The experimental investigation of building-integrated photovoltaic thermal (BIPVT) solar systems is essential to characterise the operation of these elements under real conditions of use according to the climate and building type they pertain. BIPVT systems can increase and ensure energy performance and readiness without jeopardising the occupant comfort if correctly operated. The present work presents a case study’s experimental analysis composed of a BIPVT system for heat recovery located in a controlled test room. This work contribution focuses on the presentation of the obtained measured value results that correspond to the BIPVT main boundary conditions (weather and room characteristics) and the thermal behaviour and performance of the BIPVT system, located in the Solar XXI Building, a nZEB exposed to the mild Mediterranean climate conditions of Portugal.

In the process industry, a large amount of low-grade waste heat is discharged into the environment. Furthermore, district heating and cooling systems require considerable low-grade energy. The integration of the two systems has great significance for energy saving. Because the energy demand of consumers varies in periods, the design and operation of an industrial waste heat recovery system need to match with the fluctuations of district energy demand. However, the impact of the periodic changes on the integration schemes are not considered enough in existing research. In this study, a framework method for solving above problem is proposed. Industrial waste heat was integrated with a district heating and cooling system through a heat recovery loop. A three-step mathematical programming method was used in design and operation optimization for multiperiod integration. A case study was conducted, and the results show that the multiperiod optimization method can bring significant benefits t... [more]

Energy access and waste management are two of the most pressing developmental and environmental issues on a global level to help mitigate the accelerating impacts of climate change. They are particularly relevant in Sub−Saharan Africa where electrification rates are significantly below global averages and rural areas are lacking a formal waste management sector. This paper explores the potential of integrating solar energy into a biomass pyrolysis unit as a potentially synergetic solution to both issues. The full design of a slow pyrolysis batch reactor targeted at biochar production, following a strict cost minimization approach, is presented in light of the relevant considerations. SPEAR is powered using a Cassegrain optics parabolic dish system, integrated into the reactor via a manual tracking system and optically optimized with a Monte-Carlo ray tracing methodology. The design approach employed has led to the development an overall cost efficient system, with the potential to achi... [more]

With the tight coupling of multi-energy systems, accurate multiple-load forecasting will be the primary premise for the optimal operation of integrated energy systems. Therefore, this paper proposes a Copula correlation analysis combined with deep bidirectional long and short-term memory neural network forecasting model. First, Copula correlation analysis is used to conduct correlation analysis on multiple loads and various influencing factors. The influencing factors that have a great correlation with multiple loads were screened out as the input feature set of the model to eliminate the influence of interfering factors. Then, a deep bidirectional long and short-term memory neural network was constructed. Combined with the input feature set screened by the Copula correlation analysis method, the useful information contained in the historical data was more comprehensively learned from the forward and backward directions for training and forecasting. Through the actual calculation examp... [more]

In this paper, the heat transfer of pin-fin plate unit (PFPU) under static and oscillating conditions are numerically studied using the discrete element method (DEM). The flow and heat transfer characteristics of the PFPU with sinusoidal oscillation are investigated under the conditions of oscillating frequency of 0−10 Hz, amplitude of 0−5 mm and oscillating direction of Y and Z. The contact number, contact time, porosity and heat transfer coefficient under the above conditions are analyzed and compared with the smooth plate. The results show that the particle far away from the plate can transfer heat with the pin-fin of PFPU, and the oscillating PFPU can significantly increase the contact number and enhance the temperature diffusion and heat transfer. The heat transfer coefficient of PFPU increases with the increase of oscillating frequency and amplitude. When the PFPU oscillates along the Y direction with the amplitude of 1 mm and the frequency of 10 Hz, the heat transfer coefficient... [more]

The author intended to present the relationship between the standard of living of EU citizens and the level of the development of renewable energy. It is particularly important in the context of the implementation of the sustainable development idea, by ensuring a high standard of living for both current and future generations, with rational use of available natural resources. The first, theoretical part of the article presents the problem related to the impact of renewable energy on the standard of living in a synthetic way. The second part involves empirical research conducted in all countries of the EU. To evaluate the level of renewable energy development and the standard of living, the author constructed original measures based on the TOPSIS method. Variables were selected on the basis of substantive, statistical and formal criteria (primarily the completeness and availability of data in 2019). Within the framework of the conducted study, the author obtained, among other things, a... [more]

Hydrogen is one of the modern energy carriers, but its storage and practical use of the newest hydrogen technologies in real operation conditions still is a task of future investigations. This work describes the experimental hydrogen hybrid energy system (HHS). HHS is part of a laboratory off-grid system that stores electricity gained from photovoltaic panels (PVs). This system includes hydrogen production and storage units and NEXA Ballard low-temperature proton-exchange membrane fuel cell (PEMFC). Fuel cell (FC) loses a significant part of heat during converting chemical energy into electricity. The main purpose of the study was to explore the heat distribution phenomena across the FC NEXA Ballard stack during load with the next heat transfer optimization. The operation of the FC with insufficient cooling can lead to its overheating or even cell destruction. The cause of this undesirable state is studied with the help of infrared thermography and computational fluid dynamics (CFD) mo... [more]

Energy Storage Systems (EES) are key to further increase the penetration in energy grids of intermittent renewable energy sources, such as wind, by smoothing out power fluctuations. In order this to be economically feasible; however, the ESS need to be sized correctly and managed efficiently. In the study, the use of discrete wavelet transform (Daubechies Db4) to decompose the power output of utility-scale wind turbines into high and low-frequency components, with the objective of smoothing wind turbine power output, is discussed and applied to four-year Supervisory Control And Data Acquisition (SCADA) real data from multi-MW, on-shore wind turbines provided by the industrial partner. Two main research requests were tackled: first, the effectiveness of the discrete wavelet transform for the correct sizing and management of the battery (Li-Ion type) storage was assessed in comparison to more traditional approaches such as a simple moving average and a direct use of the battery in respon... [more]

The Energy Internet paradigm is the evolution of the Internet of Things concept in the power system. Microgrids (MGs), as the essential element in an Energy Internet, are expected to be controlled in a corporative and flexible manner. This paper proposes a novel decentralized robust control strategy for multi-agent systems (MASs) governed MGs in future Energy Internet. The proposed controller is based on a consensus algorithm applied with the connected distributed generators (DGs) in the MGs in the energy internet paradigm. The proposed controller’s objectives are the frequency/voltage regulation and proportional reactive/active power-sharing for the hybrid DGs connected MGs. A proposed two-level communication system is implemented to explain the data exchange between the MG system and the cloud server. The local communication level utilizes the transmission control protocol (TCP)/ internet protocol (IP) and the message queuing telemetry transport (MQTT) is used as the protocol for the... [more]

The electricity tariffs available to customers in Poland depend on the connection voltage level and contracted capacity, which reflect the customer demand profile. Therefore, before connecting to the power grid, each consumer declares the demand for maximum power. This amount, referred to as the contracted capacity, is used by the electricity provider to assign the proper connection type to the power grid, including the size of the security breaker. Maximum power is also the basis for calculating fixed charges for electricity consumption, which is controlled and metered through peak meters. If the peak demand exceeds the contracted capacity, a penalty charge is applied to the exceeded amount, which is up to ten times the basic rate. In this article, we present several solutions for entrepreneurs based on the implementation of two-stage and deep learning approaches to predict maximal load values and the moments of exceeding the contracted capacity in the short term, i.e., up to one mont... [more]

Simultaneous satisfaction of both thermal and visual comfort in buildings may be a challenging task. Therefore, this paper suggests a comprehensive framework for the building energy optimization process integrating computational fluid dynamics (CFD) daylight simulations. A building energy simulation tool, IDA Indoor Climate and Energy (IDA-ICE), was coupled with three open-source tools including GenOpt, OpenFOAM, and Radiance. In the optimization phase, several design variables i.e., building envelope properties, fenestration parameters, and Heating, Ventilation and Air-Conditioning (HVAC) system set points, were selected to minimize the total building energy use and simultaneously improve thermal and visual comfort. Two different scenarios were investigated for retrofitting of a generic office building located in Oslo, Norway. In the first scenario a constant air volume (CAV) ventilation system with a local radiator in each zone was used, while an all-air system equipped with a demand... [more]

In this study, we investigate the degradation characteristics of E-mode GaN High Electron Mobility Transistors (HEMTs) with a p-GaN gate by designed pulsed and prolonged negative gate (VGS) bias stress. Device transfer and transconductance, output, and gate-leakage characteristics were studied in detail, before and after each pulsed and prolonged negative VGS bias stress. We found that the gradual degradation of electrical parameters, such as threshold voltage (VTH) shift, on-state resistance (RDS-ON) increase, transconductance max (Gm, max) decrease, and gate leakage current (IGS-Leakage) increase, is caused by negative VGS bias stress time evolution and magnitude of stress voltage. The significance of electron trapping effects was revealed from the VTH shift or instability and other parameter degradation under different stress voltages. The degradation mechanism behind the DC characteristics could be assigned to the formation of hole deficiency at p-GaN region and trapping process at... [more]

A technique to improve the performance of grid-connected induction motors by exploiting an auxiliary winding set is proposed in this paper. This auxiliary winding features the same distribution of the main winding, although with a reduced number of turns and it is fed by an inverter a fraction of the power in comparison with the rated size of the induction motor. As shown in the paper, through the auxiliary winding, it is possible to set the machine power factor, increasing the efficiency of the power conversion system and mitigating speed oscillations due to torque disturbances. A mitigation of the grid current peaks due to motor start-up is obtainable. First, the proposed technique is theoretically introduced, then a feasibility assessment is accomplished by simulations.

In the field of building constructions, there is undeniably a growing need to optimize the energy systems which are a key target in new modern constructions and industrial buildings. In this sense, energy systems are being traced for the development of energy distribution networks that are increasingly smart, efficient, and sustainable. Modern generation and distribution energy systems, such as microgrids control systems, are being affected by the presence of linear and nonlinear loads, resulting a distorted voltage and current waveforms. Thus, it is stated that industrial and residential building heating and cooling loads behave essentially like sources of harmonics. This paper presents a new framework based on geometric algebra (GA) to the definition of a multivectorial distortion power concept, which is represented by a bivector that is geometrically interpreted to distinguish the rotated distortion and distortion power bivectors in these kinds of loads. Both bivectors, and their re... [more]

The research presented by the authors in this paper focused on understanding the behavior of mercury during coal combustion and flue gas purification operations. The goal was to determine the flue gas temperature on the mercury emissions limits for the combustion of lignites in the energy sector. The authors examined the process of sorption of mercury from flue gases using fine-grained organic materials. The main objectives of this study were to recommend a low-cost organic adsorbent such as coke dust (CD), corn straw char (CS-400), brominated corn straw char (CS-400-Br), rubber char (RC-600) or granulated rubber char (GRC-600) to efficiently substitute expensive dust-sized activated carbon. The study covered combustion of lignite from a Polish field. The experiment was conducted at temperatures reflecting conditions inside a flue gas purification installation. One of the tested sorbents—tire-derived rubber char that was obtained by pyrolysis—exhibited good potential for Hg0 into Hg2+... [more]

Copper sinter paste has been recently established as a robust die-attach material for high -power electronic packaging. This paper proposes and studies the implementation of copper sinter paste materials to create top-side interconnects, which can substitute wire bonds in power packages. Here, copper sinter paste was exploited as a fully printed interconnect and, additionally, as a copper clip-attach. The electrical and thermal performances of the copper-sinter paste interconnections (“sinterconnects”) were compared to a system with wire bonds. The results indicate comparable characteristics of the sinterconnect structures to the wire-bonded ones. Moreover, the performance of copper sinterconnects in a power module was further quantified at higher load currents via finite element analysis. It was identified that the full-area thermal and electrical contact facilitated by the planar sinterconnects can reduce ohmic losses and enhance the thermal management of the power packages.

This paper presents a numerical study that aims at investigating the effects of different parameters on the dynamic performance of single and multi-layer encapsulated phase material (PCM) thermocline tanks. A transient, one-dimensional, two-phase, concentric-dispersion model is formulated to evaluate such performance. Encapsulated paraffin waxes having different melting-points are used as PCMs, with water as heat transfer fluid. Comprehensive comparisons between single-PCM and multiple-PCMs systems are numerically analyzed first. Second, the effects of the PCM volume fraction (VF) and the inverse Stefan number have been discussed. The results show that among the various cases the single-PCM70 system has the highest performance in terms of charging and discharging efficiency, followed by a multiple-PCMs system with average performance. Compared with the PCM40 case, the PCM70 case has a 29% increase in the output energy from the system. The VF of PCMs influences the system output, both i... [more]

This work aimed to analyze the heat transfer of micropolar fluid flow in a constricted channel influenced by thermal radiation and the Lorentz force. A finite difference-based flow solver, on a Cartesian grid, is used for the numerical solution after transforming the governing equations into the vorticity-stream function form. The impact of various emerging parameters on the wall shear stress, axial velocity, micro-rotation velocity and temperature profiles is discussed in this paper. The temperature profile is observed to have an inciting trend towards the thermal radiation, whereas it has a declining trend towards the Hartman and Prandtl numbers. The axial velocity profile has an inciting trend towards the Hartman number, whereas it has a declining trend towards the micropolar parameter and Reynolds number. The micro-rotation velocity escalates with the micropolar parameter and Hartman number, whereas it de-escalates with the Reynolds number. The Nusselt number is observed to have a... [more]

We conducted energy and exergy analyses of an adsorption chiller to investigate the effect of recooling-water temperatures on the cooling capacity and Coefficient of Performance (COP) with variable cycle modes. We investigated both the effect of the recooling-water temperature and the dead state temperature on the exergy destruction in the chiller components. Our results show that there is an optimum reheat cycle mode for each recooling-water temperature range. For the basic single stage cycle, the exergy destruction is mainly accrued in the desorber (49%), followed by the adsorber (27%), evaporator (13%), condenser (9%), and expansion valve (2%). The exergy destruction for the preheating process is approximately 35% of the total exergy destruction in the desorber. By contrast, the precooling process is almost 58% of the total exergy destruction in the adsorber. The exergy destruction decreases when increasing the recooling-water and the dead state temperatures, while the exergy effici... [more]

Along with the increase in renewable energy, research on energy harvesting combined with piezoelectric energy is being conducted. However, it is difficult to predict the power generation of combined harvesting because there is no data on the power generation by a single piezoelectric material. Before predicting the corresponding power generation and efficiency, it is necessary to quantify the power generation by a single piezoelectric material alone. In this study, the generated power is measured based on three parameters (size of the piezoelectric ceramic, depth of compression, and speed of compression) that contribute to the deformation of a single PZT (Lead zirconate titanate)-based piezoelectric element. The generated power was analyzed by comparing with the corresponding parameters. The analysis results are as follows: (i) considering the difference between the size of the piezoelectric ceramic and the generated power, 20 mm was the most efficient piezoelectric ceramic size, (ii)... [more]

In the carbon-neutral scenarios fixed by most developed countries, wind and solar resources play a significant role due to their substantial potential. Their instability can be mitigated through smarter designs of energy systems, including sector coupling and cross-border interconnections, which require detailed information on the spatial and temporal evolution of these intermittent resources. The present study aims at estimating the spatial−temporal energy potential of wind in Japan based on meteorological weather data. These data allow to analyze the potential of resources sharing to reduce power generation’s lack and excess, even in such an isolated country due to its variety of climate conditions and local energy demand. The correlation skewness is introduced as a measure of the sites’ uniqueness to identify important sites for the spatial distribution of capacity toward the efficient stabilization of supply at a national scale in a model-free fashion.

This study examined the current state of water demand and associated energy input for water supply against a projected increase in water demand in sub-Saharan Africa. Three plausible scenarios, namely, Current State Extends (CSE), Current State Improves (CSI) and Current State Deteriorates (CSD) were developed and applied using nine quantifiable indicators for water demand projections and the associated impact on energy input for water supply for five Water Service Providers (WSPs) in Kenya to demonstrate the feasibility of the approach based on real data in sub-Saharan Africa. Currently, the daily per capita water-use in the service area of four of the five WSPs was below minimum daily requirement of 50 L/p/d. Further, non-revenue water losses were up to three times higher than the regulated benchmark (range 26−63%). Calculations showed a leakage reduction potential of up to 70% and energy savings of up to 12 MWh/a. The projected water demand is expected to increase by at least twelve... [more]

The European Union strives for sharp reductions in both CO2 emissions as well as primary energy use. Electricity consuming technologies are becoming increasingly important in this context, due to the ongoing electrification of transport and heating services. To correctly evaluate these technologies, conversion factors are needed—namely CO2 intensities and primary energy factors (PEFs). However, this evaluation is hindered by the unavailability of a high-quality database of conversion factor values. Ideally, such a database has a broad geographical scope, a high temporal resolution and considers cross-country exchanges of electricity as well as future evolutions in the electricity mix. In this paper, a state-of-the-art unit commitment economic dispatch model of the European electricity system is developed and a flow-tracing technique is innovatively applied to future scenarios (2025−2040)—to generate such a database and make it publicly available. Important dynamics are revealed, includ... [more]

End-use specific residential electricity load profiles are of interest for energy system modelling that requires future load curves or demand-side management. We present a model that is applicable across countries to predict consumption on a regional and national scale, using openly available data. The model uses neural networks (NNs) to correlate measured consumption from one country (United Kingdom) with weather data and daily profiles of a mix of human activity and device specific power profiles. We then use region-specific weather data and time-use surveys as input for the trained NNs to predict unscaled electric load profiles. The total power profile consists of the end-use household load profiles scaled with real consumption. We compare the model’s results with measured and independently simulated profiles of various European countries. The NNs achieve a mean absolute error compared with the average load of 6.5 to 33% for the test set. For Germany, the standard deviation between... [more]

The role of renewable energy sources in the Polish power system is growing. The highest share of installed capacity goes to wind and solar energy. Both sources are characterized by high variability of their power output and very low dispatchability. Taking into account the nature of the power system, it is, therefore, imperative to predict their future energy generation to economically schedule the use of conventional generators. Considering the above, this paper examines the possibility to predict day-ahead wind power based on different machine learning methods not for a specific wind farm but at national level. A numerical weather prediction model used operationally in the Institute of Meteorology and Water Management−National Research Institute in Poland and hourly data of recorded wind power generation in Poland were used for forecasting models creation and testing. With the best method, the Extreme Gradient Boosting, and two years of training (2018−2019), the day-ahead, hourly win... [more]