Literature and experience show that there are large discrepancies between the calculated and measured building energy usages, where user-related parameters are significant factors with regard to energy use in low-energy buildings. Furthermore, the difficulties encountered when quantifying these parameters compound these discrepancies. The main aim of this study was to provide feedback that would help the building industry and research communities to predict more accurately the impact of the user-related parameters on energy performance. The results of the study would, subsequently, contribute to minimizing the discrepancies between calculated and measured energy use. This article analyses simulated building energy use based on randomly chosen combinations of measured user-related parameters in three recently built low-energy schools in Sweden. The results show that energy performance can span from 30 to 160 kWh/(m² y) simply by varying the combination of previously measured user-relate... [more]

The robustness of the reference circuit in a wide range of supply voltages is crucial in implanted devices. Conventional reference circuits have demonstrated a weak performance over wide supply ranges. Channel-length modulation in the transistors causes the circuit to be sensitive to power supply variation. To solve this inherent problem, this paper proposes a new output-voltage-line-regulation controller circuit. When a variation occurs in the power supply, the controller promptly responds to the supply deviation and removes unwanted current in the output path of the reference circuit. The proposed circuit was implemented in a 0.35-μm SK Hynix CMOS standard process. The experimental results demonstrated that the proposed reference circuit could generate a reference voltage of 0.895 V under a power supply voltage of 3.3 V, line regulation of 1.85 mV/V in the supply range of 2.3 to 5 V, maximum power supply rejection ratio (PSRR) of −54 dB, and temperature coefficient of 11.9 ppm/°C in... [more]

DC distribution grids are increasingly a promising solution for wind and solar integration due to good matching with DC output voltage such as photovoltaic (PV) array systems, distributed battery storage systems (BESS) and electric vehicles. To overcome the control problems involving coordination control schemes of multi-BESSs in real-time as well as operation strategies of DC grids in the long-term, this paper presents the effective adaptive coordinated droop control of multi-battery energy storage systems (MBESSs) in DC distribution grids. The adaptive coordinated droop is proposed according to the available energy levels in BESSs. With the proposed method, the dual-objectives, which are stabilization of DC voltages especially through disturbance for instance outage of BESS and enhancement of State of Charge (SOC)-balance speed among BESSs, can be achieved. Analytical derivations are established to investigate the impacts of the adaptive method. Meanwhile, the influence of the propos... [more]

The energy transformation is changing the structure of the energy sector in Europe and Germany. In this paper the current structure of the energy sector is analysed both empirically as well as theoretically. Therefore, the authors have developed the business model framework for the energy transformation (BMFE). The framework is a synthesis of classical business model designs. An exhaustive survey of existing business models based on primary data collection and a literature review leads to 638 business models. Finally, 69 prototypical business models of the energy sector are the result of the classification of these business models. The information of the business models within the BMFE is applied to show the growing importance of value creation networks in energy industry. The work represents the current status of the business models in the energy sector.

The temperature and field dependencies of electric conductivities of two types of silicone rubber-based polymers intended for use in high voltage direct current applications are presented and discussed. The conductivities obtained with the standard method by measuring a current through the material sample placed between metallic electrodes in response to the applied voltage are compared with those deduced from the measured potential decay on pre-charged material surface in an open circuit configuration. The measurements were conducted in the range of the applied electric field strength (0.5−5) kV/mm and temperatures ranging from 22 °C to 70 °C. It is shown that the values of the conductivities obtained by the two methods are in agreement and their temperature dependences obey Arrhenius law yielding similar activation energies.

Under the influence of the COVID-19 pandemic and the concurrent oil conflict between Russia and Saudi Arabia, oil prices have exhibited unusual and sudden changes. For this reason, the volatilities of the West Texas Intermediate (WTI), Brent and Dubai crude daily oil price data between 29 May 2006 and 31 March 2020 are analysed. Firstly, the presence of chaotic and nonlinear behaviour in the oil prices during the pandemic and the concurrent conflict is investigated by using the Shanon Entropy and Lyapunov exponent tests. The tests show that the oil prices exhibit chaotic behavior. Additionally, the current paper proposes a new hybrid modelling technique derived from the LSTARGARCH (Logistic Smooth Transition Autoregressive Generalised Autoregressive Conditional Heteroskedasticity) model and LSTM (long-short term memory) method to analyse the volatility of oil prices. In the proposed LSTARGARCHLSTM method, GARCH modelling is applied to the crude oil prices in two regimes, where regime t... [more]

One important goal of the climate commitment in the European Union (EU) is to reduce primary energy demand in the transport sector and increase the use of renewables, since around 33% of primary energy is consumed in this sector. Therefore, the EU ordered its member states to raise the number of electric vehicles (EVs) within Europe. Consequently, the energy demand for electricity will rise as a function of the number of EVs. To avoid local grid overload and guarantee a higher percentage of clean energy, EV charging stations can be supported by a combined system of grid-connected photovoltaic modules and battery storage. In this paper, the focus lies on the feasibility and economic aspects of such systems. To provide an overview of the different e-charging station combinations, a support tool was modelled and developed, making it possible to size and manage EVs charging stations with only a few input parameters. Thanks to its easy handling, the tool suits a wide spectrum of users. Due... [more]

The present research is focused on an experimental investigation to evaluate the mechanical, durability, and thermal performance of compressed earth blocks (CEBs) produced in Portugal. CEBs were analysed in terms of electrical resistivity, ultrasonic pulse velocity, compressive strength, total water absorption, water absorption by capillarity, accelerated erosion test, and thermal transmittance evaluated in a guarded hotbox setup apparatus. Overall, the results showed that compressed earth blocks presented good mechanical and durability properties. Still, they had some issues in terms of porosity due to the particle size distribution of soil used for their production. The compressive strength value obtained was 9 MPa, which is considerably higher than the minimum requirements for compressed earth blocks. Moreover, they presented a heat transfer coefficient of 2.66 W/(m2·K). This heat transfer coefficient means that this type of masonry unit cannot be used in the building envelope witho... [more]

Laminae are well developed in shale and generally influence fracture propagation during hydraulic fracturing. Hence, comprehensively understanding the tension and shear behaviors of shale laminae is crucial. There have been limited systematic studies thus far on the tensile and shear strength as well as fracture morphology of shale laminae. In this study, the Lower Silurian Longmaxi Shale (China) was investigated via Brazilian tensile and angle-varied plate shear tests. Five lamina types were tested, i.e., calcite (Cal), pyrite (Py), organic-enriched (Oc), the interface between Cal and Oc (Cal-Oc), and the interface between Py and Oc (Py-Oc) laminae. Results showed that the tensile strength was in the range 0.43−8.22 MPa, mainly in the order of Cal > Py > Cal-Oc > Py-Oc > Oc. The modes of fracture morphology were highly related to the occurrence, continuity, and mineralogy fillings of laminae. Shear strength parameters were within the range 22.50−29.64 MPa for cohesion and 37.29−43.60°... [more]

Flow boiling in microporous layers has attracted a great deal of attention in the enhanced heat transfer field due to its high heat dissipation potential. In this study, flow boiling experiments were performed on both porous microchannels and a copper-based microchannel, using water as the coolant. As the heat flux was less than 80 W/cm2, the porous microchannels presented significantly higher boiling heat transfer coefficients than the copper-based microchannel. This was closely associated with the promotion of the nucleation site density of the porous coating. With the further increase in heat flux, the heat transfer coefficients of the porous microchannels were close to those of the copper-based sample. The boiling process in the porous microchannel was found to be dominated by the nucleate boiling mechanism from low to moderate heat flux (<80 W/cm2).This switched to the convection boiling mode at high heat flux. The porous samples were able to mitigate flow instability greatly.... [more]

The most critical positions of a prefabricated cable accessory, from the electrical point of view, are the interfaces between the stress cone and its surroundings. Accordingly, the contact pressure on those interfaces needs to be carefully designed to assure both good dielectric strength and smooth installation of the stress cone. Nevertheless, since stress cones made from rubber are under large deformation after installation, their internal stress distribution is neither practical to measure directly by planting sensors, nor feasible to compute accurately with the conventional theory of linear structural mechanics. This paper presents one sophisticated method for computing the mechanical stress distribution in rubber stress cones of cable accessories by employing hyperelastic models in a computation model based on the finite element method. This method offers accurate results for rubber bodies of complex geometries and large deformations. Based on the method, a case study of a composi... [more]

The icing problem of wind turbine blades in northern China has a serious impact on the normal and safe operation of the unit. In order to effectively predict the icing conditions of wind turbine blades, a deep fully connected neural network optimized by machine learning (ML) algorithms based on big data from the wind farm is proposed to diagnose the icing conditions of wind turbine blades. This study first uses the random forest model to reduce the features of the supervisory control and data acquisition (SCADA) data that affect blade icing, and then uses the K-nearest neighbor (KNN) algorithm to enhance the active power feature. The features after the random forest reduction and the active power mean square error (MSE) feature enhanced by the KNN algorithm are combined and used as the input of the fully connected neural network (FCNN) to perform and an empirical analysis for the diagnosis of blade icing. The simulation results show that the proposed model has better diagnostic accurac... [more]

Since the permeant magnet synchronous generator (PMSG) has many applications in particular safety-critical applications, enhancing PMSG availability has become essential. An effective tool for enhancing PMSG availability and reliability is continuous monitoring and diagnosis of the machine. Therefore, designing a robust fault diagnosis (FD) and fault tolerant system (FTS) of PMSG is essential for such applications. This paper describes an FD method that monitors online stator winding partial inter-turn faults in PMSGs. The fault appears in the direct and quadrature (dq)-frame equations of the machine. The extended Kalman filter (EKF) and unscented Kalman filter (UKF) were used to detect the percentage and the place of the fault. The proposed techniques have been simulated for different fault scenarios using Matlab®/Simulink®. The results of the EKF estimation responses simulation were validated with the practical implementation results of tests that were performed with a prototype PMSG... [more]

Fault detection and diagnosis (FDD) has become an important subject in heat pumps due to its potential for energy savings. However, research on multiple faults occurring at the secondary fluid side of heat pumps is rare in the open literature. This study experimentally examined single secondary fluid flow rate faults (SSFF) and multiple-simultaneous secondary fluid flow rate faults (MSSFF) and their effects on the performance of a heat pump unit, which is a core component of ground source heat pump systems, and proposed FDD methodology to detect these faults. The secondary fluid flow rate faults were simulated in cooling mode by varying the evaporator and condenser secondary fluid flow rates at 60%, 80%, 100%, 120%, and 140% of the reference value according to varying outdoor entering water temperature conditions. Condenser secondary fluid flow rate faults affected the heat pump coefficient of performance(COP) significantly more than the evaporator secondary fluid flow rate fault in SS... [more]

Pre-cooling of inlet air using evaporative cooling is an effective approach to enhance the performance of air-cooled condensers in air conditioning applications. Ultrasonic mist generators have emerged as a promising alternative to conventional evaporative cooling systems based on cooling pads or spray cooling. This paper presents the developed numerical model of an ultrasonic mist generator for the evaporative pre-cooling of the inlet air of the condenser in air conditioning applications. The model was validated against the experimental data obtained in a wind tunnel experimental facility. A parametric analysis including some physical variables involved in the cooling process was carried out, including the main axial air velocity, the injection air velocity and the water mass flow rate of atomized water. The dimensionless groups water-to-air mass flow and air-to-air mass flow ratios were found to most affect the average evaporative cooling efficiency. A maximum value of 0.654 was foun... [more]

The combustion performance of a conventional rail diesel engine was investigated by measuring the exhaust gas with the respect to the number of injector holes, fuel type, and the use of exhaust gas recirculation (EGR), to provide a detailed reduction of environmental pollutants. It was found that a six- or seven-hole injector was more effective than a five-hole injector for reducing the exhaust gas. In addition, the mixing of 20% biodiesel oil with diesel most effectively reduced the HC and NOx contents. The technology generally reduced the NOx and CO contents of the exhaust, but had no significant effect on the HC and CO2 contents.

The change from a centralized to a decentralized energy supply creates new challenges in the planning of such energy supply concepts. Specialized planning tools that can cope with the complex requirements and multi-layered boundary conditions of local energy use are therefore needed. Existing methods need to be further developed and optimized to suit the complex stakeholder structures encountered in innovative district projects, as well as for research purposes. This paper presents selected aspects and challenges in the development of an application-oriented planning tool. Using a North German district as a case study, the usability of a Building Information Model as an aggregated data platform is tested in the context of a residential energy district planning process. In addition, the modeling of heating grids using a combination of Geographic Information System and open source thermodynamic tools is presented. Economic valuation methods are examined to determine the extent to which t... [more]

In 2018 the number of people without access to electricity dropped to less than 1 billion. However, the difficulty of serving these people became higher, as the locations are in the most remote areas of the world. Brazil, for example, needs to bring electricity to around 1 million people who, in the vast majority, live within the Amazon region. In this way, hybrid energy systems (HESs) count as an attractive alternative for power generation, especially in remote areas. Therefore, this article analyzes a case study of a hybrid photovoltaic-diesel system installed in the Tapajós-Arapiuns Extractive Reserve in the Brazilian Amazon region. The studied plant is composed of a photovoltaic (PV) system, a lead-acid electrochemical battery bank, a diesel generator, and electro-electronic loads with highly variable demand throughout the year. The HOMER PRO software is used as the simulation tool. The results show that the load following dispatch strategy is the best option, with 85.6% of the loa... [more]

The Trans-European Replacement Reserve Exchange (TERRE) project is the European implementation project for exchanging Balancing Energy (BE) from Replacement Reserves (RR). Its main objective is to operate a common European platform that gathers all RR Balancing Energy Orders (BEOs) from Transmission System Operators’ (TSOs) local BE markets into a Common Merit Order List (CMOL). It provides an optimized allocation of RR, covering all TSOs’ RR BE needs, by executing the Activation Optimization Function (AOF). In this paper, the mathematical formulation of the AOF is presented, which explicitly incorporates all standard products and constraints that are provisioned in the approved implementation framework. The clearing problem is formulated as a Mixed Integer Linear Programming model and solved within an iterative algorithm for the handling of Paradoxically Accepted Orders (PAOs). The modeling framework allows the coordination of two distinct market setups, i.e., the self-dispatch and ce... [more]

The concept of a single-input/multi-output thermal network was proposed by the Development of Libraries of Physical models for an Integrated design environment (DELPHI) consortium more than twenty years ago. The present work highlights the recent improvements made to efficiently derive a low-computing-effort model from a fully detailed numerical model and to characterize its performances. The temperature predictions of a deduced ball-grid-array (BGA) dynamic compact thermal model are compared to those of a realistic three-dimensional representation, including the large set of internal copper traces, as well as its board structure, which has been validated by experiment. The current study discloses a method for creating an amalgam reduced-order modal model (AROMM) for that electronic component family that allows the preservation of the geometry integrity and shortening scenarios computation. Typically, the AROMM method reduces by a factor of 600 the computation time needed to obtain the... [more]

This paper proposes an energy shaping controller of a DC/DC converter for automatic guided vehicles (AGVs) wireless power transfer (WPT). A transformer is inserted after the LCC topology to improve the transfer power, and the DC/DC boost converter is added before this topology to obtain desired systematic power dynamically. The system power transfer model is derived based on the idea of voltage transformation and the desired power can be implemented indirectly through regulating desired output voltage of DC/DC converter. With the proposed controller, this WPT system will have a much better dynamic performance and the effective working time can be increased significantly. Furthermore, this paper proposes dynamical regulation strategy for output power to get real time target power according to the charging curve of the battery. Simulation and experimental results verified the control performance of the proposed control scheme. A WPT prototype with power up to 1.65 kW was built, and 92.12... [more]

Despite globally progressing energy transition, the deployment of non-hydropower renewable energy (NHRE) in Central Asia is moderate and varies by country. This paper aims to explain why Central Asian countries with significant challenges in the energy sector are least engaged in NHRE development. In doing so, the paper first reviews scholarly work on renewable energy (RE) deployment in developing countries. For assessing the NHRE development status in Central Asian countries, the paper adopts a two-stage analytical framework. First, it assesses the current situation in these states’ energy sectors in connection to their economic growth and development, environmental sustainability and energy security. Then, it analyses the preparedness of the national energy sectors for NHRE diffusion in six dimensions: structure of energy sector, RE regulation, institutions and governance, capital and investment, infrastructure and business environment, and human capital. Based on the results of the... [more]

Herein, the spinel-layered cathode material Li1.33MnTiO4+z (0.8LiMnTiO4•0.2Li2Mn0.5Ti0.5O3) is investigated for the purpose of developing a high-capacity, low-cost, and environmentally friendly cathode for Li-ion batteries. Sol-gel synthesis is conducted and the relationships between synthesis temperature, structure, and electrochemical performance of the cathodes are studied. The effects of size and purity on the capacities of these cathodes are discussed. The samples fired at 500 and 600 °C contain an impurity phase of TiO2, thus delivering capacities of 208 and 210 mAh g−1 at C/10, respectively. The sample fired at 700 °C without the impurity phase of TiO2 shows a high capacity of 222 mAh g−1 at C/10 and capacity retention of 90.5% after 100 cycles at 1C.

Resource allocation problems are at the core of the smart grid where energy supply and demand must match. Multi-objective optimization can be applied in such cases to find the optimal allocation of energy resources among consumers considering energy domain factors such as variable and intermittent production, market prices, or demand response events. In this regard, this paper considers consumer energy demand and system-wide energy constraints to be individual objectives and optimization variables to be the allocation of energy over time to each of the consumers. This paper considers a case in which multi-objective optimization is used to generate Pareto sets of solutions containing possible allocations for multiple energy intensive consumers constituted by commercial greenhouse growers. We consider the problem of selecting a final solution from these Pareto sets, one of maximizing the social welfare between objectives. Social welfare is a set of metrics often applied to multi-agent sy... [more]

The Songliao Basin contains some of the largest volumes of oil shales in China; however, these energy sources are located in areas covered by arable land, meaning that the best way of exploiting them is likely to be environmentally friendly in situ conversion processing (ICP). Whether the oil shales of the Songliao Basin in the Qingshankou Formation are suitable for ICP remain controversial. In this paper, through sequence stratigraphic correlations, three main thick oil shale layers (N1, N2, and N3) of the Sequence1 (Sq1) unit in the first member of Qingshankou Formation (K2qn1) are confirmed as consistently present throughout the Southeastern Uplift region of the basin. The spectral trend attributes reflect that the lake reached a maximum flood surface of the K2qn1 in N2 oil shale layer, and the total organic carbon (TOC) and Fischer assay (FA) oil yield are significantly increasing. The N2 and N3 oil shale layers were deposited in a high lake level environment associated with ingres... [more]