Backup Energy Storage Research Articles

Active drying of unripened bananas (Musa Nendra) in a multi-tray mixed-mode solar cabinet dryer with backup energy storage

Uniform moisture removal inside a multi-tray mixed-mode solar cabinet dryer (MMSCD) within a limited time is a significant concern primarily due to the non-uniform temperature distribution. Primary factors such as heated air and flow rate along with preliminary considerations such as slicing, loading intensity, spacing, and choice of with or without pre-treatment influence the drying behaviour. Hence, the primary objective of the present work is to identify whether only tray sequencing can be sufficient to ensure drying uniformity inside the MMSCD. A double-pass flat plate collector containing discrete cylindrical macro-encapsulated energy storage units deliver the heated air. Untreated unripe bananas with an average initial moisture content of 180% (db) are tested. In this work, the effect of tray sequencing (peculiar pattern) under a single layer loading intensity per tray with different flake thickness, multi-tray spacing, and flow rate are studied. Drying characteristic curves revealed that with tray sequencing the final moisture content was reduced below 16% (db) in all the trays. The specific energy consumption, efficiencies (collector, pickup, drying), drying cost, and open sun drying are discussed. Thus, based on the requirement, the MMSCD along with energy storage offers greater flexibility in drying for the user and ensures drying uniformity.

Performance and Cost Analysis of Lithium-Ion Battery for Powering Off-Grid Telecoms Base Stations in Africa

Most African remote telecoms base stations are powered from diesel generators, however, these generators are losing attractiveness due to their less reliability in addition to high operational and maintenance costs. Over 65% of the loss of telecom services observed in remote areas are caused by outages resulting from diverse types of failures that these generators can suffer, on top of their impacts on the environment. As alternative, off-grid renewable energy systems are often employed in place of diesel generators due to their capability to provide reliable electricity at an acceptable cost. This study proposes an off-grid system based on PV generators and backup energy storage consisting of lithium-ion batteries as an extended solution for powering remote telecom base stations in Africa. Modelling and simulation is performed using Matlab/Simulink environment. The findings showed better characteristics of lithium-ion battery bank as compared to lead-acid unit; lithium-ion battery bank displayed higher initial current and voltage over lead-acid battery bank. Moreover, when, both battery banks reached 50 % of their state of charge, lithium-ion bank current was still higher than that of lead-acid bank. In the same vein, lithium-ion battery bank presented a slower discharge time than lead-acid battery bank on top higher values at 50 % and 70% state of charges. Lastly, the state of charge of the lead-acid battery at the end of the simulation was 50 %, while that of the lithium-ion battery bank was around 60 %.

Study on the performance evaluation and echelon utilization of retired LiFePO4 power battery for smart grid

Lithium ion batteries (LIBs), with LiFePO4 (LFP) cathodes, are being widely used in hybrid and full electric vehicles (EVs). To reduce the cost of LIBs, it is necessary to estimate the capacity of retired LFP power batteries (RLFPPBs) and investigate their echelon application. Herein, we analyze the electrochemical performance of RLFPPBs and research the echelon features in different applications according to the simulated working conditions. The results reveal that the capacities of most of the as-obtained RLFPPBs retained 77% of initial capacity, the capacity retention rate and capacity recovery rate are approximate 97% and 99% after pause for 28 days, respectively. This suggests that these RLFPPBs can be used to study the echelon utilization. Three working conditions, including back-up power, energy storage and grid frequency modulation, are simulated in this work. As a back-up power, the RLFPPBs have a longer service life of 8 years due to their excellent self-discharge performance. In energy storage application, the RLFPPBs can be used for 5667 cycles under low current density and large discharge depth. In the case of grid frequency modulation, it may be able to work for only about 1 year at 1C rate, but the depth of discharge is only 10%. Such a shorter service life, resulting from the increased electrochemical impedance, suggests that the RLFPPBs may not be suitable in grid frequency modulation. Potentially, this work presents an effective and efficient route to recycle the retired power LIBs by using the echelon utilization.

Detailed study, multi-objective optimization, and design of an AC-DC smart microgrid with hybrid renewable energy resources

Hybrid renewable system is a particular type of energy systems which can be used as Distributed Generation (DG) resources to reduce network losses and increase its efficiency. Overall, at design phase, there are two major constraints: first, availability, and second, the cost of equipment. In this paper, considering these constraints and using DGs as Renewable Energy Sources (RES) including wind turbines and photovoltaics, an intelligent method based on multi-objective particle swarm optimization is utilized. Besides, battery bank has been used as a backup unit and energy storage of the hybrid system to reduce the volatility of RESs. The purposes of this paper are: to provide a comprehensive analysis on new structures of AC and DC systems, and then, to determine the capacity and optimal design with hybrid RESs in a smart microgrid to increase the availability and reduce network costs. In order to demonstrate the possibility of proposed approach, an optimized method is designed and implemented in two scenarios (Basic, and Maximum Renewable). Effectiveness of the proposed approach is applied over a real study case. By comparing the proposed method with multi-objective genetic algorithm, simulation results show that the proposed method has effective performance in reducing costs and improving availability.

Demands on energy storage for renewable power sources

The article deals with the issue of energy storage facilities for renewable energy sources. Due to the ratio between power delivery and take-off, the energy storage system is a key element in these systems. It is useful to divide the energy storages into short, long and backup energy storage. Based on an analysis of the energy consumption of an apartment or habitable unit, it is possible to define the properties of each type of storage.

Optimization algorithm for power-source arrangement that levels the fluctuations in wide-area networks of renewable energy

Abstract Fluctuations in individual renewable-energy supplies are largely reduced by distributing the renewable energy over a wide-area transmission network. Therefore, a new analysis algorithm for determining the amount of renewable energy in a wide-area transmission network was developed in this study. Accounting for the power interchange in the transmission network and the energy storage in electric heat pumps and heat storage tanks, the objective function plans the arrangement of the electric power sources that maximizes the economic efficiency of the system. The developed algorithm was applied to Hokkaido, Japan. The areas and capacities of the introduced renewable energies, and the amount of electric power interchanged through the transmission line, were determined. The installed capacity and economic efficiency of the backup power supply and energy storage equipment (heat storage) were also investigated. In this area, the introductory rate of renewable energy was 39.5% of the total electricity production. Moreover, the cost of a distributed power-supply network was 9.99 × 1010 USD. The proposed system is equivalent to 1.88 years of Hokkaido's energy consumption.

Evaluation of the effect of flexible demand and wave energy converters on the design of hybrid energy systems

Many islands have high electricity prices due to the reliance on imported diesel. However, hybrid energy systems (HES) which combine renewable generation with backup generators and energy storage are becoming cost competitive. Diesel usually provides about 10% of the demand because most renewables are non-dispatchable and thus the complete decarbonisation requires massively oversized renewable generation and storage. By including renewables with different resource profiles and demand side management (DSM), the diesel consumption could be decreased without increasing storage and renewable generation capacities. Here a framework for the design and optimisation of HES using wind, wave and solar generation and DSM is introduced. For the Mediterranean it is shown that wave energy is not competitive but that DSM reduces the emissions and costs by 21 and 8%. In the North Sea, DSM has lower benefits because waves act as an energy store for the wind. Thus, the combination of wave energy converters (WECs) and wind turbines significantly reduces the need for backup generation and energy storage which leads to large reductions in costs (up to 40%) and emissions (up to 60%). DSM and WECs can both simultaneously reduce the cost and emissions of HES but need to be designed for the particular circumstances.

A Practical Approach in Glycerol Oxidation for the Development of A Glycerol Fuel Cell

The research on electrochemical carbon molecule oxidation started in the past years as new electrochemistries were researched for new fuel cells systems and batteries that may line up as backup energy supply and storage systems in off-grid and on-grid microgrids, as modeled by our group at the University of Twente [1-3]. By lining up these two disciplines we hope to support the bridge between new electrochemical systems on one side, (pilot) production with partner companies, prediction, and validation of systems upon implementation in microgrids by our group. The electrochemical oxidation of glycerol in alkaline aqueous solution has been studied on gold and gold coated metals (Zn-Au and Cu-Au) by voltammetry and EIS (Electrochemical impedance spectroscopy) for possible use in a new fuel cell as an outlet for the excess glycerol that is produced in the biodiesel industry. The observations show that the gold surface may change upon cycling by cyclic voltammetry. Besides, the current density shows non-linear behavior with the square root of the scan rate, implying that the reaction is not totally controlled by diffusion. EIS analysis using the EQUIVCRT software revealed that one out of twenty tested equivalent circuits fitted the data well at potentials of -0.05 V,- 0.15 V and -0.25 V vs. Ag/AgCl, identifying resistors and a Warburg element in parallel with the double layer capacitance, the elements are possibly related to the presence of double layers associated with hydroxypyrovate and oxalate ions. The results are consistent with the low-frequency error fitting analysis (10-4), AC Simulink-Matlab fitting responds and the Kronig-Kramers transform test. The tested Zn-Au and Cu-Au electrodes show similar voltammetry behavior as the gold electrode, as witnessed by the results of cycle analysis and the scan rate analysis. The discharge chronoamperometry test further shows that the Zn-Au electrode and Cu-Au have higher current densities than the gold electrode at a potential of -0.25 V vs. Ag/AgCl (5 mA cm-2, 4.5 mA cm-2, and 3 mA cm-2 respectively).

Effect of ZnCl2 impregnation concentration on the microstructure and electrical performance of ramie-based activated carbon hollow fiber

Activated carbon hollow fibers (ACHFs) with high surface area were prepared from natural ramie fibers (RFs) by one-step activation under different ZnCl2 impregnation concentrations. The results showed that the morphology and pore structure development of ACHFs depend greatly on ZnCl2 concentration because ZnCl2 not only can swell and dissolve cellulose but also can serve as skeleton of newborn pores. It obtained granular activated carbons (ACs) instead of ACHFs when ZnCl2 concentration was over a suitable range. As supercapacitor electrode, the ACHFs possessed the maximum capacity of 287 F g−1 and showed excellent stability with more than 93 % efficiency after 1000 cycles. Besides, ACHFs showed higher electrochemical performance than granular ACs even if their microstructure was similar, indicating the morphology of material is also important to the electrochemical properties. Therefore, supercapacitors using ramie-based ACHFs as electrodes possess high comprehensive properties to serve for the need of backup energy storage and high pulse power applications.

Simultaneous use of MRM (maximum rectangle method) and optimization methods in determining nominal capacity of gas engines in CCHP (combined cooling, heating and power) systems

Energy, economic, and environmental analyses of combined cooling, heating and power (CCHP) systems were performed here to select the nominal capacities of gas engines by combination of optimization algorithm and maximum rectangle method (MRM). The analysis was performed for both priority of providing electricity (PE) and priority of providing heat (PH) operation strategies. Four scenarios (SELL-PE, SELL-PH, No SELL-PE, No SELL-PH) were followed to specify design parameters such as the number and nominal power of prime movers, heating capacities of both backup boiler and energy storage tank, and the cooling capacities of electrical and absorption chillers. By defining an objective function called the Relative Annual Benefit (RAB), Genetic Algorithm optimization method was used for finding the optimal values of design parameters. The optimization results indicated that two gas engines (with nominal powers of 3780 and 3930 kW) in SELL-PE scenario, two gas engines (with nominal powers of 5290 and 5300 kW) in SELL-PH scenario, one gas engine (with nominal power of 2440 kW) in No SELL-PE scenario provided the maximum value of the objective function. Furthermore in No SELL-PE scenario (which had the lowest RAB value in comparison with that for the above mentioned scenarios), thermal energy storage was not required. Due to very low value of RAB, any gas engine in No SELL-PH scenario was not recommended.

Life cycle assessment of power generation alternatives for a stand-alone mobile house

This paper presents comparative life cycle assessment of nine different hybrid power generation solutions that meet the energy demand of a prototypical mobile home. In these nine solutions, photovoltaic panels and a wind turbine are used as the main energy source. Fuel cell and diesel generator are utilized as backup systems. Batteries, compressed H2, and H2 in metal hydrides are employed as backup energy storage. The findings of the study shows that renewable energy sources, although they are carbon-free, are not as environmentally friendly as may generally be thought. The comparative findings of this study indicate that a hybrid system with a wind turbine as a main power source and a diesel engine as backup power system is the most environmentally sound solution among the alternatives.

A Single-Stage Fuel Cell Energy System Based on a Buck--Boost Inverter with a Backup Energy Storage Unit

An energy system powered by a low-voltage fuel cell (FC) is conditioned to generate higher--voltage regulated ac voltage. The power conditioning system typically requires two power stages: a boost stage and an inversion stage. In this paper, the buck--boost inverter topology that achieves both boosting and inversion functions in a single stage is used as a building block to develop a single-phase FC-based energy system that offers high conversion efficiency, low-cost and compactness. The proposed system incorporates a backup energy storage unit to support the slow dynamics of the FC. The single-phase buck--boost inverter is voltage-mode controlled and the backup unit is current-mode controlled. The low-frequency current ripple is supplied by the backup unit that minimizes the detrimental effects of such ripple being drawn directly from the FC itself. Experimental results from a 1-kW prototype operating at 20 kHz are presented to validate the analysis and performance of the proposed system.

Modeling and control of a push–pull converter for photovoltaic microinverters operating in island mode

This paper presents the modeling and control of a push–pull converter integrated into a two-stage photovoltaic microinverter operating in island mode without backup energy storage components (batteries). A push–pull small signal model is presented, from which they are derived all transfer functions needed to implement the controllers that regulate the output current, input voltage and output voltage interacting with the MPPT algorithm. A significant contribution of the paper is the proposal of an innovative control structure that simultaneously regulates in island mode both the ac voltage and the dc voltage of the panels, in order to place it in the best operation point. Such operation point is calculated by a specific control loop that interacts with the MPPT algorithm. To validate the proposed concept, simulations in PSIM™ were carried out.

Effect of Temperature on the Capacitance of Carbon Nanotube Supercapacitors

The effect of temperature on the kinetics and the diffusion mechanism of the ions in a supercapacitor assembled with single-walled carbon nanotube (SWNT) film electrodes and an organic electrolyte were thoroughly investigated. An improved room temperature performance of the supercapacitor was observed due to the combined effects of an increase in the conductivity of the SWNT films and surface modifications on the SWNT films by repeatedly heating and cooling the supercapacitor between the temperatures of 25 and 100 degrees C. Modified Randles equivalent circuit was employed to carry out an extensive analysis of the Nyquist spectra measured at different temperatures between 25 and 100 degrees C in order to understand the fundamentals of the capacitive and resistive variations in the supercapacitor. The experimental results and their thorough analysis will have significant impact not only on the fundamental understanding of the temperature-dependent electrode/electrolyte interfacial properties but also on supercapacitor design with appropriate electrode materials for numerous industrial and consumer applications. The supercapacitor with SWNT film electrodes was capable of withstanding current densities as high as 100 A/g, yielding eminent specific power density values of about 55 kW/kg. Ultralong galvanostatic charge-discharge cycling over 200 000 cycles with a constant current density of 20 A/g at 25 and 100 degrees C, respectively, showed excellent stability in capacitance with more than 80% efficiency. The usage of such a supercapacitor potentially enables far-reaching advances in backup energy storage and high pulse power applications.

Power electronics performance in cryogenic environment: evaluation for use in HTS power devices

Power electronics (PE) plays a major role in electrical devices and systems, namely in electromechanical drives, in motor and generator controllers, and in power grids, including high-voltage DC (HVDC) power transmission. PE is also used in devices for the protection against grid disturbances, like voltage sags or power breakdowns. To cope with these disturbances, back-up energy storage devices are used, like uninterruptible power supplies (UPS) and flywheels. Some of these devices may use superconductivity. Commercial PE semiconductor devices (power diodes, power MOSFETs, IGBTs, power Darlington transistors and others) are rarely (or never) experimented for cryogenic temperatures, even when designed for military applications. This means that its integration with HTS power devices is usually done in the hot environment, raising several implementation restrictions. These reasons led to the natural desire of characterising PE under extreme conditions, e. g. at liquid nitrogen temperatures, for use in HTS devices. Some researchers expect that cryogenic temperatures may increase power electronics' performance when compared with room-temperature operation, namely reducing conduction losses and switching time. Also the overall system efficiency may increase due to improved properties of semiconductor materials at low temperatures, reduced losses, and removal of dissipation elements. In this work, steady state operation of commercial PE semiconductors and devices were investigated at liquid nitrogen and room temperatures. Performances in cryogenic and room temperatures are compared. Results help to decide which environment is to be used for different power HTS applications.