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Updated Thursday, 28 October 2021

Energies ◽  
2021 ◽  
Vol 14 (21) ◽  
pp. 7012
Author(s):  
Tian Yang ◽  
Moez Esseghir ◽  
Lyes Khoukhi ◽  
Su Pan

Energy efficiency (EE) is of great concern in cognitive radio networks since the throughput and energy consumption of secondary users (SUs) vary with the sensing time. However, the conditions of the detection probability and false alarm probability should be respected to better protect primary users (PUs) and to improve the sensing performance of SUs. Additionally, the PUs’ minimum averaged power provision should also be regarded as a key problem of interactive linking to SUs. Therefore, an integrated design between the PU and SUs is desired for the coordination of the whole cognitive radio system, especially regarding the satisfaction of EE and performance metrics. This study formulates sensing constraints in a unified way and calculates the minimum SNR of SUs, based on which the essential PU power provision is computed. Furthermore, EE is proved as a decreasing function with the PU’s active ratio, where the maximum EE is obtained corresponding to the minimum QoS requirements of the sensing process. Hence, a bisection-based method is proposed to maximize EE, which is considered as a concave function of SUs’ sensing time and has only one unique optimum. EE’s optimization was analyzed under different fusion rules for diverse SNR conditions. The optimum was also studied with sensing performance targets for various cases of PU power provision.


Energies ◽  
2021 ◽  
Vol 14 (21) ◽  
pp. 7008
Author(s):  
Iwona Markuszewska

This article explores the land use conflict. Coal exploitation precludes agricultural production and, as a result, mining-energy projects come across NIMBY (Not In My Back Yard) opposition from the farming community. An investigation was carried out in two rural communes: Krobia and Miejska Górka in the Wielkopolska Region in Poland. The aim was to obtain an answer to the following questions: (1) if acting in the name of energy security, should we accept the state government interest and start exploitation of the lignite resource? (2) If acting in the name of landowners’ rights, should we accept the local community interest and maintain the current farming production? and (3) is it possible to reconcile the interests of the conflict beneficiaries? The following qualitative methods were used: keyword and content analysis of word data, such as scientific papers, legal documents, and parliamentary questions (PQs), while the discourse analysis was focused on the policy and procedural conflicts. In the results section, possible solutions for heading off the conflict are presented. The results contribute to an integrated understanding of conflicts over mining and farming land use.


Energies ◽  
2021 ◽  
Vol 14 (21) ◽  
pp. 6991
Author(s):  
Zehou Xiang ◽  
Kesai Li ◽  
Hucheng Deng ◽  
Yan Liu ◽  
Jianhua He ◽  
...  

Tight sandstone oil and gas reservoirs are widely distributed, rich in resources, with a bright prospect for exploration and development in China. Due to multiple evolutions of the structure and sedimentary system, the gas–water distribution laws are complicated in tight sandstone gas reservoirs in the northern Ordos area. It is difficult to identify gas and water layers in the study area. In addition, in the development and production, various factors, such as the failure of the instrument, the difference in construction parameters (injected sand volume, flowback rate), poor test results, and multi-layer joint testing lead to unreliable gas test results. Then, the inaccurate logging responses will be screened by unreliable gas test results for different types of fluids. It is hard to make high-precision fluid logging identification charts or models. Therefore, this article combines gas logging, well logging, testing and other data to research the test and logging data quality classification. Firstly, we select reliable standard samples through the initial gas test results. Secondly, we analyze the four main factors which affect the inaccuracy of gas test results. Thirdly, according to these factors, the flowback rate and the sand volume are determined as the main parameters. Then, we establish a recognition chart of injected sand volume/gas–water ratio. Finally, we proposed an evaluation method for testing quality classification. It provides a test basis for the subsequent identification of gas and water through the second logging interpretation. It also provides a theoretical basis for the exploration and evaluation of tight oil and gas reservoirs.


Energies ◽  
2021 ◽  
Vol 14 (21) ◽  
pp. 6986
Author(s):  
Yang Li ◽  
Zhifu Zhou ◽  
Jian Zhao ◽  
Liang Hao ◽  
Minli Bai ◽  
...  

In this work, three-dimensional thermal simulations of single 18650 lithium-ion battery cell and 75 V lithium-ion battery pack composed of 21 18650 battery cells are performed based on a multi-scale multi-domain (MSMD) battery modeling approach. Different cooling approaches’ effects on 18650 lithium-ion battery and battery pack thermal management under fast discharging and external shorting conditions are investigated and compared. It is found that for the natural convection, forced air cooling, and/or mini-channel liquid cooling approaches, the temperature of battery cell easily exceeds 40 °C under 3C rate discharging condition. While under external shorting condition, the temperature of cell rises sharply and reaches the 80 °C in a short period of time, which can trigger thermal runaway and may even lead to catastrophic battery fire. On the other hand, when the cooling method is single-phase direct cooling with FC-72 as coolant or two-phase immersed cooling by HFE-7000, the cell temperature is effectively limited to a tolerable level under both high C rate discharging and external shorting conditions. In addition, two-phase immersed cooling scheme is found to lead to better temperature uniformity according to the 75 V battery pack simulations.


Energies ◽  
2021 ◽  
Vol 14 (21) ◽  
pp. 6987
Author(s):  
Małgorzata Rataj ◽  
Justyna Berniak-Woźny ◽  
Marlena Plebańska

The growing climate crisis forces the adoption of radical steps to neutralize our impact on the environment, despite the constantly growing demand for energy. Poland, which according to forecasts will not reach the EU target of 15% share of renewable energy sources by 2030, is nevertheless a leader in the EU in terms of the growth dynamics of the photovoltaic market. The aim of this article is to answer the question as to what caused such a huge interest in solar energy. In this article, the authors focus solely on residential installations. The dataset for the analysis was constructed on readily available national data on photovoltaics showing the key characteristics of the country and prosumers. According to this research, the prosumer’s profile shows that home photovoltaics are most interesting for the poorest households in rural municipalities, in regions with the highest unemployment rate, and among citizens of pre-retirement age. The decision to invest in photovoltaics is also influenced by the availability of subsidies and the price level of energy bills. On the other hand, no impact was found on insolation and environmental pollution. The results of the study will allow for a more conscious shaping of energy policy at the EU, national and regional levels.


Energies ◽  
2021 ◽  
Vol 14 (21) ◽  
pp. 6989
Author(s):  
Andrés Oviedo-Gómez ◽  
Sandra Milena Londoño-Hernández ◽  
Diego Fernando Manotas-Duque

COVID-19 disease shocked global economic activity and affected the electricity markets due to lockdown and work-from-home policies. Therefore, this study proposes an empirical analysis to identify the electricity spot price response during the preventive and mandatory insulation in Colombia, where the economic contraction caused the largest decrease in the electricity demand, especially in the industrial sector. The methodology applied was quantile regression to quantify the non-linear effect on the spot price returns, and two sample periods were selected to contrast the results: 2018 and 2019. The main findings showed that regulated demand variation caused the highest variability on the spot price dynamic during the strict quarantine. However, the price could not fully capture the effects of the demand change due to the short duration of the shock and, also, the price variability in 2019 was higher than 2020 by an El Niño shock.


Energies ◽  
2021 ◽  
Vol 14 (21) ◽  
pp. 6978
Author(s):  
Mateusz Marcinkowski ◽  
Dawid Taler ◽  
Jan Taler ◽  
Katarzyna Węglarz

Currently, when designing plate-fin and tube heat exchangers, only the average value of the heat transfer coefficient (HTC) is considered. However, each row of the heat exchanger (HEX) has different hydraulic–thermal characteristics. When the air velocity upstream of the HEX is lower than approximately 3 m/s, the exchanged heat flow rates at the first rows of tubes are higher than the average value for the entire HEX. The heat flow rate transferred in the first rows of tubes can reach up to 65% of the heat output of the entire exchanger. This article presents the method of determination of the individual correlations for the air-side Nusselt numbers on each row of tubes for a four-row finned HEX with continuous flat fins and round tubes in a staggered tube layout. The method was built based on CFD modelling using the numerical model of the designed HEX. Mass average temperatures for each row were simulated for over a dozen different airflow velocities from 0.3 m/s to 2.5 m/s. The correlations for the air-side Nusselt number on individual rows of tubes were determined using the least-squares method with a 95% confidence interval. The obtained correlations for the air-side Nusselt number on individual rows of tubes will enable the selection of the optimum number of tube rows for a given heat output of the HEX. The investment costs of the HEX can be reduced by decreasing the tube row number. Moreover, the operating costs of the HEX can also be lowered, as the air pressure losses on the HEX will be lower, which in turn enables the reduction in the air fan power.


Energies ◽  
2021 ◽  
Vol 14 (21) ◽  
pp. 6990
Author(s):  
Hassam ur Rehman ◽  
Jan Diriken ◽  
Ala Hasan ◽  
Stijn Verbeke ◽  
Francesco Reda

Buildings and the mobility sectors are the two sectors that currently utilize large amount of fossil-based energy. The aim of the paper is to, critically analyse the integration of electric vehicles (EV) energy load with the building’s energy load. The qualitative and quantitative methods are used to analyse the nearly/net zero energy buildings and the mobility plans of the Europe along with the challenges of the plans. It is proposed to either include or exclude the EV load within the building’s energy load and follow the emissions calculation path, rather than energy calculation path for buildings to identify the benefits. Two real case studies in a central European climate are used to analysis the energy performance of the building with and without EV load integration and the emissions produced due to their interaction. It is shown that by replacing fossil-fuel cars with EVs within the building boundary, overall emissions can be reduced by 11–35% depending on the case study. However, the energy demand increased by 27–95% when the EV load was added with the building load. Hence, the goal to reach the nearly/net zero energy building target becomes more challenging. Therefore, the emission path can present the benefits of EV and building load integration.


Energies ◽  
2021 ◽  
Vol 14 (21) ◽  
pp. 6994
Author(s):  
Alberto Carotenuto ◽  
Francesca Ceglia ◽  
Elisa Marrasso ◽  
Maurizio Sasso ◽  
Laura Vanoli

The highest economic costs of a geothermal plant are basically related to well drilling and heat exchanger maintenance cost due to the chemical aggressiveness of geothermal fluid. The possibility to reduce these costs represents an opportunity to push toward geothermal plants development. Such challenges are even more important in the sites with a low-medium temperature geothermal fluids (90–120 °C) availability, where the use of these fluids for direct thermal uses can be very advantageous. For this reason, in this study, a direct geothermal heating system for a building will be investigated by considering a plastic plate heat exchanger. The choice of a polymeric heat exchanger for this application is upheld by its lower purchase cost and its higher fouling resistance than the common metal heat exchangers, overcoming the economic issues related to conventional geothermal plant. Thus, the plastic plate heat exchanger was, firstly, geometrical and thermodynamical modeled and, after, exergoeconomic optimized. In particular, an exergoeconomic analysis was assessed on the heat exchanger system by using a MATLAB and REFPROP environment, that allows for determination of the exergoeconomic costs of the geothermal fluid extraction, the heat exchanger, and the heating production. A sensitivity analysis was performed to evaluate the effect of main design variable (number of plates/channels) and thermodynamic variable (inlet temperature of geothermal fluid) on yearly exergoeconomic product cost. Then, the proposed methodology was applied to a case study in South of Italy, where a low-medium enthalpy geothermal potential exists. The plate-heat exchanger was used to meet the space heating requests of a single building by the exploitation of low-medium temperature geothermal fluids availability in the selected area. The results show that the inlet temperature of geothermal fluid influences the exergoeconomic cost more than the geometrical parameter. The variation of the exergoeconomic cost of heat exchanger with the inlet geothermal fluid temperature is higher than the change of the exergoeconomic costs associated to wells drilling and pumping with respect to the same variable. This is due the fact that, in the selected zone of South of Italy, it is possible to find geothermal fluid in the temperature range of 90–120 °C, at shallow depth. The product exergoeconomic cost is the lowest when the temperature is higher than 105 °C; thus, the smallest heat exchange area is required. The exergoeconomic optimization determines an optimum solution with a total product cost of 922 €/y for a temperature of geothermal fluid equal to 117 °C and with a number of plates equal to 15.


Energies ◽  
2021 ◽  
Vol 14 (21) ◽  
pp. 6996
Author(s):  
Ali Faisal Murtaza ◽  
Hadeed Ahmed Sher ◽  
Filippo Spertino ◽  
Alessandro Ciocia ◽  
Abdullah M. Noman ◽  
...  

A novel maximum power point tracking (MPPT) technique based on mutual coordination of two photovoltaic (PV) modules/arrays has been proposed for distributed PV (DPV) systems. The proposed technique works in two stages. Under non-mismatch conditions between PV modules/arrays, superior performance stage 1 is active, which rectifies the issues inherited by the perturb and observe (P&O) MPPT. In this stage, the technique revolves around the perturb and observe (P&O) algorithm containing an intelligent mechanism of leader and follower between two arrays. In shading conditions, stage 2 is on, and it works like conventional P&O. Graphical analysis of the proposed technique has been presented under different weather conditions. Simulations of different algorithms have been performed in Matlab/Simulink. Simulation results of the proposed technique compliment the graphical analysis and show a superior performance and a fast response as compared to others, thus increasing the efficiency of distributed PV systems.


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