Energy efficiency programmes (EEPs) are schemes operated by utilities or other bodies in order to incentivize energy efficiency improvement, in particular by adoption of energy-efficient products and typically by means of an economic reward. Ample experience has been gained, especially in the U.S., where EEPs have been in use for decades, with the rationale of avoiding additional energy supply by improving energy efficiency. More recently, EEPs have been implemented in Europe and in Switzerland. This review paper presents insights from the U.S., the EU and especially from Switzerland, with a focus on levelised programme cost of saved energy (LPC) as a key performance indicator. These LPC values, which take the perspective of the programme operator, are typically low to very low compared to the cost of electricity supply, thereby representing an important argument in favour of their use. The country examples show that EEPs are being effectively and successfully put into practice, for ex... [more]

The use of static frequency converters, which have a high switching frequency, generates voltage pulses with a high rate of change over time. In combination with cable and motor impedance, this generates repetitive overvoltage at the motor terminals, influencing the occurrence of partial discharges between conductors, causing degradation of the insulation of electric motors. Understanding the effects resulting from the frequency converter−electric motor interaction is essential for developing and implementing insulation systems with characteristics that support the most diverse applications, have an operating life under economically viable conditions, and promote energy efficiency. With this objective, a search was carried out in three recognized databases. Duplicate articles were eliminated, resulting in 1069 articles, which were systematically categorized and reviewed, resulting in 481 articles discussing the causes of degradation in the insulation of electric motors powered by frequ... [more]

The objective of the present study is to predict how changes in the fracture treatment design parameters will affect the production performance of new gas wells in a target zone of the Marcellus shale. A recently developed analytical flow-cell model can estimate future production for new wells with different completion designs. The flow-cell model predictions were benchmarked using historic data of 11 wells and 6 different completion designs. First, a type well was generated and used with the flow-cell model to predict the performance of the later infill wells—with variable completion designs—based off the performance of earlier wells. The flow-cell model takes into account known hyperbolic forecast parameters (qi, Di, and b-factor) and fracture parameters (height, half-length, and spacing) of a type well. Next, the flow-cell model generates the hyperbolic decline parameters for an offset well based on the selected changes in the fracture treatment design parameters. Using a numerical... [more]

With widespread applications for lithium-ion batteries in energy storage systems, the performance degradation of the battery attracts more and more attention. Understanding the battery’s long-term aging characteristics is essential for the extension of the service lifetime of the battery and the safe operation of the system. In this paper, lithium iron phosphate (LiFePO4) batteries were subjected to long-term (i.e., 27−43 months) calendar aging under consideration of three stress factors (i.e., time, temperature and state-of-charge (SOC) level) impact. By means of capacity measurements and resistance calculation, the battery’s long-term degradation behaviors were tracked over time. Battery aging models were established by a simple but accurate two-step nonlinear regression approach. Based on the established model, the effect of the aging temperature and SOC level on the long-term capacity fade and internal resistance increase of the battery is analyzed. Furthermore, the storage life of... [more]

This paper presents a technical, economic, and environmental analysis and optimization of the impact of the reduction of diesel fuel subsidy in the design of an off-grid hybrid power system (OHPS). The OHPS includes a diesel generator, battery energy storage system (BESS), and a solar power system (SPS). This impact will focus on the electricity production levels of each of the OHPS components according to the increase of the fuel price and the SPS size. The Bellavista community in Ecuador was selected as the case study for this work. In this South American country, the government has begun a gradual increase in the diesel fuel price until it reaches international prices. Fifteen scenarios of OHPSs were simulated, in Homer Pro software, considering three SPS sizes and varying the diesel fuel price in five values. The annual load profile for the simulations was built based on the information of a previous study in this community. The results showed that for lower fuel prices (USD$0.26/L... [more]

Battery systems bring technical and economic advantages to electrical distribution systems (EDSs), as they conveniently store the surplus of cheap renewable generation for use at a more convenient time and contribute to peak shaving. Due to the high cost of batteries, technical and economic studies are needed to evaluate their correct allocation within the EDS. To contribute to this analysis, this paper proposes a stochastic mathematical model for the optimal battery allocation (OBA), which can be guided by the optimization of two different economic metrics: net present value (NPV) and internal rate of return (IRR). The effects of the OBA in the EDS are evaluated considering the stochastic variation of photovoltaic generation and load. Tests with the 33-node IEEE test system indicate that OBA results in voltage profile improvement (~1% at peak time), peak reduction (31.17%), increased photovoltaic hosting capacity (18.8%), and cost reduction (3.06%). Furthermore, it was found that the... [more]

In this paper, the predictive-based control with bacterial foraging optimization technique for power management in a standalone microgrid is studied and implemented. The heuristic optimization method based on the social foraging behavior of Escherichia coli bacteria is employed to determine the power references from the non-renewable energy sources and loads of the proposed configuration, which consists of a fixed speed diesel generator and battery storage system (BES). The two-stage configuration is controlled to maintain the DC-link voltage constant, regulate the AC voltage and frequency, and improve the power quality, simultaneously. For these tasks, on the AC side, the obtained power references are used as input signals to the predictive-based control. With the help of the system parameters, the predictive-based control computes all possible states of the system on the next sampling time and compares them with the estimated power references obtained using the bacterial foraging opt... [more]

This paper deals with the state and perspectives of bioenergy development in the context of exploiting the potential of available natural resources. We analyse the economic benefits of transitioning to alternative biofuel within the research task in cooperation with the Vojany black coal power plant. Within the applied methodology, a non-parametric data envelopment analysis method was used to confirm the most economically efficient types of fuels used in the combustion process. The assumption of fuel efficiency was confirmed by testing fuel combustion combinations directly in the power plant. The transition to 100% combustion of solid recovered fuel creates the potential for sustainable production of the analysed power plant and compliance with the current emission values of basic pollutants and new stricter limits, which will be binding in the EU from August 2021. The proposed solutions were analysed by Monte Carlo simulation. An estimate of the economic results achieved by the power... [more]

The role of renewable energy sources in the power grid is increasing tremendously. However, power electronic converters are used to incorporate RES into the grid without inertia. This article recommends an improved emulated inertia control approach focused on the frequency deviation and rate of change of frequency to enhance the inertia of a power system. The required inertial power calculated from emulated inertia control is delivered through hybrid energy storage systems equipped with a proper hybrid energy storage system control. The fast-varying power calculated from emulated inertia control is linked to super-capacitor. Simultaneously, the battery handles the slow varying power by regulating the DC bus voltage proportionate to the frequency variations. Further, the stability of the emulated inertia control and hybrid energy storage system controller is validated by Bode plots. The simulation results verified the correctness of the proposed emulated inertia control and hybrid energ... [more]

A high level of moisture in the insulation system of power transformers is often the cause of their failure. This can be prevented by drying a transformer in its place of installation. In the article the application of molecular sieves (MS) in the drying process of the transformer insulation system was analyzed. The water sorption isotherms of 3A MS in mineral oil, natural ester, and synthetic ester at 35 °C were determined, which was not described in the literature before. An evaluation of the influence of temperature on the drying dynamics of electro-insulating liquids using MS was also carried out. The drying dynamics were tested at three temperatures, i.e., 35 °C, 50 °C, and 65 °C, which allowed to analyze the effect of temperature on a short-term or continuous drying process. The tests showed that 3A MS’s ability to adsorb water varied depending on the type of electro-insulating liquid. The determined water sorption isotherms, described by means of Langmuir adsorption model, make... [more]

This paper proposes a robust finite-time controller (FTC) for a permanent magnet synchronous generator (PMSG)-based wind turbine generator (WTG). An adaptive observer is used for the rotor angle, rotor speed, and turbine torque estimations of the PMSG, thus eliminating the use of anemometers. The robustness of the proposed FTC regarding parameter uncertainty and the external weak power grid is analyzed. The impacts of the power grid short-circuit ratio (SCR) at the point of common coupling (PCC) on the conventional proportional-integral (PI) controller and the proposed FTC are discussed. Case studies illustrate that the proposed observer-based FTC is able to estimate the mechanical variables accurately and provides robust control for WTGs with parameter uncertainty and weak power grids.

The work is aimed at solving the problem of converting existing diesel power drives to gas fuels, which are cheaper and more environmentally friendly alternatives to diesel fuel. Method of energy efficiency increasing of alternative fuels has been improved. Thermochemical essence of energy increasing of source fuel based on the provisions of thermodynamics is considered. Alternative methanol fuel has been chosen as initial product for conversion process and its cost, energy value, and temperature conditions have been taken into account. Calculations showed that the thermal effect from combustion of the converted mixture of CO and H2 exceeds the effect from combustion of the same amount of non-convertible methanol. Fuel energy and engine power were increased due to thermochemical regeneration of exhaust gas heat. An experimental setup was created to study the operation of a converted diesel engine on methanol conversion products. Experimental studies of power, economic, and environmenta... [more]

Load flexibility management is a promising approach to face the problem of balancing generation and demand in electrical grids. This problem is becoming increasingly difficult due to the variability of renewable energies. Thermostatically-controlled loads can be aggregated and managed by a virtual battery, and they provide a cost-effective and efficient alternative to physical storage systems to mitigate the inherent variability of renewable energy sources. However virtual batteries require that an accurate control system is capable of tracking frequency regulation signals with minimal error. A real-time control system allowing virtual batteries to accurately track frequency or power signals is developed. The performance of this controller is validated for a virtual battery composed of 1000 thermostatically-controlled loads. Using virtual batteries equipped with the developed controller, a study focused on residential thermostatically-controlled loads in Spain is performed. The results... [more]

Although oscillating water column (OWC) wave energy converters are arguably one of the most studied technologies, it is not clear which chamber geometry, among all of the available alternatives, would provide the best performance at a site of interest. In this work, a numerical model based on the Navier-Stokes equations for two compressible fluids, using a volume-of-fluid interface-capturing approach, is implemented to determine the best performing OWC geometry in a case study off the Port of Vigo (NW Spain). Four general shapes of OWC are analyzed: classic, stepped-bottom, U-shaped and L-shaped, and geometrical variants are investigated. In total, 18 chamber geometries are studied, considering the same turbine geometry in all of them. It was found that the U-shaped and L-shaped designs are the most easily tuned to resonate at a period of interest. Of these two, the L-shaped performs better. The best performance is achieved for an L-shaped OWC design with a shallow entrance, a high hor... [more]

Increasing greenhouse gas emissions and more and more restrictive European Union regulations necessitate the reduction of energy demand in buildings, including hotels. A more economical way of managing and operating a facility may lead to competitive advantage and a reduction in the negative impact on the environment. This study indicated that the hotel facility wastes significant amounts of water and energy, and the main sources of losses were determined. The design assumption was to achieve savings by introducing technical improvements in the most energy and water-consuming areas. The modification consisted of replacing some of the lighting, fittings, and ventilation. The results of the achieved water and energy savings were compared with the consumption recorded in 2019. The very satisfactory final results were obtained, showing savings about 20% higher than assumed by the hotel management. Taking into account the replacement of lighting in staircases and underground garages, in add... [more]

The work presented in this paper aims to show how modern wind turbines can help to control the frequency in a small grid which suffers from large power imbalances. It is shown for an exemplary situation, which occurred in Flensburg’s distribution grid in 2019: a major blackout, which occurred after almost two hours in islanding operation, affecting almost the entire distribution grid, which supplies approximately 55,000 households and businesses. For the analysis, a wind turbine model and a grid support controller developed at the Wind Energy Technology Institute are combined with real measurements from the day of the blackout to generate a fictional yet realistic case study for such an islanding situation. For this case study, it is assumed that wind turbines with grid support functionalities are connected to the medium voltage distribution grid of the city. It is shown to what extent wind turbines can help to operate the grid by providing grid frequency support in two ways: By supply... [more]

During hydraulic fracturing, expansion of internal micro-fractures deforms the rock to different extents. Numerical studies typically assume fixed parameters; however, in the field site, parameters are likely to vary. Error accumulation underlies deviation of simulation results from actual data. In this study, it was found that the mean velocity of an in-lab active source obtained from the hydraulic fracturing experiment decreased. To explain the effect of physical parameter (velocity) on numerical simulation results, we performed numerical simulations based on the extended finite element method (XFEM) of indoor hydraulic fracturing considering the velocity variation. The simulation results considering the change of the physical parameter (velocity) of the rock sample reflect the rock damage evolution more exactly. Consequently, the real-time evolution of physical parameters during hydraulic fracturing should be considered in numerical simulations. Rock damage evolution can be better c... [more]

Fundamental mathematical principles were applied to calculate the return on investment (ROI) of a multiple inclination, rooftop-mounted, photovoltaic (PV) system that is connected to a structured tariff network. Recent history has seen a disproportionate increase in electricity tariffs within South Africa, enabling an increase in the deployment rates of PV technologies. Given the inherent uncertainty associated with simulating the electricity yield of a PV system, it can become difficult to estimate the ROI in advance. This study contributes to existing knowledge by presenting a process for calculating the ROI of a case study rooftop-mounted PV system using mathematical first principles where structured tariffs apply. The PV modules were mounted to a curved roof structure, ranging from 9° towards a southerly direction to 10° towards a northerly direction. The research results indicate that since the PV system is located within the southern hemisphere, the ROI will increase when PV modu... [more]

This paper presents a wind energy conversion system (WECS) for grid-isolated areas. The system includes a squirrel-cage induction generator (SCIG) and a battery-assisted quasi-Z source inverter (qZSI). The batteries ensure reliable and stable operation of the WECS in spite of the wind power oscillations. The maximum power is captured from both the wind turbine (WT) and the SCIG through adjustment of the WT speed and the SCIG operating flux, respectively. The utilized maximum power point tracking (MPPT) algorithms belong to the group of fuzzy logic (FL) search-based algorithms. The battery state of charge (SOC) is tracked online and controlled. When it reaches the minimum allowed level, the load is automatically disconnected; conversely, when it reaches the maximum allowed level, the battery charging is stopped via WT speed control. The load voltage root-mean-square (RMS) value and frequency are at all times controlled at grid-level values. The performance of the proposed system was exp... [more]

A refining model is developed to analyses the refining process’s energy efficiency based on the refining variables. A simulation model is obtained for longer-term refining energy analysis by further developing the MATLAB Thermo-Mechanical Pulping Simulink toolbox. This model is utilized to predict two essential variables for refining energy efficiency calculation: refining motor-load and generated steam. The conventional variable for presenting refining energy efficiency is refining specific energy consumption (RSEC), which is the ratio of the refining motor load to throughput and does not consider the share of recovered energy from the refining produced steam. In this study, a new variable, corrected refining specific energy consumption (CRSEC), is introduced and practiced for better representation of the refining energy efficiency. In the calculation process of the CRSEC, recovered energy from the refining generated steam is considered useful energy. The developed model results in 16... [more]

Biomass chemical looping gasification (CLG) is a novel gasification technology for hydrogen production, where the oxygen carrier (OC) transfers lattice oxygen to catalytically oxidize fuel into syngas. However, the OC is gradually reduced, showing different reaction activities in the CLG process. Fully understanding the CLG reaction mechanism of fuel molecules on perfect and reduced OC surfaces is necessary, for which the CLG of ethanol using Fe2O3 as the OC was introduced as the probe reaction to perform density functional theory calculations to reveal the decomposition mechanism of ethanol into the synthesis gas (including H2, CH4, ethylene, formaldehyde, acetaldehyde, and CO) on perfect and reduced Fe2O3(001) surfaces. When Fe2O3(001) is reduced to FeO0.375(001), the calculated barrier energy decreases and then increases again, suggesting that the reduction state around FeO(001) favors the catalytic decomposition of ethanol to produce hydrogen, which proves that the degree of reduct... [more]

In this paper, an efficient method to compute the phase impedance of a power distribution line is presented. This paper’s main interest is to collect and analyze the impedance−temperature profiles in distribution lines by employing real-time phasor measurement units (PMUs) voltage and current measurements. The monitoring system has been developed for microgrids integrating ocean energies within the scope of the Mexican Ocean Energy Innovation Centre (CEMIE-Océano), contributing to marine energy tools’ innovation and development. The development tool can easily be applied to other distribution network components or to monitor microgrids with renewable-energy generation.

This paper aims at presenting an energy management strategy (EMS) based upon optimal control theory for a battery−supercapacitor hybrid power system. The hybrid power system consists of a lithium-ion battery and a supercapacitor with associated bidirectional DC/DC converters. The proposed EMS aims at computing adaptive gains using the salp swarm algorithm and load following control technique to assign the power reference for both the supercapacitor and the battery while achieving optimal performance and stable voltage. The DC/DC converter model is derived utilizing the first-principles method and computes the required gains to achieve the desired power. The fact that the developed algorithm takes disturbances into account increases the power elements’ life expectancies and supplies the power system with the required power.

Automated vehicles are becoming popular across the communities of e-transportation across the globe. Hybrid electric vehicles and autonomous vehicles have been subjected to critical research for decades. The research outcomes pertinent to this topic in the literature have been motivated by the industry and researchers to emphasize automated vehicles. Part 1 of this survey addressed the critical aspects that concern the bidirectional converter topologies and condition monitoring activities. In the present part, 24- and 77-GHz low-profile printed antennas are studied for automotive radar applications. These antennas are mounted on automated vehicles to avoid collision and are used for radio tracking applications. The present paper states the types of antenna structures, feed mechanisms, dielectric material requirements, design techniques, performance parameters, and challenges at 24- and 77-GHz resonating frequency applications. The recent developments in feed methodologies, beam scannin... [more]

When the classical H∞ algorithm (HIF) is applied to estimate the state of charge (SOC) of a lithium battery, the influence of historical data is usually ignored, resulting in an increase in the estimation error. In order to improve the accuracy of SOC estimation, this paper proposes an extended exponential weighted moving average H∞ algorithm (EE-HIF) in view of the influence of historical data. By designing the Gaussian function, the weighted distribution of the data at different times can effectively reduce the estimation error caused by the inaccuracy of the lithium battery model. In addition, when the system contains Gaussian white noise and alternating current input, the proposed method can achieve a faster convergence speed and better robustness. Simulation results show the advantages of the proposed algorithm, as compared to an HIF filtering algorithm and an exponentially weighted moving average H∞ algorithm (EWMA).