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With huge demand of herbal medicine worldwide, herb residue (HR) treatment is attracting growing attention. This work proposed an integrated energy conversion system to treat and utilize HR, which contained a crushing and drying section to pretreat HR, a gasification section to convert HR into syngas, and a boiling section to produce hot steam for HR drying and herb steaming. A pilot scale plant was established to validate its feasibility. The results showed that HR with particle size below 10 mm and moisture content about 20 wt% was qualified as gasification feedstock. The energy efficiency, syngas heat value, and syngas yield during gasification reached 76.1%, 5.7 MJ/Nm3, and 0.6 Nm3/kgHR, respectively. When treating each kg of HR, 1.0167 kg of wastewater was emitted, which primarily came from HR dehydration and herb steaming. Meanwhile, 0.3292 kg of hot steam with 0.89 MJ of enthalpy would be produced per kg of HR as net energy output. This integrated system fully considered the upstream and downstream adaption of HR gasification technique. Highly efficient disposal and utilization of HR were thus achieved. It is hoped that this work could promisingly enhance the overall efficiency of herbal medicine production industry.

Energy conversion efficiencies of three pyrolysis reactors (bench-scale auger, batch, and fluidized bed) were investigated using rice straw as the feedstock at a temperature of 500 °C. The highest bio-oil yield of 43% was obtained from the fluidized bed reactor, while the maximum bio-char yield of 48% was obtained from the batch reactor. Similar bio-oil yields were obtained from the auger and batch type reactors. The GCMS and FTIR were used to evaluate the liquid products from all reactors. The best quality bio-oil and bio-char from the batch reactor was determined to have a heating value of 31 MJ/kg and 19 MJ/kg, respectively. The highest alkali mineral was found in the bio-char produced from the auger reactor. The energy conversion efficiencies of the three reactors indicated that the majority of the energy (50–64%) was in the bio-char products from the auger and batch reactors, while the bio-oil from the fluidized bed reactor contained the highest energy (47%). A Sankey diagram has been produced to show the flows of product energy from each pyrolysis process. The result will help determine which conversion process would be optimal for producing specific products of bio-char, bio-oil, and gas depending on the needs.

Energy use patterns and utilisation efficiencies in 40 factories producing palm kernel oil (PKO) in southwestern part of Nigeria were studied. The factories were stratified into small, medium and large scale categories based on the mode of operations and production capacities. Questionnaires were administered on the factories to obtain historical data on petrol, diesel and electricity consumption and PKO production outputs for seven years (1998–2004). Energy use efficiency indicators employed include: energy intensity (EI), energy cost per unit product (EC/P), energy ratio (ER), food energy ratio (FER) and percentage oil yield by weight. Results of the study indicated that averagely, 0.58, 0.53 and 0.74 GJ/103 l of PKO were needed in the small, medium and large PKO factories, respectively. The average food energy ratios in the small, medium and large mills are 2.48, 2.53 and 2.14, respectively. The corresponding values of PKO conversion ratio are 0.43, 0.50 and 0.35. Electrical energy consumption in medium and large mills was lower than thermal energy due to irregularity and decline in electricity supply from the national grid. The results of the study has provided required baseline information needed for budgeting, comparison of yearly energy consumption, forecasting energy requirements and planning expansion in PKO factories.

CO2 adsorption capture, which could be driven by various forms of energy, has been widely studied in recent years due to the equipment is easy to control with low energy consumption required. However, the existing research on the energy-efficiency aspects of temperature/vacuum swing adsorption (TVSA) for CO2 capture are primarily focus on the quantification of input energy in specific cases. As a classical concept in thermodynamics, entropy has been widely applied in researches on the energy conversion process, which could benefit an in-depth understanding on the mechanism of “heat-generalized chemical energy” conversion. However, an integrated thermodynamic research framework, which could clarify how to conduct a reasonable energy-consumption analysis of TVSA, has not been established yet. In this paper, a simplified thermodynamic cycle of 4-step TVSA was established, with the assumption of CO2 in adsorbed phase as loop fluid. With the application of the thermodynamic research framework proposed in this paper, the entropy analysis on the thermodynamic cycle was conducted. This study is concerned with application of thermodynamics concept to the CO2 adsorption engineering, which is mainly based on classical thermodynamics but also relying on adsorption physics to supply insight into the energy conversion and energy-efficient mechanism of TVSA technologies.

Exergy-based methods are powerful tools for developing, evaluating, understanding, and improving energy conversion systems. This paper deals with integrated advanced exergy-based evaluations. In addition to conventional methods, advanced exergy-based analyses consider (a) the interactions among components of the overall system, and (b) the real potential for improving each important system component. The main role of an advanced analysis is to provide energy conversion system designers and operators with information useful for improving the design and operation of such systems. Splitting the exergy destruction, the capital investment cost, and the component-related environmental impact associated with each single component of an energy conversion system into endogenous/exogenous and avoidable/unavoidable parts and using a further splitting of the exogenous exergy destruction improves (a) our understanding of the processes that take place, and (b) the quality of the conclusions for improvement obtained from the analysis. This paper discusses the main features and some recent developments in the area of advanced exergy-based methods. Application of the method to a simple air refrigeration machine confirms the correctness of the approach.

The internal resistance of a battery represents the losses due to heat generation during energy conversion. The state-of-health is used to quantify the increase (degradation) of resistance with usage. However, the current state-of-health analysis merges the total internal resistance into one component. Consequently, the underlying cause of resistance degradation is not understood leading to incorrect estimate of battery health. Therefore, this paper presents a comprehensive framework based on energy equilibrium for the categorization and health analysis of total internal resistance. It is divided into 2 components: one based on irreversible overpotential (includes polarization) effects and a new second resistance component originated from reversible entropy changes. For LiFePO4 cells used in this work, it is observed that the contribution of entropy changes (hitherto unrecognized) to the overall losses increases from 4−10% to more than 40% as state-of-charge reduces. State-of-health of each component is obtained by the determination of its associated degradation factor to quantify the underlying mechanism of resistance degradation. In conclusion, the increase in irreversible resistance is primarily attributed to the permanent loss of active material. Correspondingly, the reversible resistance increase is associated to the formation of concentration gradients in the electrodes due to past load profile and ambient conditions. Maritime and Port Authority of Singapore (MPA) Accepted version The research conducted in this paper is funded jointly by ABB Pte Ltd, Singapore and Maritime and Port Authority (MPA) of Singapore.

This paper studies the energy conversion performance and strength of a wearable thermoelectric generator consisting of a thin thermoelectric layer bonded to a flexible substrate. The thermal conductivity, Seebeck coefficient and electrical resistivity used in this paper are calculated from the fundamental formulas of carrier motion as functions of temperature. This gives more accurate calculating results and in line with actual situation. Convective heat transfer between the thermoelectric layer and the environment and the contact thermal resistance between the thermoelectric layer and the human skin are considered. Analytical solutions of power output density and axial stress in thermoelectric layer are derived. It is found that the bending of thermoelectric layer can increase the open-circuit voltage. The power output density increases to a peak value and then decreases with the length of the thermoelectric layer. On the premise of guaranteeing the strength of thermoelectric layer, the optimized length of the thermoelectric layer for obtaining maximum power output density is given.

Solar energy application in a wider spectrum has the potential for high efficiency energy conversion. However, solar cells can only absorb photon energy of the solar spectrum near the solar cell band-gap energy, and the remaining energy will be converted into thermal energy. The thermoelectric generator is a good choice to utilize this thermal energy. This paper analyses the feasibility of photovoltaic-thermoelectric (PV-TE), and reviews the current types and performance of PV-TE. Furthermore, it presents the optimization and development of PV-TE. In addition, this paper presents the challenge and efficient improvement of PV-TE in actual application. Therefore, this paper would provide a valuable reference for further research into the field of PV-TE and its applications.

Nowadays the control of greenhouse gas is probably the most challenging environmental policy issue. Since CO2 is considered the major greenhouse gas (GHG) that contributes to the global warming, enforcing technological strategies aiming to avoid or reuse CO2 emissions becomes crucial, in order to mitigate GHG environmental impact. Currently, solutions conventionally adopted to this purpose are carbon capture and storage (CCS) technologies. In this context, instead, the followed strategy aims to further improvements in energetic conversion efficiency with related reduced specific CO2 emissions (per produced kWhe). Therefore, with particular reference to the electric power generation, this paper proposes an innovative energy conversion system, based on solid oxide fuel cell (SOFC), characterized by higher efficiency and reduced CO2 emission factor respect to an analogous conventional energy plant. In particular, the innovative solution consists of combining SOFC to methane dry reforming technology, while the conventional system refers to steam methane reforming-SOFC coupling. The innovative system performance up to 65% electric efficiency as cited in the paper, was validated through simulations carried out in Aspen Plus environment.

This paper assesses the steady-state performance of cascaded IMs (induction motors) operating under voltage unbalance. Small sizes induction motors are connected in cascade instead of one big size induction motor to improve the electromagnetic system and to make the energy conversion process more efficient during both balanced and unbalanced operation. The two mechanically coupled induction motors could have the same ratings or different ratings. The paper analyzes the coupled machines system using the method of symmetrical components and MATLAB/Simulink software. The definition of the voltage unbalance using CVUF (complex voltage unbalance factor) is used. Coupling of induction motors with DC (direct current) motors is examined to investigate the effect of cascading on the electromagnetic torque of the entire set. A comparison of the effect of the unbalanced voltage on single and cascaded machines is illustrated. The purpose of such comparison is to determine which one has the best performance during the balanced and unbalanced operations. Furthermore, this paper assesses the impact of connecting induction motors in cascade on the energy conversion process.

In the present paper we demonstrate the efficient use of shape controlled flower-like ZnO (Zinc oxide) nanostructured particles as multifunctional electrode for both energy conversion and storage applications, i.e. Dye-sensitized Solar Cells (DSCs) and lithium-ion batteries. As regards DSC (Dye-sensitized Solar Cell) device, ZnO flower-like particles, prepared by a simple, low-cost and reliable hydrothermal method under mild reaction temperature, are efficiently used as photoanode in a microfluidic architectured cell in combination with NMBI (N-methylbenzimidazole), employed as additive of the electrolytic solution for the first time in a ZnO-based DSC. We obtain a remarkable sunlight conversion efficiency of 3.6%. As regards storage applications, a stable long-term ambient temperature cycling behavior in lithium cell is demonstrated, even at increasingly higher currents. Remarkable charge-discharge efficiency and specific capacity are obtained up to 200 cycles, which is the highest number of cycles reported so far for similar systems. Noteworthy, such results are achieved without the addition of foreign additives, nor during the synthesis process neither during the electrode preparation, and also no carbon coating on ZnO surface is used. The originality of the present paper consists not only in showing for the first time the efficient operation of such ZnO particles as anode in Li-ion batteries for prolonged cycling, but also in demonstrating the versatile and multifunctional use of the same material for two different energy related applications. The reported results enlighten indeed the promising prospects of the flower-like ZnO nanostructured material for the successful implementation as stable and long-term performing anodic material in the next generation of both energy conversion and storage devices.

The thermodynamic inefficiencies associated with any energy conversion process are expressed by the exergy destruction and the exergy losses associated with the process. Combustion processes exhibit very high thermodynamic inefficiencies caused by chemical reaction, heat transfer, friction, and mixing. In this paper, we discuss how to estimate the thermodynamic inefficiencies resulting from each one of these sources. The thermodynamic evaluation can be conducted with the aid of either a conventional exergetic analysis or an advanced one. The latter allows estimation of the potential for improvement of the process being considered and demonstrates the interactions among the components of the system in which combustion takes place. The paper discusses how advanced exergy-based evaluations can be used to reduce the thermodynamic inefficiencies, costs, and environmental impacts associated with energy conversion systems including combustion processes.

Splitting the exergy destruction into endogenous/exogenous and unavoidable/avoidable parts has many advantages for the detailed analysis of energy conversion systems. Endogenous is the exergy destruction obtained when all other system components are ideal and the component being considered operates with its real efficiency. The difference between total and endogenous exergy destruction is the exogenous exergy destruction caused within the component being considered by the irreversibilities in the remaining components and the structure of the overall system. Unavoidable is the part of exergy destruction within one system component that cannot be eliminated even if the best available technology in the near future would be applied. The avoidable exergy destruction is the difference between total and unavoidable exergy destruction. These concepts enhance an exergy analysis and assist in improving the quality of the conclusions obtained from this analysis. The paper presents the combined application of both concepts to vapor-compression refrigeration machines using different one-component working fluids (R125, R134a, R22 and R717) as well as azeotropic (R500) and zeotropic (R407C) mixtures. The purpose of the paper is not to evaluate these working fluids, some of which cannot be used in future, but to demonstrate the effect of different material properties on the results of advanced exergy analysis.

This paper deals with a numerical modelling devoted to predict the flow characteristics in the components of an oscillating water column (OWC) system used for the wave energy capture. In the present paper, the flow behaviour is modelled by using the FLUENT code. Two numerical flow models have been elaborated and tested independently in the geometries of an air chamber and a turbine, which is chosen of a radial impulse type. The flow is assumed to be three-dimensional (3D), viscous, turbulent and unsteady. The FLUENT code is used with a solver of the coupled conservation equations of mass, momentum and energy, with an implicit time scheme and with the adoption of the dynamic mesh and the sliding mesh techniques in areas of moving surfaces. Turbulence is modelled with the k–e model. The obtained results indicate that the developed models are well suitable to analyse the air flows both in the air chamber and in the turbine. The performances associated with the energy transfer processes have been well predicted. For the turbine, the numerical results of pressure and torque were compared to the experimental ones. Good agreements between these results have been observed.

A comprehensive method of analysis based on energetic, exergetic, emergetic and economic evaluations is proposed in the paper and the application presented. The method is applied to selected energy conversion processes (hydroelectric and thermoelectric ones and bioethanol production). Results are presented and compared while general considerations about the effectiveness of the different approaches are suggested. Emissions to the environment are also evaluated. Suitable performance indicators developed within the proposed methodological framework are defined and discussed accordingly. The method proposed here is addressed to policy makers, operators and designers working in the field of energy supply and conversion. In the authors' opinion, by jointly applying and comparing all of the methods suggested in the paper, valuable information about plant performance and possible areas of improvement are obtained. This can be helpful in the decision-making process.

This paper presents a novel dynamic simulation model for the analysis of a hybrid turboexpander system coupled with innovative high-vacuum solar thermal collectors. The model is developed in MatLab and it is able to dynamically calculate the energy, exergy, environmental, and economic performances of the investigated system, by taking into account the hourly fluctuation of thermodynamic and economic parameters (e.g. electricity cost, natural gas temperature, and flow rates, etc.). In addition, a computer-based Design of Experiment (DoE) approach was implemented for achieving the optimal design of the proposed system. A suitable case study is presented in order to show the capabilities of the developed simulation tool. Conventional and non-conventional decompression systems located in the weather zone of Messina (South-Italy) are investigated with the aim of assessing the optimal system configuration. By means of the computer-based DoE analysis, the optimal values of several design parameters (such as the number of solar thermal collectors, the volume of the hot water storage tank, and the size of the water loop pump) are calculated. Numerical results show significant primary energy savings (1.36 TWh/year) and avoided carbon dioxide emissions (348 tCO2/year). From the economic point of view, a feasible simple pay-back period of 4.51 years is achieved. The destroyed exergy of the system components are calculated, obtaining the highest value for the turbo-expander, equal to 12.0 TWh/year.

A looped-cascade thermoacoustic driven cryocooler is proposed and theoretically studied in this paper. This system is capable of achieving ideal acoustic fields by employing different-diameter resonance tubes. It overcomes the limitations of current configurations and possesses the advantages of high efficiency, large capacity and compact size. First, power matching between the engine-stage number and the working temperatures is investigated. Theoretical results show that either too few or too many engine stages induce negative effects: the former results in low efficiency and the latter results in over-high heating temperatures. Then, thermodynamic characteristics of the three-stage system are presented. Simulation results show that a cooling power of 1.17 kW and an overall relative Carnot efficiency of 15% can be achieved at 110 K, which is superior to the performance of the existing looped configurations. The distributions of key parameters are also presented for a better understanding of the energy conversion process. Finally, the effects of the crucial parameters—resonance-tube area-ratio and engine-regenerator area-ratio—are presented. Simulation results show that having an either too low or too high area-ratio has a significant negative effect on system performance due to improper phase relations and low acoustic impedance.

This study focuses on the performance and energy conversion process of cascaded induction motors (CIMs) operated under balanced and unbalanced conditions. In this paper, two mechanically combined induction motors having a similar rating (25 Hp) are investigated for comparing with a large induction motor (50 Hp) — imbalances can occur in the applied voltage, operating frequency, or both. The impacts of both unbalanced voltage and unrated frequency on maximum and steady-state torque, power factor, input active and reactive powers, stator and rotor copper losses, and total harmonic distortion (THD) in voltage and current, have been investigated through a simulated model created using Matlab/Simulink software. This work demonstrates that machine performance and efficiency are improved by introducing more electrical and mechanical advantages of cascading the electrical machines. The results show that the maximum torque of the CIMs is higher than that of a single one at different operation cases; it is increased by 18.4% during balanced operation. The total copper losses are reduced by 36.5% in balanced operation when using CIMs instead of the large motor. Consequently, the energy conversion process and performance were significantly improved.

In the general monolayer electrode of constant porosity, the conflict between the available specific surface area and the hydraulic permeability is a momentous hinder in designing the high-performance electrodes of VRFB. In this paper, several novel electrode structures with gradient or double-layered porous media (GPM or DLPM) are installed in the stack to decouple the conflict and connection between hydraulic permeability and specific surface area. Ten kinds of electrode structures with constant, linear or stepwise decreasing/increasing porosity respectively are designed and compared. The lower concentration polarization loss, higher cell energy efficiency and capacity in the stepwise and linear increasing of porosity profiles are related to the electrolyte flow uniformity in porous electrode and alleviation of conflict between permeability and specific surface area. The higher pumping losses in these arrangements serve as deteriorative factor. In the stepwise increasing porosity mode, the effects of the thickness ratio between two porous layers with different porosities, electrode thickness and porosity variation amplitude were investigated. There is an optimum thickness ratio and electrode thickness to obtain the saturated cell capacity and more energy efficiency, and the rise amplitude of porosity will reduce the system efficiency while increasing the cell capacity.

This paper reviews state-of-the-art methods of energy harvesting for implantable and wearable devices based on the available mechanical and heat energy sources in the human body. The development of a compatible and sustainable power supply for wearable and implantable devices is a demand to realize their continuous and high-performance operation, minimize the need for external energy sources, and increase the lifetime of the devices. Heat and mechanical movement are two available and reliable energy sources in the human body. Since mechanical and heat energy harvesting methods have been extensively studied over the past decades, researchers focus on developing techniques to integrate these energy harvesters with implantable and wearable electronics. Therefore, energy requirement for wearable and implantable devices, available energy level from the human body, and convenience and feasibility of the implementation are taken into account to provide full or partial power support. This survey aims to present recent findings and developments in the field of energy harvesting from continuous heat source and mechanical movements of the human body. In particular, working principles, technical details, and current status as well as issues and challenges of energy harvesting from human body including thermoelectric, photovoltaic, piezoelectric, electrostatic, electromagnetic, and triboelectric harvesters are discussed.

The study of supply and demand match increasingly becomes an enormous challenge in park integrated energy system (PIES) because it has a comprehensive relationship between multiple energy sources and multiple energy demand. This paper proposes a new type of supply and demand matching to accomplish the economic optimality of match under the same criteria, considering supply and demand changing simultaneously. The quantitative indexes of supply and demand energy conversion technologies (ECTs) is established considering the economic and technical characteristics of full life cycle comprehensively, which are defined as supplied technical cost level and demand technical cost level. Then, the novel energy supply and demand matching model is established. The loop iteration algorithm of the new matching model is established based on linear programming model. Numerical study is introduced based on the data of the cooling, heating and electrical load in a typical day. The results show that the priority order of each ECT is different when the output of all ECTs increasing gradually. The investment payback period is only 1.94 years. The new supply and demand matching model can reduce carbon emissions by 80,555 tons.

In this paper a novel polymer-based platform is applied for the fabrication of an innovative two-electrodes self-powered device integrating energy harvesting and storage sections. A multifunctional polymeric layer, made of two poly(ethylene glycol)-based sections separated by a perfluorinated barrier, is obtained by oxygen-inhibited UV-light crosslinking procedure. For the energy harvesting section, one side of the polymeric layer is adapted to enable iodide/triiodide diffusion in a dye-sensitized solar cell (DSSC), while the other side empowers sodium/chloride ions diffusion and is used for on-board charge storage in an electrochemical double layer capacitor (EDLC). The resulting photocapacitor has a planar architecture appreciably simplified with respect to other recently proposed solutions and more easily exploitable in low power electronics. The measured photo-electrical conversion and storage total efficiency is 3.72% during photo-charge, which is a remarkable value for DSSC-EDLC harvesting-storage devices literature. The obtained high frequency discharge capability enlightens promising prospects for practical applications in low power portable electronics.

Operational optimization plays a vital role in ensuring the economy, security, and environmental friendliness of integrated energy systems (IES), while the nonlinear operating characteristics of energy converters have brought significant challenges to the accurate modeling and solution. Considering the nonlinear energy conversion processes, a novel adaptive piecewise linearized weighted directed graph model of IES is proposed in this paper. To accurately construct the complex energy flow relationship in IES, a weighted directed graph is first presented to describe the energy generation, conversion, storage, consumption, and demand response, thus realizing the automatic modeling of IES. On this basis, for the diverse partial-load performance of energy converters, an adaptive piecewise linearization strategy is developed to approximate the nonlinear operating characteristics of various energy converters adaptively. By taking the system operating cost, calculation time, energy mismatch, and optimization model complexity as evaluation indicators, the effectiveness of the proposed method is verified by the numerical simulations of a typical small-scale combined cooling, heating, and power (CCHP) system and a large-scale IES in a realistic industrial park. Compared with the constant efficiency method and the equispaced piecewise linearization method, the computational efficiency and accuracy are remarkably improved by the proposed method.

Achievement of satisfactory results of measurements data reconciliation in energy conversion processes is possible only in the case of application of the so-called generalized advanced method of data validation and reconciliation. An application of this method made it possible to complete the validation model of the process (conditional equations of optimization task) including substance and energy conservation principles with additional equations describing energy conversion processes. The criterion of selection of the form of additional equations in the validation model in reconciliation calculation has been formulated based on the derived characteristic property of variables uncertainty after data reconciliation. The developed methodology has been used for example calculations of data reconciliation in the selected steam power unit. At the design stage of energy conversion systems, the problem of the number of redundant measurements, as well as their location, appears. Example calculations for the redundant measurement systems of selected energy conversion processes have been carried out. As objective functions of the combinatorial optimization tasks, the relative uncertainty of the selected energy effectiveness indicators was assumed. The results of calculations confirm the influence of the number of redundant measurements and their location in the measurement systems on the accepted criteria of optimization. An idea to apply in the data reconciliation method the measurements uncertainties expressed by fuzzy numbers has been presented. As a criterion for comparison of the results of calculations for both types of uncertainties, the relative entropy of information as well as the complex standard uncertainties of main assessment indicators of analysed combined heat-and-power unit operation supervision has been chosen. The advanced data validation and reconciliation method was introduced and developed in Poland to the thermodynamic analyses of energy conversion processes by professor Jan Szargut. The above issues constitute further researches on the development and application of this method in thermodynamics analyses performed by the author of this paper.

In this paper a new mechanistic model for the diabatic annular two-phase flow is presented and applied to prediction of dryout and post-dryout heat transfer in various channels. The model employs a computational fluid dynamics code – OpenFOAM® – to solve the governing equations of two-phase mixture flowing in a heated channel. Additional closure laws have been implemented to calculate the location of the dryout and to predict wall temperature in the post-dryout region. Calculated results have been compared with experimental data obtained in pipes and good agreement between predictions and measurements has been achieved. The presented model is applicable to complex geometries and thus can be used for prediction of post-dryout heat transfer in a wide variety of energy conversion systems.

A novel hydro-kite like ocean energy converter is proposed in this paper to harness both ocean current and wave energy. The proposed ocean energy converter is typically designed to consist of a hydro-kite like kite floating or submerged in the ocean and an energy conversion unit set on a ship. The ocean wave or current energies can be generated by pulling a pre-tensioned flexible tether that connects the hydro-kite-like kite and the energy conversion unit. The general dynamics of the novel ocean energy converter is basically described and modelled based on the dynamics of key components under both ocean wave and current conditions. The feasibility and effectiveness of the proposed ocean energy converter are evaluated through computational fluid simulations under both fully submerged ocean current and semi-submerged ocean wave conditions. The simulation results verify that the hydro-kite can be used to generate power from both ocean current and wave conditions and the design parameters of the hydro-kite such as the angle of attack, draft should be optimally controlled or designed to maximize the ocean energy generations under different ocean current speeds, wave periods and heights.

Fossil fuels cannot provide all the required energy in future due to their exhaustibility. Their utilization also leads to huge environmental problems. Therefore, it is vital to find a new inexhaustible and clean source of energy which could be easily stored and transported. Hydrogen produced by renewable energy sources has all the above mentioned advantages. There are many hydrogen production methods which could be coupled with renewable energy sources. Among them, electrolysis process is the most mature one. In this paper, a review is performed on different methods of coupling electrolyzer systems with different renewable energy sources, including solar energy, wind energy, geothermal energy, ocean thermal energy conversion system and hydroelectric energy. The focus of this study is on how these systems can be integrated and which one has the highest total efficiency. Finally, cost of hydrogen production by different energy sources is compared.

In order to realize the large-scale and normal implementation of power-to-gas technology, as well as the large-capacity storage and long-distance transportation of gas in the later stage of electric hydrogen production, a power-to-gas technology with real-time energy conversion characteristics and large-scale energy storage characteristics is studied in this paper. Firstly, the water-electricity-gas coupling process between the electrolytic cell and the methanation reactor in the power-to-gas system is discussed in detail, and the model of the power-to-gas system based on the coordination of real-time energy conversion and large-scale energy storage is proposed. Then, based on a multi-energy coupling regional integrated energy system, a highly decoupled multi-step modelling method is adopted to construct its optimal operation model, and the equivalent variable substitution method is used to transform it into a linear programming problem. Finally, the calculation results show that the proposed power-to-gas technology can further improve the energy utilization efficiency due to the complementary characteristics of the two functions, so as to effectively promote the implementation of large-scale power-to-gas projects in the future.

The challenges associated with energy of the todays world including climate change, growing demand, and interdependence of gas, heat, and electricity have encouraged energy system planners to consider the integrated exploitation or hybrid strategies, which is so-called as the energy hub. According to different definitions presented for the energy hub, various models have been proposed so far for it. In general, the equipment of an energy hub can be divided into three categories: 1) direct connections, 2) converters, and 3) energy storage system. In this paper, a linear model of the energy hub including heating, cooling, and electrical equipment for energy conversion, production, or storage was considered. The proposed model consists of two parts of design and operation, formulated for an annual period in four seasons. The e-constraint method and fuzzy weighted method were used to solve the proposed model, and the two parts of design and operation were introduced as the main problem and sub-problem, respectively. In addition to deterministic model, problem-solving space was considered as scenario-based random taking into account uncertainty in amount of load, energy price, and also production of renewable wind resources. Scenarios were simulated for production of wind resources using historical information and other scenarios were simulated using the Monte Carlo simulation method. Given solution of the problem annually, for reducing volume of calculations, number of scenarios was decreased using the K-Means method. Mathematical model of the proposed model was of the mixed-integer linear type and included binary variables of design and continuous and binary variables of operation. Capacity selection for installation was based on appropriate candidates for each of the equipment, in order to prevent installation of unrealistic capacities in design sector.

A great amount of researches on thermodynamic cycles have been active in recent years, such as ORC (organic Rankine cycle), Kalina cycle, et al. However, the ultimate aim of such researches, which could even be traced back to more than one century ago, has not changed with a tireless pursuing to Carnot cycle. In exiting researches, the working fluid, as a medium for energy conversion, is commonly considered to play an important role in the thermodynamic cycle: (1) relative to ideal cycle, most of actual power cycles in the engineering field cannot operate without working fluid; (2) energy efficiency, considering the analysis of second-law efficiency, of actual cycle has a significant decrease due to the introduction of working fluid. Thus, working fluid is a hot spot in the research of thermodynamic cycle in recent years. Zeotropic mixture, which commonly consists of two or more pure working fluids, has flexibility in thermos-physical properties with a possible potential to enhance the cycle performance. The effects of thermos-physical properties of zeotropic mixture should be considered when determining the cycle structure and the design of components. This paper presents a novel construction method of thermodynamic cycle based on the zeotropic mixture. By adding the thermodynamic coordinate of working fluid, a 3D cycle diagram based on the traditional temperature and entropy cycle diagram is applied for performance analysis of cycle. According the proposed construction method, a baseline cycle, composed by ORC sub-system and compositions regulating sub-system, is put forward and available compositions regulating techniques for such cycle are discussed as well. Finally, a representative case is described briefly and the features are summarized. This work provides a new methodology view to guide researchers in energy-efficient design of thermodynamic cycles.

In future energy systems, storage technologies for electrical energy are considered to be a key component for increasing the share of renewable energy use. Pumped thermal energy storage technologies represent a promising approach to complement established storage technologies such as pumped-hydro power storages without their geological restrictions. Assuming an ideal, reversible and adiabatic energy conversion process, the stored electrical energy can be entirely recovered. However, the efficiency of real processes is limited by irreversibilities. These exergy losses can be compensated by the integration of low temperature heat. The exergetic efficiency can be further increased by using thermal energy provided during discharging. In this paper, a fully heat-integrated, subcritical PTES using butene as the working fluid is presented. The results of a detailed numerical simulation of the cycle regarding exergy losses during heat transfer, efficiencies of machinery and parasitic energy consumption are shown. A maximum net electrical power ratio between charging and discharging of 125% is obtained, while the maximum exergetic efficiency is 59%. The conducted numerical simulation includes pressure losses and pinch points, allowing for a more in-depth understanding and for a pre-optimization of the hydraulic design.

A novel coupled hydro-pneumatic energy storage system is proposed to improve the energy and power performance of the energy storage system in hybrid mining trucks. Based on four basic layouts, representing different energy conversion and storage approaches, of compressed air energy storage system and hydraulic energy storage system, a coupled layout is proposed for the hybrid mining truck application through a comparative study of the four basic layouts in this paper. Simulation and analysis results show that the coupled layout can effectively balance the power and energy performances of the pressure energy storage system. The total benefit of hybrid mining trucks with the coupled layout in ten years is increased by 9.7% as compared with the compressed air energy storage system, and by 91.2% as compared with the hydraulic energy storage system. Moreover, the weight and volume of the coupled layout are reduced by 15.4% and 24.8% as compared with the compressed air energy storage system, respectively, and by 83.1% and 92.8% as compared with the hydraulic energy storage system, respectively.

Supercritical carbon dioxide (S-CO2) cycle is proven to be one promising alternative to provide high efficiency and has been developed for a wide range of energy conversion applications. Thermal efficiency of the S-CO2 cycle can be further improved by incorporating an appropriate bottoming cycle utilizing the residual heat. In this paper, an Organic Rankine Cycle (ORC) is added to the S-CO2 cycle for heat recovery. Different recuperative ratios of the topping S-CO2 cycle are considered and the influence of heat source initial temperature and total heat load on the bottoming ORC is evaluated. Two configurations of the S-CO2-ORC combined cycle system are presented, one without a pre-cooler and the other still with a pre-cooler, corresponding to total and partial residual heat recovery respectively. Though the entire residual heat recovery by the bottoming cycle could definitely increase the system thermal efficiency, the low ORC evaporation temperature and mediocre ORC performance leads to a limited improvement. While in the combined cycle system with a pre-cooler, higher ORC evaporation temperature could be attained and it has a remarkable effect on the ORC performance, even though part of the topping cycle residual heat is discharged to the ambient. The simulation results reveal that the S-CO2-ORC combined cycle system performance could be significantly improved through this parametric optimization. The recompression S-CO2 cycle with bottoming ORC is then analyzed and thermal performance is improved based on the previous optimization results. The bottoming ORC could effectively recover the residual heat of the topping S-CO2 cycle and increase the system thermal efficiency, thus it can be considered and applied in similar practical cases.

The artificial ground freezing (AGF) method is widely used for soil reinforcement in underground engineering. The AGF method has been confirmed very effective, however, it consumes a great deal of energy during construction. Therefore, it is of great significance to study its energy conversion and utilization, which is very important for better and more energy-efficient employment of this method. In this paper, a novel method, which could effectively calculate the energy utilization rate (EUR), is proposed to evaluate the energy conversion efficiency of a typical AGF project. First of all, the brine temperature and ground temperature are monitored and analyzed. Secondly, according to the monitored data and actual layout of freezing pipes, a sophisticated three-dimensional solid model is established, which considers the thermal-mechanical coupling and ice-water phase change. Based on the numerical simulation, the variation of the temperature field as well as the expansion process of the frozen soil curtain are analyzed, and the effectiveness of the numerical model is further validated by comparison between the measured and simulated results. Thirdly, variations of three key parameters including the output energy, elastic strain energy and heat energy during the active freezing period are calculated and analyzed. Finally, the EUR curve during the AGF process is acquired based on the calculated indicators. The trend of EUR can be divided into four stages, while the EUR is zero in the initial stage, reaches a peak of 0.79 in the rise stage, and then decreases slowly in the decline stage and stable stage. According to the EUR curve, constructive measures to improve energy conversion and utilization are proposed. It is concluded that this novel method is very effective for the assessment of energy utilization in AGF projects.

In the next decades, energy storage technologies will play a major role in decarbonizing the European heating and cooling sector. In this regard, the deployment of complementary technologies is of paramount importance for the energy transformation of the Polish heating sector. This work addresses the challenge of sizing large-scale thermal energy storage (TES) systems for combined heat and power (CHP) plants connected to district heating networks and participating in day-ahead electricity markets. In this paper, a method based on a mixed-integer linear programming approach is proposed to find the optimal capacity of TES units connected to coal-fired CHP systems. The model considers the specific investment costs of the storage technology and optimizes the annual operation scheduling of the CHP-TES system. The model is applied to the case study of a coal-fired CHP system. Four scenarios are used to investigate the performance of the CHP system and evaluate the effects of rising carbon prices on the optimal capacity of the TES unit. The results reveal that the integration of the TES leads to a significant drop in the utilization of the heat-only boilers, helping mitigate fuel and environmental costs.

As demands for energy conversion and management are increasing, accurate evaluation and prediction of energy efficiency are the prerequisites of making production strategies to improve economic benefits in the chemical industry. With the characteristics of slow variations in the chemical process and temporal correlations in the sampling data, it is more difficult for conventional estimation methods to precisely evaluate and infer the energy efficiency. To overcome these difficulties, this paper proposes a novel energy efficiency evaluation and prediction method, named slow feature partial least squares. The proposed method is integrated with slow feature analysis and partial least squares. Slow feature partial least squares can extract dynamic features from temporal behaviors of chemical products and energy media in a supervised manner and construct the model relationship. With the established model, not only are the energy efficiency levels evaluated accurately, but the tendency of energy efficiency is also inferred in advance. The effectiveness and practicality of the slow feature partial least squares method are validated by a mathematical example and an actual ethylene process. The energy efficiency results provide great support for the enhancement of energy efficiency and the development of production strategies in chemical plants with high energy consumption.

A novel bio-inspired V-shaped layout is proposed to enhance energy conversion performance for VIV hydrokinetic energy converters. The layout method is inspired by wild geese flying in a V-formation. In this paper, 2-dimensional RANS equations with the SST k- ω turbulence model are used to simulate the VIV responses at various distances. The numerical method is verified by comparing with experiments. Two-cylinder and five-cylinder V-shaped layout are investigated separately to analyze multi-cylinder interactions. The main conclusions are: (1) The VIV response of the upstream cylinder is suppressed due to the blockage effect when at small distance. (2) The energy recovery area of downstream cylinders is identified and located on the edge of the wake. (3) In the energy recovery area, the enhancement mechanism of this novel layout is the upstream and downstream vortices coalesce, resulting in a significant increase in lift force on the downstream cylinder. (4) The converted power of downstream cylinders in the energy recovery area is increased by up to 6.3%–8.4%. Future work is directed to optimize the distance among the cylinders for optimal energy conversion.

Fuel cell technology is one of the most promising, emissions free, energy conversion technology under renewable energy systems because of its wide ability in most of the commercial applications like electrical vehicles, building cogeneration and standby power supply. Mathematical models are trusted as important tools for designing and performance analysis of fuel cell based systems. Many mathematical models based on thermal, electrochemical and electrical steady states as well as dynamic have been reported in literature to evaluate performance of Proton Exchange Membrane (PEM) fuel cell, but all these models are complex and needs huge amount of data for modeling and performance testing. The present paper proposes simple, but more realistic MATLAB SIMULINK model for PEM fuel cell to evaluate its performance under different operating conditions. The performance of the proposed model is compared with single practical, 25 cm 2 active area, PEM fuel cell for model validation. The presented model is also valid for a stack having any number of cells.

Many countries have passed governmental action plans to support the installation of renewable energy sources. However, most studies dealing with the optimization of building energy systems neglect a precise modeling of such subsidies, although these subsidies are specifically designed to strongly influence system setups. Therefore, this paper extends a model for the optimization of energy systems by a more accurate consideration of storage units and enhance both models by accounting for major German pieces of legislation aimed at supporting renewable energies. Additionally, we consider typical German market characteristics, in particular the availability of multiple gas and electricity tariffs. We compare our model with the original formulation regarding a pure cost minimization and a forced reduction of CO2 emissions for three new buildings located in Germany. The results imply that the considered subsidies strongly support the installation of PV modules and CHP units. Without these subsidies, batteries and solar thermal collectors become more important. Additionally, the findings illustrate that the new storage model is slightly more accurate, but only marginally affects the total annual costs and required computing times. The conducted sensitivity analysis has shown that the obtained results are relatively robust to variations in energy tariff costs and demands.

In integrated energy systems, adjusting the energy conversion of a coupling unit changes the power flow in the connected energy systems. Also, it forces other units to adapt their generation to keep the energy balance in the energy systems. The impact on the power flow and the complexity of the interaction between single networks will increase the more coupling units are installed. The impact on the power flow can be determined by power flow calculation and optimization algorithms. However, to analyze the impact of a unit’s power change on all state variables, the available methods need to solve a second power flow or optimization. This is computationally effortful and time-consuming. Hence, this paper proposes a method that estimates such a change easily and quickly. The method extends the widely used approach of sensitivity factors in electric power system analysis to electricity-heating integrated energy systems. The sensitivity factors are derived in a straightforward way by linearization using the Jacobian matrix of a coupled power flow calculation before the change. These new sensitivity factors can precisely estimate the impact of a change on the energy system’s power flow and reduce the calculation time of new setpoints by factor eight on average.

Cold is an important cause of the death of people who fall into the water. The use of a gas generating agent to inflate an inflatable lifejacket is a kind of self-heating inflatable lifejacket, which maintains the inflation effect and portability of the original lifejacket and can also play an auxiliary heating effect. In this paper, a nitrogen-rich substance, 5-aminotetrazole 3-nitro-1,2,4-triazole (5ATNTZ) was synthesized, together with the selected oxidant and binder to complete the preparation of the gas generating agent. Commercial life jackets were selected for inflation test to explore the actual dosage and inflation effect of gas generating agent. The experimental results show that when the amount of gas generating agent is 19 g, the amount of physical coolant is 20 g, and the amount of chemical coolant is 7 g, the lifejacket is inflated and its surface temperature reaches at least 40.3 °C. The energy utilization efficiency reaches 75.17% when the chemical energy of the gas generating agent is converted into the heat of the bag and inflation work in the whole inflation process. Therefore, the gas-filled lifejacket using a gas generating agent has a good auxiliary heat effect, and is a type of self-heating inflatable lifejacket with excellent performance, which has great application value.

Wave energy is one of the most remarkable energy in the ocean, which bears attractive characteristics including inexhaustible, renewable and more predictable. Nowadays, the development of the wave energy converter (WEC) is still in the research stage; improving the efficiency is one of the key steps to promote the application process of WECs. This paper proposes a novel 3-degree-of-freedom (3-DOF) WEC called SJTU-WEC; moreover, methods to obtain the conversion efficiency for the each part are proposed. First, the principle of the SJTU-WEC is introduced, and the dynamic model of the SJTU-WEC is established; Next, the capture width ratios (CWRs) of the SJTU-WEC under different waves are obtained based on the Simulink model, and the simulation results show that optimal CWR is above 80%. A 1:80 scaled prototype of the 3-DOF mechanism is built, and the mechanical efficiency for the mechanism is tested to be about 90%. Moreover, a 1:4 scaled prototype of the energy conversion device (ECD) is built, and the efficiency of the ECD based on the power recovery method is tested to be about 80%. Finally, based on the modeling, simulation and experiment, the optimal conversion efficiency from the wave energy to the hydraulic energy of the SJTU-WEC is predicted to be more than 57.6%.

The railway track dynamic behavior shows intense characteristics in a wide frequency domain, which plays an major role in the generation of wheel-rail rolling noise and the deterioration of track structure. To monitor, study, and control the random vibration of the track system, sensors and harvesters were considered as important techniques of vibration monitoring and energy conversion to maintain the healthy service of railway system. Therefore, effectively scavenging the broadband track vibration energy has significant potential to power trackside monitoring sensor and reduce track vibration. This paper presents an efficient rail-borne piezoelectric energy harvester to collect energy from the random railway vibration in a broad frequency range, and the fractional derivative electromechanical coupling model of the coupled vehicle-track-harvester system was firstly established. The proposed piezoelectric harvester was evaluated by laboratory experiments and theoretical piezoelectric analysis with finite element method. The results indicate that the vibration reduction effect of the efficient rail-borne energy harvester is 196 times greater than the ordinary harvester in high-frequency range. Although the open-circuit voltage can be improved by increasing the thickness of the piezoelectric layer, the maximum output power remains unchanged as 1.03 W/Hz. Constrained by the safety limit of stress and deformation of the piezoelectric material, the harvester can be designed by a programmable methodology according to the rail frequency response in a wide frequency range. The output power peaks at the first two resonance frequencies are obtained as 1036.9 μW/Hz, and 8.01 μW/Hz, respectively, and the maximum values are improved by 3.0 and 15.0 times with comparison to the ordinary harvester, respectively.

In this paper, we present a novel hybrid scheme of magnetic, thermoelectric, and vibration energy harvesting (EH) system, which is directed towards the low-power sensing applications within power grids. The topology aims to address the energization of wireless sensor networks that are deployed for the condition-based monitoring purposes of electric facilities. To this end, we have investigated the energy conversion properties of the three EH modalities by means of simulation studies and in-lab experiments. Thereafter, a hybrid energy management system has been established using an ultra-low power consumption circuitry to regulate and integrate individual outputs from the front-end harvesters. During a proof-of-concept, we have observed from a developed demonstrator that a DC output voltage held steady and the output was fed into a ZigBee sensor to keep it operational meanwhile without downtime, which indicates that the power consumption of a ZigBee node can be fully covered by the harnessed energy in the context of this article. Hence, the ambient energy scavenging methodologies discussed herein are well-suited to empower energy-autonomous sensors. The work is characterized by the first demonstration of thorough assessment of the three stray energy forms in the grid and the joint utilization thereof to enhance the system loading capacity. Rather than exploiting a single ambient energy source of some kind, this hybrid and versatile option is proven to accomadate more stable power throutput, and the system signifies feasibilities and potentials to improve the problematic power supplies of the sensors that are deployed within the grid.

Small scale open solar thermal Brayton cycle with Concentrated Solar Power (CSP) system can provide an efficient, clean, sustainable and low cost energy conversion system to produce different forms of energy such as electricity. The current paper investigates various configurations of open cavity solar receivers including cylindrical, conical and spherical with an aperture of 0.02835 m2 and average irradiance values of 2.5 kW/m2. Advanced ray tracing (OptisWorks®12), as this is the latest available version) and computational fluid dynamic (CFD, ANSYS® 15) simulations are used to reduce optical and thermal losses and maximize the exit temperature of the working fluid. The received irradiance on the external surface of the helical coils inside these receiver geometries was used to predict the heat transfer fluid temperature through CFD analysis. Investigations were carried out to discover the effects of coil pitch and tube diameter on the working fluid's exit temperature. The results showed that for a pitch value of 3 mm and a tube diameter of 10 mm, the exit temperature is 401.3 K, 405.7 K and 409.4 K for each of the spherical, cylindrical and conical geometries respectively; indicating that the conical shaped receiver is more efficient than the other geometries. Moreover, the best pitch value, when the higher outlet temperature was achieved, depends on both the tube diameter and the cavity configuration. The effect of some other factors such as the ambient temperature and the pressure losses on the receiver's performance have also been investigated in this study.

Vehicle suspension vibration can cause damping oil temperature-rise, which further effects the suspension performance, rapids the suspension failure, and goes against the vehicle fuel efficiency. This paper focuses on the suspension vibration energy conversion mechanism and energy harvest potential analysis. A mathematical model is developed to characterize the oil temperature-rise and damping force change which is then verified by experimental tests. Both simulation and test results show that the damping oil temperature rises with the excitation time and damping force decreases as the oil temperature rises. The equilibrium temperature almost reaches to 105 °C under sinusoidal excitation with 0.52 m/s maximum speed, and the damping force decreases significantly when the temperature rises from −20 °C to 100 °C. Then the energy flow of regenerative suspension system is analyzed and the suspension energy regenerate potential is explored based on the quarter vehicle model and road roughness model. The model simulation results show that vehicles with large mass, relatively high driving speed, and bad driving conditions have a good application prospect for the regenerative suspension systems.

The hydrodynamic performance of Oscillating Water Column (OWC) wave energy converters depends mainly on the behaviour of the wave–OWC interaction. In this paper, a fully nonlinear 2D RANS–based computational fluid dynamics (CFD) model was used to carry out an energy balance analysis of an onshore OWC. Chamber differential air pressure and free surface elevation from published physical measurements were used to validate the CFD model. Additional validation was carried out via PIV data from available model–scale experiments to validate the CFD model's capability in capturing the flow field and the turbulent kinetic energy. The validated CFD model was then used in an extensive campaign of numerical tests to quantify the relevance of different design parameters such as incoming wave height and turbine pneumatic damping to characterise the hydrodynamic performance and wave energy conversion chain of the OWC. To capture the flow field inside the OWC in good agreement, additional refinement was required at the field of view together with utilizing either SST or RSM turbulence models rather than k-ɛ. It is found that the applied damping has crucial impacts on the energy conversion process. Also, increasing the wave height can lead to a massive drop in the system efficiency. Furthermore, both power take–off (PTO) damping and wave height play an important role in vortex formation around the upper and lower chamber's lips during the in–flow and out–flow stages.

The thermoelectric generator (TEG) is a distinctive solid-state heat engine with great potential in various scale energy harvesting. Device-level heat transfer coupled with energy conversion makes the accurate analysis of the system very complicate. In this paper, the thermodynamic analysis in a TEG module is carried out to study the influence of the contact layer resistance, Thompson Effect, Joule heat, and thermo-pellet gap heat leakage on the performance of the TEG. All expressions of power output, current, matching load resistant factor, and efficiency of the device are derived and compared with a commercial module. The equations for the simplified model are also given concisely in order to give a full picture of TEG modeling. The research can evaluate the combined influence of all the factors and redress some derivations in the existing models.

This paper introduces a novel, looped, thermoacoustically-driven cryocooler, which is a promising candidate for natural gas liquefaction applications. Several thermoacoustic heat engines of different diameters are connected end-to-end by small-diameter resonance tubes. One pulse tube cooler is connected to the branch of the last-stage engine. This system is highly reliable, efficient, and compact for a looped configuration. In particular, the system realized cascade acoustic power amplification with only a single power output, which promises large capacity and structure simplicity. Here, a three-stage traveling-wave system is designed and numerically investigated. A comparison is made with the existing multiple pulse tube cryocoolers which indicates the superior performance of this novel system. The distributions of some key parameters and the exergy loss are presented and analyzed to better understand the energy conversion process. Two area ratios are found to be critical to the engine performance. According to the calculation, using 7 MPa pressurized helium gas, a cooling power of 1300 W and a total exergy efficiency of 15.7% is achieved at 110 K with 20.2 kW input heat at 923 K.

This paper is focused on a theoretical study in search for new technological solutions in the field of electricity generation from biomass in small-scale distributed cogeneration systems. The purpose of this work is to draw readers' attention to possibilities of design complex multi-component hybrid and combined technological structures of energy conversion plants for effective use of locally available biomass resources. As an example, there is presented analysis of cogeneration system that consists of micro-turbine, high temperature fuel cell, inverted Bryton cycle module and biomass gasification island. The project assumes supporting use of natural gas and cooperation of the plant with a low-temperature district heating network. Thermodynamic parameters, energy conversion effectiveness and economic performance are examined. Results show relatively high energy conversion performance and on the other hand weak financial indices of investment projects at the current level of energy prices. It is however possible under certain conditions to define an optimistic business model that leads to a feasible project.