Energy-efficient Power Research Articles

Performance evaluation of an integrated photovoltaic module and cascading thermally regenerative electrochemical devices system

To capture the broadband sunlight, a novel coupled system composed of a photovoltaic module (PVM), the thermally regenerative electrochemical cycles (TRECs), and the thermally regenerative electrochemical refrigerators (TRERs) is proposed. The short-wave sunlight is sent to PVM to generate electricity, while the relatively long-wave sunlight (larger than 920 nm) is provided to the TRECs-TRERs for additional refrigeration. Considering the main irreversible dissipation in the cogeneration model, the expressions for the performance indexes of the combined model are deduced. Moreover, the numerical correlation between the PVM operating current and the TRECs-TRERs current is also derived. The mathematical results illustrate that the maximum energy efficiency (MEE) and maximum power density (MPD) of PVM are, respectively, 19.36% and 193.57Wm-2, and the MEE and MPD of the cogeneration system are, respectively, improved by 24.64% and 26.03% compared to a single PVM. Comprehensive parametric analyses are conducted for figuring out the dependences of the established model performance on main significant parameters as well as operating conditions, including solar irradiance, PVM operating temperature, diode ideality factor, specific charge capacity, regenerative efficiency, specific heat capacity, and internal resistance of TREC and TRER. This study results may supply some new ideas for designing and optimizing such actual coupled systems.

Energy and exergy analysis of an integrated photovoltaic module and two-stage thermoelectric generator system

To fully utilize the solar energy captured by the photovoltaic module (PVM) and improve its performance, a coupled system consisting of a PVM, the solar selective absorber (SSA) and the two-stage thermoelectric generator (TTEG) is investigated, where the TTEG considers the Peltier effect, Seebeck effect and Thomson effect. Taking account of the various irreversible losses within the coupled system, the mathematical expressions of energy conversion efficiency, power output, exergy efficiency and exergy destruction rate of the coupled system are established. The numerical results show that the maximum energy efficiency and maximum output power of the coupled system are, respectively, increased by 9.89% and 9.87% compared with a standalone PVM, and the maximum exergy efficiency is 10.4% higher than a standalone PVM. Finally, through sensitivity analysis, it can be seen that the coupled system is affected by several key parameters, including the diode ideality factor, thermoelectric elements, solar irradiance, and PVM operating temperature, so the coupled system can be improved by adjusting these parameters. The results of this paper may provide a new insight into the design and optimization of an actual coupled system.

Atomic-scale investigation of implanted Mg in GaN through ultra-high-pressure annealing

An area selective doping via ion implantation is a key technology to realize gallium nitride (GaN) based energy-efficient power devices; however, conventional annealing leads to the formation of numerous Mg-enriched defects, which result in inefficient p-type activation. The recent invention of ultra-high-pressure annealing (UHPA) has enabled a significant improvement in p-type activation efficiency. In this study, we investigated the formation of Mg-enriched defects in Mg implanted GaN followed by annealing under either conventional atmospheric pressure or ultra-high-pressure. Unlike the conventional annealing, UHPA leads to a much lower number density of Mg-enriched defects. Correlative scanning transmission electron microscopy, atom probe tomography, cathodoluminescence, and secondary ion mass spectrometry analyses have shown that the number density of Mg-enriched defects is substantially suppressed by the UHPA. The dissolved Mg concentrations in the GaN matrix for both the conventional and the UHPA samples are almost of the same value, approximately 2 × 1018 cm−3; however, the UHPA sample shows over one order of magnitude stronger intensity of donor–acceptor-pair emission than the conventional one. Thus, the implanted Mg is effectively activated as acceptors through the UHPA technique.

Development of Charging/Discharging Scheduling Algorithm for Economical and Energy-Efficient Operation of Multi-EV Charging Station

As the number of electric vehicles (EVs) significantly increases, the excessive charging demand of parked EVs in the charging station may incur an instability problem to the electricity network during peak hours. For the charging station to take a microgrid (MG) structure, an economical and energy-efficient power management scheme is required for the power provision of EVs while considering the local load demand of the MG. For these purposes, this study presents the power management scheme of interdependent MG and EV fleets aided by a novel EV charging/discharging scheduling algorithm. In this algorithm, the maximum amount of discharging power from parked EVs is determined based on the difference between local load demand and photovoltaic (PV) power production to alleviate imbalances occurred between them. For the power management of the MG with charging/discharging scheduling of parked EVs in the PV-based charging station, multi-objective optimization is performed to minimize the operating cost and grid dependency. In addition, the proposed scheme maximizes the utilization of EV charging/discharging while satisfying the charging requirements of parked EVs. Moreover, a more economical and energy-efficient PV-based charging station is established using the future trends of local load demand and PV power production predicted by a gated recurrent unit (GRU) network. With the proposed EV charging/discharging scheduling algorithm, the operating cost of PV-based charging station is decreased by 167.71% and 28.85% compared with the EV charging scheduling algorithm and the conventional EV charging/discharging scheduling algorithm, respectively. It is obvious that the economical and energy-efficient operation of PV-based charging station can be accomplished by applying the power management scheme with the proposed EV charging/discharging scheduling strategy.

Cell-Free Massive MIMO for Massive Low-Power Internet of Things Networks

In this article, we consider the application of a cell-free (CF) massive multiple-input–multiple-output (MIMO) system to low-power Internet of Things (IoT) networks. CF Massive MIMO distributes many access points (APs) in a given area and supports many IoT devices simultaneously using the same time and frequency resources. To support many IoT devices that have more than the number of service antennas within limited coherence time/frequency, the reference signal (RS) should be reused. Generally, CF Massive MIMO with massive connectivity requires a lot of power and, thus, it is difficult to use in low-power IoT networks. In this regard, we propose an energy-efficient (EE) power control scheme that can significantly reduce the radiation power of IoT devices. We note that with many IoT devices, there is a quite large amount of interference, and if we choose the radiation power based on this information, the signal-to-interference-plus-noise ratio (SINR) becomes approximately independent of the radiation power. We show that our scheme can reduce the radiation power more than 90% compared to the normal operation. We also show that with many IoT devices, there is a spectral efficiency hardening effect, and maximum ratio (MR) processing and minimum mean square error (MMSE) processing present similar performance and, thus, MR processing could be sufficient for the use in CF Massive MIMO with massive IoT connectivity.

IoT based energy efficient multipath power control for underwater sensor network

IoT based energy efficient multipath power control for underwater sensor network

An Energy-Efficient Power Allocation Scheme for NOMA-Based IoT Sensor Networks in 6G

Non-orthogonal multiple access (NOMA) is an upcoming technique to boost the capacity of visible light communication (VLC) systems which is otherwise limited by the slow modulation response of light-emitting diode (LED) sources used therein. We propose to enhance the energy efficiency of NOMA-based VLC systems, thereby making them suitable for green Internet of things (IoT) in the sixth generation (6G) networks. The proposed energy-efficient power allocation (EPA) scheme reduces the average bit error rate (ABER) and augments the system’s energy efficiency as well as its capacity and fairness. However, at high values of transmitted power, there is a trade-off between energy efficiency and ABER. We define and evaluate the energy utilization factor to study this trade-off and show that the EPA scheme has superior energy utilization than the state-of-the-art power allocation schemes. Moreover, its performance does not deteriorate appreciably when the number of connected users (or sensor nodes) is increased. Based on numerical and simulation results, we deduce that the proposed EPA scheme meets the requirements of green IoT systems in 6G networks.

Energy-efficient power scheduling and allocation scheme for wireless sensor networks

The focus in this paper is on coverage energy-efficient of WSN (wireless sensor networks). Communication path lengths of a randomly distributed BSs and sensor nodes field are characterized by distance distributions. For sensor nodes, this paper will use theory of Poisson point process (PPP) and Boolean Model (BM) to purpose a power allocation scheme results in green communication of sensor nodes. The energy allocation scheme of wireless sensor networks can help to prolong the life of the whole network. In this paper, we prove that the scheduling and allocation scheme can achieve energy saving, so as to prolong the life cycle of the whole wireless sensor networks. In the uniform placement migration case, we simulation 1000 times. In Boolean Model, There is 71.3% for power scheduling and allocation schemes and 28.7% is not. From these results, we see that, in wireless sensor networks, 20%–30% of total energy, which was being consumed from the part of power scheduling and allocation. The scheduling scheme improves response time, throughput and overall energy consumption over base case. Compared with other allocation schemes, the advantage of the scheme proposed in this paper is that the less sensors selected can still provide more than 95% detection area coverage. It will enable robust communication against cross-tier interference and co-layer interference thereby obtaining a substantial improvement in link quality.

Energy efficient scheduling and power control of massive MIMO in massive IoT networks

We present various energy efficient (EE) scheduling and power control schemes for Massive MIMO with massive Internet of Things (IoT) connectivity. To support massive IoT devices simultaneously with low latency, the reference signal (RS) is heavily reused. To increase the performance, we reorganize the distributed IoT devices in ascending and in descending orders. We show that the spectral efficiency (SE) is improved based on water-filling effect. Next, we show that a generalized power control scheme is quite effective in increasing the fairness. Nevertheless, it requires a lot of power which is not fitted to low power IoT networks. Based on these facts, we propose sigmoid function based power allocation schemes to compromise between SE/EE performance and the fairness. Numerical results verify that the proposed scheme can achieve arbitrary SE/EE performance tradeoff with satisfactory fairness.

Simulators for Designing Energy-Efficient Power Supplies Based on Solar Panels

Boosted interest in highly efficient power supplies based on renewables requires involving simulators during both the designing stage and the testing one. It is especially relevant for the power supplies that operate in the harsh environmental conditions of northern territories and alike. Modern solar panels based on polycrystalline Si and GaAs possess relatively high efficiency and energy output. To save designing time and cost, system developers use simulators for the solar panels coupled with the power converters that stabilize the output parameters and ensure the proper output power quality to supply autonomous objects: namely, private houses, small-power (up to 10 kW) industrial buildings, submersible pumps, and other equipment. It is crucial for the simulator to provide a valid solar panel I-V curve in various modes and under different ambient conditions: namely, the consumed power rating, temperature, solar irradiation, etc. This paper considers a solar panel simulator topology representing one of the state-of-the-art solutions. This solution is based on principles of classical control theory involving a pulse buck converter as an object of control. A mathematical model of the converter was developed. Its realization in MATLAB/Simulink confirmed the adequacy and applicability of both discrete and continuous forms of the model during the design stage. Families of I-V curves for a commercially available solar panel within the temperature range from −40 to +25 ∘C were simulated on the model. A prototype of the designed simulator has shown its correspondence to the model in Simulink. The developed simulator allows providing a full-scale simulation of solar panels in various operating modes with the maximum value of the open circuit voltage 60 V and that of the short circuit current 60 A. Issues of statistical processing of experimental data and cognitive visualization of the obtained curves involving the cognitive graphic tool 2-simplex have also been considered within the framework of this research. The simulator designed may serve as a basis for developing a product line of energy-efficient power supplies for autonomous objects based on renewables, including those operating in northern territories.

Effects of porosity variation in different linear and combination modes in the electrode on the performance of all‑vanadium flow battery

To improve the performance of all‑vanadium flow battery, the electrode porosity is arranged in different linear variations and combination forms, in which the electrolyte flow in the electrode, polarization characteristics, system efficiency (SE), energy efficiency (EE) and dissipative power ratio (DPR) are investigated among the sixteen combined electrodes with the porosity variation in range of ε = 0.9–0.5 and inlet velocity of Q = 10 ml/min in simulations. A novel electrode with the variable porosity in the diagonal direction along flow channel is developed to favor the permeation of electrolyte in the porous electrode. The change amplitude and offset of activation overpotential at 50% state of charge (SOC) are related to the porosity variation in electrode, and the lower concentration overpotential occurs in the area with larger porosity due to more electrolyte supply for the electrochemical reactions under lower permeation resistance. The Kirchhoff's Current law (KCL) in equivalent circuit model is employed to analyze the capacity variation with different porosity combinations in the electrode accounting for the effective capacity ratio of electrode in the consideration of porosity gap at the junction. The 66.9% system efficiency and 16.2% dissipative power ratio occur in the mode with combined electrode of horizontal linear increasing porosity and vertical linear increasing porosity, in which the higher system efficiency and lower dissipative power ratio can be obtained than those of other mentioned modes.

Modulation of Schottky barrier in XSi2N4/graphene (X = Mo and W) heterojunctions by biaxial strain

Reducing the Schottky barrier height (SBH) and even achieving the transition from Schottky contacts to Ohmic contacts are key challenges of achieving high energy efficiency and high-performance power devices. In this paper, the modulation effects of biaxial strain on the electronic properties and Schottky barrier of MoSi2N4 (MSN)/graphene and WSi2N4 (WSN)/graphene heterojunctions are examined by using first principles calculations. After the construction of heterojunctions, the electronic structures of MSN, WSN, and graphene are well preserved. Herein, we show that by applying suitable external strain to a heterojunction stacked by MSN or WSN — an emerging two-dimensional (2D) semiconductor family with excellent mechanical properties — and graphene, the heterojunction can be transformed from Schottky p-type contacts into n-type contacts, even highly efficient Ohmic contacts, making it of critical importance to unleash the tremendous potentials of graphene-based van der Waals (vdW) heterojunctions. Not only are these findings invaluable for designing high-performance graphene-based electronic devices, but also they provide an effective route to realizing dynamic switching either between n-type and p-type Schottky contacts, or between Schottky contacts and Ohmic contacts.

Hybrid Fuzzy-PI and ANFIS Controller Design for Rotor Current Control of DFIG Based Wind Turbine

Wind energy generation provides one of the best and economical solution to the growing power demand. Doubly Fed induction generator is one of the most important variable speed wind generators. Integrating advanced controllers improves its performance and efficiency. The purpose of this research work is to optimize the wind energy conversion and efficient wind power extraction by controlling rotor current. Four controllers that are PI, Fuzzy, Hybrid Fuzzy-PI and Neural network based Adaptive Neuro Fuzzy controller are designed and implemented on DFIG. Controllers’ performance is assessed in terms of transients in rotor current i.e., percentage overshoot, settling time and steady state error under varying wind speed operation. Comparison of the results demonstrates that Adaptive Neuro Fuzzy controller outperforms as compared to that of Hybrid Fuzzy-PI, Fuzzy and conventional PI regarding transient response and maximum power extraction efficiency.

A Novel STT–SOT MTJ-Based Nonvolatile SRAM for Power Gating Applications

This article proposes novel nonvolatile (NV) static random access memory (SRAM) circuits based on spin transfer torque (STT) and spin orbit torque (SOT) operated magnetic tunnel junction (MTJ) device for energy-efficient power gating circuits. In which, two different designs of 9T-2MTJs and 10T-2MTJ-based NV SRAM circuits are proposed for low power, high noise margin, and faster switching speed with less area overhead. The proposed architecture uses a smaller number of transistor combinations to accommodate low-power operation with compact cell size when compared with available pieces of literature. Also, the combination of nMOS and pMOS transistors in the proposed architecture enhances the driving capability of the circuit for both low and high input operations. Here, the electrical characteristics of the proposed designs have been compared and contrasted with the available 11T-2MTJ and 7T-2D-2MTJ non volatile static random access memory (NVSRAM) and 6T SRAM circuits using a UMC-40 nm design kit and physics-based STT–SOT MTJ Verilog-A Model. The proposed 9T-2MTJ-based NVSRAM was found to be a better alternative and offers improved performance in terms of higher restore noise margin and lower power consumption than other circuits reported at this node. Moreover, the studied 10T-2MTJ exhibits an improved write and hold noise margin than the proposed/available 9T/7T-2D/11T-2MTJ circuits.

A sustainable concept for permafrost thermal stabilization

Although permafrost thermal stabilization systems have been used for a long time already, they have always had shortcomings and limitations of performance which have become even more pronounced in the warming climate. Those could be overcome to some extent, but at high cost mainly defined by need in energy supply. We have suggested a novel concept combining improved energy efficiency and solar power to ensure significant reduction of the thawing layer (to 20 cm order). We have performed calculations for the broad range of permafrost conditions to compare traditional methods for thermal stabilization and their combination to the suggested concept. The latter only has ensured minimum thawing layer over summer even at the southern edge of permafrost extent. The importance of minimum thawing layer is discussed in terms of chemical and biological safety in the area of human activities. The layout for glaciers protection has also been considered. Estimated cost of the concept implementation (ca. 180$/m2) is just slightly higher than for widely used thermosyphons while providing much better technical performance and unique possibilities for revenue by selling (not wasting) heat and excessive electricity up to 70$/(m2yr).

Forming a Two-Tier Heterogeneous Air-Network via Combination of High and Low Altitude Platforms

In this paper, an aerial heterogeneous wireless network consists of a high altitude platform (HAP) and low altitude platforms (LAPs) as aerial base stations (ABSs) in a downlink orthogonal division multiple access (OFDMA) transmission is investigated. Two types of spectrum sharing, including spectrum underlay access (SUA) and spectrum overlay access (SOA) are employed to evaluate the inter-tier interference. Distributed problem formulation and solving method are used to reduce the computational complexity, communication overhead and system latency. Subcarrier assignment and power allocation in spectral efficiency (SE), energy efficiency (EE) and transmission power optimization problems are accomplished by the proposed two-layer algorithm. In the proposed algorithm, first, subcarrier assignment based on constraints of the optimization problems is carried out to cover both SUA and SOA with low computational complexity. Second, the proposed algorithm performs power allocation. The simulation results show the relation between spectrum reuse and inter-tier interference, such that system SE, EE and the number of served users are maximized when both spectrum reuse and inter-tier interference management are performed together.

Energy Efficient Power Allocation for Cell-Free mmWave Massive MIMO With Hybrid Precoder

This letter investigates the downlink of a cell-free millimeter wave (mmWave) massive multiple-input multiple-output (mMIMO) system, where many access points (APs) cooperatively serve a user. Although the intensive deployment of APs can dramatically improve the system capacity, it also increases the network energy consumption substantially. To track the non-concave global energy-efficiency (GEE) optimization problem, we decompose it into hybrid precoder design and power allocation design. A novel dynamic subarray with quantized phase shifters (DS-QPS) hybrid precoder is introduced, where each radio frequency (RF) chain only connects to a disjointed subset of antennas. The optimization problem of the number of RF chains is formulated as an eigenvalue maximization problem considering a realistic power consumption model. For power allocation, a new centralized framework is exploited to solve a sequence of simpler power allocation subproblems while still aiming at the GEE maximization by merging with fractional programming, non-cooperative game theory, and gradient-assisted binary search (GABS) algorithm. Simulations show that the joint design is more energy-efficient than the baselines.

Mechanism study and evaluation of high efficiency paper-based microfluidic fuel cell coupled with capillary force

Under the dual pressure of energy consumption and environmental pollution, mankind hopes to develop clean and renewable alternative energy, and the rapid development of fuel cells meets people's demand for energy-efficient power systems. The emergence of portable micro energy systems represented by microfluidic fuel cells, such as paper-based microfluidic fuel cells, has greatly enriched the means of medical detection to better cope with the threat of disease transmission. In this work, the numerical simulation method is innovatively introduced to study the paper-based microfluidic fuel cells. Both transient and steady-state modes are employed to demonstrate the whole operation process of the paper-based microfluidic fuel cell. In addition, the different structural parameters, including electrode spacing, the distance between electrode and inlet, channel thickness, and electrode length, are also investigated their influence mechanisms on cell performance. Results show that the increase of most structural parameters decreases cell output power in different degrees. Even on the premise that increasing channel thickness has a positive impact on the output power, the fuel utilization still shows a downward trend. These conclusions provide theoretical support and reference for future optimization work and accelerate the development of microfluidic fuel cells.

Thermodynamic Modeling and Performance Analysis of Vehicular High-Temperature Proton Exchange Membrane Fuel Cell System.

Since the high temperature proton exchange membrane fuel cells (HT-PEMFC) stack require a range of auxiliary equipments to maintain operating conditions, it is necessary to consider operation of related components in the design of HT-PEMFC systems. In this paper, a thermodynamic model of a vehicular HT-PEMFC system using phosphoric acid doped polybenzimidazole membrane is developed. The power distribution and exergy loss of each component are derived according to thermodynamic analysis, where the stack and heat exchanger are the two components with the greatest exergy loss. In addition, ecological functions and improvement potentials are proposed to evaluate the system performance better. On this basis, the effects of stack inlet temperature, pressure, and stoichiometric on system performance are analyzed. The results showed that the energy efficiency, exergy efficiency and net output power of the system achieved the maximum when the inlet gases temperature is 406.1 K. The system performance is better when the cathode inlet pressure is relatively low and the anode inlet pressure is relatively high. Moreover, the stoichiometry should be reduced to improve the system output performance on the basis of ensuring sufficient gases reaction in the stack.

Integrated approach for the estimation of regional low carbon potential: Application for Ho Chi Minh City, Viet Nam

Currently, multidisciplinary integrated and quantitative methodologies are necessary for policymakers in deciding a reasonable and acceptable target of greenhouse gas (GHG) reduction as well as realization of mitigation actions. Therefore, this study aims to develop an integrated methodology to harmonize the top-down and bottom-up approaches to support the development of low carbon actions at the regional or city level based on their energy-saving programs and technology status. This integrated approach is necessary to bridge the theoretical and empirical frontiers of modeling in quantifying and analyzing the feasibility of the local police framework and international cooperation in terms of climate mitigation projects. The top-down approach uses the Extended Snapshot (ExSS) tool to estimate GHG emissions and reduction potential based on macro socioeconomic information. Meanwhile, the technology-based bottom-up approach is a method to estimate the reduction potential of GHG emissions by accumulating specific energy-saving projects. Parameters related to energy service demand, energy efficiency, energy share, and dispersed power generation are harmonized in the integration process via a set of equations. Under the assumption of socioeconomic growth of Ho Chi Minh City (HCMC), which is a 1.37 times increase for population and a 4.41 times increase for GDP growth in 2030 compared to 2013, the total energy consumption will increase 3.73 times compared to 2013, which is nearly 26 million toe (Mtoe) in 2030. The total GHG emissions will also increase 4.02 times, reaching nearly 117.2 MtCO2eq if HCMC does not consider any climate change mitigation actions. However, if HCMC successfully implements the mitigation projects discussed and quantified in this study, the total GHG emissions might be lower, approximately 85.6 MtCO2eq. Analysis of the results from the two scenarios (BaU and CCAP) shows that the energy saving potential is approximately 15.0% and that the total GHG emissions reduction potential of HCMC (excluding the potential from grid power, which is outside the effort of HCMC) is 20.7% of BaU’s emissions, which is between the 8-25% reduction target of Vietnam intended nationally determined contribution. By looking at the disaggregation of reduction potential by each sector and project, policymakers can prioritize mitigation measures to meet the GHG emissions reduction target or to maximize GHG emissions reduction potential. The integrated approach requires the consistency between classifications in top-down (driving force based) and bottom-up (technology based) approaches as well as the modification and bridging of the top-down sectors and the bottom-up categories with detailed data. This method is very applicable for cities or regions that are developing climate change action plans with precise technological information.