Intermittency Issues Research Articles

Opportunity of rooftop solar photovoltaic as a cost-effective and environment-friendly power source in megacities

SummaryRooftop solar photovoltaics (RSPV) are critical for megacities to achieve low-carbon emissions. However, a knowledge gap exists in a supply-demand-coupled analysis that considered simultaneously RSPV spatiotemporal patterns and city-accommodation capacities, a pivotal way to address solar PV intermittency issues. Here, we developed an aggregated model for an RSPV + system by linking building-level potential assessment to dynamic optimization of building-related flexible loads. Taking Beijing, the capital city of China, as case in point, we show that annual RSPV potential in Beijing’s Greater-Metropolitan area amounts to 15.4 TWh, all of which could be accommodated environmentally friendly and cost-effectively through the smart operation of electric vehicles and air conditioners equipped with thermal energy storage (TES). Additionally, the RSPV + system would reduce the 8.6 GW transmission capacity otherwise required for increasing electricity demand for 2035 in Beijing. The analysis offers an important reference for sustainable RSPV development in mega-cities in China and other countries globally.

Molecularly elongated phase change materials for mid-temperature solar-thermal energy storage and electric conversion

The utilization of phase change materials (PCMs) offers state-of-the-art thermal energy storage (TES) developments to overcome the intermittency issues associated with renewable energy sources. Despite the tremendous potential of renewable energy storage at intermediate temperature (100–200 °C), the PCM options for this temperature range are limited, and most available PCM candidates are inadequate for practical applications. Herein, we present a molecular elongation design strategy to develop a series of intermediate-temperature PCMs from naturally occurring fatty materials. By increasing chain length and imparting functional moieties in the molecular backbone, we fine-tune the intermolecular interactions in resulting PCMs to achieve more than two folds higher transition temperature compared with their monomeric analogs. Through a systematic structural analysis, we also probe the fundamental basis at the molecular level for the high TES capacity (up to 228 J g−1) that lies behind the excellent performance of our developed PCMs. Further, by compositing developed PCMs with photo-absorber scaffold, intermediate-temperature solar-thermal energy storage is demonstrated for dispatchable power generation. The prototype experimental results speculate that PCM integrated solar-thermoelectric generators could be an intriguing alternative to battery-coupled photovoltaic systems.

N-Doped Nanoporous Carbon Scaffolds As Catalysts for CO2 Reduction

The need for clean energy solutions in order to significantly lower our carbon footprint is placing increasing attention on renewable energy, such as wind and solar. However, these technologies suffer from intermittency issues, thus making efficient energy storage and conversion a major requirement. One of the solutions to this problem is electrochemical CO2 reduction (CO2RR), using renewable energy to produce green fuels and chemicals. However, the reduction of CO2 is thermodynamically and kinetically unfavorable. To overcome this, the development of highly efficient and selective electrocatalysts is a key goal of CO2RR research.Carbon has been attracting interest as a promising candidate due to its high specific surface area, good conductivity, and low-cost. However, its catalytic performance is limited by the electroneutrality of the carbon atoms in the primarily graphitic lattice. In order to activate the CO2 molecules and enhance the adsorption of intermediates, a range of novel carbon catalysts has been developed, with nitrogen doping being the most common approach. The N atom has a similar size as C and thus the lattice mismatch after doping is minimal [1]. At the same time, the N atom also has a higher electronegativity than C which will break the electroneutrality of the carbon lattice and enhance the conductivity of the material [2-3]. Furthermore, N doping results in a range of N-based surface species, thus potentially allowing the tuning of the CO2RR products [4].In this work, a novel, self-supported, nanoporous carbon scaffold (NCS) was used as the carbon substrate. The NCS is a templated, binder-free mesoporous carbon material with tunable pore sizes, a high surface area, good conductivity, and scalability [5]. Here, N doping of the NCS was achieved by heat treatment in NH3. An in house flow cell that can be switched between flow-through and flow-by modes was developed, allowing the NCS to be used as a model material to understand the impact of fluid flow on mass transfer limitations in the CO2RR and on any local pH effects that may be present.The CO2RR performance was tested in the flow cell using a CO2-saturated KHCO3 solution. The bare NCS was confirmed to generated only H2, while the N-doped NCS gives roughly a 50:50 ratio of H2:CO at all potentials, with the onset potential being ca. -0.55 V vs RHE. The effect of the NCS pore size was also investigated, showing that an NCS membrane with a nominal 85 nm pore diameter produced roughly 45% CO, while the NCS-12 (12 nm pore size) material gave somewhat more CO (ca. 55-60%). At the same time, the NCS-12 gave lower current densities, despite its higher surface area, likely due to poorer pore accessibility. Furthermore, running the cell in the flow-through mode gave higher currents at all of the NCS-based catalysts, most likely due to removal of trapped gases. Current work is focused on determining the effect of the N content and the type of N-based functionalities attached to the NCS surface on the CO2RR performance.

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

Investigating Perovskite Oxide Catalysts As Bifunctional Oxygen Electrodes Using Operando XAS

With the increase in renewable energy usage comes the need for energy storage systems due to intermittency issues. Hydrogen storage systems have been identified as one solution. Unitized regenerative fuel cells (URFC) combine electrolyzers and fuel cells in one device, allowing electricity to be stored and used easily. However, the oxygen electrodes are still affected by high overpotentials and slow kinetics. Perovskite oxides have been identified as a class of materials, which are low-cost, tunable, and active for the oxygen reduction (ORR) and evolution (OER) reactions. Here, we investigate perovskites as bifunctional catalysts for ORR and OER in alkaline solution. We examine and compare two strategies for bifunctional catalysts: using one catalyst, which is able to perform OER and ORR vs. a combination of two catalysts, one active for ORR and one active for OER. Frequently, the catalysts’ performances for these two reactions are measured separately.1,2,3 Here, we investigate how these bifunctional catalysts respond to cycling between the OER and ORR regions.Ba0.5Sr0.5Co0.8Fe0.2O3 (BSCF) is known to be a promising OER catalyst.4,5,6 However, without carbon, it lacks ORR activity.4 La(1-x)SrxMnO3 (LSM) is a promising ORR catalyst.3,7 However, without modification, it has been shown to have limited OER activity.3 Separately, these catalysts lack high performance for both reactions. Here, we combine the two catalysts into a BSCF/LSM/Carbon composite electrode and compare to electrodes prepared from the constituent single material components. In addition, we have synthesized single material perovskites containing both Co and Mn that to the best of our knowledge have never been tested as electrodes for ORR/OER. In order to understand the catalysts’ behaviors under OER and ORR conditions, X-ray adsorption spectroscopy (XAS) was measured continuously while performing cyclic voltammetry. We were able to monitor the continuous changes of the Co, Mn, and Fe oxidation states and local environment during OER and ORR with remarkably high time/applied potential resolution. Our findings illustrate the reversible and irreversible changes that can occur during OER and ORR and provide strategies for future bifunctional catalyst design.References Kirsanova, M. A.; Okatenko, V. D.; Aksyonov, D. A.; Forslund, R. P.; Mefford, J. T.; Stevenson, K. J.; Abakumov, A. M. Bifunctional OER/ORR Catalytic Activity in the Tetrahedral YBaCo 4 O 7.3 Oxide. Mater. Chem. A 2019, 7 (1), 330–341.Elumeeva, K.; Masa, J.; Sierau, J.; Tietz, F.; Muhler, M.; Schuhmann, W. Perovskite-Based Bifunctional Electrocatalysts for Oxygen Evolution and Oxygen Reduction in Alkaline Electrolytes. Acta 2016, 208, 25–32.Xu, W.; Apodaca, N.; Wang, H.; Yan, L.; Chen, G.; Zhou, M.; Ding, D.; Choudhury, P.; Luo, H. A-Site Excessive (La0.8Sr0.2)1+ XMnO3 Perovskite Oxides for Bifunctional Oxygen Catalyst in Alkaline Media. ACS Catal. 2019, 9 (6), 5074–5083.Fabbri, E.; Nachtegaal, M.; Cheng, X.; Schmidt, T. J. Superior Bifunctional Electrocatalytic Activity of Ba 0.5 Sr 0.5 Co 0.8 Fe 0.2 O 3-δ /Carbon Composite Electrodes: Insight into the Local Electronic Structure. Energy Mater. 2015, 5 (17), 1402033.Fabbri, E.; Nachtegaal, M.; Binninger, T.; Cheng, X.; Kim, B.-J.; Durst, J.; Bozza, F.; Graule, T.; Schäublin, R.; Wiles, L.; Pertoso, M.; Danilovic, N.; Ayers, K. E.; Schmidt, T. J. Dynamic Surface Self-Reconstruction Is the Key of Highly Active Perovskite Nano-Electrocatalysts for Water Splitting. Mater. 2017, 16 (9), 925–931.Kim, B. J.; Fabbri, E.; Abbott, D. F.; Cheng, X.; Clark, A. H.; Nachtegaal, M.; Borlaf, M.; Castelli, I. E.; Graule, T.; Schmidt, T. J. Functional Role of Fe-Doping in Co-Based Perovskite Oxide Catalysts for Oxygen Evolution Reaction. Am. Chem. Soc. 2019, 141 (13), 5231–5240.Tulloch, J.; Donne, S. W. Activity of Perovskite La1−xSrxMnO3 Catalysts towards Oxygen Reduction in Alkaline Electrolytes. Power Sources 2009, 188 (2), 359–366.

Improvement in the Performance of an Fe/FeII Electrode in an All‐Iron Redox Flow Battery by the addition of ZnII ions

AbstractRedox flow batteries are the most promising large‐scale energy storage technologies for solving intermittency issues of renewable energy sources such as wind, solar, etc. They have favorable features over other battery technologies like high energy efficiency, intrinsic safety, independent scaling, and a long lifetime. Among various RFBs, all‐Iron redox flow batteries are an attractive choice because iron is the second most abundant metal in earth's crust, is cheap and ecofriendly. However, low charging efficiency, parasitic hydrogen evolution reaction (HER) at the negative Fe/FeII electrode, self‐discharge by electrolyte cross‐over, and poor cycle‐life (due to ferric hydroxide precipitation) are the major technical challenges to be overcome for the successful commercialization of all‐iron redox flow batteries. Herein, we report an all‐iron redox flow battery containing Fe/FeII and FeIII/FeII redox couples separated by a self‐made anion exchange membrane. We also examined the impact of adding ZnII ions on the electrochemical performance of the Fe/FeII redox couple. The coulombic efficiency, voltage efficiency and energy efficiency of the cell with 0.03 m ZnCl2 was found to be greater (90 %, 70.96 % and 63.86 %) than those of the cell without ZnCl2 (80 %, 62.06 % and 49.64 %). The results reveal that the addition of small amounts of ZnII ions to the Fe/FeII electrode suppresses the hydrogen evolution reaction and increase the cell performance.

Hybrid energy storage design and dispatch strategy evaluation with sensitivity analysis:Techno‐economic‐environmentalassessment

AbstractInternational Energy Agency reported the net‐zero carbon target by 2050 in its recent annual report. The global energy landscape is expected to anticipate an energy transition with an increase in renewable energy share from 12% to 35% for electricity sector by 2050. Most of the countries in the world had pledged to be become net‐zero or carbon neutral countries by 2050. Solar photovoltaic (PV) and wind energy will contribute 50% of energy mix in this context. Solar PV and wind energy are intermittent resources that highly depending on the weather and climate conditions. The intermittency issues caused mismatch between electricity generation and demand profiles. This will greatly affect the requirement of meeting the daily load profile, satisfying the peak demand and resulting in generation of surplus, and so on. Energy storages play a vital role in this scenario by allowing this excess energy to be stored and used to meet the demand during low energy production. Previous literature evaluated the feasibility of utilizing battery energy storage in large‐scale solar PV plant in Malaysia using load following dispatch strategy, which can be further enhanced by utilizing a hybrid energy storage system. This study aims to develop an optimized hybrid energy storage system utilizing battery and supercapacitors to complement a large‐scale solar PV system. This study also evaluates two dispatch strategies that are load following and cycle charging for three different power system configurations. Subsequently, a market leading battery is modelled with parameters such as nominal voltage, capacity, round‐trip efficiency, minimum and maximum state of charge, and maximum and minimum charge and discharge current in four different scenarios utilizing two dispatch strategies. These studies are conducted using power system and energy storage modelling tools with localized energy data for the Malaysia context. The proposed hybrid energy storage system demonstrates an improvement of about 30% in annual throughput under the load following dispatch strategy. The hybrid power system also increases the renewable energy fraction by 5% in the system. This study creates an optimized framework in the development of energy storage for grid integration that permits high level of solar PV penetration in the transmission and distribution network.

Optimization of the wood pellet supply during the continued increase of the renewable energy's proportion in the energy portfolio.

The share of renewable energy (RE) in the energy portfolio has been increasing steadily during the past decades. While the trend contributes in lowering the emission of greenhouse gases, it presents new challenges in terms of costs and intermittency. This study evaluates enhanced utilization of biomass energy as a viable solution and presents the mathematical framework for evaluating the costs associated with supplying the required amount of wood pellets. The framework addresses the uncertainty in the future price of pellets, as well as variability in the shipping and storage cost with respect to the supplier and type of facility. A case study based on the latest RE plan of the Korean government shows how the costs and net CO2 emission can change when the biomass energy is used to provide energy during the intermittency caused by the RE technologies. The results of the study suggest that a substantial difference in costs can occur depending on the supply strategy and that the biomass energy has the potential to resolve the intermittency issue while realizing the South Korean RE plan.

A History of Energy and Societal Scenarios for a World in Transition: Fifty Years of Personal Experience with Shell and Other Organisations

No-one can foresee the future with certainty. However, the development and use of alternative scenarios can help to highlight opportunities and challenges, greater or lesser realism, physical and technological options and barriers, and compatibility with other goals of sustainable development. Imagining and assessing relevant scenario elements ideally requires putting together small multidisciplinary and multi-talented teams.Over the past fifty years Shell's scenario work has envisaged energy transition – in 1971 towards greater reliance on nuclear and coal, from 1973 in response to ecological concerns, and from 1974 exploitation of solar energy resources as the single most promising ‘new’ renewable source. Hydro and hydrogen also got a mention. By 1977 particular emphasis was being placed on solar PV, while enthusiasm for coal was waning by 1975 and support for nuclear more equivocal by 1976 and withdrawn by Shell in 1978 due to the long lead times involved. In the 1977 scenario books wind, wave, ocean thermal, and biomass sources were also considered. Then in April 1986 a study of “The Greenhouse Effect” was first issued. The need to balance growing environmental concerns while providing energy services to meet increasing world demand became a growing concern.From this concern flowed support for the rapid expansion of the availability and use of renewable forms of energy in some quarters, but scepticism in others - reflected in the scenario books issued in 1975 and 1976. This apparent scepticism reflected concerns about ‘new’ renewable forms of energy being insufficiently effective due to their low power density and issues of intermittency and needed storage, rather than opposition to transition in principle, despite likely impacts on oil demand. Interest in investigating the potential of the main forms of renewable energy and their scope for energy transition continued.Here is considered the relevance of past scenarios, particularly those produced by Shell, but also the World Energy Council, UNDP, the IPCC, and others with which the author has had an involvement over the past fifty years. A list of scenario reports, related publications, and suggestions on what knowledge and skills are likely to be helpful for those involved with energy scenarios, are provided in the Annexes. It is concluded that seeking to consider a wide range of possible opportunities and threats incorporated into alternative scenarios should be of great value for individuals, business corporations and society. However, the history of the use of past scenarios is mixed: there are examples where signals were heeded, and others where they have not been – yet.

Boosting the electrochemical energy storage and conversion performance by structural distortion in metal–organic frameworks

The engineering of multifunctional materials applied to energy storage and conversion remains an important challenge in addressing the intermittency issues associated with natural energy resources. Herein, we have achieved an overall improvement in the electrochemical performance of metal–organic frameworks (MOFs) through an elaborate lattice distortion strategy. Compared to the ordered lattice in conventional materials, the partially distorted lattice in the newly synthesized MOFs contributes a completely new kinetics feature: a surface-controlled and high-rate Faradaic reaction. In-situ water splitting can be achieved by employing the lattice-distorted MOF as both the anode of an asymmetric supercapacitor and electrocatalyst, thereby converting intermittent clean energy into electrochemical energy. The lattice distortion strategy in this work provides new insight into the functional design of MOFs, and may provide a novel and economically sound strategy for practical energy sustainability.

Deployment of wind turbine in between cement silos for small power generation

This study provides an overview of Building-Integrated Wind Turbines, focusing on cement silos as wind concentrators, along with determining the amount of power that could be connected without regard to wind direction. The motivation of this research is the intermittency issue of wind stream in an open environment and non-exploration of wind turbines between cement silos. Building-Augmented Wind Turbines provide 717 W of aerodynamic power at 16 m/s, whereas Standalone Wind Turbines produce 562 W. This is due to the wind speed acceleration between buildings, which causes a concentration effect. Meanwhile, using the simulation software ANSYS, the turbine geometry is developed utilising a Computational Fluid Dynamics evaluation.

Optimal standalone data center renewable power supply using an offline optimization approach

Because of the increasing energy consumption of data centers and their CO2 emissions, the ANR DATAZERO2 project aims to design autonomous data centers running solely on local renewable energy coupled with storage devices to overcome the intermittency issue. In order to optimize the use of renewable energy and storage devices, a MILP solver is usually in charge of assigning the power to be supplied to the data center. However, in order to reduce the computation time and make the approach scalable, it would be more appropriate to use a polynomial time algorithm. This paper aims at showing and proving that it is possible to provide an optimal power profile via a deterministic algorithm using a binary search approach. Considering the main constraints of the initial problem, numerous experimental results show similar results to those given by the MILP. These promising results encourage us to continue in this direction for proposing an efficient management of the data center power supply that takes uncertainty into account.

Highly Efficient, Stable, and Scalable Integrated Hybrid Perovskite Photoelectrochemical Cells with STH>12.4% for Water Splitting

A global effort to decrease green house emissions and the cost of renewable energy technologies such as solar and wind have triggered a systematic effort in their adoption for the generation of clean electricity. However, the widespread incorporation of photovoltaic technologies has been hindered by their costs, which are still not on-par with electricity produced using non-renewables, and by intermittency issues for solar. While batteries provide a possible solution, a key challenge is their variability and lack of long-term stability. Solar fuels, which are highly scalable and offer the stability of storage in chemical bonds are a promising solution, but the technologies that enable generation are not yet efficient, scalable, and cheap.Integrated photoelectrochemical cells (PECs) directly couple the photoabsorber to the electrolyte through anticorrosion barriers and surface-deposited electrocatalysts (Fig. 1A). State-of-the-art devices use multijunction III-V panel photoabsorbers and are limited by high cost. Alternative absorbers like Si have insufficient voltage, and particle photocatalysts, while stable, are inefficient. Halide perovskites are promising next-generation photoabsorbers, providing >2V open-circuit voltage with two devices in series (photocathode + photoanode) at low cost (estimated <$100/m2 PV panels). Yet, due to their spontaneous dissolution in water at any applied bias, PECs based on HaPs have demonstrated low efficiencies (ABPE<10%, STH<6%) and stabilities.Here, we demonstrate a high-efficiency integrated hybrid perovskite based photoelectrochemical (HaP-PEC) device, which can perform bias free water-splitting at a solar-to-hydrogen (STH) efficiency of 12.4%. The HaP-PEC is enabled by two important innovations. First, by using a novel geometry, we decouple the light-absorption and electrochemical reaction interfaces for both the photocathode and the photoanode. Second, we have developed a new corrosion barrier technology, which is modular, scalable and importantly can almost perfectly translate the photovoltaic efficiency to the catalytic site.Using this approach, we report the transformation of a p-i-n perovskite solar cell (PSC) with photoconversion efficiency (PCE) > 20% into a photocathode for HER with applied-bias photoconversion efficiency (ABPE) > 20%, almost fully translating the efficiency of the parent solar cell to the Pt catalyst (Fig. 1B). Under bias at 0V vs RHE, the device was stable for up to 8h in 0.5M H2SO4. Scale-up of the photocathode to an absorber area of ~0.43 cm2 showed a decrease in the photovoltaic PCE (~10%) but again complete preservation of the photovoltaic efficiency in the ABPE (~10%). We further demonstrate the versatility of this approach by transforming an n-i-p PSC (PCE~20%) into a photoanode for OER with ABPE ~10% (due to catalyst inefficiencies, even when using Ir) (Fig. 1B). Although the n-i-p device is incapable of extended operation in acidic media (even when biased to 1.23V vs RHE it degraded continuously over 3h), when operated in series, the tandem photocathode-photoanode system achieved bias-free water-splitting at >12.4% STH and sustained this performance for over 2h. The photoanode and the bias-free system were both limited by increased overpotential from the degradation of the OER catalyst.Broadly, we have demonstrated a photoelectrode technology which uses a low-cost photo-absorber and achieves near-equal efficiencies as the photovoltaic even at large scale. To the best of our knowledge, ours is the highest STH efficiency for an integrated solar-to-hydrogen device not containing expensive III-V photoabsorbers, and fully double that of the previous record using integrated halide perovskite photoabsorbers (~6% STH). Furthermore, our approach is reaction-agnostic due to the decoupling of light absorption and electrocatalysis. This enables a facile and low-cost pathway to arbitrary solar-powered electrochemical reactions with high solar-to-chemical efficiency. Figure 1

Multifunctional UPQC operating as an interface converter between hybrid AC-DC microgrids and utility grids

This paper proposes a multifunctional hybrid unified power quality conditioner (UPQC-H), adapted to operate as an interface converter between utility grids and hybrid microgrids (H-MG). In addition to the generation of both ac and dc buses to the H-MGs, the main structure of the UPQC-H can also integrate distributed generation (DG) systems and energy storage systems (ESS) without the need for changing any control strategy. The proposed UPQC-H is built by including two additional power switches to the conventional three-phase UPQC power circuit, which in its traditional configuration is composed of two three-phase inverters used to operate as series and parallel converters. Some advantages related to the proposed UPQC-H configuration can be highlighted, as follows: 1) versatile application to any H-MG configuration; 2) natural power exchange between the H-MG ac and dc buses of both grid-connected and islanded operating modes; 3) seamless transitions between the islanded and grid-connected operating modes, and vice versa; and 4) smoothing of intermittency issues associated to renewable energy sources. Extended static and dynamic experimental results are presented to evaluate the UPQC-H performance and explore its functionalities when interfacing a 3-phase utility grid and an H-MG with integrating photovoltaic-based DG and ESS.

A dendrite free Zn‐Fe hybrid redox flow battery for renewable energy storage

AbstractAbout two thirds of global greenhouse emissions is caused by burning of fossil fuels for energy purposes and this has spurred great research interest to develop renewable energy technologies based on wind, solar power, and so on. Redox flow batteries (RFB) are receiving wide attention as scalable energy‐storage systems to address the intermittency issues of renewable energy sources. However, for widespread commercialization, the redox flow batteries should be economically viable and environmentally friendly. Zinc based batteries are good choice for energy storage devices because zinc is earth abundant and zinc metal has a moderate specific capacity of 820 mA hg−1 and high volumetric capacity of 5851 mA h cm−3. We herein report a zinc‐iron (Zn‐Fe) hybrid RFB employing Zn/Zn(II) and Fe(II)/Fe(III) redox couples as positive and negative redox systems, respectively, separated by a self‐made anion exchange membrane (AEM). The battery delivers a good discharge voltage of approximately 1.34 V at 25 mA cm−2, with a coulombic efficiency (CE) of 92%, voltage efficiency (VE) of 85% and energy efficiency (EE) of ~78% for 30 charge‐discharge cycles. Repeated galvanostatic charge/discharge cycles show no degradation in performance, confirming the excellent stability of the system. A key advancement in the present Zn‐Fe hybrid redox flow battery with AEM separator is that no dendrite growth was observed on zinc electrode on repeated charge‐discharge cycles, which was the serious drawback of many previously reported zinc based redox flow batteries.

Reversible Solid Oxide Cells: Durability of Fuel Electrodes Against Voltage Cycling

Introduction Reversible Solid Oxide Cells (rSOCs, or solid oxide reversible cells) are an attractive electrochemical energy conversion technology that can act as both a Solid Oxide Fuel Cell (SOFC) for power generation, and a Solid Oxide Electrolysis Cell (SOEC) for steam electrolysis (1). In the near future, renewable energy sources, such as wind and solar, are set to dominate energy production, however, these suffer from intermittency issues based on weather conditions. Therefore, it is desirable to adjust the supply of fluctuating electricity production from renewable energy sources to match demand using rSOCs, for hydrogen storage in the SOEC mode and for power generation using stored hydrogen in the SOFC mode. This concept is schematically described in Figure 1. The purpose of this study is to examine the degradation of rSOCs using conventional fuel electrode materials, for comparison with alternative fuel electrode materials, which are under development. Experimental Reversible voltage cycle tests simulating rSOC operation were conducted using conventional cell materials: Cermet of Ni- with Sc2O3-doped ZrO2 (ScSZ) for the fuel electrode; dense 200 m thick ScSZ membrane for the electrolyte; and La0.6Sr¬0.4Co0.2Fe0.8O0.3 oxide (LSCF) air electrode with Gd-doped CeO2 (Gd0.1Ce0.9O2) acting as a buffer layer between the ScSZ electrolyte. A Pt-based reference electrode was deposited beside the air electrode, such that the fuel electrode potential was measured as the voltage between the fuel electrode and the reference electrode. The durability of the fuel electrodes were evaluated at an operating temperature of 800C. Air was supplied to the air electrode, while 50%-humidified hydrogen was supplied to the fuel electrode. Reversible operation was investigated by repeatedly changing between the SOFC and SOEC modes by switching the direction of current for up to 1,000 cycles, as shown in Figure 2. The current density in the SOFC and SOEC modes are expressed as positive and negative values, respectively. The current sweep rate was 1.5 mA cm-2 s-1. Current density was varied within ± 0.2 A cm-2, and the fuel electrode potential was measured at the peak current of ± 0.2 A cm-2 for each cycle. Here, the performance degradation of the Ni-cermet fuel electrode was examined by switching between the SOEC mode and the SOFC mode, simulating possible rSOC operation conditions. Results and discussion Figure 3 shows the fuel electrode potential measured at ± 0.2 A cm-2, every 50 cycles. Degradation within 1,000 cycles was calculated to be 30.6%, as the average value of voltage degradation between the SOFC and SOEC modes. Such degradation could be associated with microstructural changes, e.g. due to a redox reaction between Ni and NiO (2), during rSOC operation. Such degradation could be reduced by using redox-tolerant fuel electrode materials, in which redox-stable materials are used as the stable backbone in the porous electrode structure. Current-voltage characteristics, rSOC cycle durability, and long-term stability of various fuel electrodes will be presented, including alternative co-impregnated electrodes (3,4). Such results will be compared with those using the conventional Ni-cermet fuel electrode. Acknowledgements A part of this study was supported by “Research and Development Program for Promoting Innovative Clean Energy Technologies Through International Collaboration” of the New Energy and Industrial Technology Development Organization (NEDO). Collaborative support by Prof. H. L. Tuller, Prof. B. Yildiz, and Prof. J. L. M. Rupp at Massachusetts Institute of Technology (MIT) is gratefully acknowledged.

Energy storage sizing and enhanced dispatch strategy with temperature and safety considerations: A techno‐economic analysis

AbstractMalaysia signed Paris agreement in 2015 as global response to climate change and committed to lower the greenhouse gases emissions by 45% by 2030. Under this national initiative, Malaysia government planned a series of large scale solar (LSS) projects and regulated by Energy Commission. It is aimed to achieve installed capacity of 1 GW by 2020. One of the main drawbacks for using solar energy is the intermittent issue in solar power generation. This will affect the power quality and reliability of the power grid especially in the LSS systems. This article aims to identify and optimize the most technically and economically viable energy storage system (ESS) for selected locations among the ongoing mega projects. The location selection for this study is based on the largest solar capacity planned for Peninsular Malaysia. This project involved development of hybrid scheme including Flywheel and nine different types of battery at six locations in Malaysia using Energy Commission Malaysia's data. Comprehensive power systems have been developed with different storage options applied to selected locations. This is followed by extensive techno‐economic evaluation using net present cost, levelized cost of electricity including costs of ESS, operation &amp; maintenance, initial capital investment, replacement cost, revenue from ESS, annual throughput, and so on. Comparative studies under two different dispatch strategies with local contextualized data for LSS projects in Malaysia have been carried out. The optimal ESS type both technical and economically has been identified. In addition to this, performance of battery ESS with and without temperature consideration has been evaluated. Last, data from a net metering scheme is used to analyze the ESS types that exhibit best performance. Safety concerns related to these ESS types have been provided. Last, this article also presents the adaptability and replicability of the proposed methodology in countries that planned for LSS with local contextualized data.

Solar Field Output Temperature Optimization Using a MILP Algorithm and a 0D Model in the Case of a Hybrid Concentrated Solar Thermal Power Plant for SHIP Applications

Using solar power for industrial process heat is an increasing trend to fight against climate change thanks to renewable heat. Process heat demand and solar flux can both present intermittency issues in industrial systems, therefore solar systems with storage introduce a degree of freedom on which optimization, on a mathematical basis, can be performed. As the efficiency of solar thermal receivers varies as a function of temperature and solar flux, it seems natural to consider an optimization on the operating temperature of the solar field. In this paper, a Mixed Integer Linear Programming (MILP) algorithm is developed to optimize the operating temperature in a system consisting of a concentrated solar thermal field with storage, hybridized with a boiler. The MILP algorithm optimizes the control trajectory on a time horizon of 48 h in order to minimize boiler use. Objective function corresponds to the boiler use, for completion of the heat from the solar field, whereas the linear constraints are a simplified representation of the system. The solar field mass flow rate is the optimization variable which is directly linked to the outlet temperature of the solar field. The control trajectory consists of the solar field mass flow rate and outlet temperature, along with the auxiliary mass flow rate going directly to the boiler. The control trajectory is then injected in a 0D model of the plant which performs more detailed calculations. For the purpose of the study, a Linear Fresnel system is investigated, with generic heat demand curves and constant temperature demand. The value of the developed algorithm is compared with two other control approaches: one operating at the nominal solar field output temperature, and the other one operating at the actual demand mass flow rate. Finally, a case study and a sensitivity analysis are presented. The MILP’s control shows to be more performant, up to a relative increase of the annual solar fraction of 4% at 350 °C process temperature. Novelty of this work resides in the MILP optimization of temperature levels presenting high non-linearities, applied to a solar thermal system with storage for process heat applications.

Utilization of Crystalline and Amorphous Silica as a Sintering Inhibitor in Iron/Iron Oxide Thermochemical Water Splitting Cycle

Hydrogen as a chemical fuel and energy carrier can provide the path to solar energy storage to overcome the intermittency issues. Hydrogen can be produced by various methods; among them is the thermochemical water splitting of metal/metal oxide reduction oxidization (redox) reactions. Many redox cycles were identified, including the non-volatile redox pair, such as the iron/iron oxide. This redox pair has the capability to produce Hydrogen with rapid reaction rates especially when it is used in powder form due to the high specific reactive surface area. Yet, this pair suffers from sintering at temperatures exceeding 500°C. Sintering adversely affects the Hydrogen production process and inhibits the recycling of the powder. To overcome sintering, experimental investigations using elemental iron and silica were conducted as detailed in this paper. The oxidation of elemental iron (Fe) powder by steam to produce Hydrogen was carried out using a fluidized bed reactor. The investigations aimed at developing a practical sintering inhibition technique that can allow repeated redox cycles, stabilize the powder reactivity, and maintain Hydrogen production. The experimental investigations involved varying the fluidized bed temperature between 630–968°C. The steam mass flow rate was set to 2 g/min. To inhibit sintering, solid-state mixing of crystalline, or amorphous silica with porous iron powder was used at various iron/silica volume fractions. The investigations showed that mixing iron with silica hinders the sintering but reduces the Hydrogen yield. Mixing iron with crystalline silica with 0.5, 0.67, and 0.75 apparent volume fraction reduces the Hydrogen yield compared to pure iron by 20, 30, and 45%, respectively. Mixing iron with amorphous silica reduces the Hydrogen yield by 35 and 45%, as compared to pure iron, for iron 0–250 and 125–355 µm particle size distribution, respectively. The Hydrogen production rate for iron/amorphous silica mixtures surpassed that of the iron/crystalline silica. Mixing iron with amorphous silica prevented sintering at elevated bed temperatures in the range of 850°C, and only clumping occurred. The clumped samples restored their original powder condition with minimum agitation. Thus, solid-state mixing of amorphous silica with iron powder can be a promising technique to retard iron/iron oxide particles sintering.

Corrosion in Molten Salts for Solar Thermal Power

Global energy needs continue to grow steadily with increasing population and standard of living. While fossil fuels have been a major source of our energy, they are no longer favorable due to their greenhouse gas emissions and atmospheric pollution; the development of carbon-free sources of energy is crucial. Solar energy promises unlimited amounts of emissions-free energy but suffers from intermittency issues that require expensive secondary energy storage systems to act as baseload power. A thermal energy storage (TES) system can store heat and provide a continuous source of power. Concentrated solar power (CSP) is carbon-free and can ideally be combined with a TES system to provide continuous power. These combined systems operate by focusing a large area of sunlight onto a receiver that contains a TES material to convert the sunlight into thermal energy.