Intermittent Renewable Sources Research Articles

Title: Static Cell and Porous Electrode Model for Cycling Behavior of Aqueous Organic Redox Active Materials

Aqueous Organic Redox Flow Batteries (AORBs) have shown growing potential as a stationary energy storage technology for regulating intermittent renewable sources. For long charge/discharge duration systems, the capital cost of a redox flow battery asymptotically approaches the cost of the electroactive material.[i] Therefore, for commercialization of this technology, proper evaluation of the redox active electrolytes is needed. The capacity retention over time and over cycling is one of the most vital criteria for evaluation. For very stable electrolytes with fade rates less than about 10% per year, disentangling cycle-denominated and time-denominated fade can be very difficult for flow batteries due to longer cycle time and noise due to pumping and splashing. Thus, we have used a sealed, static, non-flow cell to achieve capacity measurements with greater cycling frequency and reduced noise, as shown in Figure 1. To isolate decomposition from crossover through the membrane or apparent capacity fade due to changes in the resistance of the cell, we use volumetrically unbalanced, compositionally symmetric cells with potentiostatic cycling.[iii] For proper capacity fade rate evaluation, material properties of the electrode and electrolyte should be considered when setting up cycling protocols because the amount of accessed charge depends on these properties. Thus, simulations from porous electrode models that consider these material properties can inform appropriate cycling conditions.Using Newman’s porous electrode theory[iv] to model our static cell, we have simulated the spatial distribution of ions and potentials over time in response to time-varying applied potentials. From the transient behavior, we simulated the potentiostatic cycling of these cells. The simulations show how the physics inside porous electrodes and cycling performance depend on material properties. For example, the diffusivities can affect the spatial distributions of ions across a porous electrode, as shown in Figure 2 (left), as well as the minimum acceptable time for cycling and the accessed capacity for given cycling parameters, as shown in Figure 2 (right). Using the same porous electrode model for simulations, we aim to show differences between apparent and real capacity fade. [i] F. R. Brushett, M. J. Aziz, and K. E. Rodby. ACS Energy Lett. 2020, 5, 879−884 [ii] D. G. Kwabi, Y. Ji, and M. J. Aziz. C hem. Rev. 2020, 120, 14, 6467–6489 [iii] M.A. Goulet and M. J. Aziz, “Flow Battery Molecular Reactant Stability Determined by Symmetric Cell Cycling Methods”. Journal of The Electrochemical Society, 165 (7) A1466-A1477 (2018) [iv] J. Newman and C. W. Tobias, J. Electrochem. Soc., 1962, 109, 1183 Figure 1

Comparative analysis of HESS (battery/supercapacitor) for power smoothing of PV/HKT, simulation and experimental analysis

Photovoltaic and hydrokinetic systems are increasing their penetration in electrical distribution systems. This leads to problems of power fluctuations due to the intermittence of renewable sources that could compromise the stability and quality of the power grid. To address this issue, this paper presents a feasibility study of three power smoothing methods for a photovoltaic-hydrokinetic system using laboratory equipment to optimally replicate the real behavior of this type of hybrid system. The proposed algorithms are based on a hybrid storage system with supercapacitors and lithium-ion batteries, several analyzes are presented based on technical and economic parameters.The results demonstrate the feasibility of power smoothing methods for real systems, the comparison between the algorithms highlights the characteristics of the Enhanced Linear Exponential Smoothing Method, reducing the energy cost and regulating the point of common coupling voltage. Moreover, the sensitivity studies show that the energy exchange with the utility grid is affected according to the variations in the capacity of the batteries and the response to power smoothing can decrease or improve depending on the size of the supercapacitors.

Enhancement of loadability and voltage stability in grid-connected microgrid network

– The implementation of demand response programs in microgrid network applications enables end-consumers to participate in active load shaping, peak shaving, and supply-demand balancing activities. However, the impact of demand response programs on microgrid performance subjected to renewable energy intermittency, network flow constraints, loadability, and voltage stability is not acknowledged to the full extent. To cover this research gap, a tri-level stochastic framework is proposed to enhance the grid-connected microgrid performance in terms of loadability, voltage stability, and optimal scheduling. At the first level, a stochastic scenario-based approach deals with the intermittency of renewable sources. The interdependency of loading level on voltage profile is investigated in level two, implementing utility-oriented and customer-oriented demand-side management schemes. Unlike most previous research, flexible price elasticity-based incentive-driven and price-driven demand response programs are implemented to shape the load demand. Moreover, four distinct seasonal load profiles were considered: summer, winter, spring, and fall. Finally, the recently reported nature-inspired Harris Hawk Optimizer is incorporated in level three to optimize the costs and enhancement of microgrid loadability. The enhanced version of the IEEE 69 bus radial distribution network has been implemented and analyzed to demonstrate the effectiveness of the proposed tri-level framework. The obtained simulation results show that the voltage profile is enhanced by 6.58%, and microgrid loadability is improved by 34.64%. The significance of the proposed work to attain sustainable development goals and various practical insights for the benefit of multi-stakeholder is also discussed.

Flexible cryogenic air separation unit—An application for low-carbon fossil-fuel plants

The rapid integration of intermittent renewable sources into the electricity grid is driving the need for a flexible cryogenic air separation unit (ASU) coupled with a low-carbon fossil-fuel plant. However, the state-of-the-art ASU process is highly integrated and nonlinear, which can significantly restrict its ramping rate. In this work, we study the fundamental dynamics of a state-of-the-art double-column ASU, focusing on the dynamic characteristics of the highly integrated and nonlinear heat and mass transfers, and we propose basic control methods for achieving high process ramping rates. We found that the vapor–liquid countercurrent flows in the low-pressure column are critical to the cryogenic rectification of air, which governs the ramp rate of the ASU. This countercurrent flow structure is created through a complex heat integration process in the ASU. Here, this process is simplified as a countercurrent heat transfer to reduce the complexity of studying the ASU dynamics. To preserve this flow structure, the heat integration is maintained so that its heat duty follows the ASU load, using several basic controllers on the critical stream flowrates. A flow-driven dynamic ASU model is built in Aspen Plus Dynamics to capture the basic ramping dynamics. This model revealed a fundamental mismatch in the dynamics in the ASU column that causes a significant loss of O2 product purity when ramping down the ASU and slightly increases the purity when ramping up. Based on these findings, we propose a basic control method for rapidly ramping down/up the ASU while maintaining O2 product purity. Simulation results show the ASU basic dynamic process successfully ramps at a rate up to 10 %/min (40–100 % load) while maintaining the O2 product purity at 95.2–95.6 mol%.

Liquid air energy storage for ancillary services in an integrated hybrid renewable system

High shares of intermittent renewable sources cause volatile frequency movements that could jeopardize the continuous operation of the grid. Liquid Air Energy Storage (LAES) is an emerging technology that not only helps with decarbonisation of energy sectors, but also has potentials for reliable ancillary services. In this paper, a hybrid LAES, wind turbine (WT), and battery energy storage system (BESS) is used to investigate their contributions in fast frequency control. The inertial control, droop control and combined inertial and droop terms are applied on each source of the hybrid renewable system and a comprehensive analysis is conducted to study their impacts on the frequency nadir improvement. The analysis shows that LAES with combined inertial and droop control terms along with inertial control of WT and BESS provide reliable frequency control. To further improve the frequency nadir, a Fuzzy control is proposed and applied on the LAES. The proposed control system provides a more adaptive performance against disturbances. Also, experimental tests are conducted to validate the proposed control method using a real-time hardware-in-the-loop test rig. The simulation and experimental results show that LAES in a hybrid renewable system can significantly contribute to the frequency control when variable gain control schemes are implemented.

Evaluation of startup time for a model contra-rotating pump-turbine in pump-mode

A larger part of the electricity is today from intermittent renewable sources of energy. However, the energy production from such sources varies in time. Energy storage is one solution to compensate for this variation. Today pumped hydro storage (PHS) is the most common form of energy storage. Usually, it requires a large head, which limits where it can be built. In the EU project ALPHEUS, PHS technologies for low- to ultra-low heads are explored. One of the concepts is a contra-rotating pump-turbine (CRPT). The behaviour of this design at time-varying load conditions is today scarce. In the present work, the impact of the startup time for a CRPT is analysed through computational fluid dynamics (CFD) simulations. The analysis includes a comparison between a coarse and a fine CFD model. The coarse model produces acceptable results and is 50 times cheaper, this model is thus used to assess the startup time. It is found that longer startup times generate lesser loads and peak values. A startup time of 10 s may be a sufficient alternative as the peak loads are heavily reduced compared to faster startups. Furthermore, there is not much difference between a startup time of 20–30 s.

An integrated smart thermo-chemical energy network

Managing the intermittency of renewable sources together with transient (hourly to daily to seasonal) energy demands is one of the principal challenges of delivering a net-zero energy system. Smart multifunctional thermo-chemical energy networks represent an alternative energy network and storage system, a solution based on the distribution of energy via thermo-chemical material rather than thermal energy, gas, fuels or electricity– an option that has scope for integrated short- and long-term energy storage. This is the first research work to realise such a system and demonstrate how it might operate using smart control strategies and how thermo-chemical fluids (TCFs) can be used as a medium for timely energy storage and distribution. The experimental study also describes the effect of steady and variable heat sources on TCF regeneration performance and estimates the potential of thermo-chemical energy networks, which would be particularly beneficial in buildings with high energy consumption for humidity control. This research proves the practicality of the design idea for such a network, which would be governed by centralised control, regenerated by steady or transient heat loads and capable of supplying a variety of demands in an experimental setting. The energy and economic potential of the network were also assessed, identifying temperature and humidity control application scenarios with energy savings of more than 60% compared to conventional operation and payback periods of 6.6–9.7 years.

Design of High-Power Solid-State Transformers with Grain-Oriented Electrical Steel Cores

The paper proposes a simple structure of high-power solid-state transformers (SSTs) able to control the energy flow in critical lines of the medium-voltage (20 kV) distribution grid. With an increasing number of renewable intermittent sources connected at the nodes of the meshed distribution grid and a reduced number of nodes connected to large power plants, the distribution grid stability is more and more difficult to achieve. Control of the energy flow in critical lines can improve the stability of the distribution grid. This control can be provided by the proposed high-power SSTs operating a 20 kV with powers over 10 MW. This function is difficult to achieve with standard SST technologies that operate at high frequencies. These devices are made with expensive magnetic materials (amorphous or nanocrystalline cores) and a limited power by SST cells. The required total power is reached by assembling many SST cells. On the other hand, existing SST designs are mainly aimed at reducing the equipment’s size and it is difficult to design small objects able to operate at high voltages. The authors propose to use cores made with grain-oriented electrical steel (GOES) thin strips assembled in wound cores. Experimental results obtained, with GOES wound cores, show that the core losses are lower for a square voltage than for a sine one. This counterintuitive result is explained with an analytical calculus of eddy currents and confirmed by a non-linear time-stepping simulation. Therefore, simple converter structures, operating with rectangular voltages and low switching losses, are the best solutions. Experimental results also show that the core losses decrease with temperature. Consequently, high-power SST cells can be made with transformers whose GOES cores are hotter than coils for reducing core losses and keeping copper losses at low levels. The paper proposes an appropriate transformer mechanical structure that avoids any contact between the hot GOES wound core and the winding, with a specific cooling system and thermal insulation of the hot GOES wound core. The proposed design makes it possible to build SST cells over 1MW and full SSTs over 10 MW at moderate costs.

Redox Flow: How Low Can You Go? High-Throughput Battery Lifetime Characterization for Grid-Scale Energy Storage

Aqueous Organic Redox Flow Batteries (AORFBs) have emerged as potentially disruptive technologies for the storage of electrical energy from intermittent renewable sources. With the goal of cost-effective, safe, and scalable stationary electricity storage systems, AORFBs could eclipse Li-ion batteries due to their inherent non-flammability, lack of materials scarcity fluctuations, and intrinsic decoupling of energy and power capacities. We have previously demonstrated that calendar life, rather than cycle life, limits molecular lifetimes in AORFBs due to various molecular instabilities that lead to side reactions, thus inhibiting performance [1]. The continued synthetic effort to produce stable redox-active organics has improved molecular design strategies to the point that the most stable chemistries now degrade at less than 1% per year [2].With further lifetime increases, the measurement of lower capacity fade rates now necessitates higher precision coulometry methods [3] and the use of thermally accelerated decomposition protocols [4,5] to determine which stabilizing approaches are most effective without waiting for multi-month cycling tests to quantify capacity fade.In this presentation, I highlight a high-throughput setup we have recently developed for the electrochemical screening of candidate molecules in AORFBs. We demonstrate the effect that cycling protocols can have on measured capacity fade rates and propose figures of merit for cell-to-cell variability. Finally, we explore accelerated decomposition protocols to expedite the screening process of candidate molecules for long lifetime AORFBs, which may enable massive grid penetration of intermittent renewable energy.[1] M.-A. Goulet and M. J. Aziz, “Flow Battery Molecular Reactant Stability Determined by Symmetric Cell Cycling Methods,” Journal of The Electrochemical Society , 165, A1466 (2018).[2] M. Wu, Y. Jing, A. A. Wong, E. M. Fell, S. Jin, Z. Tang, R. G. Gordon, M. J. Aziz, “Extremely Stable Anthraquinone Negolytes Synthesized from Common Precursors,” Chem, 6, 1432 (2020).[3] T. M. Bond, J. C. Burns, D. A. Stevens, H. M. Dahn, and J. R. Dahn, "Improving Precision and Accuracy in Coulombic Efficiency Measurements of Li-Ion Batteries,” Journal of The Electrochemical Society, 160, A521 (2013).[4] D. G. Kwabi, K. Lin, Y. Ji, E. F. Kerr, M.-A. Goulet, D. De Porcellinis, D. P. Tabor, D. A. Pollack, A. Aspuru-Guzik, R. G. Gordon, and M. J. Aziz, “Alkaline Quinone Flow Battery with Long Lifetime at pH 12,” Joule, 2, 1894 (2018).[5] D. A. Stevens, R. Y. Ying, R. Fathi, J. N. Reimers, J. E. Harlow, and J. R. Dahn, "Using High Precision Coulometry Measurements to Compare the Degradation Mechanisms of NMC/LMO and NMC-Only Automotive Scale Pouch Cells,” Journal of The Electrochemical Society, 161, A1364 (2014).

Stochastic Optimal Design of Household-Based Hybrid Energy Supply Systems Using Sample Average Approximation

In terms of energy production, combining conventional and renewable energy sources prove to be more sustainable and cost-effective. Nevertheless, efficient planning and designing of such systems are extremely complex due to the intermittency of renewable sources. Many existing studies fail to capture the stochasticity and/or avoid detailed reliability analysis. This research proposes a practical stochastic multi-objective optimization tool for optimally laying out and sizing the components of a grid-linked system to optimize system power at a low cost. A comparative analysis of four state-of-the-art algorithms using the hypervolume measure, execution time, and nonparametric statistical analysis revealed that the nondominated sorting genetic algorithm III (NSGA-III) was more promising, despite its significantly longer execution time. According to the NSGA-III calculations, given solar irradiance and energy profiles, the household would need to install a 5.5 (kWh) solar panel tilted at 26.3° and orientated at 0.52° to produce 65.6 (kWh) of power. The best battery size needed to store enough excess power to improve reliability was 2.3 (kWh). The cost for the design was $73520. In comparison, the stochastic technique allows for the construction of a grid-linked system that is far more cost-effective and reliable.

Leveraging Temperature-Dependent (Electro)Chemical Kinetics for High-Throughput Flow Battery Characterization

Aqueous Organic Redox Flow Batteries (AORFBs) have emerged as potentially disruptive technologies for the storage of electrical energy from intermittent renewable sources for use over long discharge durations when the wind isn’t blowing, and the sun isn’t shining. AORFBs could become preferred solutions for grid-scale storage due to their potentially low-cost active materials, inherent non-flammability, and intrinsic decoupling of energy and power capacities. We have previously demonstrated that calendar life, rather than cycle life, limits molecular lifetimes in AORFBs due to various molecular instabilities that lead to side reactions, thus inhibiting performance [1]. For accurately determining molecular fade rates, we utilize potentiostatic holds to avoid artifacts caused by drifts in internal resistance and we study volumetrically unbalanced, compositionally symmetric cell configurations to distinguish molecular fade from membrane crossover. Our group’s synthetic effort has continued to improve molecular design strategies to the point that the most stable molecules degrade at less than 1% per year [2]. With further lifetime increases, the measurement of lower capacity fade rates now necessitates higher precision coulometry methods [3] and the use of thermally accelerated decomposition protocols [4,5] to determine which stabilizing approaches are most effective without waiting for multi-month cycling tests to quantify capacity fade.We have recently developed a high-throughput setup for cycling AORFBs at elevated temperatures, providing a new dimension in the flow battery characterization space to explore. An in-depth study comparing previously published redox-active organic molecules [2,4,6] has been performed using the protocol discussed above. Capacity fade rates as a function of temperature are evaluated in the high-throughput setup using high-precision coulometry, and the ability to extrapolate fade rates to lower operating temperatures is also explored. Collectively, these results highlight the relevance of accelerated decomposition protocols to expedite the screening process of candidate molecules for long lifetime AORFBs, which may enable massive grid penetration of intermittent renewable energy.[1] M.-A. Goulet and M. J. Aziz, “Flow Battery Molecular Reactant Stability Determined by Symmetric Cell Cycling Methods,” Journal of The Electrochemical Society , 165, A1466 (2018).[2] M. Wu, Y. Jing, A. A. Wong, E. M. Fell, S. Jin, Z. Tang, R. G. Gordon, M. J. Aziz, “Extremely Stable Anthraquinone Negolytes Synthesized from Common Precursors,” Chem, 6, 1432 (2020).[3] T. M. Bond, J. C. Burns, D. A. Stevens, H. M. Dahn, and J. R. Dahn, "Improving Precision and Accuracy in Coulombic Efficiency Measurements of Li-Ion Batteries," Journal of The Electrochemical Society, 160, A521 (2013).[4] D. G. Kwabi, K. Lin, Y. Ji, E. F. Kerr, M.-A. Goulet, D. De Porcellinis, D. P. Tabor, D. A. Pollack, A. Aspuru-Guzik, R. G. Gordon, and M. J. Aziz, “Alkaline Quinone Flow Battery with Long Lifetime at pH 12,” Joule, 2, 1894 (2018).[5] D. A. Stevens, R. Y. Ying, R. Fathi, J. N. Reimers, J. E. Harlow, and J. R. Dahn, "Using High Precision Coulometry Measurements to Compare the Degradation Mechanisms of NMC/LMO and NMC-Only Automotive Scale Pouch Cells,” Journal of The Electrochemical Society, 161, A1364 (2014).[6] Y. Ji, M.-A. Goulet, D. A. Pollack, D. G. Kwabi, S. Jin, D. De Porcellinis, E. F. Kerr, R. G. Gordon, and M. J. Aziz, “A Phosphonate-Functionalized Quinone Redox Flow Battery at Near-Neutral pH with Record Capacity Retention Rate,” Advanced Energy Materials, 9, 1900039 (2019).

High Accuracy Measurements for Rapid Evaluation of Extremely Low Decomposition Rates of Redox Active Molecules

Aqueous Organic Redox Flow Batteries (AORFBs) have potential to disrupt the energy storage technology market for renewable energy sources. To combat the issue of intermittency[i] for these energy sources, AORFBs use non-volatile, potentially cheap, and abundant materials to deliver decadal time scale energy storage with the advantage of decoupled energy and power density by scaling the former with the size of electrolyte tank volumes and scaling the latter with the area of the electrode surface where the reactions take place. Because many candidates have been discovered and remain to be discovered for applications as redox active molecules with long chemical lifetimes in AORFBs, in this work we developed a setup for quickly and accurately evaluating molecular decomposition.To make AORFBs more competitive for commercialization, our group has fine-tuned the electrochemical properties of active organic molecules via new synthetic approaches to achieve capacity fade rates lower than 1% per year.[ii] To better understand the decomposition mechanisms of these redox active species in AORFBs, we have also developed volumetrically unbalanced, compositionally symmetric cell cycling methods to evaluate capacity losses solely from decomposition and not from active species crossover through the membrane or changes in internal resistance of the battery.[iii] While the symmetric cell cycling technique allows isolating molecular decomposition as the source of capacity fade for AORFBs, for evaluating extremely low decomposition rates, flow batteries can require run times from several weeks to months due to noise in capacity measurements from temperature and pressure fluctuations or droplets in the batteries losing contact with solution being pumped to react in the cell. Additionally, since we have experienced slight variations in fade rates across cells with the same experimental conditions, decomposition rates should be determined from several cycling experiments, not one.[iv] In order to more quickly and more accurately evaluate extremely low decomposition rates, we have developed a simple static cell into which electrolyte is injected into porous electrodes and sandwiched together by current collectors without a flow system. By removing the complexities of the flow system, we may determine capacity fade rates in much shorter times and with lower uncertainties. [i] J. Rugolo and M. J. Aziz, “Electricity storage for intermittent renewable sources.” Energy Environ. Sci., 2012, 5, 7151 [ii] M. Wu et al., “Extremely Stable Anthraquinone Negolytes Synthesized from Common Precursors”. Chem 6,1–11 June 11, 2020 [iii] M.A. Goulet and M. J. Aziz, “Flow Battery Molecular Reactant Stability Determined by Symmetric Cell Cycling Methods”. Journal of The Electrochemical Society, 165 (7) A1466-A1477 (2018) [iv] Eric Michael Fell and Michael J. Aziz 2021 Meet. Abstr. MA2021-01 207

Unraveling the Structural Sensitivity of CO2 Electroreduction at Facet-Defined Nanocrystals via Correlative Single-Entity and Macroelectrode Measurements.

The conversion of CO2 into value-added products is a compelling way of storing energy derived from intermittent renewable sources and can bring us closer to a closed-loop anthropogenic carbon cycle. The ability to synthesize nanocrystals of well-defined structure and composition has invigorated catalysis science with the promise of nanocrystals that selectively express the most favorable sites for efficient catalysis. The performance of nanocrystal catalysts for the CO2 reduction reaction (CO2RR) is typically evaluated with nanocrystal ensembles, which returns an averaged system-level response of complex catalyst-modified electrodes with each nanocrystal likely contributing a different (unknown) amount. Measurements at single nanocrystals, taken in the context of statistical analysis of a population, and comparison to macroscale measurements are necessary to untangle the complexity of the ever-present heterogeneity in nanocrystal catalysts, achieve true structure-property correlation, and potentially identify nanocrystals with outlier performance. Here, we employ environment-controlled scanning electrochemical cell microscopy to isolate and investigate the electrocatalytic CO2RR response of individual facet-defined gold nanocrystals. Using correlative microscopy approaches, we conclusively demonstrate that {110}-terminated gold rhombohedra possess superior activity and selectivity for CO2RR compared with {111}-terminated octahedra and high-index {310}-terminated truncated ditetragonal prisms, especially at low overpotentials where electrode kinetics is anticipated to dominate the current response. The methodology framework described here could inform future studies of complex electrocatalytic processes through correlative single-entity and macroscale measurement techniques.

Control and Power Management Strategy for Shunt DC Electric Spring Integrated DC Microgrid

Incorporation of intermittent renewable sources and nonlinear loads to DC microgrid (DCMG) has increased its vulnerability to voltage instability and flicker. An innovative Demand Side Management (DSM) program that can help in mitigating these voltage disruptions is the deployment of DC Electric Spring (DCES) technology. In this regard, this paper focuses on small signal modeling and controller design of shunt DCES (ShDCES) in DCMG. The test system comprises of an MPPT controlled Solar Photo-Voltaic (SPV) system, battery-operated DCES and various loads. The MATLAB / Simulink performance analysis of the system indicates that, with the incorporation of power management strategy, the ShDCES configuration has enhanced the power quality of SPV-fed DCMG with fast dynamic response in comparison with its “series” counterpart. The effective utilization of battery operated DCES on the load side, instead of the source side, makes it less battery dependent, resulting in enhancement of battery life and lesser environmental hazards. The simulation results are also validated using real-time simulator OP4510 RTS.

Liquid Metal Battery for Energy Storage

The world is shifting towards renewable energy sources as it is well known that we are running out of conventional sources. But renewable sources are seasonal they are not available constantly all the time. This brings us the need for storage devices capable of handling huge power grids. From considering the above factor we came up with a new type of battery called Liquid Metal Battery. These batteries are possible candidates for massive and economically feasible large-scale stationary storage and as such could be key components of future energy systems based mainly or exclusively on intermittent renewable electricity sources. The project at hand focuses on the possible material selection for making the battery, Cell chemistry, modelling of battery voltage and finally making a physical working model of the Liquid Metal Battery. All these followed with obtaining the designed battery's performance characteristics, allowing for more insight. Finally, the main intention for the development of this battery is for powering huge loads like cities when a large deficit exists between power generation from renewable sources and demand. Thereby reducing the requirement for conventional sources. Keywords—Cell Volage, Anode material, Cathode Material, Electrolyte, Outer Casing, Deep Cycling, Open Circuit Voltage

Highly selective metal-organic framework-based (MOF-5) separator for non-aqueous redox flow battery

• A facile and scalable process is developed to fabricate separator for NARFB. • The separator achieves 100% materials utilization and excellent repairability. • The separator shows a remarkable ionic selectivity of 26.6 and delivers 99.7% CE. • 0.04% per cycle capacity decay over 200 cycles of the NARFB. Non-aqueous redox flow batteries (NARFBs) are promising in the grid-scale energy storage for the harvesting of the intermittent renewable power sources. However, the lack of efficient separator is still impeding their further development. A flexible nanoporous separator is prepared through a “rolling dough” strategy, with zinc metal-organic framework (MOF-5) and polytetrafluoroethylene as the substrate. The prepared separator shows a remarkable ionic selectivity of Li + over N-(ferrocenylmethyl)-N,N-dimethyl-N-ethylammonium ions (Fc1N112 + ) at a high ratio 26.6. A Li-based hybrid NARFB constructed with the separator exhibits substantially high Coulombic efficiency 99.7% and average discharge capacity 2.26 Ah L −1 with capacity retention 99.96% per cycle over 200 cycles at 4 mA cm −2 . The excellent performance is attributed to the MOF nanoparticles and the designed composite structure, which achieves both high ionic selectivity and chemical stability simultaneously. This work provides a facile and efficient strategy to fabricate high-performance separator for NARFBs.

Sustainable Energy Transition for Renewable and Low Carbon Grid Electricity Generation and Supply

The greatest sustainability challenge facing humanity today is the greenhouse gas emissions and the global climate change with fossil fuels led by coal, natural gas and oil contributing 61.3% of global electricity generation in the year 2020. The cumulative effect of the Stockholm, Rio, and Johannesburg conferences identified sustainable energy development (SED) as a very important factor in the sustainable global development. This study reviews energy transition strategies and proposes a roadmap for sustainable energy transition for sustainable electricity generation and supply in line with commitments of the Paris Agreement aimed at reducing greenhouse gas emissions and limiting the rise in global average temperature to 1.5°C above the preindustrial level. The sustainable transition strategies typically consist of three major technological changes namely, energy savings on the demand side, generation efficiency at production level and fossil fuel substitution by various renewable energy sources and low carbon nuclear. For the transition remain technically and economically feasible and beneficial, policy initiatives are necessary to steer the global electricity transition towards a sustainable energy and electricity system. Large-scale renewable energy adoption should include measures to improve efficiency of existing nonrenewable sources which still have an important cost reduction and stabilization role. A resilient grid with advanced energy storage for storage and absorption of variable renewables should also be part of the transition strategies. From this study, it was noted that whereas sustainable development has social, economic, and environmental pillars, energy sustainability is best analysed by five-dimensional approach consisting of environmental, economic, social, technical, and institutional/political sustainability to determine resource sustainability. The energy transition requires new technology for maximum use of the abundant but intermittent renewable sources a sustainable mix with limited nonrenewable sources optimized to minimize cost and environmental impact but maintained quality, stability, and flexibility of an electricity supply system. Technologies needed for the transition are those that use conventional mitigation, negative emissions technologies which capture and sequester carbon emissions and finally technologies which alter the global atmospheric radiative energy budget to stabilize and reduce global average temperature. A sustainable electricity system needs facilitating technology, policy, strategies and infrastructure like smart grids, and models with an appropriate mix of both renewable and low carbon energy sources.

Comparative sustainability study of energy storage technologies using data envelopment analysis

The transition to energy systems with a high share of renewable energy depends on the availability of technologies that can connect the physical distances or bridge the time differences between the energy supply and demand points. This study focuses on energy storage technologies due to their expected role in liberating the energy sector from fossil fuels and facilitating the penetration of intermittent renewable sources. The performance of 27 energy storage alternatives is compared considering sustainability aspects by means of data envelopment analysis. To this end, storage alternatives are first classified into two clusters: fast-response and long-term. The levelized cost of energy, energy and water consumption, global warming potential, and employment are common indicators considered for both clusters, while energy density is used only for fast-response technologies, where it plays a key role in technology selection. Flywheel reveals the highest efficiency between all the fast-response technologies, while green ammonia powered with solar energy ranks first for long-term energy storage. An uncertainty analysis is incorporated to discuss the reliability of the results. Overall, results obtained, and guidelines provided can be helpful for both decision-making and research and development purposes. For the former, we identify the most appealing energy storage options to be promoted, while for the latter, we report quantitative improvement targets that would make inefficient technologies competitive if attained. This contribution paves the way for more comprehensive studies in the context of energy storage by presenting a powerful framework for comparing options according to multiple sustainability indicators.

Triangular Intuitionistic Fuzzy Aggregating and Ranking Function Approach for the Rating of Battery ‘End-of-Life’ Handling Alternatives

The increased adoption of intermittent renewable sources in the energy sector has also increased the use of battery storage systems. However, the negative impact which the improper disposal of batteries has on the environment has stirred debates on its sustainability. To ensure the proper disposal of battery waste, there is a need to identify and rank the most preferred battery ‘end-of-life’ handling alternatives. This paper focuses on identifying the most preferred ‘end-of-life’ handling alternatives for batteries using a modified triangular intuitionistic fuzzy aggregating and ranking function (TIFARF) model. To test the proposed modified TIFARF model, opinions from experts in the Nigerian renewable energy sector were collected, and the results show that the most preferred alternative is incineration, with a closeness coefficient of 0.130, while the least preferred alternative is recycling, whose closeness coefficient is 0.112. The results are an indication of a lack of facilities needed for the proper recycling of battery remains after their lifetime; if adequate facilities are available, the opinion of experts may be biased towards other alternatives. Future studies should focus on more battery ‘end-of-life’ handling alternatives and on countries with adequate facilities that can be used to manage batteries at the end of their lifespan.

Analysing utility-based direct load control programmes for heat pumps and electric vehicles considering customer segmentation

Utility controlled heat pumps and electric vehicles via Direct Load Control (DLC) programmes could potentially be a solution for tackling challenges in the distribution networks by balancing intermittent renewable electricity sources. However, in many countries, DLC programmes do not have satisfactory enrolment rates. This paper investigates acceptance and preferences of DLC programmes for heat pumps and electric vehicles (EV) offered by a local Distribution System Operator (DSO), using a discrete choice experiment on a sample of 556 respondents residing in Switzerland. We first found that the acceptance ranged between 33% and 71% in different socio-economic groups. Secondly, multinomial logit results showed that financial incentives were the most preferred attribute for heat pumps, whereas it was the overriding option for the EV DLC programme. Finally, we explored the source of heterogeneity in preferences among different socio-economic groups with a latent class model. Preferences are found to differ between three classes, different gender and employment groups tend to be sensitive to different attributes of the DLC programmes. We draw attention to attributes of the utility based DLC programmes and provide policy recommendations to successfully address the diverse household preferences when deploying DLC programmes.