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Nowadays, multi-functional systems driven by solar energy have been explored to alleviate the crisis of energy and freshwater scarcity. However, it remains a great challenge to integrate multi-functions into one hybrid system with a monolithic material, which can harvest, convert and store solar energy synergistically. Here, we firstly propose a multi-functional carbon nanotube paper, which starts from a material level to solve these problems. The carbon nanotube paper is fabricated by vacuum filtration. It exhibits high efficiency of solar-thermal conversion. Secondly, three types of energy conversion/storage systems (e.g., solar-thermal evaporation system, solar-thermoelectric generation system, and supercapacitor) are constructed based on the carbon nanotube paper, which extend the research to a device level. The solar-thermal evaporation system shows an evaporation rate of 1.28 kg m-2h−1 under simulated sunlight irradiation of 1 kW m−2. The solar-thermoelectric generation system demonstrates a stable electric power generation with an output voltage of 100 mV under light irradiation of 1 kW m−2. The supercapacitors perform the energy storage function with an areal specific capacitance of 19.6 mF cm−2. These devices and systems can be used in freshwater generation (0.84 kg m-2h−1, sunlight irradiation of 1 kW m−2), water purification/desalination (inorganic ions rejection larger than 99.9%) and portable solar charging system (maximum output voltage of 5 V). Finally, a hybrid energy system is innovatively proposed from the system level to simultaneously produce freshwater, generate and store electric power. Through the synergetic coupling of solar conversion and storage technologies, the hybrid energy system can supply sustainable freshwater and electricity for remote areas in daily life, highlighting the superiority of multi-energy (thermal energy, electrical energy, and electrochemical energy) complementary.

Along with the chic fad energy industry field, the graphene application in energy conversion and management does bring about some benefits in terms of the energy transfer and storage development, the achievement it exerts on the multifaceted innovate approaches. Both current and previous studies on energy conversion, energy storage and energy transfer development, many research results are sufficient to show that all graphene products including graphene paper, film, foam and fiber have a significant role in improving performance. In the energy conversion research on the graphene paper, it has been recently demonstrated that putting the graphene into triboelectric nanogenerators practice possesses higher output performance than traditional generator, which has a maximum strain as large as 200% without evident degradation of the electrical properties. In terms of energy transfer, the graphene fiber application on the battery can significantly increase the charge and discharge rates with enhanced storage capacity of 763 F g−1. On the energy storage research, the graphene foam can enhance a high density of solar thermal storage up to 269.8 kJ kg−1 for long-term. Nano-graphene and graphene coating provide feasibility for the miniaturization of energy storage equipment which inspired the possibility for portable and foldable devices. The work done in this paper can effectively help promote the application of graphene in energy field. Based on our work, the researchers can choose graphene products (graphene paper, graphene film, graphene foam or graphene fiber) efficiently according to the research object in the future.

Conversion of energy with the highest possible efficiency is of primary importance in processes with high intensity of energy flows, among which the most significant are those in thermal power plants. The paper deals with the influence of coal composition on the conversions taking place in power plants. The analysis of energy conversions treats, above all, the heat loss due to the exhaust flue gas. The analyses of the power plants use of electric powers are focused on the processes of coal pulverising and exhaust flue gas cleaning. The results of the analyses are graphically presented.

The objective of this paper is to carry out a dynamic exergetic assessment of a large complex building. Results in this paper show that although the building and its Heating, Ventilation, and Air Conditioning (HVAC) systems with an energetic efficiency of 122.6% meet energy performance regulations, their overall exergetic efficiency is extremely low (3.68%). This emphasizes the importance of exergy analysis in buildings to improve the quality match between energy supply and demand, and consequently, to increase the sustainability of the building energy system. From the exergy point of view, the main sources of thermodynamic inefficiencies in the considered building are energy conversion systems, energy distribution layer, and energy released to the environment with 54, 21 and 16% of the total exergy destruction, respectively. However, among these sources of inefficiency, only the last one can be detected through an energy analysis. The exergetic efficiency of the system decreases when the exergy demand decreases, but the same energy sources are used to fulfill the demand. This reveals a potential to improve the efficiency of the building’s energy system through the implementation of an exergy-based control strategy. The high-temperature heating network provides around 26% of the low-temperature heating demand. From the exergy point of view, however, this share is approximately 46%. This indicates that the quality of the supplied energy from the high-temperature heating network is much higher than required and the heat transfer from the high-temperature to the low-temperature heating network decreases the exergetic efficiency of the building.

The manufacturing sector has been one of the most significant energy consuming and CO2 emitting sectors over the past three decades. Therefore, it is important to have energy flow models of manufacturing processes to identify efficiency improvement and waste heat recovery opportunities with very specific targets. One of the best methods to pinpoint such locations is by referring to manufacturing process step models. Such models can be created on a large scale per industry and on small scale per process within an industry branch. Industry level modeling provides energy saving contingency by large magnitude where the impact on the economy and environment can be observed more visibly especially when sequential trends are identified. The methodology, reviewed in this paper, describes how to model energy flows on an industry scale by deriving the connection between key energy conversion activities on the one hand – including energy purchased/sold and onsite electricity generated, and the key end uses on the other hand. Industry-level energy flow model, referred to in this work, does not assume any specific system. That feature makes it scalable and allows analysis of manufacturing at various levels starting with single processes and finishing at sector and national economy levels. A combined analysis of the procedure is described in detail for creating process step models of manufacturing processes. The availability of U.S. national databases to calibrate these models is discussed and the challenges that arise in finding and using such databases are identified and analysed. In addition to addressing generic data issues associated with energy flow models, the paper also focuses on energy and material models and presents several examples of energy-intensive manufacturing processes, producing industrial gases, textiles, pulp and paper. Finally, importance of water use in onsite energy conversion and process end uses in various industries is addressed along with the sources of where this important data can be found to complete the energy flow modeling.

Transformation optics based metamaterial thermal harvesting devices, which provides power and efficiency related advantages by manipulating and concentrating thermal fluxes, have attracted considerable research interests. The potential utilizations are significant for improving the energy conversion efficiencies in existing collecting technologies including heat storages, solar thermal collectors, full cells, etc. However, most of the current researches on thermal harvesting devices are mainly focused on continuous shape profiles based on the scattering cancellation. In this paper, we propose a novel method for fabricating desirable polygonal thermal harvesting devices with homogeneous and nonsingular parameters through linear mapping function. Four polygonal concentrating schemes with fewer kinds of natural materials filling inside the functional regions are demonstrated in transient states. The expected harvesting performances are achieved for each proposed polygonal scheme. Furthermore, the proposed thermal harvesting performances are investigated as a function of the dense degree of the medium-layer configurations. In general, this paper demonstrates a novel method for designing non-continuous shape polygon harvesting devices with corresponding validations. Improved concentrating behaviors would be achieved with denser medium configurations, implemented as appropriately arranged fractions. The findings could have potentials for designing novel transformation optics devices and providing improved energy conversion efficiencies in existing collecting technologies.

The paper is part of the development of a novel underwater isothermal Compressed Air Energy Storage (CAES) system. Compared to conventional CAES plant, the performances of this system only depend on the electrical energy required for a round-trip cycle; performances of each sub-system of the power conversion process takes part of the overall efficiency. Consequently, this work is focused on an optimal energy management of the electrical power conversion system driving the isothermal hydro-pneumatic mechanism enabling the air compression/expansion. After examining inherent characteristics of conversion components challenging the overall conversion efficiency, we propose an efficient platform layout based on the segmentation of the energy conversion multiplying power conversion systems with different power ranges. Then, we establish control laws required by the electrical multi-machines system in order to drive pumping systems closed to their best efficiency points. However, these laws subject the conversion platform to a transient and variable operating needing the design of robust controller structures. Finally, we develop a dynamic reversible modelling of the multi-physic conversion platform along with the control scheme. The layout is modelled on Matlab® Simulink® environment and the paper closes with simulation results. We evaluate the dynamic performances of the compressed air storage system in both storage and production mode. Moreover, the effectiveness of power segmentation for the grid integration of the proposed system is discussed.

Recently thermoelectric generation (TEG) systems are gaining popularity due to their increased power density and wide applications in industrial and energy conversion applications. This paper presents a novel optimal control technique for TEG systems under non-uniform temperature distribution (NUTD). Although centralized MPPT control can reduce the footprint and cost of MPPT of TEG systems and provide excellent advantages over the cross-tied, string, and distributive control configurations, it suffers from drawbacks caused by NUTD on the hot or cold sides of TEG modules. Specifically, the bypass diodes streamline the power flow in centralized TEG systems, which may generate multiple local maxima in electrical characteristics curves of TEG systems. To resolve such issues, this paper implements a novel MPPT control technique based on a swarm intelligence (SI)-based optimization algorithm, Equilibrium Optimization (EQO). To study the effectiveness of the proposed EQO technique, five distinct case studies were used. Additional sensitivity analysis and statistical studies were also done to analyze the comparative performance. The results show that the power tracking efficiency can be increased to 99.68% with 1.8–8% more energy harvesting. The stable voltage and current transients can be achieved with a min tracking time of 180 ms, achieving up to 46% faster GM tracking and 238% faster settling time than some conventional MPPT control techniques. In light of experimental simulations, it is safe to conclude that the proposed EQO-based technique outperforms the existing control techniques for TEG systems under all concerned operating conditions.

This letter discusses the model for solar desalination productivity proposed in the paper ‘‘Solar desalination using humidification–dehumidification processes. Part II. An experimental investigation’’, [Energy Conversion and Management, 45 (2004) 1263–1277] by Nafey et al. (2004). In their study, the dimensional analysis is used to deduce the model, and the physical variables considered include the total solar energy incident through day, energy of water input to unit, energy of air input to unit, air flow rate, feed water flow rate, productivity, cooling water flow rate, average inlet temperature of cooling water, average water inlet temperature to water heater, average air inlet temperature to air heater, average ambient temperature through day and average wind speed through day. It is found that there are some mathematical issues should be improved in the derivation processes. Since Nafey’s paper has been a well-cited publication on solar humidification-dehumidification desalination and often serves as a reading to newcomers in this field, this letter aims to rectify the issues and to provide a complete derivation.

Human walking induces a lot of mechanical energy available for harvesting. It is promising to use such energy to reduce the energy supply of wearable electronics and robotic equipment such as exoskeleton. This paper mainly deals with the design and performance analysis of the energy recovery system based on fluid power transmission principle. Firstly, modeling and simulation of single foot walking motion were carried out to investigate the human walking dynamics to explore the variation of energy produced by human walking within a gait cycle. Together with gait characteristics measurement, the foot-ground interaction force in the horizontal and vertical directions is obtained. Then, the energy recovery system based on the working principle of volumetric pump was designed to convert the human walking induced mechanical energy into hydraulic energy directly and achieve energy storage with accumulator in the meantime. The energy recovery results obtained under different conditions of walking speed and load carrying are considered by numerical simulation and experimental verification. It is shown that the output power in average of the recovery mechanism by single foot walking at 5.56 km/h is around 3.2 W, and the captured power can be increased with higher precharge pressure of accumulator. Comparisons indicate that power and its density of the system proposed in this paper are far greater than that achieved by electric generation, providing a potential solution for hydraulically actuated walking mechatronic systems.

This paper examines the transport phenomena and optimal performance of an integrated concentrated photovoltaic and photoelectrochemical hydrogen reactor. Individual components and the overall system are studied experimentally including the performance of the concentrator, spectrum-splitting mirror, electrolyser, reactor, and photovoltaic module. Integrating the solar concentration with a spectrum-splitting mirror allows simultaneous photovoltaic electricity generation and direct photonic energy conversion to produce hydrogen via electrolytic and photoelectrochemical water splitting. A multi-objective optimization of the integrated system is performed with machine learning and integration of a neural network. This yields a relationship between the system inputs and outputs. The neural network is used to optimize the overall system through a genetic algorithm. Numerical and experimental results are presented and discussed in the paper.

In this paper a brief review on application of nanofluids in heat exchangers has been addressed. One of the barriers to increase the capacity of different industries is the lack of response of heat devices in higher capacities. In addition, increasing capacity leads to an increase in pressure drop and this is one of the most important restrictions on the large industries. Conventional methods of increasing heat transfer greatly increase the pressure drop, and according to the results of previous studies, using the special nanofluids, the thermal efficiency of the heat exchanger can be increased significantly, which is one of the most important thermal devices in the industry. In this research, firstly a review of nanofluids studies and introduction of nanofluids is presented, then their simulation methods are investigated, and finally, studies on the used tubes in the heat exchangers have been investigated, and studies of the plate heat exchanger, helical heat exchanger, shell and tube heat exchanger, and double-tube heat exchanger have been examined. The enhancement of thermal and hydraulic performance of heat exchangers is very important in terms of energy conversion, and also is important in the economic recovery of systems through savings. This paper examines previous studies on heat exchangers and using of nanofluids in them. The purpose of the paper is not only to describe the previous studies, but also to understand the mechanisms of heat transfer in the field of using nanofluids in heat exchangers, and also to evaluate and compare different heat transfer techniques. Finally, it can be concluded that the nanofluids in most cases improve heat transfer, which reduce the volume of heat exchangers, saving energy, consequently water consumption and industrial waste.

The authors would like to add some corrections to the published paper “An integrated system for sewage sludge drying through solar energy and a combined heat and power unit fuelled by biogas”, Energy Conversion and Management, Volume 171, 1 September 2018, Pages 587-603. The corrections provided here do not affect main findings and conclusions of the original paper.

This study presents some comments on paper “Classification of solar radiation zones and general models for estimating the daily global solar radiation on horizontal surfaces in China’’, [Energy Conversion and Management, 2017.10.043.] proposed by Liu et al. (2017). In their paper, the selected 4 models were studied before by Almorox and Hontoria (2004) in Spain and they did not present all discussion of their results which indicated that the cubic model gave a slight improve rather than the quadratic and linear models. The proposed general global solar radiation model is not new, it was developed and evaluated before by Rensheng et al. (2006).

Energy flows and energy conversion efficiencies of commercial plug-in hybrid-electric vehicles (PHEV) are analyzed for parallel and series PHEV topologies. The analysis is performed by a combined analytical and simulation approach. Combined approach enables evaluation of energy losses on different energy paths and provides their impact on the energy consumption of the PHEV. Thereby the paper reveals energy conversion phenomena of different PHEV topologies operating according to charge depleting and charge sustaining modes as well as according to different test cycles. It is shown in the paper that amount of the energy depleted from both on-board energy sources is significantly influenced by the efficiencies of energy conversion chains from on-board energy sources to the wheels. It is also shown that energy used to power the PHEV according to particular test cycles varies based on its operating mode, which influences energy flows on different energy paths within the PHEVs and consequently overall energy consumed by the PHEV. The paper additionally discusses well-to-wheel efficiencies considering different realistic well-to-tank scenarios. It is shown that well-to-tank efficiency of electric energy generation significantly influences optimal operating mode of the PHEV if consumption of primary energy sources is considered.

The aim of this two part paper is to present the results of extensive simulation and analytical analysis of the energy conversion efficiency in parallel hybrid powertrains. The simulation approach is based on an accurate and fast forward facing simulation model of a parallel hybrid powertrain and a conventional internal combustion engine powertrain. The model of the ICE is based on a verified dynamic model that provides sufficiently small time steps to model adequately the dynamics of electric systems during transient test cycles. Models of the electrical devices enable computation of the instantaneous energy consumption, production and storage as well as computation of the instantaneous energy losses and component efficiencies. Moreover, the paper offers an analytical approach based on the energy balance in order to analyze and predict the energy conversion efficiency of hybrid powertrains. The analysis covers a broad range of parallel hybrid powertrain configurations from mild to full hybrids. Combined simulation and analytical analysis enables deep insight into the energy conversion phenomena in hybrid powertrains. The paper reveals the conditions and influences that lead to improved fuel economy of hybrid powertrains with the emphasis on determining the optimum hybridization ratio. The theoretical background, simulation program and brief analysis of one test cycle are presented in Part 1, whereas the extensive analysis and parametric study is presented in the companion paper, Part 2.

This paper presents a new variable mass energy transformation and storage (VMETS) system using ammonia–water solution (NH3–H2O) as working fluid. The system has a wide range of working temperature. It can be used to shift load with a diurnal energy storage system for cooling in summer, heating in winter, or hot water supplying all year long. It can also be used to store refrigerating energy for various industrial and commercial applications. The key to the system is to regulate the chemical potential by controlling the refrigerant mass fraction in the working fluid with respect to time. As a result, by using a solution storage tank and an ammonia storage tank, the energy transformation and storage can be performed at the desirable time to provide low cost cooling and heating efficiently. As the first part of our study, this paper presents the principle and dynamic models of the VMETS system and performs the numerical simulation when the system works in the cooling and heating modes, respectively, under the full storage strategy. The simulation predicts the dynamic behavior of the VMETS system under various operation conditions and shows that the VMETS system for cooling in summer is also suitable for heating in winter or for hot water supplying all year long by adjusting the initial solution concentration. The energy conversion efficiency of the system is larger than that of conventional thermal energy storage (TES) systems, especially under the condition of system operation for heating or hot water supplying in the heating mode. These simulation results are very helpful for detailed design and control of the system. To investigate the system performance under the partial storage strategy, modeling and numerical simulation will be performed in a subsequent paper.

This paper reviews the present state of the art on self rectifying air turbines, which could be used for wave energy conversion. The overall performances of the turbines under irregular wave conditions, which typically occur in the sea, have been evaluated numerically and compared from the viewpoints of their starting and running characteristics. The types of turbine included in the paper are: (a) Wells turbine with guide vanes (WTGV); (b) turbine with self-pitch-controlled blades (TSCB); (c) biplane Wells turbine with guide vanes (BWGV); (d) impulse turbine with self-pitch-controlled guide vanes (ISGV); and (e) impulse turbine with fixed guide vanes (IFGV). As a result, under irregular wave conditions, it is found that the running and starting characteristics of impulse type turbines could be superior to those of the Wells turbine. Moreover, the authors have explained the mechanism of the hysteretic behavior of the Wells turbine and the necessity of links for improvement of the performance of the ISGV.

This paper has the intention of discussing about a recently published paper by M.T. Hagh et al. (2014). In the discussed paper the combined heat and power economic dispatch (CHPED) problem solved by applying an improved group search algorithm. To show the performance of the algorithm, three large scale test systems were simulated. In modelling, consideration of both valve point effect and prohibited zones in the operation of power units distinguishes discussed paper from earlier works. However, there are some errors in the reported results. This discussion clarifies calculations and presents corrigendum to the results.

This paper develops nonlinear models for diesel–electric powertrains used in medium- and heavy-duty hybrid-electric vehicles and describes a new method for designing optimal controllers for highly coupled drivetrains. Current applications of heavily loaded, heavy-duty drives call for the use of comprehensive, innovative ways of handling a large variety of nonlinear phenomena in order to optimize performance and energy conversion, to shape steady-state characteristics and to meet other desired specifications. It is evident that energy conversion and optimal energy management should be integrated and thoroughly studied. This paper demonstrates the application of derived nonlinear models of drivetrain components (diesel, synchronous generator, traction motor) analyzes the nonlinear energy conversion and develops an innovative design method to control these highly nonlinear diesel–electric systems. Fundamental analysis and design methods, such as the Lyapunov stability theory and admissibility concept, are used to attain nonlinear analysis, design and motion control. The developed concept in nonlinear analysis and design allows one to synthesize optimal tracking controllers for highly nonlinear systems with minimal approximating simplifications and assumptions used in the model development. New promising analytical results are presented along with a supporting example involving a controlled, 40-ton vehicle with a hybrid-electric drivetrain. Experimental data is reported to validate the results.

In our published paper, Gueymard’s model showed a performance that was significantly worse than the results obtained by other authors like Utrillas et al. [3] or Kambezidis et al. [4]. As a consequence, Dr. Gueymard has called our attention to the existence of an erratum [2] to his original paper [1], where the correct values of some of his model coefficients are given. Unfortunately, we had not taken into account these correct coefficient values in our publication. Therefore, the comments it contains about the results of Gueymard’s model are obviously not valid. As a consequence, we have repeated the performance evaluation of Gueymard’s model using the correct coefficients. The new results effectively show noticeable differences, as described further below.

The objective of this paper is to show that for the optimal design of an energy system, where there is a trade-off between exergy saving during operation and exergy use during construction of the energy system, exergy analysis and life cycle analysis should be combined. The two methods are often used separately, but a limited number of studies has been carried out in which they are combined in some way. An exergetic optimisation of a heat exchanger has been carried out on the basis of the life cycle analysis method in this paper. The optimisation takes into account irreversibilities due to frictional pressure drops and the temperature difference between the hot and cold stream and irreversibilities due to the production of the materials and the construction of the heat exchanger. As an example of this type of heat exchanger, a water to water heat exchanger in a city heating system has been selected. The influence of the configuration of the heating system, including the energy conversion, on the optimisation of the heat exchangers has been shown. The analysis of the heat exchanger in which exergy analysis and life cycle analysis are combined gives the design conditions of the heat exchangers which lead to the lowest life cycle irreversibility.

This paper reviews some leading novel energy conversion approaches which are aimed at improving power generation efficiency and/or reducing harmful emissions. Some of the concepts used for cycle improvement are higher top temperatures, improved combustion systems, evasion of the Carnot limit by integration with fuel cells and direct nuclear energy conversion to power (the nuclear generator), reduction of exergy destruction by staging and the use of exergy-efficient combustion processes, the use of lower temperature heat sinks and the use of renewable, environmentally-benign energy sources. Some of the systems described in this paper are hybrid multi-temperature source cycles (including the hybrid solar-powered/fuel-assisted Rankine cycle), high-temperature chemical gas turbine cycles, fuel-cell-topped Rankine cycles, high temperature ejector-topping power cycles and hybrid nuclear/fossil fuel power generation systems. The use of space (the extra-terrestrial environment) for energy conversion improvement is also discussed.

The paper studies the performance of a novel generator, consisting of a ball tightly sandwiched between two dielectric elastomeric membranes for energy harvesting. The membranes are built into a housing subjected to external ambient random vibrations, so that the relative motion between the ball and the membranes deforms the latter allowing energy conversion. A dynamic model of the nonlinear mechanical and electrical behaviour of the device is presented, and a novel approach for estimating the mean output energy of the device is developed. An explicit analytical formula for the mean output power, derived and presented for the first time, allows comparing the generator performance depending on the level of nonlinearity and the membranes deformation rate. A comparison of the generator performance for the linear and nonlinear device properties is demonstrated. The numerical results of the Monte-Carlo simulations are presented and agreed well with the derived analytical estimation.

A novel hybrid parabolic trough power system that integrates direct steam generation and molten salt systems is proposed in this study to stably and efficiently operate solar power plants. The feedwater from the power block is preheated and evaporated in a low temperature direct steam generation solar field. A high-temperature solar field using molten salt as heat transfer fluid is employed to superheat and reheat the steam to 540 °C. The heat transfer model based on energy conversion and balance is applied to numerically investigate the overall performance of various power plants. This paper presents a comparative study of the effects of different locations, steam turbines, and system configurations on the outputs of the power plants. The hybrid systems exhibit favorable system stability and reliability and an excellent overall performance. The molten salt loop percentages of hybrid systems with and without reheat section are only 45.1% and 37.4%, which lead to low energy loss in the operation period and low molten salt freezing protection energy. The annual thermal energy productions of the hybrid systems with and without the reheat section in Tonopah are 685.1 and 691.7 GWh, and the percentages of energy required for freezing protection of those systems are 3.2% and 2.7%, respectively. The hybrid systems with reheat section exhibit optimal electricity production and economic performances compared with those of other configurations. The electricity production increments of novel systems in Tonopah and Lhasa are 14.0% and 14.8%, respectively, compared with those of molten salt systems.

Hydraulic excavators are essential excavation machines, with more than 3.8 million sets in use in the mining, and engineering and architectural engineering construction fields. However, during the working process, a large amount of gravitational potential energy is wasted, causing low energy efficiency and poor emissions. Taking a large-scale excavator as an example, during a certain 90° excavation process, the gravitational potential energy wastage of the working device is approximately 975.1 kJ, which amounts to at least 20% of the energy consumption of the entire machine, causing significant energy waste and serious pollution. And, during the boom lowering process, the changing rate of potential energy is about 406.4 kW. In order to improve the energy efficiency of hydraulic excavators, the recovery of this huge energy that changes rapidly with low cost and high efficiency is a big problem that must be solved. This paper proposes a gravitational potential energy recovery scheme with an energy conversion cylinder and a hydraulic accumulator. Using this scheme, the gravitational potential energy of the working device can be stored and reused directly, without increasing the cost and install power of the machine largely. In the study, first, the system parameters are designed, following which the multidisciplinary dynamic model of the hydraulic excavator is established. The influence of the accumulator parameters on the energy recovery ratio is studied based on the model. The results demonstrate that with the newly designed system more than 75.9% of the gravitational potential energy can be stored in the accumulator during the lowering process. Moreover, during a certain lifting process, the input energy to the pump can be reduced by 52%. On this basis, a 76 t hydraulic excavator test system is constructed using the above principle. The experimental results match strongly with the co-simulation results. The energy consumption can be reduced to approximately 238 kJ during a certain 90° excavation cycle, and the system can reduce the carbon dioxide emissions by 28088.4 kg per year. The energy-saving and emission-reduction effects are remarkable; furthermore, this principle can directly be applied to other lifting machines.

In this paper, we report a hybrid generator to harness energy from low-frequency ambient vibrations. The generator is designed with a piezoelectric energy harvester (PEH) patch, a triboelectric nanogenerator (TENG) patch, a spring-mass system and an amplitude limiter. The spring-mass system receives energy from excitations and applies forces to the piezoelectric element and the triboelectric layers. The unique amplitude limiter is deliberately introduced into the system, not only achieving the desired frequency up-conversion effect, but also boosting the voltage responses significantly. The limiter also causes hardening nonlinearity and dynamic bifurcation triggering superharmonic resonance so that the generator resonates at a frequency of about 3 Hz. Furthermore, the proposed PEH adopts the strong compressive operation mode, and employs a truss mechanism to effectively amplify the impact forces. In experiments, open-circuit voltages are 58.4 V from PEH and 60 V from TENG under an excitation of 1.0 g at resonance. The hybridized generator is capable of achieving a maximum power of 19.6 mW from the two sources with matched impedances. The working bandwidths of the PEH and the TENG reach up to 5.39 Hz and 7.25 Hz, respectively, out of our targeted frequency domain [2.5 Hz, 10 Hz] due to the multiple resonances and nonlinearity. In the applications to charge capacitors, the high saturation voltage and relatively short charging time validate the effectiveness of our power management technique. Furthermore, the generator proves to be able to effectively scavenge energy from human body motions and charge a capacitor of 4.7 μF to 7.6 V in around 50 s, which indicates a great potential of practical applications in wearable devices.

To ameliorate the adaptability of the ship waste heat recovery system (SWHRS) to the variable energy demand, this paper proposes a CO2-mixture-based SWHRS providing refrigerating output as well as adjustable heating and electrical output. The adjustability deriving from mixture composition regulation profits from liquid separation condensers. A scientific vessel YUKUN is selected as the recovery target, the energy demand characteristics of which in different seasons (spring/autumn, summer, and winter) and conditions (sailing and berthing) are exploited to determine six operating modes. Well-designed configurations of SWHRS’s subsystems with different energy exportation emphases improve the matching of SWHRS to changes in energy demand. Moreover, composition adjustment corresponding to various energy requirements further modifies the energy conversion tendency of waste heat to heating or electrical energy desired by the target ship. Comparative research demonstrates that SWHRS possesses certain superiority over the non-adjustable system due to the regulation of mixture composition corresponding to variation in energy requirement. Thus, the SWHRS can reduce the fuel consumption rate by 4.9% to 17.2% compared to the original waste heat recovery system in YUKUN at different modes. Based on actual operating data, the SWHRS can realize a decline of 10.3% in the annual fuel consumption rate. Hence, a fuel charge of 245 000 USD could be saved for YUKUN equipped with SWHRS for one year.

The ocean contains copious available natural resources and energy. Ocean in situ power generation technology, directly harvesting energy from ocean fluids, is the crux of solving the problem of power supply for eupelagic or deep-sea exploration equipment. However, the ultralow frequency and wide-flow-rate characteristics of ocean fluids have brought severe challenges to in situ power generation in the ocean. In this paper, we develop a broadband rotary piezoelectric-electromagnetic hybrid generator to effectively harvest the energy of wide-flow-rate and ultralow frequency fluids. By using rotational torque to directly drive deformation of piezoelectric films, the hybrid generator effectively collects extremely low-speed rotational energy (as low as 0.01 Hz), with the efficiency and speed of energy conversion of the piezoelectric component of the generator being respectively 8.2 times and 60 times higher than that of a traditional piezoelectric cantilever beam harvester. The integration of the electromagnetic component further improves the energy harvesting performance of the generator over a wide flow velocity range. Compared with existing energy harvesters, the water-driven power generation per unit flow rate is enhanced by a factor of 75.5. The output power density of the proposed underwater bubble power generation system using the hybrid generator is 287 mW/m3, which is 275 times higher than previous devices. This work provides a viable approach to blue energy exploitation, especially ocean in situ power generation, and opens up many prospects for underwater cable-free power supply to eupelagic or deep-sea equipment.

This study offers an efficient method to improve manufacturing technique of metallic bipolar plates (BPPs) so as to simultaneously reduce contact resistance (CR) and maximize power density in proton exchange membrane fuel cell (PEMFC). CR plays an important role in the energy conversion in the cell and can be normally reduced by coating on the BPP surface. Nevertheless, the effect of fabrication process on the CR has not been revealed, especially for the welding and forming characteristics. In this paper, a comprehensive three-dimensional finite element model of BPP/gas diffusion layer (GDL) assembly was established to investigate the influences of coating, weld and dimensional error on the CR, which are produced during the fabrication process of metallic BPPs. Experiments were carried out to validate the accuracy of the model. The results indicate that direction and distribution of the current in the cell change significantly with altering the weld path of metallic BPPs, which are different from graphite BPPs. 47% CR reduction is observed for the case of dense weld arrangement. For the coating process, it is found that the necessity of coating on both sides of single BPP is quite low if channel number is less than 20. Statistic simulation was conducted to investigate the effect of dimensional error on CR. Specially, 14.5% increment in CR is found when the dimensional error exceeds 30 μm. The methodology developed is beneficial to the fabrication management of metallic BPPs and the efficiency improvement of PEMFC.

Microcogeneration systems guarantee the reduction of primary energy consumption and greenhouse gas emissions in residential sector, by reducing fossil fuels demand and grid losses with respect to conventional energy conversion systems. Energy, environmental and economic benefits can be obtained sharing the cogenerated thermal and electric energy among different end-users to increase the operating hours of the microcogeneration plant with respect to the scenario in which energy demand of each end-user is satisfied by a single cogeneration system. This paper analyses a microcogeneration system used to satisfy electric, space heating and domestic hot water demands of two separate residential buildings located in Spain in a load sharing approach. It consists of a natural gas fuelled internal combustion engine with a thermal and electric power of 12.5 kW and 5.5 kW, respectively. An auxiliary boiler with a nominal thermal power of 24 kW, is also included. The domestic hot water and the heating requirements are managed by means of two different thermal energy storages. The proposed energy conversion systems were experimentally analysed in a test facility in Vitoria Gasteiz (Spain). The models representing the components and the buildings have been implemented in TRNSYS 17. The energy, environmental and economic performance of proposed system are compared with those achieved by a traditional system based on separated energy production. The results highlight that the load sharing between users with different load profiles leads to better environmental and thermo-economic results with respect to the conventional system. The microcogeneration plant works for about 3000 hours per year achieving a primary energy saving of 12.1% and a reduction of equivalent CO2 emissions equal to 27.8%. The payback period of the analysed solution is equal to 11.9 years unless economic support mechanisms are considered. The results of this study show that the introduction of a microcogeneration system in load sharing approach leads to energy, environmental and economic benefits even considering two separate residential buildings, occupied by users with different behaviour.

In the course of energy conversion, steam turbine is one of the most important equipment, but the wet steam at the low-pressure stage will cause losses. The losses caused by condensing flow not only reduce the efficiency of steam turbine but also influence reliability. This paper firstly numerically investigated the Dykas cascade using the modified model, and compared with the experimental data. The results showed that the modified model had an enormous advantage in predicting the condensing flow. Besides, the advantage was obvious in calculating the pressure distribution of the blade and shock angle emerged in the blade trailing edge. Secondly, a novel dehumidification structure was proposed and the effect was calculated and discussed. The result showed that the novel structure had a positive effect on reducing the nucleation zone and the liquid mass fraction. Besides, the influence of different passage diameters was investigated, the conclusion can be drawn: both the liquid mass fraction of the outlet and the nucleation zone decrease with the increment of the passage diameter. Finally, an improved dehumidification structure which can be easily manufactured was presented and the structure with different φ was calculated. The results showed that when φ = 0 , the dehumidification efficiency was remarkable, and the structure can be easily manufactured. However, the decrement of the liquid mass fraction was inconspicuous with the further increment of φ .

Thermoacoustic engine, with the outstanding characteristics of high reliability and environmental benignity, is one of the most attractive and promising energy conversions to recover low-grade thermal energy. In this paper, a three-stage looped thermoacoustic electric generator, consisting of a three-stage looped thermoacoustic engine and a linear alternator, was proposed and built. To obtain a better coupling between the thermoacoustic engine and the linear alternator, the acoustic impedance of the linear alternator has been adjusted by modulating the external electric resistance/compliance and the frequency. The frequency was adjusted by adopting the He-Ar mixture. Additionally, the location and the length of compliance tube have been optimized to improve the acoustic field in the system. Upon optimization, a maximal thermal-to-electric efficiency of 1.51% can be achieved at the hot temperature of 120 °C with He-Ar mixture as the working fluid, in which the mole fraction of helium was 0.63. Furthermore, the system has also been tested in the hot temperature range of 90 °C–200 °C. Results show that the thermal-to-electric efficiency stabilizes at around 1.5% when hot temperature is in the range of 120 °C–170 °C.

Using high-performance expanders is one of the keys to improve the efficiency of Organic Rankine Cycle (ORC). However, in large expansion ratio conditions, the performance deterioration caused by under-expansion seriously affects the performances of the ORC. For single-screw expanders, it is possible to utilize the kinetic energy of the screw groove exhaust to produce extra power. But there is still a lack of theoretical support for optimizing the exhaust kinetic energy utilization process of this new expander at present. Therefore, the energy conversion mechanism of Single Screw Expander with exhaust Kinetic energy Utilization (SSEKU) was investigated in this paper, and a mathematical model of SSEKU was developed to investigate the energy conversion mechanisms and predict the performances. The results show that introducing exhaust kinetic energy utilization process in single screw expander can reduce under-expansion losses effectively, and the effects in large size expanders were stronger than that in small scale machines. It was also found that the maximum increase in isentropic efficiency was 3.01, 5.47, and 9.38 percentage points for the expander with a screw diameter of 117 mm, 200 mm, and 350 mm, respectively.

Tethered multirotor axial flow turbines have been proposed to overcome the many challenges associated with extracting ocean current energy where deep waters render seabed mounting strategies infeasible. However, flexible systems are inherently more susceptible to perturbation than fixed systems. The effects of flow misalignment on the hydrokinetic energy conversion of multirotor coaxial turbines have been investigated recently; however, the spatial dynamics and equilibrium behaviors of tethered coaxial turbines have not been well characterized, limiting the ability of designers to explicitly tailor the device behavior. In this work, a computational model of a dual-rotor coaxial turbine is presented, and the model is employed to explore the equilibrium behavior of the turbine with variations in parameters. A complete characterization of the hydrostatic state of the system and a comparative study of representative tethered turbine simulation cases is also presented. Two important findings are presented. First, that a positively buoyant dual-rotor turbine that is anchored to a surface-dwelling platform can operate where the turbine is located at some desired depth below the surface. Second, that more than one turbine system may be anchored to a single point while maintaining the desired orientation and position of each turbine to avoid collision and maximize energy production. The results and methods presented in this paper may be used to inform application-specific coaxial turbine design and to develop additional targeted empirical and simulation studies.

The energy density of wave power in China is relatively low compared with that of the wave power in Europe. Simply improving the shape or size of the energy-capturing mechanism for a wave energy converter (WEC) cannot directly result in a larger energy output. Instead, a solution of array-type energy-capturing mechanism integrating marine structure bares practical application potential to increase the power take-off (PTO) productivity. To exploit the conditions in China, a WEC system integrating oscillating-array-buoys with a floating platform is proposed and sea trials of a 10 kW prototype confirmed the feasibility of the floating-array-buoys WEC (FABWEC) system for wave energy conversion. However, sea trials data indicated that the energy conversion performance of the mechanical transmission design in the FABWEC system was relatively poor under the low wave energy density, suggesting the urgency of improving energy conversion and storage system to the increase of system performance. Herein, a hydraulic transmission and accumulator system (HTAS) is designed to replace the original mechanical transmission and flywheel system (MTFS), aiming to enhance the total energy conversion performance of the FABWEC system. The hydrodynamic simulation and numerical solution of the wave energy capture mechanism in the FABWEC system are carried out to facilitate the design and main components selection of the HTAS. And then the simulation and optimization of the designed HTAS are performed by the hydraulic simulation software. It is worth noting that there have been few reports on the operating performance of the HTAS with respect to buoys. In the hydraulic optimization process, the final optimization parameters of the HTAS are obtained by comparing the dynamic characteristics of the system, including system pressure, flow rate, motor torque and angular velocity, under the conditions with or without accumulator, with different buoy numbers and with different buoy phase differences. The simulated results show that the accumulator could effectively damp out the fluctuations in output power to turn the wave energy into a dispatchable power source; The energy conversion and output performances of the HTAS behave better with the increase of the buoys number and buoys phase difference, but the space and cost factors need to be taken into consideration in the actual operation; Within the research scope of this paper, the HTAS has an optimal performance for energy conversion and output when the number of buoys on one side of the floating platform is 5 and the phase difference between the buoys is 60°; Under the optimized conditions, the average output power of the hydraulic motor after stable operation of the HTAS can reach 5.8 kW. Significantly, the optimized HTAS could deliver the required electricity power steadily under the low wave energy density and has been practically applied to the next generation FABWEC prototype.

Air pollution with dust is particularly noticeable in winter. This problem is visible especially in those living areas in which furnaces fed by low-quality fuels are used for heating houses and flats. One of the possible ways of limiting the number of used furnaces may be heating and powering of the housing estates and villages by specially designed combined heat and power (CHP) steam (or vapor) power plants. To be competitive to other heating technologies these systems should be cheap, reliable and easy to operate. Therefore, their design should be as simple as possible. Steam or organic Rankine cycle (ORC) energy conversion systems utilizing simple volumetric expanders, which can be applied for distributed power generation are meeting these conditions. The article presents literature review as well as selected thermodynamic and design issues concerning these systems. Literature review gave an outlook on the modeling, experiments, operating conditions and possible configurations of steam and ORC CHP systems. Then, model of the CHP system was implemented in computer software. Thanks to the positive technical features and ability to operate with wet gas the screw machine was selected as the system’s expander. Selected experimental data obtained from the literature review were used for system modeling. Especially the operating conditions of the selected expander (i.e., maximum mechanical power, maximum inlet pressure, expansion ratio and internal efficiency) were assumed based on the experimental results, technical data and information reported in different papers. Expander’s operating conditions and technical data (in particular the value of maximum working fluid pressure allowable at the inlet to the expander) were the basis for pre-selection of working fluids which are possible to apply in the modelled system and selection of the heat source thermal parameters. Modeling was proceeded for different conditions and the results show that depending on the operating conditions and applied working fluid electric power output of the CHP system ranges between 1570 and 2511 kWe (for heat source temperature of 200 °C) and between 1583 and 2631 kWe (for heat source temperature of 150 °C). However, not only maximum power output should be considered as the selection criteria of the system design and working fluid choice. The other important criteria are related to maximization of the obtained electric power, minimization of the vapor pressure at the outlet of the vapor generator and at the inlet to the expander, minimization of the working fluid flow, minimization of fuel consumption and maximization of the temperature of the working fluid at the outlet of the expander. The modeling results show that from all cases studied the ORC CHP power plant utilizing screw expander, using MD2M as working fluid and featuring the electric power of 1570 kWe fed by rapeseed oil is the best possible solution if technical assessment criteria are taken into consideration. Such a system can cover the heating demands of ca. 9615 flats.

Rotary systems and nanofluids are frequently used in energy conversion and management systems. In this paper, a numerical study is performed to evaluate the application of metallic nano-particles in a rotary system filled with a lubricant from first and second laws of thermodynamics points of view. The nano-lubricant (lubricant based nanofluid) is considered inhomogeneous with dependent transport properties on nano-particles volume fraction, nano-particles size and the temperature. A two-phase model is undertaken to account for the Brownian motion and thermophoresis diffusion. The principal objective centers in the advantages and penalties of using nano-lubricant over the pure lubricant on the basis of first and second law (of thermodynamics). The numerical results demonstrate that the nano-particles enhance the thermal performance of the rotary system. However, undesirable aspect from hydro-dynamical and second law (of thermodynamic) perspectives are reported. While a nano-lubricant with limited volume fraction in low speed rotary system is recommended, the disadvantages of nano-lubricants with high volume fractions and/or used in a high-speed rotary system are dominant to nano-lubricants advantages and must be avoided.

Progress of efficient thermal energy storage (TES) has become a key technology for the development of energy conversion system. Among TES technologies, sorption thermal energy storage (STES) has drawn burgeoning attentions due to its advantages of high energy density, little heat loss and flexible working modes. Based on STES, this paper presents an innovative resorption sorption energy storage (RTES), and the experimental system is established and investigated for energy storage and upgrade. 4.8 kg and 3.9 kg MnCl2 and CaCl2 composite sorbents are separately filled in the sorption reactor, and expanded natural graphite treated with sulfuric acid (ENG-TSA) is integrated as the matrix for heat transfer intensification. It is indicated that the highest energy storage density are 662 kJ/kg and 596 kJ/kg when heat input temperature is 125 °C and heat release temperature are 130 °C and 135 °C, respectively. For different heat input and release temperature, the energy efficiency and exergy efficiency range from 27.5% to 40.6% and from 32.5% to 47%, respectively. The novel RTES system verifies the feasibility for energy storage and upgrade, which shows the great potential for low grade heat utilization especially for industrial process.

The advantageous performance on energy conversion of triangular prisms in Flow Induced Motion Energy Conversion (FIMEC) system has been verified by previous researches. In this paper, the magnetic flux density (B) was introduced into the mathematical model to analyze damping (ctotal), active power (Pharn) and energy conversion efficiency (ηharn) in FIMEC system. A physical model was established to adjusted the magnetic flux density (B) by varying the excitation voltages (VB) of Power Take-Off System (PTO). Free decay tests proved that physical model matched well with the mathematical model. Based on the physical model, the Flow Induced Motion (FIM) characteristic and energy conversion were analyzed and discussed, furthermore a control strategy to harness energy in galloping branch for Hard Galloping (HG) was proposed and verified. As B is high HG occurs, otherwise soft galloping (SG) occurs. By using the control strategy, the galloping can be self-excited by adjusting B, which is beneficial to the energy conversion of FIM. In the tests, the peaks of active power and efficiency are Pharn ≈ 2W and ηharn ≈ 3.1% in Vortex Induced Vibration (VIV) upper branch, Pharn ≈ 21.5 W and ηharn ≈ 3.5% in galloping branch.

With the development of wave energy conversion technology, more and more wave power generation devices begin to appear. However, the wave energy capture efficiencies of proposed wave energy converters (WECs) are generally low, especially in some areas where wave energy resource is not rich. Instead, a solution of array-type WECs bears practical potential to increase the wave energy capturing capacity. In this paper, a novel floating-array-buoys WEC (FABWEC) system is presented as the basic model and the structure of its energy capture mechanism, oscillating-array-buoys, is optimized to improve the wave energy capture efficiency. A mathematical model is developed to calculate the efficiency of buoy capturing wave energy. The simulated FABWEC models of different buoys spacing, buoys placement modes and buoys actuating arm lengths are established and analyzed by the hydrodynamic software to assess the efficiency performances. The optimization model is ultimately obtained by comparing the performances of different models. Furthermore, the physical model experiments are carried out under laboratory conditions to verify the optimization results of simulation. The results show that for the cylindrical oscillating-array-buoys, the wave energy capture efficiency could be effectively improved by increasing the buoys spacing appropriately, placing the buoys vertically and arranging the lengths of buoy actuating arms staggered; The average efficiency of buoys capturing wave energy in a wave period can reach 0.36 according to simulated investigation, which is about 38% higher than that of the basic model; The experimental performances are consistent with the simulation results, and the experimental power output of the optimized model can reach up to 1.64 W. Compared with the basic model, the average power output of the experimental optimized model is improved about 50% and the output curve is more stable. It is significant that the optimization model of array-buoys structure verified by simulation and experimental investigation has been practically applied to the next generation FABWEC system, which provides a beneficial experience for the practical application and efficient operation of wave power generation devices.

The mismatch between the load and pump sources and the restriction of energy recovery lead to large energy losses and lower energy efficiency in high power multi-actuator hydraulic systems. To obtain high energy efficiency, this paper develops a Multi-Source Network Hydraulic System (MSNHS) with multiple actuators and a corresponding power management strategy (PMS) to reduce the throttling losses and recover energy. The multiple energy-saving power modes based on the path of power transmissions, composed of different combinations of six power units with energy conversion and transfer, are implemented on MSNHS to supply and regenerate or recover power for various load conditions. Thus, the power consumption models of each power unit are established to analyze the power consumption characteristics for itself and power modes. On this basis, the switching supervisory controller is proposed to select an optimal mode for the current condition by utilizing an objective optimized function of minimal power consumption. Besides, the switching rules among power modes are designed, and the logical threshold control is presented for the multi-mode switching under different working conditions. The combination of the switching supervisory controller of optimal mode and the logical threshold control realizes the power management of the MSNHS with multiple actuators to accommodate with time-varying load and recover potential energy. The experimental validation is conducted on the MSNHS platform by simulating a 90° truck-loading cycle of the excavator. Experimental results demonstrate that the PMS applied to the MSNHS can downsize engine input power by up to 60.27% compared with the theoretical calculation of conventional one, and then improve overall system energy efficiency.

This paper presents an experimental investigation of a novel optical water filter used for Photovoltaic/Thermal and Concentrating Photovoltaic/Thermal modules. A water layer is used as a spectrum splitter of solar radiation placed above the photovoltaic cells and as a thermal working fluid simultaneously. The water layer absorbs the ultraviolet and part of infrared, which are not used by the photovoltaic, but transmits the visible and some of infrared to the solar cell surface which are used by the photovoltaic. In this work, the transmittance of the optical water filter was measured for different water thicknesses (1, 2, 3, 4, and 5 cm) and radiation wavelength ranging from 0.35 to 1 μm. Results show that there is a significant effect of the water layer thickness on the transmittance of the spectra where the transmittance decreases as the water layer increases. Moreover, energy conversion rate of photovoltaic with the optical water filter at different water layer thicknesses has been determined.

How to produce electricity safely and without pollution is an important issue to our world. The solar thermoelectric generator can realize direct solar­electric energy conversion. However, the output power of the traditional solar thermoelectric generator is instability because of the instantaneity of the solar energy. In this paper, the paraffin/expanded graphite phase change materials were used in the solar thermoelectric generator to realize the thermal management of the solar energy. Expanded graphite improves the thermal conductivity and the anti-leakage ability of the paraffin; therefore, the prepared phase change materials have higher thermal response speed and wider application than the pure paraffin. As a result, when the temperatures of the phase change materials with different melting points (50 °C, 60 °C, 70 °C, and 80 °C) enter their own phase transition regions, the open circuit voltages of the corresponding systems also enter the stable output platforms. This verifies the excellent thermal management performance of the phase change materials on solar thermoelectric generator. In addition, the output voltage is considerable and the maximum value is 2.697 V for 80 °C PCMs. When the solar irradiation disappears, the latent heat of paraffin can still keep the system operating. Meanwhile, a mathematical model with high accuracy was also proposed.

This paper presents a multi-layer cantilever piezoelectric energy conversion structure for pavement, which avoids weakening the electrical output after the mass contact and realizes the coordinated vibration of each cantilever piezoelectric energy harvester and road driving. In order to ensure the structure meets the requirements of power generation and durability when applied in road engineering, based on the power generation theory of energy harvester, the structural parameters related to the electrical output magnitude are clarified. Based on the power generation performance and durability of energy conversion structure under typical road traffic characteristics, the optimal cantilever position and vibration amplitude are determined, which lay the foundation for the development and application of energy harvester in road field. The results indicate that the improved structure has the best power generation performance and durability with the condition of the distance from the piezoelectric material to the fixed end of 7 mm and the vibration amplitude of 4 mm under under typical road traffic conditions. The output voltage of the monolithic energy harvester at 5 Hz vibration frequency is 5.2 V, the output power can reach 3.14 mW, and the power density is 0.0063 mW/mm3. This power level and power density are significantly higher than other mechanisms. The structure will make it possible to co-vibrate with the driving, and the structural parameters avoid the misunderstandings of traditional designs that only the power generation performance is valued and the durability can be ignored, which make the structure can be used for collecting electric energy in pavement.

With recent technical advances, Combined Cooling, Heating and Power (CCHP) system offers a practical and economical alternative to conventional energy conversion systems. Benefits of these systems are more marked with employing efficient thermodynamic cycle and using renewable energy resources. In this regard in the present work, a novel geothermal driven CCHP system, in which the ejector transcritical CO2 cycle is integrated with conventional Rankine cycle, is proposed (system a). The proposed system is then modified by replacing the gas cooler with an internal heat exchanger to make a more efficient CCHP system (system b). To investigate the first and second law performance of the proposed systems, thermodynamic models are developed and parametric analysis is carried out to examine the influences of design variables. The results indicated that, the gas cooler of conventional system can be replaced by an internal heat exchanger for a wide range of practical operating conditions and this replacement can improve the exergy efficiency, net output power and output cooling respectively by 30.9%, 49.1% and 75.8% at the expense of 39.1% reduction in heating output. Also a comparison is made between the two proposed systems in this work with similar systems (based on ejector transcritical CO2 cycle) proposed previously by other researchers and superiority of proposed systems in this paper is revealed and discussed.

Exergy-based analysis is a powerful method to evaluate, understand, and improve energy conversion processes. Compared with conventional exergy analysis, advanced exergy analysis can identify the improvement potential of each component and the interactions among components of the whole system. In this paper, the ash agglomerating fluidized bed (AFB) gasification process is simulated in Aspen Plus (version 8.0). Based on the simulation results, advanced exergy analysis is carried out to study the performance of the AFB gasification process. The exergy efficiency of the AFB gasification process is 82.13% and the total exergy destruction is 4670 kW. The result shows that 54.18% of the total exergy destruction can be avoided. The AFB gasifier has the largest potential for reducing exergy destruction. In addition, sensitivity analysis is performed to research the effects of carbon conversion, pressure and temperature on the exergy destruction of the AFB gasifier.

Because of the ever-growing demand for energy in today’s world, new efficient multi-generation systems are much sought after. Analyzing the practicality and performance of such innovative systems, especially ones utilizing novel energy conversion technologies, has been a popular subject among scientists. In this paper, a comprehensive assessment of a novel multi-generation system driven by a molten carbonate fuel cell is presented from thermodynamic, exergoeconomic, and environmental viewpoints. The proposed system consists of a molten carbonate fuel cell for electricity generation, a heating process heat exchanger for superheated steam generation, a generator-absorber heat exchanger cycle for generating cooling load, and a desalination subsystem for producing freshwater. To investigate the performance of the system, the influences of two important parameters, namely current density and fuel cell operating temperature, are studied on the generated cell voltage as well as the production rates of the products, the energy and exergy efficiencies, the cost rate, the cost per unit exergy, and the carbon dioxide emission rate. According to the results, the net electrical power production and the energy and exergy efficiencies of the proposed system are 1439 kW, 79.9%, and 51.9%, respectively. Also, the investment cost rate of the system is 30.4 $/h, which results in the production of the mentioned outputs with a total cost per unit exergy of 21.6 $/GJ. Moreover, the carbon dioxide emission rate of the system is found to be 247 kg/MWh.

To evaluate the performance of a photovoltaic panel, several parameters must be extracted from the photovoltaic. Among the methods developed to extract photovoltaic parameters from current-voltage (I-V) characteristic curve, metaheuristic algorithms are the most used nowadays. The aim of this paper is to present the inaccuracies occurred in the parameter’s identification of the photovoltaic cell using metaheuristic technics published in Energy Conversion and Management. The results presented by different authors do not meet the objective function. To prove it, an algorithm is proposed to check the accuracy of the proposed results; a simple tool, General Algebraic Modeling System is also proposed to extract the best values of parameters of a photovoltaic cell.