This study comprehensively analyzed the heat loss and total heat transfer coefficient (U-value) of a single-span experimental plastic greenhouse covered with a double layer of 0.1 mm thick polyethylene. The air temperature and heat flux (W m−2) of the greenhouse components were measured from 18:00 to 06:00, and the energy balance equations under steady-state conditions were determined. The heat flux and U-value of the roof, sides, front and rear, and floor of the greenhouse were determined and compared. The results showed that these values for the roof play an important role in determining the heat load in the greenhouse, and that the average heat transfer through the floor is very small. The average U-value of the greenhouse cover is a comprehensive value which takes the U-values of the roof, sides, and front and rear into account through the use of an area−weighted average method. Finally, an average U-value of 3.69 W m−2 °C −1 was obtained through the analysis of the variations in t... [more]

This paper focuses on the application using a solar-powered unmanned aerial vehicle (UAV) to inspect mountain sites for the purpose of safety and rescue. An inspection path planning problem is formulated, which looks for the path for an UAV to visit a set of sites where people may appear while avoiding collisions with mountains and maintaining positive residual energy. A rapidly exploring random tree (RRT)-based planning method is proposed. This method firstly finds a feasible path that satisfies the residual energy requirement and then shortens the path if there is some abundant residual energy at the end. Computer simulations are conducted to demonstrate the performance of the proposed method.

Direct Current (DC) grids are considered an attractive option for integrating high shares of renewable energy sources in the electrical distribution grid. Hence, in the future, Alternating Current (AC) and DC systems could be interconnected to form hybrid AC-DC distribution grids. This paper presents a two-step state estimation formulation for the monitoring of hybrid AC-DC grids. In the first step, state estimation is executed independently for the AC and DC areas of the distribution system. The second step refines the estimation results by exchanging boundary quantities at the AC-DC converters. To this purpose, the modulation index and phase angle control of the AC-DC converters are integrated into the second step of the proposed state estimation formulation. This allows providing additional inputs to the state estimation algorithm, which eventually leads to improve the accuracy of the state estimation results. Simulations on a sample AC-DC distribution grid are performed to highligh... [more]

Strategic and tactical factors come into play in shop competitiveness where, in addition to the products sold, other marketing mix variables must also be considered. There are also subjective factors, such as perceptions through the senses. This became even more important when, as a result of the COVID-19 crisis and the forced closure of certain establishments with physical sales, it was necessary to increase profitability and efficiency. The aim of this study was to determine the exact role of sensory marketing in shop efficiency and profitability, based on the guiding principles of technology, innovation, and respect for the environment. We conducted an exploratory and experimental study consisting of the creation of a sensory strategy through the adaptation of the Hulten, Broweus and Van Dijk model on a specific establishment in the current era of Industry 4.0. The results indicate an increase in sales as well as customer satisfaction and happiness after implementing the relevant st... [more]

The development of strategies for distribution network management is an essential element for increasing network performance and reducing the upgrade of physical assets. This paper analyzes a multi-timescale framework to control the voltage of distribution grids characterized by a high penetration of renewables. The multi-timescale solution is based on three levels that coordinate Distributed Generation (DG) and Energy Storage Systems (ESSs), but differs in terms of the timescales and objectives of the control levels. Realistic load and photovoltaic generation profiles were created for cloudy and clean sky conditions to evaluate the performance features of the multi-timescale framework. The proposed solution was also compared with different frameworks featuring two of the three levels, to highlight the contribution of the combination of the three levels in achieving the best performance.

The automotive industry has been rapidly transforming and moving further from internal combustion engines, towards hybrid or electric vehicles. A key component for the successful adoption of the aforementioned approach is their Energy Management Systems (EMSs). In the proposed work, we describe in detail a custom EMS, with unique characteristics, which was developed and installed in a hydrogen-powered prototype vehicle. The development of the EMS was based on off-the-shelf components and the adoption of a Robot Operating System (ROS), a meta-operating system developed for robotic-oriented applications. Our approach offers soft real-time control and the ability to organize the controller of the EMS as a straightforward and comprehensive message system that provides the necessary inter-process communication at the core of the EMS control procedure. We describe in detail the software-based implementation and validate our approach through experimental results obtained while the prototype w... [more]

Residential water heaters use a substantial amount of electrical energy and contribute to 25% of the energy usage in the residential sector. This raises concern for users in countries with flat rate electricity fees and where fossil fuels are used for electricity generation. Demand side management of tanked water heaters is well suited for energy-focused load reduction strategies. We propose a strategy for providing an electric water heater (EWH) with the optimal temperature planning to reduce the overall electrical energy usage while satisfying the comfort of the user. A probabilistic hot water usage model is used to predict the hot water usage behaviour for the A*-based optimisation algorithm, which accounts for water stratification in the tank. A temperature feedback controller with novel temperature and energy-correcting capabilities provides robustness to prediction errors. Three optimal control strategies are presented and compared to a baseline strategy with the thermostat alway... [more]

Increasing energy demand and environmental regulations around the world provide an adequate framework for developing methods of obtaining energy from renewable sources. Wind force is a resource with a high potential through which green energy can be obtained with no negative impact on the environment. Different turbine typologies have been developed, which can convert the wind force into mechanical and electrical energy through turbine rotational motion. Starting from the classic vertical-axis SAVONIUS rotor model, other models have been designed, which, according to the numerical studies and experimental test results, show higher performance parameters in operation. Such models present specific rotor blade geometries to achieve better operational results in terms of shaft torque and generated power. There are multiple research results from numerical analysis on virtual models or experimental tests that use rotor models in different constructive configurations aiming to improve operati... [more]

The overturning and eccentric abrasion of the slipper worsens the lubrication characteristics and increases the friction power loss and kinetic energy consumption of the slipper/swashplate interface to reduce the axial piston pump efficiency. A coupling lubrication numerical model and algorithm and a micro-chamfering structure are developed and proposed to predict more precisely and improve the lubrication characteristics of the slipper/swashplate interface. The simulation results reveal that the slipper without micro-chamfering overturns and contacts with the swashplate, while the one with micro-chamfering forms a certain oil film thickness to prevent this contact effectively. The minimum total power loss of the slipper/swashplate interface has to be effectively ensured under the worst working conditions, such as the high pressure, the low speed, the maximum swashplate inclination angle and the minimum house pressure. The optimal micro-chamfering width and depth are 1.2 mm and 3.5 μm... [more]

In order to reduce the load demand of buildings in Japan, this study proposes a grid-tied hybrid solar−wind−hydrogen system that is equipped with a maximum power point tracking (MPPT) system, using a fuzzy logic control (FLC) algorithm. Compared with the existing MPPTs, the proposed MPPT provides rapid power control with small oscillations. The dynamic simulation of the proposed hybrid renewable energy system (HRES) was performed in MATLAB-Simulink, and the model results were validated using an experimental setup installed in the Chikushi campus, Kyushu University, Japan. The techno-economic analysis (TEA) of the proposed system was performed to estimate the optimal configuration of the proposed HRES, subject to satisfying the required annual load in the Chikushi campus. The results revealed a potential of 2% surplus power generation from the proposed HRES, using the FLC-based MPPT system, which can guarantee a lower levelized cost of electricity (LOCE) for the HRES and significant sav... [more]

Leading-edge erosion at wind turbine blades cause a loss in profit for wind farm owners, in particular offshore. The characterization of the rain erosion environmental load at wind turbine blades is based on the long-term rain rate and wind speed observations at 10-minute resolutions at coastal stations around the North Sea, Baltic Sea, and inland. It is assumed that an IEA Wind 15 MW turbine is installed at each station. The leading-edge lifetime is found to increase from the South to the North along the German and Danish North Sea coastline from 1.4 to 2.8 years. In the Danish and German Baltic Sea, the lifetime in the West is shorter (~2 years) than further East (~3 to 4 years). It is recommended to use a time series of 10 years or longer because shorter time series most likely will cause an overestimation of the lifetime. The loss in profit due to leading-edge erosion can potentially be reduced by ~70% using the erosion-safe mode, i.e., reduce the tip speed during heavy rain events... [more]

In adsorption heat pumps, the adsorbent is typically combined with heat conducting structures in order to ensure high power output. A new approach for the direct integration of zeolite granules into a copper structure made of short copper fibers is presented here. Zeolite NaY granules with two different grain sizes are coated with copper fibers and powder and sintered to larger structures. The sorption dynamics of these structures were measured and evaluated in terms of heat and mass transfer resistances and compared to the loose grain configuration of the same material. We found that the thermal conductivity of such a composite structure is approximately 10 times higher than the thermal conductivity of an adsorbent bed with NaY granules. Sorption equilibrium measurements with a volumetric method indicate that the maximum uptake is not altered by the manufacturing process. Furthermore, the impact of the adsorbent−metal structure on the total thermal mass of an adsorption heat exchanger... [more]

Natural gas (NG) engines have very broad application prospects. The pilot-ignited NG diesel engine can be organized into two combustion modes according to the sequence of oil and gas injection: (1) High-pressure direct injection, where NG is mainly diffused combustion; and (2) partially premixed compression ignition, where NG is mainly premixed combustion. In this study, we used CONVERGE to explore the influence of the NG injection timing on the distribution of the mixture equivalence ratio, ignition characteristics, thermal efficiency, emission, and combustion reaction rate under the two combustion modes. We also used a multi-step soot model to analyze the particle mass and quantity. We showed herein that the NG injection timing significantly affects the mixture distribution in the cylinder, thereby consequently affecting the combustion process. Both very early and very late injection times were not conducive to NG combustion. In addition, the mass, quantity, and diameter of the soot... [more]

In a recent contribution, Ref. [1] study the life cycle impacts of a noise-reducing technology for a combined heat and power plant [...]

The effects of COVID-19 have had devasting effects on both health and economies in 2020. At the same time, the lockdown and the downturn of economic activity resulted in a decrease in energy consumption and an accompanying reduction in greenhouse gas emissions. In this article, a comparison with the temperature adjustment of energy use is presented for the main carriers of electricity, natural gas, and oil products in the residential, tertiary, industry, and transport (road transport, domestic aviation, and navigation) sectors in 2020 against the previous two years in Greece, along with the corresponding emissions. As the comparison covers the entire year, both COVID peaks in the March−April and November−December periods and the corresponding lockdown effects as well as seasonal variations are included. The analysis shows a reduction, adjusted for temperature, of 3528 GWh in electricity and 10,286 GWh in transport, and an increase of 1916 GWh in heating and other final uses for a net 1... [more]

The improper management of goat manure from concentrated goat feeding operations and food waste leads to the emission of greenhouse gasses and water pollution in the US. The wastes were collected from the International Goat Research Center and a dining facility at Prairie View A&M University. The biochemical methane potential of these two substrates in mono and co-digestion at varied proportions was determined in triplicates and processes were evaluated using two nonlinear regression models. The experiments were conducted at 36 ± 1 °C with an inoculum to substrate ratio of 2.0. The biomethane was measured by water displacement method (pH 10:30), absorbing carbon dioxide. The cumulative yields in goat manure and food waste mono-digestions were 169.7 and 206.0 mL/gVS, respectively. Among co-digestion, 60% goat manure achieved the highest biomethane yields of 380.5 mL/gVS. The biodegradabilities of 33.5 and 65.7% were observed in goat manure and food waste mono-digestions, while 97.4% wer... [more]

In the comment of Heijungs and Cucurachi [...]

Constantly growing distributed energy generation based on renewable sources creates a number of new challenges for electrical power system operation. One of the challenges is islanding detection. Unintentional islanding, which can cause health and safety hazards for the personnel, is currently being experienced by a growing number of consumers/prosumers especially in the case of photovoltaic inverters. This work presents a new islanding detection method based on synchrophasor measurements. The proposed method works in either a passive or hybrid mode. In a passive mode, a single phasor measurement unit (PMU) in the island region is used. In a hybrid mode, one PMU in the island and another one outside the island are exploited. The proposed method was verified in conducted laboratory tests that confirmed the applicability of PMUs data for effective detection and monitoring of unintentional islanding.

This paper presents the use of a three-phase four-wire shunt active power filter to improve the power quality in the Department of Industrial Electronics of a large enterprise from Romania. The specificity is given by the predominant existence of single-phase consumers (such as personal computers, printers, lighting and AC equipment). In order to identify the power quality indicators and ways to improve them, an A-class analyzer was used to record the electrical quantities and energy parameters in the point of common coupling (PCC) with the nonlinear loads for 27 h. The analysis shows that, in order to improve the power quality in PCC, three goals must be achieved: the compensation of the distortion power, the compensation of the reactive power and the compensation of the load unbalance. By using the conceived three-leg shunt active power filter, controlled through the indirect current control method in an original variant, the power quality at the supply side is very much improved. In... [more]

The use of artificial intelligence (AI) in companies is advancing rapidly. Consequently, multidisciplinary research on AI in business has developed dramatically during the last decade, moving from the focus on technological objectives towards an interest in human users’ perspective. In this article, we investigate the notion of employees’ trust in AI at the workplace (in the company), following a human-centered approach that considers AI integration in business from the employees’ perspective, taking into account the elements that facilitate human trust in AI. While employees’ trust in AI at the workplace seems critical, so far, few studies have systematically investigated its determinants. Therefore, this study is an attempt to fill the existing research gap. The research objective of the article is to examine links between employees’ trust in AI in the company and three other latent variables (general trust in technology, intra-organizational trust, and individual competence trust).... [more]

Significant amounts of produced water, spent drilling fluid, and drill cuttings, which differ in composition and characteristics in each drilling operation, are generated in the oil and gas industry. Moreover, the oil and gas industry faces many technological development challenges to guarantee a safe and clean environment and to meet strict environmental standards in the field of processing and disposal of drilling waste. Due to increasing application of nanomaterials in the oil and gas industry, drilling wastes may also contain nanometer-scale materials. It is therefore necessary to characterize drilling waste in terms of nanomaterial content and to optimize effective methods for their determination, including a key separation step. The purpose of this study is to select the appropriate method of separation and pre-concentration of silver nanoparticles (AgNPs) from drilling wastewater samples and to determine their size distribution along with the state of aggregation using single-pa... [more]

This paper presents the effect of a composite poly(3,4-ethylenedioxythiophene) polystyrene sulfonate PEDOT:PSS and copper-doped nickel oxide (Cu:NiOx) hole transport layer (HTL) on the performance of perovskite solar cells (PSCs). Thin films of Cu:NiOx were spin-coated onto fluorine-doped tin oxide (FTO) glass substrates using a blend of nickel acetate tetrahydrate, 2-methoxyethanol and monoethanolamine (MEA) and copper acetate monohydrate. The prepared solution was stirred at 65 °C for 4 h and spin-coated onto the FTO substrates at 3000 rpm for 30 s in a nitrogen glovebox. The Cu:NiOx/FTO/glass structure was then annealed in air at 400 °C for 30 min. A mixture of PEDOT:PSS and isopropyl alcohol (IPA) (in 1:0.05 wt%) was spun onto the Cu:NiOx/FTO/glass substrate at 4000 rpm for 60 s. The multilayer structure was annealed at 130 °C for 15 min. Subsequently, the perovskite precursor (0.95 M) of methylammonium iodide (MAI) to lead acetate trihydrate (Pb(OAc)2·3H2O) was spin-coated at 4000... [more]

Power capacitors suffer multiple impulse voltages during their lifetime. With the multiple impulse voltage aging, the internal insulation, oil-film dielectric may deteriorate and even fail in the early stage, which is called accumulative effect. Hence, the time-domain dielectric response of oil-film dielectric with multiple impulse voltage aging is studied in this paper. At first, the procedure of the preparation of the tested samples were introduced. Secondly, an aging platform, impulse voltage generator was built to test the accumulative effect of capacitor under multiple impulse voltage. Then, a device was used to test the time-domain dielectric response (polarization depolarization current, PDC) of oil-film dielectric in different aging states. And finally, according to the PDC data, extended Debye model and characteristic parameters were obtained by matrix pencil algorithm identification. The results indicated that with the increase of impulse voltage times, the time-domain dielec... [more]

The electrochemical performance of modified natural graphite (MNG) and artificial graphite (AG) was investigated as a function of electrode density ranging from 1.55 to 1.7 g∙cm−3. The best performance was obtained at 1.55 g∙cm−3 and 1.60 g∙cm−3 for the AG and MNG electrodes, respectively. Both AG, at a density of 1.55 g∙cm−3, and MNG, at a density of 1.60 g∙cm−3, showed quite similar performance with regard to cycling stability and coulombic efficiency during cycling at 30 and 45 °C, while the MNG electrodes at a density of 1.60 g∙cm−3 and 1.7 g∙cm−3 showed better rate performance than the AG electrodes at a density of 1.55 g∙cm−3. The superior rate capability of MNG electrodes can be explained by the following effects: first, their spherical morphology and higher electrode density led to enhanced electrical conductivity. Second, for the MNG sample, favorable electrode tortuosity was retained and thus Li+ transport in the electrode pore was not significantly affected, even at high ele... [more]

Perovskite solar cells have progressed very steadily, reaching power conversion efficiencies (PCE) beyond 20% while also improving their lifetimes up to 10,000 h. A large number of cell architecture and materials for active, transporting and electrode layers have been used, either in blends or in nanostructured layers. In this article, a set of perovskite solar cells have been designed, fabricated and characterized with special focus on their lifetime extension. The inclusion of 5-amino-valeric acid iodide (5−AVAI) as interlayer in a methyl-amino lead-iodide (MAPI) perovskite solar cell has provided additional stability in cells with PCE > 10% and T80 = 550 h. Experiments for up to 1000 h with solar cells at maximum power point under continuous illumination with solar simulator have been carried out (1 kW/m2, AM1.5G, equivalent to more than six months of outdoor illumination in locations such as Southeast Spain, with an average irradiation of 1900 kWh/m2/year). The addition of molecula... [more]