary conversion. It was possible to equip the PWs so as to enable improvements in oblique waves to beam sea conditions as well as in the head sea conditions. This paper examined not only the PWs but also the application and effects of the end walls (EWs) with the slit. The EWs were very useful to improve the efficiency.

An experimental study on a trapezoidal pendulum wave energy converter in regular waves

Experimental studies were conducted on a trapezoidal pendulum wave energy converter in regular waves. To obtain the incident wave height, the analytical method (AM) was used to separate the incident and reflected waves propagating in a wave flume by analysing wave records measured at two locations. The response amplitude operator (RAO), primary conversion efficiency and the total conversion efficiency of the wave energy converter were studied; furthermore, the power take-off damping coefficients corresponding to the load resistances in the experiment were also obtained. The findings demonstrate that the natural period for a pendulum wave energy converter is relatively large. A lower load resistance gives rise to a larger damping coefficient. The model shows relatively higher wave energy conversion efficiency in the range of 1.0–1.2 s for the incident wave period. The maximum primary conversion efficiency achieved was 55.5%, and the maximum overall conversion efficiency was 39.4%.

Numerical analysis of primary conversion efficiency of oscillating water columns with multiple chambers

The authors investigate the primary conversion efficiency of Oscillating Water Columns (OWCs) with multiple water chambers and air chambers.Two-dimensional frequency-domain numerical models to estimate the primary conversion efficiency of a two-chamber OWC with two air chambersand a two chamber OWC with one air chamber are developed. The numerical results are compared with that of a conventional one chamber OWC with equivalent total chamber width and front opening. The wave induced force is calculated using the boundary element method based on the velocity potential theory. Assuming air to be an ideal gas, the air flow is calculated using an equation of state and the equations of conservation of mass and energy. Boundary integral equations are formulated to calculate the air pressure in the air chambers, the reflection coefficient and the primary conversion efficiency of each of the chambers as well as the combined efficiency. In addition, the behaviour of these physical quantities with the variation of the nozzle ratio, the relative water depth, the depth of the curtain wall and the width of the front-chamber are investigated using the calculated results.

Experimental study on load characteristics in a floating type pendulum wave energy converter

A floating type pendulum wave energy converter (FPWEC) with a rotary vane pump as the power take-off system was proposed by Watabe et al. in 1998. They showed that this device had high energy conversion efficiency. In the previous research, the authors conducted 2D wave tank tests in regular waves to evaluate the generating efficiency of FPWEC with a power take-off system composed of pulleys, belts and a generator. As a result, the influence of the electrical load on the generating efficiency was shown. Continuously, the load characteristics of FPWEC are pursued experimentally by using the servo motors to change the damping coefficient in this paper. In a later part of this paper, the motions of the model with the servo motors are compared with that of the case with the same power take-off system as the previous research. From the above experiment, it may be concluded that the maximum primary conversion efficiency is achieved as high as 98% at the optimal load.