This paper presents a multiagent system (MAS) day-ahead co-operation framework between renewable energy resources (RESs) and Battery Energy Storage Systems (BESSs) owned by different stakeholders. BESSs offer their storage services to RESs by shifting RES power to sell it during profitable peak-hours (aka; time-shifting). The MAS framework consists of three phases. Phase-one is a pre-auction phase that defines the maximum charging and discharging BESS power limits. These limits guarantee a reliable distribution system operation without violating the buses’ voltage limits or the ampacity of the branches. Phase-two is an auctioning phase between the BESS-agents and the RES-agents. Each agent has a different owner with a specific profit agenda and risk levels. The agent tries to maximize the profit potential of the owner. The agents use historical trade data and expected weather conditions to maximize profitability. Phase-three is called the post-auctioning phase, in which the agreement b... [more]

In the modern power system, Flexible Alternating Current Transmission System (FACTS) devices are widely used. An increased share of the distributed generation (DG) and the development of microgrids change the power flows in the existing distribution networks as well as a conventional power flow direction from the transmission to the distribution network level which may affect the overall stability aspects. The paper shows the FACTS devices’ implementation influence on the performance of the distribution network with integrated renewable energy sources (RES) observing the aspects of the oscillatory stability and the low-voltage motor starting. The FACTS devices, in particular the static var compensators (SVC), have been allocated according to a novel algorithm proposed in the paper. The algorithm uses an iterative process to determine an optimal location for implementation and rating power of SVC considering active power losses minimization, improvement of the voltage profile and maximi... [more]

A new government report on climate change shows that global emissions of greenhouse gases have increased to very high levels despite various policies to reduce climate change. Building energy accounts for 40% of the world’s energy consumption and accounts for 33% of the world’s greenhouse gas emissions. This study applied the LEAP (Long-range energy alternatives planning) model and Bass diffusion method for predicting the total energy consumption and GHG (Greenhouse Gas) emissions from the residential and commercial building sector of Sejong City in South Korea. Then, using the Bass diffusion model, three scenarios were analyzed (REST: Renewable energy supply target, BES: Building energy saving, BEP: Building energy policy) for GHG reduction. The GHG emissions for Sejong City for 2015−2030 were analyzed, and the past and future GHG emissions of the city were predicted in a Business-as-Usual (BAU) scenario. In the REST scenario, the GHG emissions would attain a 24.5% reduction and, in t... [more]

The biomass industry is growing due to the current search for greener and more sustainable alternatives to fossil energy sources. However, this industry, due to its singularity, presents several challenges and disadvantages related to the transportation of raw materials, with the large volumes that are usually involved. This project aimed to address this internal logistics situation in torrefied biomass pellets production with two different biomass storage parks, located in Portugal. The main park receives raw material coming directly from the source and stores it in large amounts as a backup and strategic storage park. The second park, with smaller dimensions, precedes the production unit and must be stocked daily. Therefore, a fleet of transport units with self-unloading cranes is required to help to unload the biomass at the main park and transport the raw material from this park to the one preceding the production unit. Thus, the main goal was to determine the dimensions of the fle... [more]

The integration of commercial onshore large-scale wind farms into a national grid comes with several technical issues that predominately ensure power quality in accordance with respective grid codes. The resulting impacts are complemented with the absorption of larger amounts of reactive power by wind generators. In addition, seasonal variations and inter-farm wake effects further deteriorate the overall system performance and restrict the optimal use of available wind resources. This paper presented an assessment framework to address the power quality issues that have arisen after integrating large-scale wind farms into weak transmission grids, especially considering inter-farm wake effect, seasonal variations, reactive power depletion, and compensation with a variety of voltage-ampere reactive (Var) devices. Herein, we also proposed a recovery of significant active power deficits caused by the wake effect via increasing hub height of wind turbines. For large-scale wind energy penetra... [more]

This study investigates the frequency−temperature relations between the phase angle φ and admittance Y for composites of cellulose, synthetic ester, and water nanoparticles. We determined the activation energy value for the relaxation time of a phase shift angle ΔWφ ≈ (0.783 ± 0.0744) eV, which was related to the shift of φ(f) waveforms in higher frequency area with increasing temperature. We found that the position of admittance frequency waveforms in double logarithmic coordinates was simultaneously influenced by the temperature dependence of admittance and its relaxation time. Activation energy values for the relaxation time of admittance ΔWτ ≈ (0.796 ± 0.0139) eV and the activation energy value of admittance ∆WY ≈ (0.800 ± 0.0162) eV were determined. It was found that all three activation energy values were identical and their average was ΔW ≈ (0.793 ± 0.0453) eV. Impregnation with synthetic ester resulted in a decrease of activation energy by 0.26 eV compared to the impregnation w... [more]

Bipolar Membrane Reverse Electrodialysis (BMRED) can be used to produce electricity exploiting acid-base neutralization, thus representing a valuable route in reusing waste streams. The present work investigates the performance of a lab-scale BMRED module under several operating conditions. By feeding the stack with 1 M HCl and NaOH streams, a maximum power density of ~17 W m−2 was obtained at 100 A m−2 with a 10-triplet stack with a flow velocity of 1 cm s−1, while an energy density of ~10 kWh m−3 acid could be extracted by a complete neutralization. Parasitic currents along feed and drain manifolds significantly affected the performance of the stack when equipped with a higher number of triplets. The apparent permselectivity at 1 M acid and base decreased from 93% with the five-triplet stack to 54% with the 38-triplet stack, which exhibited lower values (~35% less) of power density. An important role may be played also by the presence of NaCl in the acidic and alkaline solutions. Wit... [more]

The proliferation of solar power systems could cause instability within existing power grids due to the variable nature of solar power. A well-defined statistical model is important for managing the supply-and-demand dynamics of a power system that contains a significant variable renewable energy component. It is furthermore important to consider the inherent uncertainty in the data when modeling such a complex power system. Gaussian process regression has the potential to address both of these concerns: the probabilistic modeling of solar radiation data could assist in managing the variability of solar power, as well as provide a mechanism to deal with uncertainty. In this paper, solar radiation data was obtained from the Southern African Universities Radiometric Network and used to train a Gaussian process regression model which was developed especially for this purpose. Attention was given to constructing an appropriate Gaussian process kernel. It was found that a carefully construc... [more]

A thermal model is proposed to analyze the performance of an indirect solar dryer (ISD) with latent heat storage using phase change material (PCM). The estimations are compared with experimental data presented in the scientific literature taken in real conditions. The validated thermal model is used in order to address a comprehensive analysis of the performance of the ISDs under the same operation conditions, the model is able to estimate the temperatures of glass cover, absorber plate, PCM, useful heat, thermal and storage efficiencies, and variables that are difficult to measure experimentally such as liquid fraction, heat losses, and accumulated energy of the ISDs. Three study cases are considered: Case 1 consists of two collectors with and without alternating nocturnal and diurnal operation (benchmarking case). Case 2 and 3 consist in a unique collector operating continuously for 24 h with PCM and without PCM, respectively. It was determined that the use of PCM in ISD increased th... [more]

The cost of solar PV has been reduced to a level such that the levelized cost of solar electricity is either cheaper or competitive relative to the grid electricity. So, a low-cost integration of solar PV with grid can be a cost-effective solution for clean cooking. The usual technique of using grid-tied inverters contribute ~20% towards the energy cost. The proposed system incorporates a control circuit that connects grid electricity to the solar PV via a DC link and provides a DC output eliminating the requirement of grid-tied inverters. Most of the cooking utensils either have a resistive heating element or an electronic control circuit that is insensitive to input AC or DC and no modification is needed for the cooking utensils while using with DC voltage. In the proposed system, preference for power delivery is always given to the solar PV and the grid effectively operates as the backup for the system when solar PV output fluctuates due to varying weather and climatic conditions. A... [more]

The present study explores the entropy generation, flow, and heat transfer characteristics of a dissipative nanofluid in the presence of transpiration effects at the boundary. The non-isothermal boundary conditions are taken into consideration to guarantee self-similar solutions. The electrically conducting nanofluid flow is influenced by a magnetic field of constant strength. The ultrafine particles (nanoparticles of Fe3O4/CuO) are dispersed in the technological fluid water (H2O). Both the base fluid and the nanofluid have the same bulk velocity and are assumed to be in thermal equilibrium. Tiwari and Dass’s idea is used for the mathematical modeling of the problem. Furthermore, the ultrafine particles are supposed to be spherical, and Maxwell Garnett’s model is used for the effective thermal conductivity of the nanofluid. Closed-form solutions are derived for boundary layer momentum and energy equations. These solutions are then utilized to access the entropy generation and the irrev... [more]

The electricity-heat integrated system can realize the cascade utilization of energy and the coordination and complementarity between multiple energy sources. In this paper, considering the thermal comfort of users, taking into account the difference in dynamic characteristics of electric and heating networks and the response of users’ demands, a dispatch model is constructed. In this model, taking into account the difference in the time scale of electric and thermal dispatching, optimization of the system can be improved by properly extending the thermal balance cycle of the combined heat and power (CHP) unit. Based on the time-of-use electricity prices and heat prices to obtain the optimal energy purchase cost, a user demand response strategy is adopted. Therefore, a minimum economic cost on the energy supply side and a minimum energy purchase cost on the demand side are considered as a bilevel optimization strategy for the operation of the system. Finally, using an IEEE 30 nodes pow... [more]

Due to the recent development of information and communication technology (ICT), various studies using real-time data are now being conducted. The microgrid research field is also evolving to enable intelligent operation of energy management through digitalization. Problems occur when operating the actual microgrid, causing issues such as difficulty in decision making and system abnormalities. Using digital twin technology, which is one of the technologies representing the fourth industrial revolution, it is possible to overcome these problems by changing the microgrid configuration and operating algorithms of virtual space in various ways and testing them in real time. In this study, we proposed an energy storage system (ESS) operation scheduling model to be applied to virtual space when constructing a microgrid using digital twin technology. An ESS optimal charging/discharging scheduling was established to minimize electricity bills and was implemented using supervised learning techn... [more]

This paper summarizes the literature on detection of islanding resulting from distributed generating capabilities in a power distribution system, with emphasis on the rural distribution systems. It is important to understand the legacy technology and equipment in the rural distribution electrical environment due to the growth of power electronics and the potential for adding the new generations of intelligent sensors. The survey identified four areas needing further research: 1. Robustness in the presence of distribution grid disturbances; 2. the future role of artificial intelligence in the islanding application; 3. more realistic standard tests for the emerging electrical environment; 4. smarter sensors. In addition, this paper presents a synchro-phasor-based islanding detection approach based on a wireless sensor network developed by the University of Texas at Austin. Initial test results in a control hardware-in-the-loop (CHIL) simulation environment suggest the effectiveness of th... [more]

This paper presents a novel converter for boosting the low-voltage output of thermoelectric energy harvesters to power standard electronic circuits. The converter can start up from a fully depleted state of the system off a bipolar ±13 mV input and can boost it to output voltages of up to 5 V. The converter comprises two transformers, one for each polarity that are multiplexed between an oscillator (used during startup) and a flyback converter (used during normal operation). To eliminate leakage currents in the input stage, the unused converter is completely turned off at startup and both converters are automatically shut off if the input power is found to be too low. Measurement results of the converter designed in a 180 nm CMOS process demonstrate a peak end-to-end conversion efficiency of 85% and nearly perfect impedance matching over the full input voltage range. This is the first time that a converter for ultra-low bipolar input voltages achieves the same performance as a unipolar... [more]

Currently, Kenya depends mainly on oil, geothermal energy and hydro resources for electricity production, however all three have associated issues. Oil-based electricity generation is environmentally harmful, expensive and a burden to the national trade balance. The rivers for hydropower and their tributaries are found in arid and semi-arid areas with erratic rainfall leading to problems of supply security, and geothermal exploitation has cost and risk issues amongst others. Given these problems and the fact that Kenya has a significant yet underexploited potential for photo voltaic (PV)-based power generation, the limited—although growing—exploitation of solar PV in Kenya is explored in this paper as a means of diversifying and stabilising electricity supply. The potential for integration of PV into the Kenyan electricity generation mix is analysed together with the sociotechnical, economic, political, and institutional and policy barriers, which limit PV integration. We argue that th... [more]

This paper proposes a fresh state error feedback linearization control method with disturbance observer (DOB) and L2 gain for a quadruple-tank liquid-level system. Firstly, in terms of the highly nonlinear and strong coupling characteristics of the quadruple-tank system, a state error feedback linearization technique is employed to design the controller to achieve liquid-level position control and tracking control. Secondly, DOB is purposed to estimate uncertain exogenous disturbances and applied to compensation control. Moreover, an L2-gain disturbance attenuation technology is designed to resolve one class of disturbance problem by uncertain parameter perturbation existing in the quadruple-tank liquid-level system. Finally, compared with the classical proportion integration differentiation (PID) and sliding mode control (SMC) methods, the extensive experimental results validate that the proposed strategy has good position control, tracking control, and disturbance rejection performan... [more]

The maximal power that is absorbed by a wave energy converter can be estimated from the far-field behavior of the waves that are radiated by the device. For realistic estimates, constraints must be used to enforce restrictions on the set of admissible motions when deriving the maximal absorption width. This work is dedicated to the numerical computation of the maximal absorption width under constraints for devices with several non-trivial degrees of freedom. In particular, the method is applied to a model of SBM Offshore’s S3 wave energy converter, a bulging horizontal cylinder. The results are compared with a more classical approach, which consists of computing the linear dynamic response of the wave energy converter interacting with the waves. The far-field maximal absorption width can be seen as an upper bound to evaluate what would be the power captured by a perfect control strategy. The method also shows that the absorption width of the S3 wave energy converter is larger for wavel... [more]

In Longwall Top-Coal Caving (LTCC), the shape of the loose body (LB) and top-coal boundary (TCB) formed after the first coal-drawing are the initial conditions for the common coal-drawing period. Taking the Panel 12309 in Wangjialing coal mine as the research object, the weight of the blocks of caved top coal was measured on-site, and the distribution of their equivalent diameter was calculated. By using a coupled numerical method, the “Finite difference method (FDM)−Discrete element method (DEM)” numerical model was established, and the evolutions of the drawing body (DB), LB, and TCB were obtained. The results show that, in the initial stage of first coal-drawing (0−8.09 s), the amount of DB reached its maximum of 7.18 m3 (0.89 m3/s) and then decreased to a stable value of 0.44 m3/s. The relationships between the characteristic parameters of DB, LB, and TCB and the drawing time were fitted. Taking the second derivative of each parameter with respect to time as its sensitivity (η), it... [more]

To advance commercialisation of ocean wave energy and for the technology to become competitive with other sources of renewable energy, the cost of wave energy harvesting should be significantly reduced. The Mediterranean Sea is a region with a relatively low wave energy potential, but due to the absence of extreme waves, can be considered at the initial stage of the prototype development as a proof of concept. In this study, we focus on the optimisation of a multi-mode wave energy converter inspired by the CETO system to be tested in the west of Sicily, Italy. We develop a computationally efficient spectral-domain model that fully captures the nonlinear dynamics of a wave energy converter (WEC). We consider two different objective functions for the purpose of optimising a WEC: (1) maximise the annual average power output (with no concern for WEC cost), and (2) minimise the levelised cost of energy (LCoE). We develop a new bi-level optimisation framework to simultaneously optimise the W... [more]

Catalytic hydrocracking represents an optimal process for both heavy petroleum fractions and Fischer−Tropsch (FT) wax upgrading because it offers high flexibility regarding the feedstock, reaction conditions and products’ quality. The hydrocracking of a heavy vacuum gas oil with FT wax was carried out in a continuous-flow catalytic unit with a fixed-bed reactor and a co-current flow of the feedstock and hydrogen at the reaction temperatures of 390, 400 and 410 °C and a pressure of 8 MPa. The increasing reaction temperature and content of the FT wax in the feedstock caused an increasing yield in the gaseous products and a decreasing yield in the liquid products. The utilisation of the higher reaction temperatures and feedstocks containing the FT wax showed a positive influence on the conversion of the fraction boiling above 400 °C to lighter fractions. Although the naphtha and middle distillate fractions obtained via atmospheric and vacuum distillations of the liquid products of hydrocr... [more]

Artificial intelligence-based solutions and applications have great potential in various fields of electrical power engineering. The problem of the electrical reliability of power equipment directly refers to the immunity of high-voltage (HV) insulation systems to operating stresses, overvoltages and other stresses—in particular, those involving strong electric fields. Therefore, tracing material degradation processes in insulation systems requires dedicated diagnostics; one of the most reliable quality indicators of high-voltage insulation systems is partial discharge (PD) measurement. In this paper, an example of the application of a neural network to partial discharge images is presented, which is based on the convolutional neural network (CNN) architecture, and used to recognize the stages of the aging of high-voltage electrical insulation based on PD images. Partial discharge images refer to phase-resolved patterns revealing various discharge stages and forms. The test specimens w... [more]

The 20-year cumulative fatigue damage of an offshore jacket substructure was estimated under the long-term local environmental conditions in the Taiwan Strait. Because of the nonlinearity of wave load for slender members of the structure, time-domain simulations of the dynamic finite element model were conducted for each sea state. By utilizing the Dirlik method to process the stress signals, the fatigue damages of joints were computed. Concerning the computational time, we propose a probability-based method of using a representative combination of environmental conditions in this study, which can considerably reduce the required number of evaluations prior to determining fatigue damage, thereby improving the process of preliminary design. The results show that only three sea states among 120 can represent 28% of the average damage ratio, and up to 17 sea states fully resolved the fatigue life.

The paper concerns the analysis of harmful emissions during the combustion process in households. The subject of the analysis is a low emission heating device with an output of 50 kW for burning biomass of forest origin (low-quality hardwoods or softwoods). The proposed boiler is automatically fed from the connected container by means of a screw conveyor. In this way, the optimum amount of fuel is supplied for maximum heat output (adjustment of the ratio of primary air to fuel). The proposed biomass heating system is equipped with a primary and secondary air supply system and exhaust gas sensors. This ensures optimal regulation of the air mixture and efficient and clean combustion. Proper control of the combustion process, control of the air supply by means of a lambda sensor and power control of the system ensure a low-emission combustion process. The system precisely adjusts to the heat demand. This results in highly efficient heating technology with low operating costs. In the prese... [more]

This paper presents a detailed geological map at the 1:20,000 scale of the Tocomar basin in the Central Puna (north-western Argentina), which extends over an area of about 80 km2 and displays the spatial distribution of the Quaternary deposits and the structures that cover the Ordovician basement and the Tertiary sedimentary and volcanic units. The new dataset includes litho-facies descriptions, stratigraphic and structural data and new 234U/230Th ages for travertine rocks. The new reconstructed stratigraphic framework, along with the structural analysis, has revealed the complex evolution of a small extensional basin including a period of prolonged volcanic activity with different eruptive centres and styles. The geological map improves the knowledge of the geology of the Tocomar basin and the local interplay between orogen-parallel thrusts and orogen-oblique fault systems. This contribution represents a fundamental support for in depth research and also for encouraging geothermal exp... [more]