The worldwide spread of the COVID-19 pandemic in 2020 forced most countries to intervene with policies and actions—including lockdowns, social-distancing and smart working measures—aimed at mitigating the health system and socio-economic disruption risks. The electricity sector was impacted as well, with performance largely reflecting the changes in the industrial and commercial sectors operations and in the social behavior patterns. The most immediate consequences concerned the power demand profiles, the generation mix composition and the electricity price trends. As a matter of fact, the electricity sectors experienced a foretaste of the future, with higher renewable energy penetration and concerns for security of supply. This paper presents a systemic approach toward assessing the impacts of the COVID-19 pandemic on the power sector. This is aimed at supporting decision making—particularly for policy makers, regulators, and system operators—by quantifying shorter term effects and id... [more]

This paper deals with the estimation of core temperature (Tc) of a Lithium (Li) ion battery using measured ambient and surface temperatures. The temperatures were measured using thermocouples placed at appropriate locations. A second order thermal model was considered for the core temperature (Tc) estimation. A set of coupled linear ordinary differential equations (ODEs) were obtained by applying Kirchhoff’s current and voltage laws to the thermal model. The coupled ODEs were redefined in the discrete state space representation. The thermal model did not account for small changes in surface temperature (Ts). MATLAB/Simulink were used for modelling a Kalman filter with appropriate process and measurement noise levels. It was found that the temperatures closely followed the current patterns. For high currents, Tc dominated the surface temperature by about 3 K. Tc estimation plays a very important role in designing an effective thermal management and maintaining the state of health (SOH)... [more]

An in-situ method is proposed for monitoring and estimating the power degradation of mc-Si photovoltaic (PV) modules undergoing thermo-mechanical degradation tests that primarily manifest through cell cracking, such as mechanical load tests, thermal cycling and humidity freeze tests. The method is based on in-situ measurement of the module’s dark current-voltage (I-V) characteristic curve during the stress test, as well as initial and final module flash testing on a Sun simulator. The method uses superposition of the dark I-V curve with final flash test module short-circuit current to account for shunt and junction recombination losses, as well as series resistance estimation from the in-situ measured dark I-Vs and final flash test measurements. The method is developed based on mc-Si standard modules undergoing several stages of thermo-mechanical stress testing and degradation, for which we investigate the impact of the degradation on the modules light I-V curve parameters, and equival... [more]

This paper presents the performance evaluation of a stator modular ring permanent-magnet generator to be embedded in a shrouded wind turbine. That is done to increase the power conversion for the same turbine area when compared to more conventional ones. An adapted structure allows the assembling of the prototype, aiming to verify its performance under controlled conditions. Aiming to verify the accuracy of an analytical subdomain model for a large diameter machine, the evaluation compares the results obtained by the electromagnetic finite element method and experimental measurements. The results of the components of the air-gap flux density, back EMF and electromagnetic torque obtained by the proposed analytical model and finite-element method are in good agreement with the experimental measurements. The experimental measurements of the iron loss and copper loss show that the prototype efficiency can reach 90% approximately.

Equivalent power system impedance is an important electrical quantity from many points of view. Areas in which this parameter plays an important role include, in particular: Voltage stability analysis, power quality, or fault condition analysis. Power system impedance estimation in real operation conditions can be performed by one of the non-invasive methods described by different authors. This paper aims to investigate and compare seven different methods for power system impedance estimation based on voltage and current variations measurement. After a brief description of selected methods, these methods were applied for power system impedance estimation in the case of two simple simulation tests and then in the case of three real measured data. Voltage and current changes used for power system impedance estimation in real conditions were measured in high voltage (HV) and medium voltage (MV) substations feeding steel mill with the electric arc furnace (EAF) operation. As the results pr... [more]

Over the past few years, electricity demand has been on the rise. This has resulted in renewable energy resources being used rapidly, considering the shortage as well as the environmental impacts of fossil fuel. A renewable energy source that has become increasingly popular is photovoltaic (PV) energy as it is environmentally friendly. Installing PV modules, however, has to ensure harsh environments including temperature, dust, birds drop, hotspot, and storm. Thus, the phenomena of the non-uniform aging of PV modules has become unavoidable, negatively affecting the performance of PV plants, particularly during the middle and latter duration of their service life. The idea here is to decrease the capital of maintenance and operation costs involved in medium- and large-scale PV power plants and improving the power efficiency. Hence, the present paper generated an offline PV module reconfiguration strategy considering the non-uniform aging PV array to ensure that this effect is mitigated... [more]

In this paper, a nonlinear controller is proposed to manage the rotational speed of a full-variable Squirrel Cage Induction Generator wind turbine. This control scheme improves upon tractional vector controllers by removing the need for a rotor flux observer. Additionally, the proposed controller manages the performance through turbulent wind conditions by accounting for unmeasurable wind torque dynamics. This model-based approach utilizes a current-based control in place of traditional voltage-mode control and is validated using a Lyapunov-based stability analysis. The proposed scheme is compared to a linear vector controller through simulation results. These results demonstrate that the proposed controller is far more robust to wind turbulence than traditional control schemes.

Fuel catalytic additives have been tested for many years. Herein, their influence on the overall efficiency of combustion engines is investigated, and their pro-ecological impact is assessed. The majority of this research concerns diesel engines. Despite many advantages, to this day, the use of catalytic additives has not become widespread. Wishing to clarify the situation, a research group from the Wroclaw University of Science and Technology decided to investigate this matter, starting with verification tests. This article presents the methodology and results of testing an actual diesel engine, and evaluates the effects of the use of a fuel catalytic additive. The focus was on the analysis of fuel consumption and exhaust gas emissions from a Doosan MD196TI engine. The tested additive was a commercial fuel performance catalyst (FAMAX) with up to 5% ferric chloride as an organometallic compound. The proportion of the mixture with the fuel was 1:2000. These studies provide an energy and... [more]

In the array design of the vertical axis wind turbines (VAWT), the wake effect of the upstream VAWT on the downstream VAWT needs to be considered. In order to simulate the velocity distribution of a VAWT wake rapidly, a new two-dimensional numerical method is proposed, which can make the array design easier and faster. In this new approach, the finite vortex method and vortex particle method are combined to simulate the generation and evolution of the vortex, respectively, the fast multipole method (FMM) is used to accelerate the calculation. Based on a characteristic of the VAWT wake, that is, the velocity distribution can be fitted into a power-law function, a new correction model is introduced to correct the three-dimensional effect of the VAWT wake. Finally, the simulation results can be approximated to the published experimental results in the first-order. As a new numerical method to simulate the complex VAWT wake, this paper proves the feasibility of the method and makes a preli... [more]

Improving energy efficiency is an effective way to address the issues of economic development, energy saving and emissions reduction. For any important industries it is therefore necessary to measure energy efficiency and set a practical target for it. In this paper, we use CCR, SBM and energy intensity to measure the energy efficiency of the paper industries of 22 EU countries. Results indicate that the SBM and CCR efficiency value is more meaningful for policy makers than that of energy intensity, as measurement results of energy intensity deviate from reality and economic efficiency. The CCR and SBM have roughly the same fluctuation trends and the average SBM energy efficiency value is 0.71, always 10 percent lower than CCR model, as it takes simultaneous account of both the optimal input-output and has more discriminatory power in efficiency measurement. Furthermore, EU policy makers could improve energy efficiency by raising energy prices. As for the 2030 EU target of energy savin... [more]

Electric vehicles (EVs) generally use an electric heating system to provide heat. However, the heating system consumes a large amount of energy, and therefore reduces the mileage of the vehicle. The energy consumption can be reduced by replacing the electric heating system with a heat pump air conditioning system. Such systems achieve an effective heating of the vehicle interior, but do not provide a defog or dehumidification function. Consequently, the inside surface of the windshield tends to fog in cold weather; leading to poor driver visibility and an impaired road safety. Accordingly, the present study proposes a novel high-efficiency heating, ventilation and air conditioning (HVAC) system with both heating and defog/dehumidification functions for electric vehicles. The effectiveness of the proposed system is investigated experimentally using a simulated cabin placed in a temperature and humidity-controlled test chamber. The experimental results confirm that the HVAC system achiev... [more]

Heaving buoy wave energy converters (WEC) are floating oscillators, commonly modeled as single-degree-of-freedom vibrating systems. As the wave frequencies change according to the sea state, these devices must be controlled to maximize energy absorption. A new short-term reactive loading control technique is proposed that maximizes power absorption. The control is realized through tuning the effective stiffness of the vibrating system; thus, adjusting its natural frequency to meet the incident waves energy frequency achieving near-to-resonance operation and maximum power absorption. This stiffness is adjusted using an external stiffness, whose value is varied by a continuously variable transmission (CVT) mechanism connected to the buoy. The system equations were derived then solved analytically to calculate the controller bandwidth. Experiments demonstrated promising results for near-resonance tuning at different input frequencies. Results show that an optimized damping value exists at... [more]

Although Poland is one of the leading recipients of the waste stream in the European Union (EU), it is at the same time below the average in terms of efficiency of their use/utilization. The adopted technological solutions cause waste processing rates to be relatively low in Poland. As a result, the report of the Early Warning and Response System (EWRS) of the EU indicated Poland as one of the 14 countries of the EU which are at risk in terms of possibility of achieving 50% recycling of waste. This article discusses the implemented technological solutions, and shows the profitability of the investment and the values of the process heat demand both for extractor and reactor. The experimental part analyzed the composition of the input and output of the process and compared it to the required fuel specifications. Attention was drawn to the need to improve the recycling process in order to increase the quality of manufactured fuel components. As potential ways of solving the problem of low... [more]

This research reviews the impact on emissions from the engine fueled with the fuel containing a large share of bio-components, in particular with 30% n-Butanol. The research was carried out using a diesel engine. It has been shown that it is possible to achieve a double positive ecological effect concerning CO2 emissions. There was a decrease in CO2 emission from the engine with the fuel contained a significant share of bio-carbon. At the same time, NOx and Filter Smoke Number (FSN) emissions have been reduced together (FSN in large percentage). Usually, if NOx emissions are reduced, FSN increases, and vice versa. The paper shows also that the use of n-Butanol (bio, but nonfood) in the future is more effective than larger amounts of higher fatty acids methyl esters, although the full withdrawal of these esters seems unjustified.

Detailed understanding of hot gas path flow and heat transfer characteristics in gas turbine systems is imperative in order to design cooling strategies to meet the stringent requirements in terms of coolant usage to maintain critical components below a certain temperature. To this end, extensive research has been carried out over the past four decades on advanced thermal diagnostic methods to accurately measure heat transfer quantities such as Nusselt number and adiabatic film cooling effectiveness. The need to capture local heat transfer characteristics of these complex flow systems drives the development of measurement techniques and the experimental test facilities to support such measurements. This article provides a comprehensive overview of the state-of-the-art thermal diagnostic efforts pertaining to heat transfer measurements in rotating gas turbine blade internal and external cooling and rotor-stator disc cavity, all under rotating environments. The major investigation effort... [more]

Geothermal source heat pump (GSHP) systems as renewable energy systems are being more frequently installed as part of the zero-energy building drive. However, in South Korea, where a large amount of heating load can be required, maintaining high system performance by using only a GSHP is difficult owing to the gradual degradation of its thermal performance. The performance of a solar-assisted GSHP system was therefore experimentally analyzed and compared with a GSHP-only system. The results showed that the heating coefficient of performance of the GSHP-only operation was 5.4, while that of the solar-assisted GSHP operation was 7.0. In the case of the GSHP-only system, the maximum temperature of the heat pump water supply on the heat source side was initially 13.1 °C, but this rapidly decreased to 11.4 °C during operation. For the solar-assisted GSHP system, the temperature of the water supply to the heat source side of the heat pump was controlled at 15−20.9 °C, and the power consumpti... [more]

NOx emissions in compression-ignition engines can be reduced, either through the application of engine-internal methods, i.e., making sure that as little NOx as possible is produced as a result of the mixture combustion processes, or through the use of catalytic converters designed to reduce nitrogen oxides, including NH3-SCR or HC-SCR converters. Converters using ammonia offer high conversion rates, but they tend to be problematic in terms of their operation. For this reason, converters using hydrocarbons for the purpose of NOx reduction have been gaining in popularity. An Ag/Al2O3-SiO2 converter is an example of such a catalytic converter. This paper describes the process of preparing such a converter and characterises the porosity and acidity of its surface. The dispersion of silver was assessed based on oxygen absorption tests on crystallites of sliver and based on TEM images of crystallites of silver. The conversion of NO2, NO and propane was assessed depending on the temperature.... [more]

The globalized world has experienced significant environmental degradation together with raising global production and population. In this context, the employment of renewable energy use has become crucial for a sustainable environment and development. In the research, the mutual causality among renewable energy, trade and financial globalization, real GDP per capita, and CO2 emissions in EU transition economies experiencing the integration with global economy was explored through bootstrap panel Granger causality test for the period of 1995−2015. The causality analysis revealed a unilateral causality from trade globalization to renewable energy in Estonia, Latvia, and Slovenia, and from renewable energy to trade globalization in Croatia and Lithuania. However, no significant causality between financial globalization and renewable energy was revealed. On the other side, a unilateral causality from CO2 emissions to renewable energy in Lithuania and Slovenia, and from renewable energy to... [more]

The “European Green Deal” has ambitious aims, such as net-zero greenhouse gas emissions by 2050. While the European Union aims to make its energies greener, Russia pursues power-goals based on its status as a geo-energy superpower. A successful “European Green Deal” would have the up-to-now underestimated geopolitical advantage of making the European Union less dependent on Russian hydrocarbons. In this article, we illustrate Russian power-politics and its geopolitical implications by analyzing the illustrative case of the North Caucasus, which has been traditionally a strategic region for Russia. The present article describes and analyses the impact of Russian intervention in the North Caucasian secessionist conflict since 1991 and its importance in terms of natural resources, especially hydrocarbons. The geopolitical power secured by Russia in the North Caucasian conflict has important implications for European Union’s energy supply security and could be regarded as a strong argument... [more]

Mediterranean countries produce up to 97% of the total global olive production. Besides being a serious environmental burden, olive mill waste represents a potential resource of useful materials for recovery and valorization. In this work, the adsorption characteristics and potential of bioadsorbent material manufactured by alkali treatment of olive cake was evaluated. The resultant bioadsorbent was able to purify biodiesel to meets both ASTM D6751 and EN 14214 standards. Further, the sorption equilibrium was investigated at 25 °C. Langmuir, Freundlich, and Temkin isotherms fit to the experimental data were evaluated by applying the non-linear Chi-square test. Freundlich and Temkin isotherms were shown to adequately described the adsorption isotherms of the produced bioadsorbent.

This work presents a numerical study that investigates the optimum post-injection strategy and internal exhaust gas recirculation (iEGR) application with intake valve re-opening (2IVO) aiming to optimize the brake specific nitric oxide (bsNO) and brake specific soot (bsSoot) trade-off with reasonable brake specific fuel consumption (BSFC) via 1D engine cycle simulation. For model validation, single and post-injection test results obtained from a heavy-duty single cylinder diesel research engine were used. Then, the model was modified for 2IVO application. Following the simulations performed based on Latin hypercube DoE; BSFC, bsNO and bsSoot response surfaces trained by feedforward neural network were generated as a function of the injection (start of main injection, post-injection quantity, post-injection dwell time) and iEGR (2IVO dwell) parameters. After examining the effect of each parameter on pollutant emission and engine performance, multi-objective pareto optimization was perfo... [more]

Bio-oils from biomass pyrolysis can be a resource for upgrading to chemicals or fuels. Here, for the first time, we compare the composition of bio-oils produced from two feedstocks (wheat straw, softwood) in pyrolysis units of different mode of operation (continuous—rotary kiln vs. batch) using Fourier transform ion cyclotron resonance mass spectrometry (FTICR MS) in different ionization modes (APPI (+), ESI (+/−)). Our results demonstrate that the pyrolysis unit design had only a minor influence on the composition of bio-oils produced from low-mineral containing wood biomass. Yet, the wheat straw-derived bio-oil produced in the continuous unit comprised lower molecular weight compounds with fewer oxygen-containing functional groups and lower O/C and H/C ratios, compared to bio-oils from batch pyrolysis. Longer residence time of vapours in the heated zone in the rotary kiln and a higher mineral content in wheat straw resulted in increased catalytically-mediated secondary reactions that... [more]

Integrated transmission-and-distribution (T&D) modeling is a new and developing method for simulating power systems. Interest in integrated T&D modeling is driven by the changes taking place in power systems worldwide that are resulting in more decentralized power systems with increasingly high levels of distributed energy resources. Additionally, the increasing role of the hitherto passive energy consumer in the management and operation of power systems requires more capable and detailed integrated T&D modeling to understand the interactions between T&D systems. Although integrated T&D modeling has not yet found widespread commercial application, its potential for changing the decades-old power system modeling approaches has led to several research efforts in the last few years that tried to (i) develop algorithms and software for steady-state and dynamic modeling of power systems and (ii) demonstrate the advantages of this modeling approach compared with traditional, separated T&D sy... [more]

Ceiling radiant cooling panel (CRCP) systems are being increasingly applied to commercial buildings due to their high thermal comfort level and energy efficiency. It is recommended that CRCP systems should be operated at a relatively high chilled water temperature to prevent condensation and save energy. However, even though a high chilled water temperature is effective for achieving condensation-free operation and high chiller efficiency, it can lead to insufficient cooling capacity. In this study, a method of enhancing the cooling capacity of CRCP systems was investigated through mock-up chamber tests. The open-type installation of CRCPs and the combination of air circulators were used to enhance the cooling capacity and energy performance of CRCP systems. Experimental results showed that compared to a conventional CRCP system, the cooling capacity of an open-type CRCP system with air circulators increased by up to 26.2%, and its cooling energy consumption decreased by up to 26.4%. A... [more]

The highly varying character of district heating (DH) demand results in low capacity utilization of the DH plants, as well as increased use of fossil fuels during peak demand. The aim of this study is to present an overview and a comprehensive classification of measures intended to manage these load variations. A systematic literature review was conducted based on previously defined search strings as well as inclusion and exclusion criteria. Two scientific databases were used as data sources. Based on 96 detected publications, the measures were categorized as (1) complementing DH production in heat-only boilers (HOBs), or geothermal or booster heat pumps (HPs) (usually controlled by the DH company), (2) thermal energy (TE) storage in storage units or in the network (controlled by the company), and (3) demand side measures, which can be strategic demand increase, direct demand response (DR), or indirect DR. While the company has control over direct DR (e.g., thermal storage in the therm... [more]