Lithium-ion batteries exhibit significant performance degradation such as power/energy capacity loss and life cycle reduction in low-temperature conditions. Hence, the Li-ion battery pack is heated before usage to enhance its performance and lifetime. Recently, many internal heating methods have been proposed to provide fast and efficient pre-heating. However, the proposed methods only consider a combination of unit cells while the internal heating should be implemented for multiple groups within a battery pack. In this study, we investigated the possibility of timing control to simultaneously obtain balanced temperature and state of charge (SOC) between each cell by considering geometrical and thermal characteristics of the battery pack. The proposed method schedules the order and timing of the charge/discharge period for geometrical groups in a battery pack during internal pre-heating. We performed a pack-level simulation with realistic electro-thermal parameters of the unit battery... [more]

Latvia’s industrial energy efficiency policy imposes the implementation of mandatory energy audits and energy management systems in large industrial enterprises and large industrial electricity consumers to improve industrial competitiveness, to move towards a carbon-neutral economy and to increase the security of supply. Companies affected by this energy efficiency policy are obliged to report to the national energy efficiency monitoring system on energy efficiency measures indicated in energy audits or energy management systems with the highest savings or economical potential. The purpose of this study was to assess the initial outcomes of the first industrial energy efficiency program in Latvia, using data from the national energy efficiency monitoring system, including an analysis of individual energy audit reports, and benchmarking it with findings from a similar program, thereby revealing untapped energy efficiency and CO2 emission reduction potential. Although the national monit... [more]

In wireless charging devices, a transmitter that applies a single inverter to output dual-frequency can effectively solve the charging incompatibility problem caused by different wireless charging standards and reduce the equipment volume. However, it is very difficult to solve the switching angle of the modulated dual-frequency waveform, which involves non-linear high-dimensional multi-objective optimization with multiple constraints. In this paper, an improved differential evolution (DE) algorithm is proposed to solve the transcendental equations of switching angle trains of dual-frequency programmed harmonic modulation (PHM) waveform. The proposed algorithm maintains diversity while preserving the elites and improves the convergence speed of the solution. The advantage of the proposed algorithm was verified by comparing with non-dominated sorting genetic algorithm II (NSGA II) and multi-objective particle swarm optimization (MOPSO). The simulation and experimental results validate t... [more]

National Grid, the UK’s largest utility company, has produced a number of energy transition scenarios, among which “2 degrees” is the most aggressive in terms of decarbonization. This paper presents the results of a combined prospective net energy and environmental life cycle assessment of the UK electricity grid, based on such a scenario. The main findings are that the strategy is effective at drastically reducing greenhouse gas emissions (albeit to a reduced degree with respect to the projected share of “zero carbon” generation taken at face value), but it entails a trade-off in terms of depletion of metal resources. The grid’s potential toxicity impacts are also expected to remain substantially undiminished with respect to the present. Overall, the analysis indicates that the “2 degrees” scenario is environmentally sound and that it even leads to a modest increase in the net energy delivered to society by the grid (after accounting for the energy investments required to deploy all t... [more]

A systematic method to evaluate the economic operating performance of existing combined heat and power (CHP) or combined cooling heat and power (CCHP) generation systems is applied. Two key performance indicators are selected to evaluate both the technical and the economic performance, based on operating recording data; the capacity factor and the capital recovery. The case study for eight projects in Athens is presented with the purpose to reveal the current situation of CHP in Greece and identify reasons that are hindering its penetration. Interesting conclusions were reached from the analysis. Only two out of the eight projects managed to achieve the break-even point in less than four years since the beginning of their operation, while oversizing phenomena were noticed in many cases leading in extremely low capacity factors.

In an open-winding machine, three-phase stator currents can be controlled such that the input armature currents may contain the third-harmonic current component in addition to the fundamental. Considering this attribute of open-winding patterns, a harmonic current field excitation technique for a wound rotor synchronous machine (WRSM) is proposed in this paper based on the control of time-harmonic magneto-motive force. Two inverters connected to both terminals of the stator winding are controlled so that the input armature current generates an additional third-harmonic current component. This third-harmonic component generates a vibrating magnetic field that induces a current in the specially designed rotor harmonic winding. The current is supplied as DC current to the rotor excitation winding to generate a rotor field by using a full-bridge diode rectifier in order to achieve brushless operation. The proposed dual-inverter-controlled brushless operation for a WRSM is executed in ANSYS... [more]

In the present work, the electrical and thermal performances of a newly designed PV/T (photovoltaic/thermal) air collector, which was proposed and fabricated by the author, have been investigated experimentally in the natural weather conditions. The PV/T air collector has a single-pass double-flow air channel. Also, a non-uniform cross-section transverse rib was attached at the back surface of the PV (photovoltaic) module to improve the heat transfer performance between the PV module and flowing air. The experiment was carried out in an outdoor field on a clear day with various air mass flow rates ranges from 0.0198 kg/s to 0.07698 kg/s. In the results, it was found that the average thermal efficiency of the PV/T collector increased from 35.2% to 56.72% as the air mass flow rate increased. The average electrical efficiency also increased from 14.23% to 14.81% with an increase in an air mass flow rate, but the effect of air mass flow rate on the increase in electrical efficiency was inc... [more]

Increasing concentrations of greenhouse gases in the atmosphere are leading to increased production and use of biofuels. The industrial development of biodiesel production and the use of biodiesel in the EU transport sector have been ongoing for almost two decades. Compared to mineral diesel production, the process of producing biodiesel is quite complex and expensive, and the search for new raw materials and advanced technologies is needed to maintain production value and expand the industrial production of biodiesel. The purpose of this article is to review the application possibilities of one of the new technologies—simultaneous extraction of oil from oily feedstock and transesterification (in situ)—and to evaluate the effectiveness of the abovementioned process under various conditions.

Thermochemical storage provides a volumetric and cost-efficient means of collecting energy from solar/waste heat in order to utilize it for space heating in another location. Equally important to the storage density, the dynamic thermal response dictates the power available which is critical to meet the varied demands of a practical space heating application. Using a laboratory scale reactor (127 cm3), an experimental study with salt in matrix (SIM) materials found that the reactor power response is primarily governed by the flow rate of moist air through the reactor and that creating salt with a higher salt fraction had minimal impact on the thermal response. The flowrate dictates the power profile of the reactor with an optimum value which balances moisture reactant delivery and reaction rate on the SIM. A mixed particle size produced the highest power (22 W) and peak thermal uplift (32 °C). A narrow particle range reduced the peak power and peak temperature as a result of lower pack... [more]

This paper presents a battery-aware stochastic control framework for residential energy management systems (EMS) equipped with energy harvesting, that is, photovoltaic panels, and storage capabilities. The model and control rationale takes into account the dynamics of load, the weather, the weather forecast, the utility, and consumer preferences into a unified Markov decision process. The embedded optimization problem is formulated to determine the proportion of energy drawn from the battery and the grid to minimize a cost function capturing a user-defined tradeoff between battery degradation and financial expense by user preferences. Numerical results are based on real-world weather data for Golden, Colorado, and load traces. The results illustrate the ability of the system to limit battery degradation assessed using the Rain flow counting method for lithium ion batteries.

In passive solar buildings, energy can be stored using either sensible heat materials or latent heat materials. Phase change materials (PCM) can contribute to temperature control in passive solar buildings when melting occurs near to comfort temperature required for building’s interior spaces. The use of finite element method (FEM) as a numerical methodology for solving the thermal problem associated with heat transfer in current building materials and PCMs make sense, as it is a well-known technique, generalized and dominated, however, still little applied to the domain of building physics. In this work, a solar model was developed and applied in order to simulate numerically the effect of solar radiation incidence on each face of the test cells (with different solar exposures) without neglecting the main objective of the recommended numerical simulation: the study of the action of PCM. During the experimental campaign, two test cells with distinct inner layers were used to evaluate t... [more]

The increase in global electricity demand, along with its impact on climate change, call for integrating sustainability aspects in the power system expansion planning. Sustainable power generation planning needs to fulfill different, often contradictory, objectives. This paper proposes a multi-objective optimisation model integrating four objective functions, including minimisation of total discounted costs, carbon emissions, land use, and social opposition. Other factors addressed in the model include renewable energy share, jobs created, mortality rates, and energy diversity, among others. Single-objective linear optimisations are initially performed to investigate the impact of each objective function on the resulting power generation mix. Minimising land use and discounted total costs favoured fossil fuels technologies, as opposed to minimising carbon emissions, which resulted in increased renewable energy shares. Minimising social opposition also favoured renewable energy shares,... [more]

Copper coordination complexes have emerged as a group of transition metal complexes that play important roles in solar energy conversion, utilization and storage, and have the potential to replace the quintessential commonly used transition metals, like Co, Pt, Ir and Ru as light sensitizers, redox mediators, electron donors and catalytic centers. The applications of copper coordination compounds in chemistry and energy related technologies are many and demonstrate their rightful place as sustainable, low toxicity and Earth-abundant alternative materials. In this perspective we show the most recent impact made by copper coordination complexes in dye-sensitized solar cells and other energy relevant applications.

The focus of this paper is the potential electrification of specialized agricultural tractors involved in vineyards and orchards. This category of machinery has not received research attention to date; however, regulations are encouraging lower emissions and higher efficiency, requiring the adoption of new technologies. Traction makes up only a limited part of this application, and the working cycle is not trivial; therefore, the design of the system is not straightforward. This study takes advantage of experimental measurements carried out under real operating conditions on a traditional specialized tractor, which was chosen as performance target. The performance requirements of the hybrid powertrain components are investigated, with particular focus placed on the electric motor. According to the dimension constraints, the design of the electric motor is carried out considering the requirements in terms of its thermal-equivalent torque and overload capability. The results are validate... [more]

In modern power systems, reliable provision of grid services (e.g., primary and ancillary services) are highly dependent on automation systems in order to have monitoring, processing, decision making and communication capabilities. The operational flexibility of automation systems is essential for the reliable operation of power systems during and after disruptive events. However, this is restricted by integrated hardware-software platforms. Therefore, it will be difficult to reconfigure control strategies during run time. This paper presents the concept of Grid Function Virtualization (GFV) as a potential approach to improve the operational flexibility of grid automation systems. GFV has been proposed to offer a new way to deploy and manage grid services by leveraging virtualization technology. The main idea of GFV is to run grid services (i.e., software implementation of services) independently from underlying hardware. To realize the important design considerations, the GFV architec... [more]

Non-intrusive load monitoring (NILM) is a process of estimating operational states and power consumption of individual appliances, which if implemented in real-time, can provide actionable feedback in terms of energy usage and personalized recommendations to consumers. Intelligent disaggregation algorithms such as deep neural networks can fulfill this objective if they possess high estimation accuracy and lowest generalization error. In order to achieve these two goals, this paper presents a disaggregation algorithm based on a deep recurrent neural network using multi-feature input space and post-processing. First, the mutual information method was used to select electrical parameters that had the most influence on the power consumption of each target appliance. Second, selected steady-state parameters based multi-feature input space (MFS) was used to train the 4-layered bidirectional long short-term memory (LSTM) model for each target appliance. Finally, a post-processing technique wa... [more]

There are three strategic levels for successful energy planning in cities: 1) Integration strategy for integrating energy planning into urban planning institutions; 2) Practice strategy for developing suitable energy planning practices in urban planning institutions, and 3) Vision strategy for the creation and integration of energy visions and scenarios required for long-term decarbonisation. The vision strategy is critical but not well researched and is the focus of this article. Using Strategic Energy Planning (SEP) as an analytical framework, the vision strategy of eight forerunner European cities are analysed. Some critical elements of SEP include the use of long-term targets, holistic energy system thinking, and retention of scenarios. The results indicate that the level of understanding and practice of the vision strategy is still deficient in the cities. Cities often use the practice of urban planning, which does not fit very well with energy planning, particularly with the visi... [more]

Access to electricity for every South African citizen, including rural dwellers, is a human right issue guaranteed by the government’s laws and policies. However, many remote rural areas still suffer from a lack of this very important amenity, due to the expensive prospect of connecting them to the central national grid. The feasible approach to connecting the rural communities to electricity supply is suggestively through the use of microgrid solutions. The microgrid technology is a very recent and viable option for the energy revolution. Microgrids result from the incorporation of energy storage systems, distributed generators, and localized loads. The application of this technology requires deliberate and extensive work on the operational architecture and the policy framework to be adopted. The energy storage devices form an integral part of the microgrid configuration or architecture to make sure more maintainable and constant operation is attained. This paper presents a review of... [more]

The paper presented herein investigates the effects of using supplementary cementitious materials (SCMs) in quaternary mixtures on the compressive strength and splitting tensile strength of plain concrete. In addition, environmental benefits resulting from the proposed solutions were analysed. A total of four concrete mixtures were designed, having a constant water/binder ratio of 0.4 and total binder content of 352 kg/m3. The control mixture only contained ordinary Portland cement (OPC) as binder, whereas others incorporated quaternary mixtures of: OPC, fly ash (FA), silica fume (SF), and nanosilica (nS). Based on the obtained test results, it was found that concretes made on quaternary binders containing nanoadditives have very favorable mechanical parameters. The quaternary concrete containing: 80% OPC, 5% FA, 10% SF, and 5% nS have shown the best results in terms of good compressive strength and splitting tensile strength, whereas the worst mechanical parameters were characterized... [more]

Research on the development of plants grown for energy purposes is important for ensuring the global energy supply and reducing greenhouse gas emissions, and simulation is an important method to study its potential. This paper evaluated the marginal land that could be used to grow sugarcane in the Guangxi Zhuang Autonomous Region. Based on the meteorological data from 2009 to 2017 in this region and field observations from sugarcane plantations, the sensitivity of the APSIM (Agricultural Production Systems sIMulator) model parameters was analyzed by an extended Fourier amplitude sensitivity test, and the APSIM model was validated for sugarcane phenology and yields. During the process of model validation, the value of the determination coefficient R2 of the observed and simulated values was between 0.76 and 0.91, and the consistency index D was between 0.91 and 0.97, indicating a good fit. On this basis, the APSIM sugarcane model was used to simulate the sugarcane production potential o... [more]

This paper presents work focused on the development, evaluation and use of a 3D model for investigation of the radiative heat transfer in rotary kilns. The model applies a discrete-ordinates method to solve the radiative transfer equation considering emission, absorption and scattering of radiation by gas species and particles for cylindrical and semi-cylindrical enclosures. Modelling input data on temperature, particle distribution and gas composition in the radial, axial and angular directions are experimentally gathered in a down-scaled version of a rotary kiln. The model is tested in its capability to predict the radiative intensity and heat flux to the inner wall of the furnace and good agreement was found when compared to measurements. Including the conductive heat transfer through the furnace wall, the model also satisfactorily predicts the intermediate wall temperature. The work also includes a first study on the effect of the incident radiative heat flux to the different surfa... [more]

Heat demand dominates the final energy use in northern cities. This study examines how changes in heat demand may affect solutions for zero-emission energy systems, energy system flexibility with variable renewable electricity production, and the use of existing energy systems for deep decarbonization. Helsinki city (60 °N) in the year 2050 is used as a case for the analysis. The future district heating demand is estimated considering activity-driven factors such as population increase, raising the ambient temperature, and building energy efficiency improvements. The effect of the heat demand on energy system transition is investigated through two scenarios. The BIO-GAS scenario employs emission-free gas technologies, bio-boilers and heat pumps. The WIND scenario is based on large-scale wind power with power-to-heat conversion, heat pumps, and bio-boilers. The BIO-GAS scenario combined with a low heat demand profile (−12% from 2018 level) yields 16% lower yearly costs compared to a bus... [more]

This paper considered the electrochemical behavior of new electrospun separators for lithium-ion batteries on the basis of nano- and microfibers of polyvinylidene fluoride (PVDF) and its polymer composition, with polytetrafluoroethylene (PTFE) having advanced electroconductive properties over conventionally used separators based on polypropylene (PP) and glass-fibers (GF). Such advancement is associated with the low density of electrospun material leading to lower mechanical strengths. However, its use in the electrochemical systems with middle-voltage anode materials where dendrite growth is excluded is very prospective. The performance at the operation of the separators were investigated in the three-electrode-containing laboratory half-cells having Li4Ti5O12 as the electrode under investigation. Galvanostatic charge and discharge tests of cells were conducted under variation of the experimental conditions: the current varied in the range 0.1 C−1 C, and 1C cycling was conducted over... [more]

The aim of this study was to determine the effects on methane production of the addition of microalgae biomass of Arthrospira platensis and Platymonas subcordiformis to the common feedstock used in agricultural biogas plants (cattle manure, maize silage). Anaerobic biodegradability tests were carried out using respirometric reactors operated at an initial organic loading rate of 5.0 kg volatile solids (VS)/m3, temperature of 35°C, and a retention time of 20 days. A systematic increase in the biogas production efficiency was found, where the ratio of microalgae biomass in the feedstock increased from 0% to 40% (%VS). Higher microalgae biomass ratio did not have a significant impact on improving the efficiency of biogas production, and the biogas production remained at a level comparable with 40% share of microalgae biomass in the feedstock. This was probably related to the carbon to nitrogen (C/N) ratio decrease in the mixture of substrates. The use of Platymonas subcordiformis ensured... [more]

The restoration of continuous surface lignite mines entering the closure phase is a long-term, complex and multidisciplinary project. During the evaluation of alternative restoration technologies, various environmental, technical, economic and social parameters are investigated. In this framework, for the selection of the lower risk restoration alternative, the analysis of the associated risks should be incorporated into the decision-making process. This work provides an overview of practical risk management problems and solutions in mining restoration projects. Moreover, it introduces a multi-criteria methodology for the improvement of the decision-making process in the evaluation of restoration alternatives and the selection of the optimal one, considering a continuous surface mining project. The proposed method is a combination of the analytical hierarchy process (AHP) for the quantification of risk factors and the technique for order of preference by similarity to ideal solution (T... [more]