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Abstract: The pulp and paper industry both uses and produces large amounts of energy and rising fuel prices bring along significant challenges to the sector. Several strategies can be applied in order to remain competitive e.g. an increase in energy efficiency, a switch in fuel and/or a novel energy conversion technology. In this study, we investigate if improved energy conversion strategies can reduce energy costs, primary energy use and CO2 emissions of paper mills within different European countries (The Netherlands, Poland and Sweden). Our results show that differences in history and availability of resources has led to different conversion strategies in the three countries. We found that a natural gas combined cycle, which is largely implemented in The Netherlands due to long term domestic availability of natural gas, has the lowest primary energy demand. Due to a long history of low electricity prices, CHP has not been common in Sweden. Many Swedish mills use biomass as an energy source and due to low CO2 emissions of the national grid the CO2 emission profile of the Swedish paper industry is very low. Our results imply that future conversion routes for the Swedish paper and board industry are again wood based; in case of increasing electricity prices these would be biomass gasification based CHP solutions. With a reduction of 800kg CO2/ton paper on average, a switch from coal to biomass would reduce CO2 emissions in the Polish pulp and paper industry with approximately 0.6Mton/year. A carbon price of 20–25€/ton would, according to our results, be enough to provoke this switch. Due to the high share of natural gas, the CO2 emission reduction potential of the Dutch paper industry (1.5Mton/year) is even larger than in Poland. Due to high biomass prices and relative low CO2 emission profile of natural gas, a carbon prices of more than 60€/ton CO2 would be needed to provoke a switch in The Netherlands. Provided with few alternatives, the most effective strategy in The Netherlands would be an increase in energy efficiency. [Copyright &y& Elsevier]

In scenarios where wide-amplitude shock excitation is encountered, a routine bistable configuration struggles to achieve satisfactory energy transfer, and a sensible combination of multiple nonlinear oscillators with different stiffness mechanisms can be exploited to achieve optimal vibration mitigation performance. In this paper, a nonlinear energy conversion and multi-stiffness combination inspired dynamic vibration absorber (NECMC-DVA) is proposed with a magnetic-spring tunable nonlinear stiffness element as the substructure. Parametric studies are performed for different modes of magnet-spring tunable nonlinear stiffness unit arrays considering transient impulses and harmonic excitation. The NECMC-DVA device, which comprises bistable oscillators, cubic stiffness oscillators, and hybrid stiffness oscillators, is also experimentally demonstrated for its synergistic performance in vibration mitigation and energy harvesting. The performance of the NECMC-DVA is measured under transient impulses and harmonic excitations. It has been found that the NECMC-DVA, which consists of a bistable oscillator, a cubic stiffness oscillator, a hybrid stiffness oscillator, energy-capture elements, and motor sequences, achieves high-efficiency nonlinear energy transfer and significant shock robustness in wide-amplitude impulsive scenarios. The NECMC-DVA with hybrid energy sinks demonstrates more remarkable targeted energy transfer and energy conversion performance than its pure bistable oscillator counterpart. Furthermore, the NECMC-DVA prototype can achieve adaptive vibration control modulation and energy conversion management through motion control boards by monitoring ambient excitation signals. Therefore, the NECMC-DVA enables integrated active and passive mitigation and energy harvesting to simultaneously accommodate multi-source indeterminate vibration and shock environments. [Display omitted] • A nonlinear energy conversion and multi-stiffness combination inspired dynamic vibration absorber (NECMC-DVA) is proposed. • The NECMC-DVA exhibits excellent vibration mitigation and energy harvesting synergistic performance. • The energy dissipation mechanism of NECMC-DVA is exposed by analyzing the behavior of nonlinear oscillator dynamics. • The prototype of NECMC-DVA is capable of achieving adaptive vibration control modulation and energy conversion management. [ABSTRACT FROM AUTHOR]

In recent years, the potential of Solid oxide fuel cell (SOFC) technologies as energy conversion devices with high efficiency and zero‑carbon emissions has been underestimated, where high fuel utilization plays a crucial role. Although the SOFC system with anode off-gas single recirculation has received much attention as a means to increase fuel utilization, this problem is not thoroughly addressed. To overcome this limitation, this paper proposes a novel SOFC system concept featuring anode off-gas "dual" recirculation, designed to maximize fuel utilization up to the theoretical limit of 100%. This innovative approach inherently eliminates carbon dioxide emissions through an integrated carbon capture process, thereby maintaining systematic carbon balance. A comparative analysis among the novel dual recirculation system, traditional single-pass, and other anode off-gas recirculation systems, reveals that the proposed system outperforms existing configurations. It achieves electrical and overall combined heat and power efficiencies of 49.6% and 85.7%, respectively, even after accounting for the energy required for carbon capture. This represents a 21.5% increase in electric efficiency over the single recirculation system, with a six-fold increase in tail-gas CO 2 concentration, reaching 26.3%. The study categorizes the four analyzed systems into "open" or "closed" based on whether the anode off-gas is directly discharged into the environment. Systematic investigations into carbon deposition potential, fuel utilization, flow rate, operating voltage, carbon capture ratio, and condensation temperature disclose distinct patterns between open and closed systems. The closed configurations exhibit superior performance, suggesting they are more suitable for SOFC applications. [Display omitted] • Merit of fuel utilization to SOFC systems is reevaluated. • Novel SOFC system with anode off-gas dual recirculation is proposed. • The system achieves systematic fuel utilization of 100%. • The system achieves superior energy and carbon capture performance. • Introduced "open" and "closed" SOFC system categories. [ABSTRACT FROM AUTHOR]

The concept of "more- and all-electric aircraft" has become increasingly popular over the last two decades, leading to a boost in the extensive utilization of airborne electromagnetic actuators such as permanent magnet synchronous machines (PMSMs). Inevitably, considerable waste heat is generated during operation due to the incomplete energy conversion, which is a great challenge for conventional onboard thermal control systems. If the huge generated heat cannot be removed efficiently there will be a sharp temperature rise in thermal-sensitive components of the onboard devices. This overheating will cause operational failures which are intolerable in aerospace applications. Aiming to improve the current thermal protection system and gain greater compatibility with the current PMSM system, this paper proposes a phase change material-based (PCM-based) thermal protection strategy using commercial wax in two equivalent PMSMs. A comparative investigation shows that the machine temperature with PCM-based cooling strategy can be reduced under most operating conditions (the maximum temperature drop is 13.7 °C), demonstrating the advantages of deploying the proposed PCM-based cooling scheme. Further data processing towards the heat absorption-dissipation matching between the utilized PCM and the working mode of the cooling object is conducted. A dimensionless correlation of dimensionless temperature peak difference (DTPD) as a function of the pulsed factor, presented in Eq. (17), reveals an average relative error of ±4.5%. Based on the correlation, an optimal pulsed factor of ∼1.764 is calculated to reach a matching condition. Such a method can be promoted to wider applications using PCM as a cooling medium beyond the currently-utilized two types of machines in this paper. • Phase-change-material-based cooling for electromagnetic machines is proposed. • Optimal intermittent operating conditions were identified experimentally. • Two different machine types were considered for a broad application. • Based on experimental data, a correlation was developed for a universal guide. [ABSTRACT FROM AUTHOR]

To further explore the multi-energy complementary potential on multi-time scales under variable operating conditions, a refined modeling and collaborative configuration method for Electric-Hydrogen-Thermal-Gas Integrated Energy Systems (EHTG-IES) with hybrid energy storage system (HESS) is proposed in this paper. To commence with, an advanced operation model for the EHTG energy conversion equipment is formulated by incorporating their nonlinear operating characteristics under variable operating conditions. Next, the distinct features of HESS with different energy medium are accurately depicted with various effective linear-reduction and relaxation strategies. Then, the coupling design day method and the intra-day and inter-day state superposition strategy are combined to efficiently model the time horizon. Lastly, a co-optimal configuration model of the EHTG-IES is devised, with the aim of minimizing total annual cost. The case study validates that the refined modeling of coupled components leads to a 3.18% reduction in cost and 5.05% reduction in carbon emissions significantly. This paper also assessments the synergy and substitution benefits of multiple low-carbon technologies and finds that diurnal and seasonal hydrogen storage have a large part of overlapping roles, and hydrogen-based system contributes a deeper utilization of seasonal thermal storage. The sensitivity analysis indicates that the current carbon tax policy has a negligible impact on the carbon emissions, equivalent to about 1% of the gas price, but appropriately increasing attention on low carbon allows for an emission decrease of 28.62% at a cost increase of 4.38%. [Display omitted] • Various low-carbon technologies are finely modeled considering non-linear features. • Linear-reduction and relaxation strategies are developed for hybrid energy storage. • The complementary potential of low-carbon technologies is utilized and explained. • Cost and CO 2 emissions are reduced thanks to the refined model for the system. [ABSTRACT FROM AUTHOR]

In this paper, a scheme of pulse combustion mode with pulse input of gas is proposed to solve the problems of low output electrical performance and energy conversion efficiency of combustion-based thermoelectric systems under limited heat dissipation conditions, which is based on experiments. The characteristics of the thermoelectric system show that pulse combustion mode can increase the instantaneous temperature difference, so as to achieve the excitation effect on the output power. The relationships among output power, system efficiency, excitation intensity and pulse input parameters, and the geometry of thermoelectric modules are obtained. The influence of pulse input parameters on the excitation intensity is interactive, and top dead center of pulse inlet power is the parameter that has the greatest influence on the performance. Compared to the constant combustion mode, the pulse combustion mode can increase the output power by up to 28.3%. A maximum output power of 7.15 W with air-cooled heat dissipation and a maximum system efficiency of 3.26% were experimentally obtained, which is a 30% increase in efficiency over current air-cooled heat dissipation thermoelectric systems. Therefore, this paper can provide solutions for more practical power supply, provide effective and feasible guidance for the study of thermoelectric systems, and provide useful insights into the electrical properties of thermoelectric systems. [Display omitted] • An air-cooled combustion based thermoelectric system was built. • A scheme of pulse combustion mode with pulse input of gas is proposed. • The pulse combustion mode can increase the output power by up to 28.3%. • High output power and efficiency results were obtained by experiment. • The power shortage is alleviated under limited heat dissipation conditions. [ABSTRACT FROM AUTHOR]

Molecular solar thermal (MOST) system is a new technology to collect, transform and store solar energy. The mechanism of photochemical reaction and component transport of molecular photoswitches in the reactor is still unclear. In this paper, a simulated theoretical framework for energy conversion rate and energy storage efficiency of solar energy collection and conversion devices based on a molecular solar thermal system was presented. The mathematical model of the photochemical reaction studied was based on an azobenzene derivative, which acted as a molecular photoswitch that can store energy by the switch of molecular structures. The microscopic parameters of reactants were obtained by quantum mechanics calculation and applied to the macroscopic energy conversion analysis of reaction processes. The theoretical framework can predict the conversion and energy storage efficiency of photoisomerization reactions, and can be used for component transport analysis, energy conversion analysis and reaction rate contribution analysis in reactors. We focused on the influence of macroscopic factors, including the flow velocity, inlet reactants concentration and reactor size on the photoisomerization energy storage process. The results of the theoretical analysis were in good agreement with those of existing laboratory equipment. The relative error of the conversion rate is only 0.71% in the photostable state, and the maximum relative error of the conversion rate is 10.99% in the whole process. In addition, in the photochemical reaction, we introduced the concept of absorbance field for the absorbance attenuation caused by the absorption of photons in the medium, so that the local material conversion, absorbance and energy conversion of this type of photochemical reaction can be more clearly understood. This simulated theoretical framework allows the study of molecules in a macroscopic setting, thereby establishing a link between practical engineering and basic chemistry, and providing guidance for the design of molecular solar thermal systems in the future. • The theoretical framework for evaluating molecular solar thermal (MOST) systems was established. • The coupling mechanism of photochemistry and component transport was elucidated. • The concept of absorbance field was introduced for photochemistry systems to optimize calculation. • The macroscopic factors were considered to establish a link between practical engineering and basic chemistry. [ABSTRACT FROM AUTHOR]

The paper deals with the energy transition, focusing on the decisions to be taken about the change in the energy conversion capacity of specified portion of the universe, such as industrial or domestic districts, regions, countries, etc. Conversion capacity is intended here as the set of all energy conversion and storage units characterized by type, size and number, and interacting with the natural gas and electricity grids. The goal is to find guidelines for new installations, obtained by simulations of a model able to describe properly the behavior of each energy conversion technology and the interaction with grids. The model is based on a traditional MILNP approach, but contains unique features in the literature, which allow to obtain results of general validity for applications to very different geographical areas, or to countries including very different regions that transmit energy with each other or export/import it from abroad. The main novelty of this work is to identify the best planning for the decarbonisation of energy demand sectors, according to the criterion of minimum cost, both at global and at regional level. The results applied to the case of Italy allow identifying clearly the energy demand sectors to which new installations should be applied first to minimize the cost for the total energy system, and the units that must be foreseen to satisfy these energy demands, i.e. a precise strategy for the energy transition towards a 100% renewable system. • A multi-regional model is built to find the most convenient energy transition path. • General guidelines for Western countries are derived from the Italian case study. • Replacement of boilers with heat pumps allows increasing RES share from 20 to 30%. • For RES share >60%, PtG is the low-carbon strategy for high temperature heat demand. • Transportation is the last energy sector that should be decarbonized. [ABSTRACT FROM AUTHOR]

How to extract the running feature information and realize multi-type faults diagnosis is the key to carry out intelligent operation and maintenance of energy conversion machinery. The pumped storage unit (PSU) has various operating conditions, both energy storage and power generation. It may lead to diversified types of failures under the joint influence of hydraulic and mechanical factors. The existing data-driven models often show excellent diagnostic performance with laboratory-specific fault types or single subsystem but are not satisfactory when applying real operating scenarios or migrating to other devices. Therefore, a universal hydraulic-mechanical diagnostic framework integrating signal acquisition, feature extraction and fault recognition is proposed in this paper. In Stage 1, eight types of datasets caused by the hydraulic-mechanical coupling characteristics via abnormal on-field measurements form an on-site benchmark; for Stages 2 and 3, a novel refined composite multiscale cosine similarity Lempel-Ziv complexity method is proposed to quantify the various fault features based on multiscale signal processing and the nonlinear dynamics methodology, and random forests model is introduced to realize the efficient recognition of different status signals. Its core advantage is versatility, which is not limited to specific components but can be applied to different subsystems of pumped storage, such as hydraulic system (identification of vortex conditions, detection of hydraulic imbalances) and mechanical system (wear of shaft, bearing and runner). This framework is applied in the micro PSUs, the comprehensive experiments show that all evaluation indexes are above 92%. Various comparative analysis indicates that the framework is not only applicable to the detection and analysis of hydraulic anomalies but also has a competitive advantage in the diagnosis of hydraulic-mechanical faults. It is suitable for fault detection of different subsystems in real power stations, and also could be flexibly extended to other rotating energy storage systems, as a helpful tool to improve energy conversion efficiency and reduce maintenance cost. [Display omitted] • Building a universal hydraulic-mechanical diagnostic framework. • Eight types of datasets caused by the hydraulic-mechanical coupling characteristics form an on-site benchmark. • Verifying the superiority of the framework by applying in the micro pumped storage system. • Providing a potential tool to improve energy conversion efficiency and reduce maintenance cost. [ABSTRACT FROM AUTHOR]

Highlights • A 1-D model was proposed to predict fuel's spray combustion characteristics. • N -pentanol causes multiple effects on the evaporation and ignition processes of both fuels. • Physical ignition delay of biodiesel blends occupied less proportion than that of diesel blends. • The effects of the parameters of the Arrhenius-typed correlation were discussed. • New correlations focused on the liquid length and ignition delay were proposed. Abstract Spray mixing and combustion processes are regarded as the major factors that determine the energy conversion efficiency and emission level of internal combustion engines. However, the related researches mainly rely on 3D flow simulation or optical engine experiments, which are highly expensive and time-consuming. In order to provide a more convenient solution, this paper developed a one-dimensional semi-phenomenological model to achieve accurate and efficient predictions on spray combustion characteristics. The model was constructed by a dimensionless spray theoretical model and limited experimental data of macroscopic spray characteristics. Inside the proposed model, a physical module was used to physical module spray air-fuel mixing conditions like fuel distribution and evaporation. Besides, an improved Arrhenius-typed correlation concerning injection parameters and environment variables was introduced to describe the chemical ignition characteristic of spray combustion. The optical experiment results showed that this method is simple and effective, and the forecasting is satisfactory. Based on the new model, the influences of blending n -pentanol on the spray combustion characteristics of diesel and biodiesel were investigated. On the physical aspect, the critical fuel concentration at liquid length position decreases with n -pentanol is blended into both fuels in the most cases, but witnessed a significant leap in 1200 K condition, especially for diesel blends; the physical ignition delay times of both diesel and biodiesel blends decreases first and go up later. On the chemical aspect, the join of n -pentanol caused the gap between the physical delay time and the chemical delay time much narrower, but the ignition patterns were different in diesel blends and biodiesel blends. Moreover, this paper proposed a series of correlations focused on the liquid length and ignition delay of n -pentanol blends sprays. These correlations covered wide conditions and showed better prediction accuracy than traditional ones. [ABSTRACT FROM AUTHOR]

Highlights • Exhaustive study of ANNs used in wind energy systems, identifying the most employed techniques. • ANNs classified into: forecasting and predictions; fault detection and diagnosis; optimal control; design optimization. • A statistical analysis of the current state (and future trends) in this field is done. Abstract Wind energy has become one of the most important forms of renewable energy. Wind energy conversion systems are more sophisticated and new approaches are required based on advance analytics. This paper presents an exhaustive review of artificial neural networks used in wind energy systems, identifying the methods most employed for different applications and demonstrating that Artificial Neural Networks can be an alternative to conventional methods in many cases. More than 85% of the 190 references employed in this paper have been published in the last 5 years. The methods are classified and analysed into four groups according to the application: forecasting and predictions; design optimization; fault detection and diagnosis; and optimal control. A statistical analysis of the current state and future trends in this field is carried out. An analysis of each application group about the strengths and weaknesses of each ANN structure is carried out. A quantitative analysis of the main references is carried out showing new statistical results of the current state and future trends of the topic. The paper describes the main challenges and technological gaps concerning the application of ANN to wind turbines, according to the literature review. An overall table is provided to summarize the most important references according to the application groups and case studies. [ABSTRACT FROM AUTHOR]

This paper proposes a reconfigurable power module system for hybrid micro-grid to reduce the designing cost with standardized software and hardware components. The developed system is composed of three layers including application function layer, interconnection layer and physical layer with the capability to be interfaced with different types of energy resources for the hybrid micro-grid. By implementing the multi-layer power module system, the energy conversion designing procedures for different types of resources can be generalized and automated with less cost on the specified application scenarios. The control functions for different energy resources can be extracted from the application function layer. The desired number of standardized power modules can be integrated from the physical layer to form different power converter topologies. The coordination of the power converter, micro-controller, sampling, high level control is managed by the interconnection layer to construct the complete energy conversion system. The major advantageous results cover three aspects. Firstly, the proposed reconfigurable system generalizes the energy conversion of the hybrid micro-grid with different AC and DC resources. Secondly, the designing procedures of the hybrid micro-grid energy conversion system are simplified with less cost for various interfaced applications. Thirdly, the energy conversion performance and reliability of the micro-grid is improved with standardized power modules and self-restoration capability. The experimental test verified the proposed system. • Reconfigurable hybrid micro-grid based on standardized power electronic module system. • Multi-layer reconfigurable system is designed to be interfaced with distributed energy resources. • Standardized power electronic modules form a range of power converter topologies. • Repetitive design costs of hybrid micro-grid energy conversion systems are reduced while improving performance. [ABSTRACT FROM AUTHOR]

This paper presents the unique design and processing conditions of a micro-CAES device that generates, stores and delivers electrical energy with highly efficient total energy conversion. The micro-CAES installation is divided into six parts, where air, the energy carrier, is compressed, stored, heated and expanded in appropriate sections. We focus mainly on the post-preparation section, where the air mass flow is pulse heated and controlled by Pulse Width Modulation (PWM), and the expansion section, where multiple piston drives are used to achieve maximum energy conversion efficiency or the required amount of electricity to be fed into the grid. We discover that the controllability of expansion process performance is improved by exploiting the inertia of the following elements in multiple reciprocating engines: piston, piston rod, connecting rod, crank, and crankshaft, connected with air injection dynamics and pulse heating by Thermal Energy Storage (TES). Furthermore, we investigate the efficiency using our own zero-dimensional mathematical model illustrating the complex dynamics of air processing. The mathematical model was compared with experimental data for the single-drive air expander, showing qualitatively and quantitatively satisfying model reliability. Moreover, we performed a sensitivity analysis to determine the best number of reciprocating drives involved in the expansion section and the best operating conditions. The use of the PWM function of mass flow of air supplied the expander with an index of 0.5 together with pulsating air heating in the expander installation, including three- reciprocating drives, allows a maximum total energy conversion efficiency of 81%. The presented piston drive expander seems to be a promising solution for micro-CAES in residential and industrial applications, especially where additional low-temperature waste heat is available, and an intermittent control strategy is implemented. [Display omitted] • Original construction of the air expander includes multi-piston-drives. • The micro-CAES with air preheat and PWM control strategy ware implemented. • Obtained maximum efficiency of piston-drive micro-CAES is 81%. • Generated electrical power could be control with overall efficiency change up to 10%. [ABSTRACT FROM AUTHOR]

Multi-energy industrial parks, composed of the district energy supply system and terminal industrial loads, are dominant energy consumers with over 50% occupation of total energy consumption. Considering the energy conversion in the district energy supply system and adjustment of production subtasks in terminal industrial loads, the industrial parks could provide considerable flexibility for utility multi-energy systems to deal with contingencies. However, industrial parks may have multiple uncertainties originating from the production subtasks' variability, distributed renewable energy's fluctuation, and random failures of equipment. These uncertainties could make the flexibility assessment of industrial parks unreliable, which may further exacerbate utility system risks. To address the problem, this paper innovatively proposes the concept of probabilistic integrated flexible regions and corresponding characterization approaches, which can effectively describe the credible multi-energy adjustment ability of industrial parks. First, the energy-material flows in the industrial park are modeled considering multiple uncertainties while subject to constraints such as operating limits of equipment, energy and material balancing, and production targets. Then, the modeling and calculation methods of probabilistic integrated flexible regions are given. These regions are labeled with certain probability requirements and visualized in the input multi-energy space. Using a real-world test system that produces air conditioning equipment in China, the results show that the proposed model can effectively reflect the probability characteristics of the integrated flexibility under multiple uncertainties. For this test system, the area of a highly credible integrated flexibility, represented by the probabilistic integrated flexible region with 99% probability, is about half of that obtained by the deterministic model. That is, half of the integrated flexibility evaluated by the deterministic method in the test system may not be practically utilized considering the impacts of uncertainties. Therefore, the proposed method could provide a credible and comprehensive evaluation of the multi-energy industrial park's flexibility considering multiple uncertainties. • Exploiting the multi-energy(integrated) flexibility of industrial parks • Describing the probability characteristics of the integrated flexibility • Uncertainties in industrial parks shrink their integrated flexibility • Facilitating the interaction between demand and utility side in energy systems [ABSTRACT FROM AUTHOR]

Recent developments in the energy sector require a combination of renewable carbon sources (e.g. biomass) and water electrolysis as a basis for electrical energy storage. While many approaches concentrate on the usage of hydrogen from electrolysis with CO 2 for the generation of second generation fuels like synthetic natural gas, the presented paper introduces a combination with the Heatpipe Reformer biomass gasification process: This process produces a synthesis gas, which can be fully and directly converted to methane using additional hydrogen produced in an electrolyser. Furthermore, the applied nickel catalyst is able to convert higher hydrocarbons in the syngas, increasing methane yield and resulting in higher process efficiencies and no additional scrubbing for the adaptation of the CHO stoichiometry is necessary. The Heatpipe Reformer also allows pressurized gasification, which is beneficial for a subsequent methanation step. The full process chain including a 100 kW gasifier and a bench scale methanation reactor was operated in a test campaign for approx. 20 h at different pressure levels. This paper presents results from the process of gasification and methanation as well as the conversion of higher hydrocarbons. An energy balance finally evaluates the entire process in terms of efficiency. [ABSTRACT FROM AUTHOR]

Using forest-based biomass to produce bio-energy and bio-fuels could provide economic, environmental, and social benefits for communities. However, variability in biomass availability and high cost of delivered feedstock impact the profitability of the supply chain. Therefore, optimization models were developed in previous studies to design cost effective and profitable biomass-based supply chains at strategic level. Medium term variations in biomass supply and demand are not usually accounted for in strategic models. This may affect the feasibility of strategic plans prescribed by the optimization model at tactical level. To solve this issue, an integrated model is developed in this paper that includes strategic and tactical decisions simultaneously in order to optimize forest-based biomass supply chains. In addition to yearly variations in biomass supply, which can occur due to changes in harvest level, monthly variations in biomass availability, bioenergy/biofuels demand, and losses during preprocessing and storage of biomass are incorporated in the model. Other unique features of this model compared to the few integrated models developed in previous studies are as follows. (1) Decision regarding opening a new conversion facility is made yearly, not just at the beginning of the planning horizon. (2) A multi-product (heat, electricity, bio-oil and pellets) supply chain is considered. (3) The impact of fossil-based energy prices on bio-conversion investment decisions are accounted for in the model. (4) The optimization problem is modeled in a way that the global optimum solution is obtained within a reasonable time. Using a case study in Interior British Columbia, it is shown in the paper that the capacity of conversion technologies and the amount of procured biomass prescribed by the strategic model would not be sufficient to meet the monthly demand of bioenergy. Moreover, the net present value of the strategic model is overestimated due to underestimating the demand and procurement cost, and ignoring storage costs. It is shown that these issues are resolved using the integrated model. [ABSTRACT FROM AUTHOR]

Development of electric mobility and sustainable energy result in new technologies such as contactless electric vehicle charging and roadway energy harvesting methods, but also self-healing asphalt roads. By combining these technologies a new concept of Future Sustainable Roads for Electric Mobility is created and presented in the paper. This paper bridges the gap created by these unilateral technology developments using a multi-disciplinary approach including placing cautions when necessary and suggesting viable alternatives for optimal utilization of these energy transfer and conversion techniques. Through theoretical analysis, simulations, and tests on lab-scale experimental prototypes, the impact of our proposal is showcased. Thermal and loss models are developed for self-healing asphalt. Also, integration study of solar roads and contactless charging is performed. Applying the insight gained from the results, it is discussed how some challenges also pave a way towards interesting opportunities, for instance, infrastructure sharing for material use optimization and efficient mosaic integration. Finally, an economic viability case study is presented for a future Dutch highway with such newly emerging components. [ABSTRACT FROM AUTHOR]

The exploitation of ocean energy is currently recognized as an abundant, geographically diverse and renewable energy source that could benefit European citizens by increasing energy independence, enhancing economic growth, creating jobs, allowing decarbonization or serving as a complement to other renewable sources within the global energy mix. Of the various types of ocean energy (wave, tidal, offshore wind, salinity gradient and thermal gradient), this paper is focused on technologies with which to harness the energy from ocean currents. This energy will have considerable possibilities in the future thanks to its high predictability and its enormous potential for the production of electricity. Most of the review papers concerning tidal energy systems are focused on engineering topics. However, there continues to be limited information as regards other aspects, such as those of an economical, social, political, legislative and environmental nature which, together with their interrelationships, need to be dealt with as a whole in order to detect the key drivers that could affect the success or failure of making tidal energy technologies marketable. The objective of this review paper is to address this gap by providing a detailed strategic analysis based on the most up-to-date literature, reports and guidelines. The paper discusses the different disciplines of which the PESTEL analysis (political, economical, social, technological, environmental and legal) is composed and provides different strategies/recommendations through which to mitigate many of the risks identified in order to facilitate the successful development of these technologies and bring them onto the market. Finally, some recent advances in tidal technologies developed by our research group (GIT-ERM) are also highlighted in the technological part of this paper. [ABSTRACT FROM AUTHOR]

A new reliability assessment approach to Integrated Energy Systems (IESs) is introduced in this paper. The optimal load curtailment (OLC) algorithm and reliability assessment algorithm are both improved in the proposed approach. For the OLC problem, this paper develops a hierarchical decoupling optimization framework for both the energy hub optimal dispatch and the optimal power flow problems. This feasible solution can make the OLC calculation more efficient and accurate. For the reliability assessment algorithm, an impact-increment based state enumeration (IISE) method is accommodated for IESs to accelerate the reliability assessment process. Also, a reduction technique of higher order contingencies is presented for the reliability evaluation of IESs to further enhance the computational efficiency. Case studies are performed on an IESs test case combined the IEEE-33 bus system with 14-node gas system and a practical case combined the IEEE 118-bus power system with Belgian natural gas network Numerical results demonstrate the efficient and robust performance of the proposed approach. Besides, the impacts of energy conversion process and energy hubs on IESs reliability are analyzed in detail. [ABSTRACT FROM AUTHOR]

• Thermochemical energy storage of methane reforming using slag is researched. • High temperature slag can be used as energy source and catalyst bed. • Thermochemical storage efficiency first rises and then drops during reforming. • Optimal flow rate and slag bed length exist for maximum energy storage efficiency. In iron and steel industry, production process is accompanied by a large amount of residual heat as high temperature slag. Methane reforming with carbon dioxide is one of the typical chemical energy storage processes, and it can be applied to use residual heat and reduce carbon dioxide emission. In this paper, thermochemical energy storage performance of methane reforming using high temperature slag is researched. According to experimental and numerical results, high temperature slag can be used as energy source and catalyst for thermochemical energy storage process by methane reforming. Slag is almost non-porous material, and its activation energy is higher than that of common catalyst, so slag only has high catalytic activity under high temperature. During methane reforming process, methane conversion and thermochemical storage efficiency first increases and then decreases with reaction rate dropping, and the position with maximum reaction rate gradually changes from front of slag bed to the end. Many factors including inlet conditions and reactor structure can affect thermochemical storage performance. Increase of slag initial temperature can improve methane conversion and thermochemical energy storage efficiency. As reactant flow rate decreases or slag bed length rises, methane conversion gradually increases, while thermochemical energy storage efficiency first increases and then decreases. With suitable conditions, thermochemical energy storage efficiency of slag can be higher than 60%. [ABSTRACT FROM AUTHOR]

Park-level integrated energy system (PIES) is crucial for improving the efficiency of an energy system and has a terrific prospect. Photovoltaic/thermal (PV/T) is significant for improving the economic performance of PIES with electric and heat loads. However, the research on PIES considering PV/T is insufficient at present. Therefore, a PIES planning model considering PV/T is proposed in this paper. Firstly, the elaborate model of PV/T considering the heat transfer process is established. Moreover, a novel hot water model is proposed for a more accurate description of energy conversion. Based on the PV/T and hot water model, the PIES planning model is established. Then, nonlinear terms introduced by the PV/T model and hot water model are linearized by various methods, such as the piecewise McCormick envelope. Besides, robust optimization method is adopted to overcome the uncertainty, Finally, the case study is conducted to verify the effectiveness of the planning model. The result shows that the electrical output of PV/T is 8.19% higher on average than that of photovoltaic (PV) equipment, the application of PV/T can reduce 17.66% of the PIES total cost on average and the novel hot water model can better reflect the temperature characteristic of hot water. • A detailed photovoltaic/thermal model is established and linearized. • A new hot water model is proposed to describe its characteristics more accurately. • The planning model of the PIES based on the above model is proposed. • A robust optimization method based on column and constraint generation is adopted. • The average total cost of PIES is reduced by 17.66% after the application of PV/T. [ABSTRACT FROM AUTHOR]

Steady-state energy flow calculation (EFC) is the cornerstone of the long-term operation assessment of integrated energy systems (IES). The conventional EFC methods mainly focus on calculation speed and efficiency. However, the robustness is often ignored, which may result in a failure in finding the solutions under ill-conditioned and unsolvable situations. To address this issue, this paper proposes a robust EFC method for integrated electricity-gas-heat system. First, a novel robust EFC method based on Levenberg–Marquardt (L–M) method is proposed for a comprehensive formulation of the energy flow model combining the electricity, natural gas, district heating system and detailed interdependence. Further, a consecutive adaptive damping factor updating approach is proposed. It enables a secure search step to avoid the flutter in iteration process, thus enhancing computational efficiency and convergence for EFC. In addition, the influence of the direction and the size of search step are jointly considered. It is helpful to guarantee solutions for both ill-conditioned and unsolvable situations. Numerical simulation results demonstrate the strong robustness, convergence and universality of the proposed EFC method that works under diversified operation modes, e.g., well-conditioned mode, inappropriate initial values, heavy load mode, and ill-conditioned operation mode. • The integrated electrical, gas and heat system with detailed interdependence energy conversion is formulated. • A novel energy flow calculation method is proposed to enhance the calculation robustness and convergence efficiency. • Numerical simulations are carried out to validate the proposed method. • Satisfactory robustness and universality in multi-categories: well-conditioned, ill-conditioned and unsolvable situations. [ABSTRACT FROM AUTHOR]

• Design a novel island micro energy grid incorporating biomass waste energy conversion, desalination, and power-to-hydrogen devices (BSP-MEG) • Propose a robust multi-objective optimal dispatching model for BSP-MEG considering the worst scenario. • Design a hybrid differential evolution algorithm to solve the multi-objective problem considering adaptive adjustment variation factor. • Discuss the influence of robust coefficient and prediction errors on the optimal dispatching strategy. • Verify the coordination optimization effect of biomass waste energy conversion, desalination, and power-to-hydrogen devices. To realize renewable and self-sustainable energy supply in island region, based on geographical characteristics with abundant renewable resources, an optimal model for island micro energy grid (MEG) is designed incorporating biomass waste energy conversion system (ECS), desalination, and power-to-hydrogen (BSP-MEG) Firstly, the mathematical model is designed, including models of power generators, ECS, desalination and power-to-hydrogen (P2H) devices, etc. Next, the multi-objective scheduling optimization model is designed, containing conventional scheduling model (Scheduling optimization objectives and constraints established with minimum operation and environment costs) and stochastic scheduling model (Minimum Conditional Value-at-Risk objective specific to volatility and uncertainty of renewable generations based on robust stochastic optimization method). Then, to solve the multi-objective optimization problem (MOP), a hybrid differential evolution algorithm is proposed based on local optimal and external archiving strategies. Finally, the MEG of YongXing Island is selected as an example. The results show (1) BSP-MEG effectively realized multi-energy cooperative optimization, and promote intra-day peak shaving. (2) BSP-MEG reduced operating costs, environmental costs and Conditional Value-at-Risk (CVaR) by 78.2%, 61.8% and 77.9% respectively, while curtailment rate by 25.6 to 0.9%. (3) Whether in general scenario or worst, BSP-MEG can realize self-production and self-sale of energy and material, of which risk resistance ability is better. (4) By designing local optimal and external archiving strategies, hybrid differential evolution algorithm performs better in solving complex MOP. In general, the optimization model proposed in this paper can improve the utilization of renewable resources, alleviate the shortage of fresh water, and help realize renewable and sustainable energy supply. [ABSTRACT FROM AUTHOR]

The research on photovoltaic conversion is continuously overtaking technological challenges and modern PV cells can nowadays be efficiently combined with solar concentrators. In this paper a new photovoltaic solar concentrator model based on non-imaging optics and embedding high efficiency multi-junctions cells is presented. The concentrator has been optimized to maximize the electricity production but it is thought to work in cogeneration to allow also for thermal energy by recovering the residual heat, since an active cooling system for the cells is necessary. The efficiency enhancement is obtained thanks to the high matching between the collected solar irradiance and the receiver electrical features. The aim of the paper is the definition of the number of residential utilities connected to the system in order to minimize the exchange of energy with the network and also the use of auxiliary boiler. Also the optimal size of electric and thermal storage to be integrated to the concentrator, has been determined as function of the number of utilities. To achieve these goals a parametric analysis has been carried out by the use of an in-house-developed calculation code considering a whole year of operation in order to estimate the energy fluxes and the economic performance. Furthermore, the maximum capital cost of the system has been estimated in order to achieve a return on the investment in ten or twenty years. According to the Authors’ knowledge, the novelty of this study regards the implementation of this kind of photovoltaic solar concentrator – for combined heat and power production – in a residential application. [ABSTRACT FROM AUTHOR]

The development on tidal turbine technology is ongoing with focus on several aspects, including hydrodynamics, operation and environment. Before considering an area for exploitation, tidal energy resource assessments in pre-feasibility energy extraction areas must include the relevant characteristics of the device to be used. The present paper uses the momentum source approach to represent a floatable tidal energy converter (TECs) in a coastal hydro-morphodynamic model and to perform model simulations utilising different TEC array schemes by quantifying the aggregated drag coefficient of the device array. Simulations for one-month periods with nested models were performed to evaluate the hydrodynamic impacts of energy extraction using as output parameters the reduction in velocity and water-level variation differences against a no-extraction scenario. The case study focuses on representing the deployment of floatable E35 Evopod TECs in Sanda Sound (South Kintyre, Argyll, Scotland). The range in power output values from the simulations clearly reflects the importance of choosing the location of the array, as slight changes in the location (of <1 km) can approximately double the potential power output. However, the doubling of the installed capacity of TECs doubles the mean velocity deficit and water-level differences in the area surrounding the extraction point. These differences are amplified by a maximum factor of 4 during peak flood/ebb during spring tides. In the simulations, the drag coefficient is set to be constant, which represents a fixed operational state of the turbine, and is a limitation of coastal models of this type that cannot presently be solved. Nevertheless, the nesting of models with different resolutions, as presented in this paper, makes it possible to achieve continuous improvements in the accuracy of the quantification of momentum loss by representing turbine characteristics close to the scale of the turbine. [ABSTRACT FROM AUTHOR]

The pulp and paper industry is a fundamental sector of the economy of many countries. However, this sector requires real collaboration and initiatives from stakeholders to reduce its significant consumption of energy and emission of greenhouse gases. Heat exchangers are examples of equipment in pulp mills that are subjected to undesirable and complex phenomena such as evolution of fouling over time, which leads to inefficiency in terms of energy consumption and unplanned shutdowns, resulting in ineffective maintenance strategies and production costs. Therefore, there is a clear need to develop an accurate predictive maintenance tool that helps mill operators avoid such situations. It is necessary for that tool to effectively track the fouling evolution level and, based on it, deploy a reliable prognostics approach to estimate more accurately the time-to-clean of this equipment. This study presents a new hybrid prognostics approach for fouling prediction in heat exchangers. The proposed approach relies on the fusion of information of different prediction horizons to estimate the time-to-clean. Employing long short-term memory, it allows adaptation of long-term predictions by accurate short-term predictions using multiple non-linear auto-regressive exogenous models. This fusion not only captures the changes in degradation trend over time, but also ensures a good accuracy of prognostics results in both the short- and long-term horizons for planning maintenance actions. The effectiveness of the proposed approach was successfully proven on real industrial data collected from a pulp mill heat exchanger located in Canada. • New adaptive prognostic approach based on fusion of short and long-term predictors. • Selection of relevant physical parameters for monitoring of fouling evolution. • Accurate long-term fouling prediction by using short-term predictors. • High accuracy of fouling time-to-clean in a real heat exchanger plant. [ABSTRACT FROM AUTHOR]

• A design tool for energy conversion and noise characterization in outdoor ducts. • 2-D modeling and analysis for an outdoor duct exposed to solar radiation. • Definition, expression and unit for different types of noise due to various power systems in an outdoor duct. • Validation of design tool with experimental results. • Noise calculation examples and charts for various types of noise. The aim of this paper is to present a design tool with its guiding principles for energy conversion and noise characterization of an exterior rectangular duct often installed on building envelopes for pre-conditioning of fresh air. The energy conversion in an exterior rectangular duct is a function of solar irradiation, air gap width, mass flow rate and pressure, wall and air temperatures. A generalized two dimensional thermal analysis of an outdoor duct is presented by placement of surface and air nodes into two adjacent stacks of control volumes representing outer and inner walls of duct. A matrix solution procedure is adopted by constituting conjugate heat exchange of conduction, convection, radiation and ventilation heat transport. The rectangular duct model is built by a metallic exterior wall exposed to a steady heat flux generation due to solar heat gain and a well-insulated back panel as its counterpart wall. The model improves the results of traditional thermal models for the cases where: (i) there are sections of conjugate heat exchange; and (ii) stack effect due to thermal buoyancy necessitates 2-D nodal analysis for distant composite nodes. The design tool is supported with some numerical and experimental results of an airflow window with a photovoltaic (PV) solar wall installed in an outdoor test-room. Furthermore, some examples of noise characterization calculations are illustrated using devised noise measurement equations. [ABSTRACT FROM AUTHOR]

Highlights • Probabilistic power curve model to quantify uncertainty of wind energy conversion. • Data clearing methods based on intuitive rules and density-based clustering. • Use of new model inputs – pitch angle and wind direction – improves model accuracy. • Novel index is proposed to evaluate performance of probabilistic power curve model. Abstract This paper proposes probabilistic wind turbine power curve (WTPC) models to quantify the uncertainties of energy conversion and highly scattered relationships of actual wind speed to power. First, new model inputs (i.e. pitch angle and wind direction) and novel data clearing methods are presented to improve the model accuracy, which is rare in the previous studies. Second, the models are established based on three nonparametric algorithms, i.e. Monte Carlo, neural network, and fuzzy clustering. Third, to fill the research gap on model evaluation, the desirable properties of a probabilistic WTPC model are defined as expected variance ratio (EVR), and this index is formulated by calculating the cumulative gaps between the simulated and actual power distribution in each wind speed segment. Data from two Chinese wind farms are used to validate and compare the proposed methods using the mainstream deterministic index and the proposed EVR. Results show that (i) new model inputs and data clearing methods are able to improve the accuracy for probabilistic models regardless of the afterwards modelling method; (ii) fuzzy outperforms other probabilistic models. [ABSTRACT FROM AUTHOR]

Highlights • Ubiquitous energy signifies an access to energy everywhere and any time. • Definitions and criteria for ubiquitous energy technologies and systems. • A systematic review of the latest innovations in energy generation, storage and distribution. • Research and development should focus on the portability, scalability and integrability. Abstract The continuous and rapid development of energy technology challenges the scientific community to ponder the long-term energy evolution from the perspective of sustainable energy transition. We state that one of the key challenges for the new (post-fossil) energy era is to guarantee to all energy users an access to adequate resources of energy everywhere and at any moment of time. To crystallize the key ideas of such a pervasive energy supply chain into a single concept, we introduce the concept 'ubiquitous energy'. The main contribution of our paper is to create a discussion framework for the concept and to identify the most relevant technology pathways for the realization of 'ubiquitous energy'. Hence, we first present the background of the concept and discuss matters concerning the 'quality of energy to be present everywhere'. Secondly, we review the latest innovations in energy technology with respect to the energy supply chain and summarize technology pathways to 'ubiquitous energy'. To that end, we describe a systematic framework to classify energy technologies under energy generation, storage, transmission and distribution. We conclude that 'ubiquitous energy' covers various solutions in both scope and degree of integration, but the most prominent trend of development is the use of distributed and shared resources and local energy supply chains. Here, the research should focus on integrated and mobile energy conversion and storage options and wireless power transmission. [ABSTRACT FROM AUTHOR]

Highlights • A new approach for the calculation of quarter-hourly CO 2eq intensity is presented. • Effects of charging strategies on the environmental impact of BEVs are derived. • Large amounts of CO 2eq emissions are saved by optimizing the charging time. • The temporal variation of CO 2eq intensity in winter is small compared to summer. • The CO 2eq savings potential is significantly greater during the day than at night. Abstract In many countries, the replacement of internal combustion engine vehicles (ICEVs) with battery electric vehicles (BEVs) offers an opportunity to reduce CO 2 equivalent (CO 2eq) emissions in traffic. BEVs have significantly greater energy conversion efficiency from energy storage to wheel (tank-to-wheel [TTW]) and zero tailpipe emissions; these features are in stark contrast to the environmental burdens posed by vehicle production and electricity generation (well-to-tank [WTT]). Since CO 2eq emissions from vehicle use of BEVs account for the majority of the entire life cycle emissions, it is important to closely examine the CO 2eq intensity of electricity generation, which varies based on the sources of energy in the electricity mix of each country and time of day. This paper compares the environmental impact of diesel and electric buses in the city of Aachen throughout their life cycles and analyzes the effects of electricity generation with reference to variation in charging time. Based on recorded driving profiles, the vehicle dynamics of the longitudinal motion are simulated, and the energy demand as a function of the altitude profile and ambient temperature is calculated. The calculation of the quarter-hourly CO 2eq intensity is combined with the vehicle life cycle model in order to examine the effects of electricity generation on BEV life cycle emissions. To analyze the correlation between charging time and BEV environmental impact, different charging scenarios are defined, and CO 2eq savings from replacing ICEVs with BEVs are estimated. Scenario analyses are conducted over both short- and long-term time scales to predict the future environmental and economic benefits and costs of BEVs compared to ICEVs. The results demonstrate a significant dependency of BEV environmental impact on charging time, which varies by time of day and season. At night, the contribution of renewable energies to the electricity mix is low, and the variation in CO 2eq intensity is limited; therefore, the environmental impact of charging time is lower compared to charging at noon. The larger CO 2eq emissions of BEV production are compensated for all scenarios within the first year of operation. However, if BEVs are charged with electricity generated exclusively by lignite-fired power plants, more CO 2eq emissions are released over their lifetimes compared to ICEVs; this scenario also holds when ICEVs are fueled with biodiesel. Overall, the positive environmental balance of BEVs is not based on a low CO 2eq intensity, but on the greater energy conversion efficiency and the possibility of recuperating braking energy. These properties are particularly advantageous in urban traffic. [ABSTRACT FROM AUTHOR]

Highlights • Local CO 2 emission factors of China's coal chemical products are published. • The total CO 2 emission from China's coal chemical industry was 607 Mt in 2015. • The spatial disparity of CO 2 emission from China's coal chemical industry is great. • CO 2 emission from modern coal chemical industry is predicted to be 417 Mt in 2020. • Carbon capture, utilization, and storage has great potential to reduce its emission. Abstract As the largest producer of coal chemical products in the world, China faces tremendous pressure to reduce its carbon emission. An accurate quantification of the carbon dioxide (CO 2) emission of coal chemical industry in China is therefore necessary. However, due to the variety of coal chemical products and limitations of CO 2 emission factors, the total CO 2 emission of coal chemical industry has yet to be determined. In this study, local CO 2 emission factors of coal chemical products in China are published based on first hand data from twenty-three coal chemical enterprises and the total CO 2 emission of China's coal chemical industry is extrapolated. The provincial-level spatial distribution of the CO 2 emission of coal chemical industry is presented to assist the government in identifying key emission reduction areas. Additionally, scenario analysis of CO 2 emission for China's modern coal chemical industry in 2020 is conducted to determine whether the development of the modern coal chemical industry will have a significant impact on future CO 2 emission, as well as the effect of carbon capture, utilization and storage technologies on the reduction in carbon emission. The estimate shows that the total CO 2 emission of the coal chemical industry in 2015 was 607 million tonnes (Mt), accounting for approximately 5.71% of China's total CO 2 emission. The figure is higher than the total annual CO 2 emission of a country such as Canada (555 Mt) or Brazil (486 Mt). Quantifying the emission of the coal chemical industry is therefore critical to understand the global carbon budget. The spatial distribution shows that Shandong, Inner Mongolia and Shanxi release one-third of the coal chemical industry's total CO 2 emission. Considering the development of the modern coal chemical industry, its CO 2 emission is predicted to be as high as 416.52 million tonnes in 2020. However, the CO 2 emission could be reduced by 317.98 million tonnes when carbon capture, utilization and storage are applied to process and energy systems simultaneously. This paper quantifies the CO 2 emission of the coal chemical industry in China for the first time, identifies key chemical products and the provinces in which they are produced, explores the carbon reduction potential by scenario analysis, and provides specific data to support the assessment of effective CO 2 reduction policy. [ABSTRACT FROM AUTHOR]

Highlights • A new generalised approach to modelling multi-energy systems is presented. • Arbitrarily complex multi-energy converter topologies can be readily modelled. • Developed flexible energy demand/production models can be used in demand management. • The method is suitable for a range of optimisation-based management applications. Abstract A requirement for new sources of flexibility in meeting energy demand and the growing interest in the interaction between energy sectors have drawn attention to multi-energy systems, which can offer numerous benefits, e.g. providing flexibility to counteract the intermittency of renewable generation and increase energy efficiency. In order to maximise these benefits, advanced control methods are required. The model predictive control methodology is a promising candidate for such applications as it is capable of incorporating economic and operational objectives whilst respecting various technical, regulatory and environmental constraints. In order to implement such a control strategy effectively, it is necessary to develop appropriate system models. This paper presents a novel generalised modelling framework for multi-energy systems that is particularly well suited, though not limited to, predictive control applications. The proposed approach is capable of representing energy converter arrangements of arbitrary complexity containing multiple energy vectors, as well as multi-directional energy flow, multi-generation and multi-mode devices, a wide range of controllable producers/consumers, energy storage and flexible loads. The effectiveness of the approach is demonstrated using a representative case study based on three buildings at the University of Manchester where the developed model is incorporated into a model predictive control scheme. The simulation results show how the controller minimises the cost of purchasing energy whilst satisfying operational constraints, and managing various types of flexible demand. [ABSTRACT FROM AUTHOR]

Highlights • A procedure for the optimisation of tidal array size through surrogate modelling is introduced. • Array size is defined by means of two design variables: number of rows and number of turbines per row. • Tidal array is placed in a channel of a multi-inlet costal lagoon with complex feedback mechanisms. • A numerical model is set-up and validated to assess effects of arrays in hydro- and morphodynamics. • Multi-objective optimisation models are formulated considering environmental constraints. Abstract This paper investigates the optimum tidal energy converter array density at a tidal inlet by applying surrogate-based optimisation. The SBO procedure comprises problem formulation, design of experiments, numerical simulations, surrogate model construction and constrained optimisation. This study presents an example for the Faro-Olhão Inlet in the Ria Formosa (Portugal), a potential site for tidal in-stream energy extraction. A 35 kW Evopod™ floating tidal energy converter from Oceanflow Energy Ltd. has been used for array size calculations considering two design variables: (1) number of array rows, and (2) number of tidal energy converter per row. Arrays up to 13 rows with 6–11 tidal energy converters each are studied to assess their impacts on array performance, inlets discharges and bathymetry changes. The analysis identified the positive/negative feedbacks between the two design variables in real case complex flow fields under variable bathymetry and channel morphology. The non-uniformity of tidal currents along the array region causes the variability of the resource in each row, as well as makes it difficult to predict the resultant array configuration interactions. Four different multi-objective optimisation models are formulated subject to a set of performance and environmental constraints. Results from the optimisation models imply that the largest array size that meets the environmental constraints is made of 5 rows with 6 tidal energy converter each and an overall capacity factor of 11.6% resulting in an energy production of 1.01 GWh year−1. On the other hand, a higher energy production (1.20 GWh year−1) is achieved by an optimum array configuration, made of 3 rows with 10 tidal energy converters per row, which maximises power output satisfying environmental and performance restrictions. This optimal configuration permits a good level of energy extraction while having a reduced effect on the hydrodynamic functioning of the multi-inlet system. These results prove the suitability and the potential wide use of the surrogate-based optimisation method to define array characteristics that enhance power production and at the same time respect the environmental surrounding conditions. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Switching control and sliding mode control are combined to control a buck converter. • The novel design of the switching sliding surface can address the singularity problem. • Multi-type restrictive condition can guarantee the stability of the SSMC system. • The SSMC strategy can simplify the implementation of exponential circuit. Abstract In this paper, a switching sliding-mode control strategy is proposed for the voltage control of a buck converter in auxiliary energy source. The aim of this study is to solve the singularity problem of the terminal sliding-mode control strategy and simplify the implementation of the exponential operation of the non-singular terminal sliding-mode control strategy in practical applications. To achieve this goal, the state-space model of the buck converter in the auxiliary energy source is established. Furthermore, a novel switching sliding surface is defined based on the non-singular terminal sliding-mode control strategy. To ensure the stability of the switching sliding-mode control system, a multi-type restrictive condition, including non-singular type and reachable type, is designed based on equivalent control law and Lyapunov stability criterion, respectively. Simulations and experiments are presented to verify the effectiveness of the proposed switching sliding-mode control strategy. The results show that both the non-singular terminal sliding-mode control and the switching sliding-mode control can effectively solve the singularity problem. Compared with the terminal sliding-mode control strategy, the non-singular terminal sliding-mode control and the switching sliding-mode control strategies have over 18% and 34.4% settling-time improvement of voltage adjustment to deal with the large load variation, respectively. The proposed switching sliding-mode control strategy can not only ensure the robust voltage control of the buck converter in the auxiliary energy source, but also simplify the implementation of exponential circuit in practical applications. [ABSTRACT FROM AUTHOR]

In response to the oil crises of the 1970s, energy accounting experienced a revolution and became the much broader field of energy analysis, in part by expanding along the energy conversion chain from primary and final energy to useful energy and energy services, which satisfy human needs. After evolution and specialization, the field of energy analysis today addresses topics along the entire energy conversion chain, including energy conversion systems, energy resources, carbon emissions, and the role of energy services in promoting human well-being and development. And the expanded field would benefit from a common analysis framework that provides data structure uniformity and methodological consistency. Building upon recent advances in related fields, we propose a physical supply-use table energy analysis framework consisting of four matrices from which the input-output structure of an energy conversion chain can be determined and the effects of changes in final demand can be estimated. Real-world examples demonstrate the physical supply-use table framework via investigation of energy analysis questions for a United Kingdom energy conversion chain. The physical supply use table framework has two key methodological advances over the building blocks that precede it, namely extending a common energy analysis framework through to energy services and application of physical supply-use tables to both energy and exergy analysis. The methodological advances enable the following first-time contributions to the literature: (1) performing energy and exergy analyses on an energy conversion chain using physical supply-use table matrices comprised of disaggregated products in physical units when the last stage is any of final energy, useful energy, or energy services; (2) performing structural path analysis on an energy conversion chain; and (3) developing and utilizing a matrix approach to inhomogeneous units. The framework spans the entire energy conversion chain and is suitable for many sub-fields of energy analysis, including net energy analysis, societal energy analysis, human needs and well-being, and structural path analysis, all of which are explored in this paper. [ABSTRACT FROM AUTHOR]

Performing rigorous technical and commercial assessment of wave energy converters (WECs) numerically, before engaging in expensive wave tank and open ocean tests, is vital for the economically successful development of prototypes. To that end, this paper presents a high-fidelity wave-to-wire simulation platform (the HiFiWEC ), where a Computational Fluid Dynamics (CFD)-based numerical wave tank is coupled to a high-fidelity power take-off (PTO) model, which enables assessment of WEC performance with greater accuracy than with previous wave-to-wire approaches. A test case, simulating the performance of a heaving point absorber type WEC in realistic conditions, is presented and compared against traditional lower fidelity modelling methods. The WEC response is evaluated with a number of different approaches, including different techniques to model hydrodynamic wave-structure interactions and the power take-off system, and the benefits of the HiFiWEC are highlighted. The results highlight that excessive simplifications in the modelling of the PTO system can lead to significant overestimation in generated energy output, with relative deviations ( ∊ ) of up to 150% compared to the HiFiWEC . In addition, uncertainty in viscous drag parameters added to hydrodynamic models based on boundary element method solvers, reinforce the necessity of CFD-based models for applications where high-fidelity is essential. Finally, it is demonstrated that minor/insignificant inaccuracies in the hydrodynamic model ( ∊ = 0.5 % ) can result in significant differences in the estimation of the final energy generation ( ∊ = 7 % ), highlighting the need for a coupled high-fidelity platform. [ABSTRACT FROM AUTHOR]

Plasma-assisted methane (CH 4 ) activation is a promising way for a hydrogen (H 2 ) production. In this paper, we describe our studies of microsecond and nanosecond pulsed spark discharge plasmas use in a CH 4 pyrolysis for a H 2 production. The dependence of CH 4 conversion and gas discharge product composition on discharge power, discharge gap length and gas flow rate are studied. The electrical and optical characteristics of the discharges are also studied to reveal discharge plasma parameters and chemical reactions leading to CH 4 pyrolysis. Experimental results show that H 2 and acetylene (C 2 H 2 ) are the major gas discharge products accompanied by trace gas discharge products, such as ethane (C 2 H 6 ), ethylene (C 2 H 4 ) and carbon. The highest CH 4 conversion and H 2 yield, 91.2% and 38.4%, respectively, are achieved with an energy conversion efficiency of 44.3% using the microsecond pulsed spark discharge at a gap length 6 mm and a gas flow rate 50 mL/min. The carbon balance under the studied operating parameters varies from 66.7% to 92.8%. The morphology of carbon deposition is presented by two crystal forms identified by SEM and Raman spectral analyses. Finally, comparatively low electron temperature and high vibrational molecular temperature are observed in our experiments, which suggests that V-V transition for CH 4 excitation process and V-T transition for CH 4 heating process play important roles in CH 4 pyrolysis sustained by the pulsed spark discharge. [ABSTRACT FROM AUTHOR]

Thermoelectric devices have potential energy conversion applications ranging from space exploration through to mass-market products. Standardised, accurate and repeatable high-throughput measurement of their properties is a key enabling technology. Impedance spectroscopy has shown promise as a tool to parametrically characterise thermoelectric modules with one simple measurement. However, previously published models which attempt to characterise fundamental properties of a thermoelectric module have been found to rely on heavily simplified assumptions, leaving its validity in question. In this paper a new comprehensive impedance model is mathematically developed. The new model integrates all relevant transport phenomena: thermal convection, radiation, and spreading-constriction at junction interfaces. Additionally, non-adiabatic internal surface boundary conditions are introduced for the first time. These phenomena were found to significantly alter the low and high frequency response of Nyquist spectra, showing their necessity for accurate characterisation. To validate the model, impedance spectra of a commercial thermoelectric module was experimentally measured and parametrically fitted. Technique precision is investigated using a Monte-Carlo residual resampling approach. A complete characterisation of all key thermoelectric properties as a function of temperature is validated with material property data provided by the module manufacturer. Additionally, by firstly characterising the module in vacuum, the ability to characterise a heat transfer coefficient for free and forced convection is demonstrated. The model developed in this study is therefore a critical enabler to potentially allow impedance spectroscopy to characterise and monitor manufacturing and operational defects in practical thermoelectric modules across multiple sectors, as well as promote new sensor technologies. [ABSTRACT FROM AUTHOR]

To mitigate the global warming threat, CO 2 emission reduction is an irreversible trend for the sustainable development of power systems. Among various low-carbon technologies, gas-fired power plants and power-to-gas facilities play an important role to reduce emissions, and they are increasing the interdependency between electricity and natural gas systems. Considering also the increasing penetration of wind power generation, this paper proposes a low-carbon economic dispatch model under both constraints of the electricity and natural gas systems. To reduce CO 2 emission and improve the wind power utilization, mathematical formulations of the post-combustion carbon capture system and power-to-gas facility are presented in the proposed model. Additionally, a flexible operation mode of post-combustion carbon capture system and power-to-gas facility is further analyzed. The objective function of the presented model is to minimize the total cost, which consists of the operation cost, the CO 2 processing cost and the penalty cost of wind power curtailment. Then the optimization model is converted into a mixed integer linear programming problem for efficient computation purpose. Numerical case studies are carried out to validate the effectiveness of the proposed model and the flexible operation mode. [ABSTRACT FROM AUTHOR]

European Directive 2010/31/EU stated that by the end of 2020 all new buildings should be nearly Zero-Energy Buildings (nZEB). Since such buildings require a low quantity of energy for heating, they can utilize energy from the return line of a District Heating (DH) system. Further, this new type of buildings can successfully be integrated into the fourth generation of heat distribution technology, which is the new trend in the DH industry. On the other hand, existing building stock has a service lifetime of around 50 years, indicating that the required supply temperature in the DH system cannot be lowered beneath a certain level. Hereafter, together with new types of buildings and different policies, this could lead to changes in heat demand profiles of the DH system. The above-mentioned situation in the building market will lead to changes in heat load profiles and unavoidably influence the performance indicators of energy conversion units. Therefore, the focus in this paper was devoted to operation analysis of ethanol-based a Combined Heat and Power (CHP) plant with combined cycle technology under changeable demand conditions and different temperature levels in the DH system. In this paper different temperature levels of the DH system together with two temperature control strategies were considered. Further, the analysis included different heat demand profiles. The analysis was performed in Aspen HYSYS simulation software and data post processing was made by MATLAB. The results found that effective plant operation is highly dependent on heat load profile. Temperature control strategies did not induce a significant change in overall power production in CHP. The decrease in the supply temperature did not show a significant impact on plant performance. However, increase in temperature difference between supply and return lines led to higher power production and better overall plant performance. Further, it was concluded that it is rather difficult to operate CCPP connected to low energy building stock. This means that the CCPP is suitable for high-density heat areas, while it has poor energy performance indicators in low heat density areas. [ABSTRACT FROM AUTHOR]

This paper is aimed to analyze design criteria, setting up, control strategies and experimental tests related to a power configuration of DC micro-grid for fast charging of full electric and plug in hybrid vehicles. The proposed DC fast charging architecture is derived by an analysis comparing the main characteristics of well known architectures, mainly based on AC and DC bus, taking also into account the integration of renewable energy sources (RESs) with stationary energy storage systems and fleets of road electric/hybrid vehicles. On the base of the proposed architecture a laboratory prototype of charging station has been realized by means of a 20 kW AC/DC bidirectional grid tie converter interconnected with two different power DC/DC converters of similar rated power. In this micro-grid architecture the AC/DC converter realizes a conversion stage at 790 V DC, whereas other two converters allow either the electric vehicle battery packs to be charged or an energy storage buffer to save electric energy and support the main grid during the fast charging operations. The laboratory tests described in this paper are mainly devoted to characterize the laboratory demonstrator, in different operative conditions, such as vehicle-to-grid (V2G), charging/discharging operations of different types of storage systems and fast charging operations of road electric vehicles. Then the study of the proposed power conversion architecture is focused on the evaluation of charging/discharging power, efficiency, energy flux management and its impact on the main grid. In addition proper control strategies are evaluated and implemented, allowing the proposed architecture to follow the required operations. The obtained experimental results demonstrate real advantages in terms of charging times and power requirements from the main grid, when adopting DC buffer architecture for fast charging operations. Finally, these results support the identification of a knowledge base, useful to evaluate energy management and control strategies to be adopted for DC charging stations and each one of their power converters in a smart grid scenario with distributed generation systems. [ABSTRACT FROM AUTHOR]

This paper outlines the results for a set of experiments carried out on Vertical Axis Autorotation Current Turbine (VAACT) which is an innovative concept among the other low-head hydrokinetic energy converters. The VAACT is a one degree of freedom hinged plate which utilizes the autorotation phenomenon to rotate about its vertical axis in uniform water current. The state of the art on this turbine is application of the extra moment of inertia and also flapped shape of the rotor blade to improve the autorotation characteristics as the principle of operation of the turbine. Investigation of the effect of the extra moment of inertia and the flap on the operational characteristics such as maximum attainable angular velocity and tip speed ratio, obtainable torque of the turbine and its performance is the main objective of this paper. The VAACT harvests energy efficiently from very low head current. The performance of the flapped configuration of this turbine reaches up to 33% in the very low current velocity. The highest efficiencies occur in the range of 0.65–0.85 of tip speed ratio and also in the range of 0.6–0.7 of the non-dimensional moment of inertia. Furthermore, this study has shown that the flap increases the power coefficient significantly by a factor of up to 5 compared to flat plate type. [ABSTRACT FROM AUTHOR]

This paper presents and discusses a new methodology to determine the pre-setting of the radiator and balancing control valve, as one of the basic parameters in the process of the heating installation hydraulic balancing. Example calculations are also made for selected control valves using the proposed and alternative methodologies, including the methodology generally accepted and used in practice. A comparison of the results is presented. It is shown that the proposed methodology gives results consistent with experimental data. It is also more accurate and versatile than the other methodologies discussed in the paper. [ABSTRACT FROM AUTHOR]

Improving efficiency is an enduring effort for all work-heat conversion cycles. Ideal regenerators working with ideal gases bring about a lossless work and heat transfer over a temperature gradient, but real gases give rise to an “intrinsic” heat loss in regenerators because of the time-averaged enthalpy flow associated with the pressure dependence. Real gas effects play a vital role on the coefficient of performance (COP) of regenerators of refrigeration cycles working at the temperatures close to or below the critical point. The “intrinsic” heat loss of real gases degrades the theoretical COP of regenerators to as low as 1% of the Carnot efficiency. In this paper, an approach of heat input or removal aiming to improve the COP is proposed. The theoretical analysis of this approach reveals the underlying mechanism. It is shown that the theoretical COP of an ideal regenerator working with a real gas applying this approach is identical to the Carnot efficiency. A simplified approach of heat input is further analyzed. The Carnot efficiency can be attained under certain circumstances, and it is possible to obtain over 90% of the Carnot efficiency with a discrete method. The theory of improving the COP with the approach of heat input in discrete regenerator locations is supported by the experiment results found in the relevant literature. This new approach provides a potential way to significantly improve the efficiency of the regenerator of the refrigeration cycle working at the temperatures close to or below the critical point. This approach may further provide a reference for studies of the heat pump cycle and the engine cycle working with real gases. [ABSTRACT FROM AUTHOR]

In this paper, a solar co-producing electricity and solar syngas is originally proposed through synergistically combining a solar photovoltaic process and a solar thermochemical process. A transmitting photovoltaics is adopted and enables the ultraviolet and visible spectra to be converted into electricity. The infrared spectrum penetrates through the transmitting photovoltaics and is converted into high-grade chemical exergy of solar syngas through thermochemical reaction, rather than being converted into waste heat. The energy conversion models of the transmitting photovoltaics and solar thermochemical reactor are described. The total efficiency of solar-to-both electricity and solar syngas can be achieved to 55%. Furthermore, the influence of the key parameters on the solar cogeneration system performance is disclosed, such as the cut-off wavelength, solar cell types and production ratio. Our results would be expected to provide a new pathway of cascade utilization of the concentrating sunlight according to the spectrum distribution. [ABSTRACT FROM AUTHOR]

The direct-fired supercritical CO 2 power cycle not only has the potential of reaching high efficiency but also has inherent ability to capture almost all of the combustion derived CO 2 . A novel direct-fired supercritical CO 2 power cycle layout is proposed in this paper, using the syngas produced by coal gasification as the fuel. The proposed cycle layout is specially designed to facilitate heat integration between the power cycle, the fuel conversion process and other auxiliary subsystems. Heat from the air compressor intercooler and the low temperature syngas is introduced to the regenerator to correct its imbalanced heat exchange, a typical problem of the supercritical CO 2 power cycle that is caused by the abrupt physical property variation. Design considerations of the proposed cycle layout are discussed in detail. The result shows that the net efficiency is 42.1%, with near-zero CO 2 emissions. The proposed cycle layout is then further modified by integrating more heat from the oxygen compressors and the syngas compressor, which reduces the hot end temperature difference of the regenerator to less than 10 °C and increases the net efficiency to 43.7%. Heat integration through novel cycle layout has been proved essential to guarantee the high efficiency of the supercritical CO 2 power cycle. [ABSTRACT FROM AUTHOR]

The conceptual design phase is the first step in the design process of an engineering system. Most engineering systems, including cogeneration plants, may and likely will experience some malfunctions during its life cycle. The metrics typically considered in the conceptual design phase (and for analysis and optimization) of energy systems are cost, efficiency and environmental impacts. Quite rarely are operational considerations about malfunctions integrated during the conceptual design phase. Resilient design, or design for resilience, addresses this gap as illustrated here in the area of energy conversion and conservation of energy processes by examining the conceptual design of a cogeneration plant. Resilient design is a relatively new research field where the engineering system is designed such that it can optimally recover from failures. The main challenge is to quantify the resilience in early design phases, since there is not much detailed information about system components available at this point. To address these challenges, this paper introduces a novel resilient design framework that uses new metrics within a Monte Carlo-based assessment approach. The framework is exercised on conceptual designs of cogeneration plants. Results from this framework are compared against those from a methodology based on complex networks theory that has been previously suggested in the literature. The former presented more consistent results than the latter and we discuss the differences. Results also show that the concept with higher efficiency was not the one with higher resilience. Finally, we discuss how to integrate specific failure probabilities information into the framework (should that information be available), and deliberate on relations between resilience, fault handling strategies and design requirements. [ABSTRACT FROM AUTHOR]

The effective design of Distributed Energy Systems (DES) is subject to multiple uncertainties related to aspects like the availability of renewable energy, the building energy demands, and the energy carrier prices. Nevertheless, current practices involve the use of deterministic design models, which overlook uncertainty and can lead to suboptimal DES configurations that fail to deliver the desired performance. A necessary condition in order to obtain robust DES designs against uncertainty is the understanding of uncertainty’s impacts and main drivers. Therefore, this paper presents a novel methodological framework for the investigation of uncertainty in the context of DES design, which combines optimisation-based DES models and techniques from Uncertainty Analysis (UA) and Global Sensitivity Analysis (GSA). Moreover, the application of the framework is illustrated with a case study for the optimal DES design of a Swiss urban neighbourhood. Embarking from a deterministic DES design model, first, all sources of uncertainty are identified and appropriate probabilistic descriptions are assigned to all uncertain model parameters. UA is then performed using Monte Carlo (MC) simulations to quantify the impacts of uncertainty. Results reveal substantial variations in terms of economic and carbon performance of the optimal DES, but also in terms of optimal DES configurations. Moreover, the UA results indicate that the optimal system costs are mostly higher than the deterministic cost estimates, while the inverse is observed for the case of carbon emissions. Additionally, in many of the MC simulations, the resulting optimal DES configurations deviate significantly from the deterministically obtained designs, which confirms the risk of suboptimal decisions in deterministic design processes. Moreover, the results of UA can function as decision support by identifying the DES configurations that are optimal for most realisations of uncertainty. Finally, to identify the uncertain parameters that are mostly responsible for the variation of the economic performance of the DES, a two-step GSA is launched, combining the Morris method and the variance-based Sobol method. Results of the GSA indicate the energy demand patterns and the energy carrier prices as primarily responsible for the variability of the optimal system cost, while parameters like the investment costs and the technical characteristics of the technologies exert only minimal influence. The results of GSA, besides offering a better understanding of uncertainty to DES designers, also identify the parameters for which additional effort needs to be invested to reduce their uncertainty and, as a result, the uncertainty associated with DES design. [ABSTRACT FROM AUTHOR]

The electric power, gas, and heat systems work on different but complementary time and space scales. Multiple energy systems (MES) yields an increase on the efficiency and flexibility of energy supply. The coupling between different forms of energy bring difficulties in the planning of the overall energy system. This paper proposes a novel optimal planning method for a community level MES that jointly determines the optimal generation, conversion and delivery of electricity, heat, cooling, and other services. First, configuration planning of a community level MES is introduced and defined using the energy hub (EH) concept. Then, the planning problem is presented with the objective of minimizing the sum of the investment and operating costs, with variables that represent the selection of energy converters or storage and their relationships. The model is then formulated as a mixed-integer linear programming (MILP) problem based on graph theory. The proposed model does not requires any pre-assumptions on the configurations of the EH so that it can plan the MES starting from scratch. Finally, an illustrative example is provided to describe the functioning of our proposed method. A numerical case study for the planning of a subsidiary administrative center in Beijing, China is presented to demonstrate the effectiveness and superiority of the proposed method. [ABSTRACT FROM AUTHOR]

Water-energy nexus refers to the interdependence between water resources and energy conversion, and it encompasses the multiple phases of electric power generation and water processing and distribution. Current policies for the utilization of freshwater resources in electric power generation regulate the thermal discharges and their effect on the aquatic life. Water withdrawals and consumption polices are mainly prescribed at the regional level instead. This paper focuses on the effects of water policy constraints on electric power generation in changing climate conditions. A river basin is simulated, which hosts two hydraulically linked power generating stations, namely an upstream hydropower plant with reservoir and a downstream thermal power plant. Two alternative cooling designs are tested for the thermal power plant, i.e. once-through and wet tower cooling. Severe drought conditions leading to small river flows and high water temperatures are analyzed, and the limitations to the energy conversion at the thermal plant stemming from the water policies are quantified. The results show that some small flexibility in the water policy constraints during extreme droughts can secure a significant amount of energy to the power system, which would have been curtailed otherwise. Remarkably, the relaxation of 1.5 °C in the water policy constraints prevents the curtailment of 42% of the generation capacity of a 1000 MW e thermal plant during the analyzed 24 h drought scenario. In general, the type and the required amount of constraint relaxation depend on the environmental conditions and are to be judged case-by-case. Furthermore, the smart scheduling of water resources grants a 7% increase of the energy converted during droughts in the hydraulically linked hydro and thermal power plants. Finally, the analysis shows that once-through cooling systems are extremely sensitive to changes in water flow and temperature opening space for less sensitive technologies, i.e. wet cooling towers. [ABSTRACT FROM AUTHOR]