Off-grid Condition Research Articles

A High-Resolution Time Reversal Method for Target Localization in Reverberant Environments

Reverberation in real environments is an important factor affecting the high resolution of target sound source localization (SSL) methods. Broadband low-frequency signals are common in real environments. This study focuses on the localization of this type of signal in reverberant environments. Because the time reversal (TR) method can overcome multipath effects and realize adaptive focusing, it is particularly suitable for SSL in a reverberant environment. On the basis of the significant advantages of the sparse Bayesian learning algorithm in the estimation of wave direction, a novel SSL is proposed in reverberant environments. First, the sound propagation model in a reverberant environment is studied and the TR focusing signal is obtained. We then use the sparse Bayesian framework to locate the broadband low-frequency sound source. To validate the effectiveness of the proposed method for broadband low-frequency targeting in a reverberant environment, simulations and real data experiments were performed. The localization performance under different bandwidths, different numbers of microphones, signal-to-noise ratios, reverberation times, and off-grid conditions was studied in the simulation experiments. The practical experiment was conducted in a reverberation chamber. Simulation and experimental results indicate that the proposed method can achieve satisfactory spatial resolution in reverberant environments and is robust.

Photocatalytic degradation of paracetamol on immobilized TiO2 in a low-tech reactor by solar light for water treatment

Photocatalytic water treatment is an appealing concept to mineralize organic contaminants in contaminated water. In this study, the UV-resistant drug paracetamol (PCT) in aqueous solution is degraded by using a solar irradiated loop-reactor equipped with a TiO2 (P25) photocatalyst. The catalyst powder was dispersed in a geopolymer surface coating applied to aluminum-U-profiles connected by filament-printed polymer elements. Different assays with variations in initial PCT concentration were performed under natural solar radiation to determine the degradation kinetics of the PCT and correlate it to applied solar radiation energy density. Depending on experimental conditions, degradation efficiencies of 37.0–75.1 % were achieved within 3 h. Control samples without catalyst show no degradation. No degradation of the catalyst activity was observed within 42 h of operation time. The study shows the feasibility of this simple and scalable reactor design and coating technology for water purification under off-grid conditions provided sufficient solar radiation is available.

Development and assessment of a solar-driven charging station integrated with liquid CO2 as an energy storage option

It is expected that there will soon be a substantial increase in the number of charging stations developed and built in the near future due to a drastic increase in the number of electric vehicles. Charging stations pose a major concern for the grid because of the additional load they will generate. The development of self-sufficient and renewable-powered charging stations is therefore essential. This study develops a novel solar-powered charging station that integrates liquid CO2 as an energy storage option for dedicated off-grid conditions. Solar energy is captured and stored by converting gaseous CO2 into liquid to operate the system without requiring grid power. The stored liquid CO2 is then expanded via turbine for power generation when solar power is unavailable or insufficient to meet demand. We investigate the effects of utilizing yearly dynamic solar data and yearly average solar data on estimating off-grid conditions and system performance. Based on the results, it appears that using yearly averages can lead to an error of 37 % in estimating the solar PV area to be allocated for off-grid conditions. The total area of PV panels is found to be 100,723 m2, and it results in 63,938 m2 for the cases when yearly dynamic and yearly average solar data are used. The overall energy and exergy efficiencies of the developed systems are further calculated to be 0.062 and 0.066, respectively.

Techno-economic analysis of optimal hybrid renewable energy systems – A case study for a campus microgrid

People are becoming more aware of the benefits of renewable energy. In recent years, a lot of research deals with the use of energy systems during on-grid or off-grid conditions, however, grid-connected systems may cause a power crisis to the grid. With the addition of renewable components, it is hard for the grid to keep balance. In hybrid systems, contradiction between net present cost (NPC) and excess electricity, unmet load, and capacity shortage always appears. Excess electricity, unmet load, and capacity shortage appear when the demand and supply are unbalanced, indicating the underutilization of energy. In this paper, we aim to overcome the aforementioned contradiction by conducting a case study for the first time on the implementation of a Hybrid Renewable Energy System (HRES) for a university campus in Selangor, Malaysia. Four different designs of HRES are proposed and compared. They are the Wind-Biogas-Battery System (Design A), Wind-Biogas-PV-Battery System (Design B), Wind-Biogas-Hydrogen Module-Battery System (Design C), Wind-Biogas-Diesel Generator-Battery System (Design D). The most optimal system will be selected based on the evaluation of three main criteria, i.e., cost analysis, electricity production analysis, and gas emission analysis.

Research on the control strategy of interlinking converters for photovoltaic storage hybrid microgrid

This article mainly solves the problem of accurate power distribution and stable running in the photovoltaic storage hybrid microgrid and studies different control strategies of the interlinking converter connected to the AC-DC subnet under on-grid and off-grid conditions. The relationship between DC-side voltage, active power and active current is analyzed in the on-grid, and the DC voltage stability is supported by using a closed-loop voltage and current; in the off-grid mode, an improved bidirectional sag control method based on unitization processing is adopted, in which the power to be transmitted by the converter is differed from the actual value as the reference input of the current loop on the traditional double sag control, which can coordinate the power transmission between subgrids more precisely; And the action threshold is designed for the problem of repeated switching of converter operating modes. The results of simulation show that the converter able effectively to judge the magnitude and power direction in both parallel and off-grid operation modes, which ensures the normal operation of the important loads inside the subnets on both sides, thus verifying the feasibility of the control method.

Techno-economic assessment on hybrid energy storage systems comprising hydrogen and batteries: A case study in Belgium

This paper introduces a Techno-Economic Assessment (TEA) on present and future scenarios of different energy storage technologies comprising hydrogen and batteries: Battery Energy Storage System (BESS), Hydrogen Energy Storage System (H2ESS), and Hybrid Energy Storage System (HESS). These three configurations were assessed for different time horizons: 2019, 2022 and 2030, under both on-grid and off-grid conditions. For 2030, a sensitivity analysis under different energy scenarios was performed, covering other trends in on-grid electric consumption and prices, CO2 taxation and the evolution of hydrogen technology prices from 2019 until 2030. The selected case study is the Research Park Zellik (RPZ), a CO2-neutral sustainable Local Energy Community (LEC) in Zellik, Belgium. The software HOMER (Hybrid Optimisation Model for Electric Renewable) has been selected to design, model and optimise the defined case study. The results showed that BESS was the most competitive when the electric grid was available among the three possible storage options. Additionally, HESS was overall more competitive than H2ESS-only, regardless of the grid connection mode. Finally, as per HESS, hydrogen was proved to play a complementary role when combined with batteries, enhancing the flexibility of the microgrid and enabling deeper decarbonisation by reducing the electricity bought from the grid, increasing renewable energy production and balancing toward an island operating mode.

Technical and 2E Analysis of Hybrid Energy Generating System with Hydrogen Production for SRM IST Delhi-NCR Campus

This work intends to perform technical and 2E (economic & environmental) analysis for the proposed hybrid energy generating system for a part load at SRM IST at the Delhi-NCR campus, India. The investigation has been done for electricity generation and hydrogen production through renewable energy sources, mainly solar energy. It is in line with the Indian Government’s initiatives. The proposed hybrid system has to meet the electric load demand of 400 kWh/day with a peak load of 74.27 kW and hydrogen load demand of 10 kg/day with a peak demand of 1.86 kg/h. The analysis has been performed for both on-grid and off-grid conditions. As a result, optimum results have been obtained off-grid condition, with $0.408 per kWh cost of energy, $16.6 per kg cost of hydrogen, low O&M cost ($21,955 per year), a high renewable fraction (99.8%), and low greenhouse emissions (247 kg/year). In addition, sensitivity analysis has been performed between—(1) the solar PV array size & the number of battery strings, with NPC, renewable fraction & CO2 emissions as sensitivity variables, and (2) reformer capacity & hydrogen tank capacity, with NPC as sensitivity variable.

Optimum Design of a Renewable-Based Integrated Energy System in Autonomous Mode for a Remote Hilly Location in Northeastern India

Integration of a grid with an under-developed remote hilly area faces various technical and geographical challenges. Thus, generation of power from renewable resources in off-grid conditions has become one of the most cost-effective and reliable solutions for such areas. The present research deals with the possible application of an integrated solar/hydro/biomass/battery-based system to generate power in autonomous mode for a remote hilly town of a northeastern Indian state. Four different cases of the integrated energy system (IES) were designed using the hybrid optimization model for electric renewable (HOMER Pro), examining the performance of each case. The best combination of the integrated system was chosen out of several cases depending upon the optimized solution that can meet the load demand of the proposed hilly town sustainably, reliably and continuously. The simulation results show that the integrated battery/biomass/hydro/solar-based system is the best optimized, cheapest and most suitable solution to generate renewable-based power for the specified location, having the lowest net present cost (NPC) of USD 644,183.70 with a levelized cost of energy (COE) of 0.1282 USD/kWh. Further, the result also indicates that the optimized configuration reduces the emission of CO2 gas in the environment compared to the battery/biomass/hydro system having the worst emission rate. A sensitivity study was also carried out with variation in load, hydro stream flow and solar irradiation, respectively that may largely affect the technical as well as economical aspect of an integrated energy system.

Evaluating the resilience benefits of marine energy in microgrids

Marine energy resources could promote clean energy and resilience of coastal and island microgrids, and thus, these applications are a key future market for marine energy development. To demonstrate these benefits, this paper illustrates how inclusion of wave resources into energy resilience solutions can improve overall grid efficiency and sustainability, as well as maintain electricity supply during grid outages. The paper describes a case study evaluation of the potential to add wave energy to the Moloka'i grid as Hawaii strives to meet a 100% clean energy target. The Microgrid Component Optimization for Resilience tool is used to simulate operation in off-grid conditions and size different combinations of wave, solar photovoltaic (PV), wind, storage, and fuel resources required to meet resilience objectives. This research investigates how including wave resources in a microgrid contributes to reducing or eliminating biofuel generation, producing a zero-greenhouse gas emission profile in the latter case, and avoiding the over-sizing of PV and battery systems to accommodate periods of unavailability or high demand. Insight from this paper supports the value proposition of wave resources for future markets and informs the relationship between marine generators and microgrids or isolated grids.

Distributed Generation Photovoltaic System Based on Fuzzy Logic

Abstract: Most of the Developing Countries in the world have facing the demand of unavoidable power demand. Due to this high demand, we facing the high-power losses and increase of the transmission lines. In our India we are totally based on the thermal & nuclear power plant and it’s also going to end in few Years. The continues power demand can cause reduction of the voltage levels and affect the system stability, that causes the failure in power system Network and make the transmission line in the stressed condition. In the current situation we going towards the renewable energy, and it’s gaining the attention around the globe. The renewable energy matches the load demand and full-fill it according to the load demand. To step in renewable energy, we have to study it carefully to avoid any unwanted issues occurs in the system and do not make it unstable. The main issue that faces by the consumers is, the solar system gets off during the main supply failure and the total load shifted on the Diesel generator. Due to this Diesel generator get more consumption of diesel and get heavily loaded. To avoid this Heavy load on Diesel Generator we have to use the solar plant during off-grid conditions with the help of smart synchronization between the photovoltaic system and Diesel Generator. Thus, the result of smart synchronization of Photovoltaic system and diesel generation, we get the less load on Diesel generator as compare to the photovoltaic system.

Smart conveyor roller system for self-powered product size identification in electrically off-grid condition via hybridization of triboelectric-electromagnetic generators

With the advent of Industry 4.0, the automation and digitalization of product transportation in factories have attracted much attention. In this paper, a fully stand-alone smart conveyor system based on the integration of triboelectric sensor (TES) and electromagnetic generator (EMG) for self-powered real-time monitoring and identification, called an IoTE conveyor system (Integration of TES and EMG assisted conveyor system), is proposed. In this system, the roller acts as the TES by simply modifying its surface. The roller with TES can generate the triboelectric signal, which contains relevant information about the transported product such as material, size, and movement speed. The generated triboelectric signal is collected, analyzed, and transmitted to the user device by the MCU, which includes a Bluetooth module. The EMG and mechanical power transmission elements are designed to harvest the rotational kinetic energy of the roller and supply the electric power required to operate the MCU. The product information is wirelessly transmitted to the smartphone of users by the Bluetooth module and is visually displayed in real-time. The potential of the proposed IoTE conveyor system in sensing, analyzing, and transmitting product information without the need for additional electric power supply is expected to serve as a cornerstone for the manufacturing industry to realize the development of net-zero smart factories.

AC unbalanced and DC load management in multi-bus residential microgrid integrated with hybrid capacity resources

This paper presents a control scheme including resources and load management in the residential DC microgrid. The DC microgrid is supported by fuel-cell, solar-cell and battery. The DC, AC single-phase and AC three-phase loads with 50 Hz frequency are integrated. The DC microgrid is connected to the external 60 Hz AC three-phase network. An efficient multi-bus topology is proposed for the microgrid and it is formed by various AC/DC buses to supply the loads and managing the resources. The main bus of system is a 470 V DC bus and it is connected to the external 440 V/60 Hz AC grid. The main DC bus supplies three LV, MV and HV DC buses with 100, 220, and 110–380 V, respectively. The HV DC bus produces a variable output DC voltage between 110 and 380 V in order to regulate the load power (i.e., motor speed). The MV DC bus is connected to 220 V/50 Hz AC single-phase loads. The connections between DC microgrid with AC loads and AC external gird are made by single-phase or three-phase inverters. The interface inverters between DC bus and AC loads are operated to control power, torque, speed, frequency and voltage of loads. The unbalanced AC loads are appropriately balanced by proper control of interface inverters. The resources and inverters are efficiently controlled to enable operation of residential building under both off-grid or grid-tied conditions. The coordination of fuel-cell, solar-cell and battery can supply a fixed 8 kW power to external grid and supply the internal loads under all outages and off-grid conditions. The simulations demonstrate that the proposed control realizes all the objectives including AC/DC load management, unbalanced load amendment, frequency adaptation, and off-grid operation.

Smart Conveyor Roller System for Self-Powered Product Size Identification in Electrically Off-Grid Condition Via Hybridization of Triboelectric-Electromagnetic Generators

Smart Conveyor Roller System for Self-Powered Product Size Identification in Electrically Off-Grid Condition Via Hybridization of Triboelectric-Electromagnetic Generators

Small-signal modeling and analysis of a three-phase virtual synchronous generator under off-grid condition

The current small-signal models of inverters that mimic synchronous generators usually use the steady-state equation of feeder line and load, and ignore the dynamic characteristics of voltage and current controller of inner loop. Thus, some important dynamics of the system will be omitted. To capture the dynamics more accurately, firstly, a small-signal model of a three-phase isolated inverter that mimics a synchronous generator was developed in this paper, and a comparison between the corresponding simulink model and the small-signal model was presented to validate the model correctness. Then, participation factor was calculated, which showed the relation between the state variables and eigenvalues. Based on the model, several root locus plots as a function of the system parameters was obtained. An individual eigenvalue sensitivity analysis of a certain eigenvalue close to the real axis disclosed different parameters’ contribution to the oscillation mode. Finally, a disturbance test with simulink model and the small-signal model under multiple sets of parameters was carried out and the results can accurately reflect the oscillation mode, which verified the correctness of the parameters effect on the conjugate eigenvalues.

Hybrid System Assessment in On-Grid and Off-Grid Conditions: A Technical and Economical Approach

Photovoltaic systems can strengthen the energy matrix aiming at energy sustainability, however, their intermittence, the availability time frame and seasonality effects are complicating aspects for the operation of these systems. To mitigate such problems, a possible measure is the operation of hybrid systems (HS) associated with storage systems to meet the energy demand. This study presents real operational scenarios for the management of a hybrid mini-grid installed in the Amazon region in Brazil, capable of managing energy supply and demand, changing the generation curve, reducing fossil fuel consumption and energy costs, in addition to providing flexibility and operational safety to the electrical operating under on-grid or off-grid conditions. Through technical and economic analyses, the objective of this study is to show that hybrid systems can be implemented in small and medium consumers, in addition to generating a new market option for utilities. This research evaluates the operation of HS concurrently with the electrical grid and the results show that the system meets the technical requirements, in addition to bringing financial and ecological benefits. This information can support the decisions of consumers, utilities and energy operators for the development of the national market for on-grid and off-grid HS.

Transient study of series-connected pumps working as turbines in off-grid systems

In the current world economic environment where reducing energy costs is a high priority, it is not surprising that sustainable water and energy management are key topics among the water and electric industry. Specifically, water suppliers, pump manufacturers, and operatives of small hydropower systems, all recognize that pumps working as turbines can be an efficient, simple, and economic approach to generating power and recover the excess of energy in water pressurized systems. In both, variable operating flow rate conditions (ex: presence of different water users) impose the need to augment the range of a proper pump as turbine system. One solution is to associate several pumps as turbines in series to increase the recovered energy. In that context, this work assesses their reliability at transient off-grid conditions by two pumps as turbines connected in series. Each one has an identical self-excited induction generator feeding a three-phase and balanced resistive load. Changes (increase/decrease in values) were applied to the resistive loads and the bank of capacitors at one group only, which allowed examining how changes affect the overall two-group system dynamics. Results show that one change in the first pump as turbine group will significantly affect the other group dynamics. For example, a decrease in load of the first group will affect the flow and head of the other system, until reaching a new equilibrium point. However, as both groups are not mechanically connected, they can achieve different equilibrium speeds. Furthermore, the highest impact occurred in the group where no changes were imposed. The first group maintained its global efficiency value, while the second had its efficiency decreased by about 8%. Similarly, an increase in the capacitance value caused a reduction in its efficiency (lesser but around 2%). Finally, a numerical model was developed and validated through experimental tests to be an applicable prediction model.

Techno-economic optimisation of stand-alone hybrid renewable energy systems for concurrently meeting electric and heating demand

Current power sector around the world is mostly dependent on unsustainable, environmentally hazardous non-renewable energy system. As such, a cost-effective and sustainable yet environmentally benign renewable energy system should be developed to meet the ever increasing energy demand. The hybrid renewable energy system generates a considerable amount of excess energy while meeting the reliable power in an off-grid condition. Research into the recovering excess energy from the stand-alone renewable energy resources to meet the residential heating demand gets less attention. The key objective of this research is to investigate the optimisation of hybrid renewable energy system using the excess energy generated by its own sources to satisfy the electric and thermal loads for a remote community. Hybrid optimization model for electric renewable software tool is used to examine the techno-economic feasibility of the hybrid energy system. The proposed system configuration consists of photovoltaic module, wind turbine, battery, thermal load controller, and gas boiler. An electric boiler utilizing the excess energy from renewable energy sources only is used as the thermal load controller to meet the thermal demand. A detailed comparison between the hybrid system meeting both electric and thermal, hybrid system meeting only electric load, and the diesel-only option has been investigated. Results of these analyses indicate that the optimised PV/Wind/Batt-based hybrid option offers a lower cost of energy (COE = 0.255 $/kWh) when the system meets the thermal load by using the thermal load controller and the gas boiler than without utilising excess energy (0.274 $/kWh). In addition, a substantial reduction of hardware components capacity and the associated net present cost can be achieved by utilising excess energy via thermal load controller and the gas boiler to meet the thermal demand than without using excess energy. Potential cost reduction and environmental benefits can be attained by the optimised PV/Wind/Batt-based hybrid system than that of the diesel generator-based option. Finally, the optimised system is compared with the results obtained using genetic algorithm to validate the findings of the hybrid optimization model for electric renewable software tool. The genetic algorithm optimisation technique shows that the proposed system is highly reliable (99.92 %) while meeting the electric and thermal demands.

Renewable Energy-Aware Sustainable Cellular Networks with Load Balancing and Energy-Sharing Technique

With the proliferation of cellular networks, the ubiquitous availability of new-generation multimedia devices, and their wide-ranging data applications, telecom network operators are increasingly deploying the number of cellular base stations (BSs) to deal with unprecedented service demand. The rapid and radical deployment of the cellular network significantly exerts energy consumption and carbon footprints to the atmosphere. The ultimate objective of this work is to develop a sustainable and environmentally-friendly cellular infrastructure through compelling utilization of the locally available renewable energy sources (RES) namely solar photovoltaic (PV), wind turbine (WT), and biomass generator (BG). This article addresses the key challenges of envisioning the hybrid solar PV/WT/BG powered macro BSs in Bangladesh considering the dynamic profile of the RES and traffic intensity in the tempo-spatial domain. The optimal system architecture and technical criteria of the proposed system are critically evaluated with the help of HOMER optimization software for both on-grid and off-grid conditions to downsize the electricity generation cost and waste outflows while ensuring the desired quality of experience (QoE) over 20 years duration. Besides, the green energy-sharing mechanism under the off-grid condition and the grid-tied condition has been critically analyzed for optimal use of green energy. Moreover, the heuristic algorithm of the load balancing technique among collocated BSs has been incorporated for elevating the throughput and energy efficiency (EE) as well. The spectral efficiency (SE), energy efficiency, and outage probability performance of the contemplated wireless network are substantially examined using Matlab based Monte–Carlo simulation under a wide range of network configurations. Simulation results reveal that the proper load balancing technique pledges zero outage probability with expected system performance whereas energy cooperation policy offers an attractive solution for developing green mobile communications employing better utilization of renewable energy under the proposed hybrid solar PV/WT/BG scheme.

Experimental tests to validate the simulation model of a Domestic Trigeneration Scheme with hybrid RESs and Desalting Techniques

Experimental tests of a small polygeneration plant unit based on hybrid renewable energy and desalination have been used to validate a novel model simulation of this plant. It provides electricity by coupling photovoltaic/thermal collectors and a micro-wind turbine, fresh water by means of hybrid desalination (membrane distillation, and reverse osmosis), and sanitary hot water coming from the photovoltaic/thermal collectors and an evacuated tubes collector. Plant was designed to operate in off-grid conditions and conventional energy storage systems were used (lead acid batteries and hot water tank). Simulation model was performed in TRNSYS environment and it was fully validated by comparing several key plant measurements. The analysis was focused on five typical days of summer, fall and winter. Some differences found in experimental and simulated values were analysed. To reduce those gaps, some modifications have been suggested to the model or the pilot unit respectively. As a result, a validated model in TRNSYS of the plant was obtained. This model can be used for the further scale up of new projects to cover any other scheduled demands of power and water in isolated areas, whenever is based on the combination of the abovementioned technologies.

A photovoltaic textile design with a stainless steel mesh fabric

Solar energy is one of the most popular energy sources among the other renewable energies. Photovoltaic technology is a clean way to generate electricity from sunlight. Flexible photovoltaics enable portable electronic devices to power at off-grid conditions. Stainless steel mesh fabric was used as a substrate and electrode allowing the light to reach the photoactive layer. The photoactive layer and hole transport layer were deposited by the means of dip-coating like in the textile industry. The metal back electrode was evaporated in a thermal evaporator under vacuum. Promising results were obtained from photovoltaic measurements. About 0.69% power conversion efficiency was obtained from textile-based solar cells in this study. The textile-based metal fabric enables a flexible photovoltaic structure that can be integrated on non-planar surfaces to generate electricity, and also mesh structure allows the light to reach the photoactive layer.