Penetration Of Intermittent Renewable Energy Research Articles

A distributionally robust energy management of microgrid problem with ambiguous chance constraints and its tractable approximation method

As the penetration of intermittent renewable energy increases in microgrid systems, flexible power generation resources cause the power imbalance problem. To improve the absorption of renewable energy and to deal with its uncertainty more effectively, this paper proposes a distributionally robust approximate model for microgrid with ambiguous chance constraints (DR-CCP). First, the distributionally robust model with ambiguous chance constraints is a semi-infinite chance constrained planning problem, which is computationally difficult and inefficient, so the use of Chernoff's inequality to derive a safe tractable approximation form for the ambiguous chance constraint on the basis of a probability distribution for ambiguous sets including bounded perturbations with mean zero, transforms it into a mixed integer linear programming problem that can be directly solved using CPLEX to solve it. Then, the optimal value of the proposed model is used to approximate equivalent conditional value at risk (CVaR), and the relationship with CVaR is established. The optimal solution of our model is employed to construct multiple sets of comparison models, enhancing the richness of numerical experiments. Finally, to validate the feasibility and effectiveness of our proposed model, a series of diverse tests are performed on the IEEE 33-bus power distribution system.

(Invited) Understanding Capacity Fade Behavior in Aqueous Organic Redox Flow Batteries Via Zero-Dimensional Models and High-Throughput Cell Cycling

Aqueous Organic Redox Flow Batteries (AORFBs) have emerged as promising and potentially disruptive technologies for the storage of electrical energy from intermittent renewable sources for use over long discharge durations when the sun isn’t shining and the wind isn’t blowing. AORFBs could become preferred over Li-ion batteries for grid-scale stationary storage due to their potentially low-cost active materials made of Earth-abundant elements, their inherent non-flammability, and the intrinsic decoupling of energy and power capacities in the flow battery design. Our group has 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]. To accurately determine molecular fade rates, we utilize potentiostatic cycling to avoid artifacts caused by drifts in internal resistance and employ volumetrically unbalanced compositionally symmetric cell configurations to distinguish molecular fade from membrane crossover or the two sides drifting out of balance.We have developed a high-throughput setup for AORFBs, capable of cycling cells at elevated temperatures, providing a new dimension in the flow battery characterization space to explore multiple cell parameters simultaneously. The recent incorporation of the decay of active material into zero-dimensional cell-cycling models for AORFBs [2,3] allows for exploration of the causes of various trends seen in flow cell temporal capacity behavior. Complemented by zero-dimensional modelling, we explore temporal capacity evolution in symmetric cells driven by different capacity fade mechanisms such as active species degradation [4], self-discharge [5], and membrane crossover. Collectively, these results highlight the relevance of electrochemical techniques to understand molecular degradation in AORFBs and 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] S. Modak and D. G. Kwabi, “A Zero-Dimensional Model for Electrochemical Behavior and Capacity Retention in Organic Flow Cells,” Journal of the Electrochemical Society, 168, 080528 (2021).[3] B. J. Neyhouse, J. Lee, F. R. Brushett, “Connecting Material Properties and Redox Flow Cell Cycling Performance through Zero-Dimensional Models” Journal of The Electrochemical Society, 169, 090503 (2022).[4] D. G. Kwabi, Y. Ji, M. J. Aziz, “Electrolyte Lifetime in Aqueous Organic Redox Flow Batteries: A Critical Review,” Chemical Reviews, 120, 6467 (2020).[5] E. M. Fell, D. De Porcellinis, Y. Jing, V. Gutierrez-Venegas, R. G. Gordon, S. Granados-Focil, M. J. Aziz, “Long-term stability of ferri-/ferrocyanide as an electroactive component for redox flow battery applications: On the origin of apparent capacity fade,” ChemRxiv (2022). https://chemrxiv.org/engage/chemrxiv/article-details/62913087f89e5d4e6ee8828d

A distributionally robust approximate framework consider CVaR constraints for energy management of microgrid

As the penetration of intermittent renewable energy increases in microgrid systems, flexible power generation resources cause the power imbalance problem. To improve the absorption of renewable energy, this paper proposes a distributionally robust (DR) approximate framework considering conditional value-at-risk measures for energy management of microgrids based on cooperative scheduling energy storage and direct load control operations. First, combined with CVaR and DR theory, DR CVaR constraints that can quantitatively the power balance risk of microgrid is constructed. Then, to improve the efficiency of solving DR CVaR constraints, it is tractably approximated using Jensen’s​ inequality, and the approximate error of DR CVaR constraint is analyzed by comparing two different Jensen’s inequality gap expressions so that the decision maker can select the appropriate approximate DR CVaR constraint according to the actual needs. Finally, the appropriate DR CVaR framework of the microgrid is transformed into mixed-integer linear programming that can be directly solved by CPLEX. The approximate framework has the characteristics of risk aversion measurement, linear efficient solving, and flexible decision-making. And it is also verified on the IEEE 33-bus distribution system through a wide range of different tests.

Leveraging Temperature-Dependent (Electro)Chemical Kinetics to Accelerate Redox Flow Battery Active Material Characterization

Aqueous Organic Redox Flow Batteries (AORFBs) have emerged as promising and potentially disruptive technologies for the storage of electrical energy from intermittent renewable sources for use over long discharge durations when the sun isn’t shining and the wind isn’t blowing. AORFBs could become preferred over Li-ion batteries for grid-scale stationary storage due to their potentially low-cost active materials made of earth-abundant elements, their inherent non-flammability, and the intrinsic decoupling of energy and power capacities in the flow battery design. Our group has 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]. To accurately determine molecular fade rates, we utilize potentiostatic cycling to avoid artifacts caused by drifts in internal resistance and employ volumetrically unbalanced, compositionally symmetric cell configurations to distinguish molecular fade from membrane crossover or cell unbalancing. Redox-active organic molecule stability has improved to the point that the most stable chemistries degrade at less than 1% per year [2]. With further lifetime increases, the measurement of lower capacity fade rates necessitates higher precision coulometry methods [3] and thermally accelerated degradation protocols [4] to determine which stabilizing approaches are most effective without waiting for multi-month cycling tests to quantify capacity fade.We have developed a high-throughput setup for cycling AORFBs at elevated temperatures, providing a new dimension in the flow battery characterization space to explore. Capacity fade rates of previously published redox-active organic molecules, as functions of temperature, are evaluated in the high-throughput setup providing the ability to extrapolate fade rates to lower operating temperatures. The effect of temperature on electrochemical regeneration [5,6] of decomposed organic molecules is also explored. Collectively, these results highlight the importance 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, 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. A. Stevens, R. Y. Ying, R. Fathi, J. N. Reimers, J. E. Harlow, 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).[5] M. Wu, M. Bahari, E. M. Fell, R. G. Gordon, M. J. Aziz, “High-performance anthraquinone with potentially low cost for aqueous redox flow batteries”, Journal of Materials Chemistry A, 9, 26709 (2021).[6] Y. Jing, E. W. Zhao, M.-A. Goulet, M. Bahari, E. M. Fell, S. Jin, A. Davoodi, E. Jónsson, M. Wu, C. P. Grey, R. G. Gordon, M. J. Aziz, “In situ electrochemical recomposition of decomposed redox-active species in aqueous organic flow batteries,” Nature Chemistry, 14, 1103, (2022).Figure caption: Capacity fade rates of an anthraquinone derivative, measured in symmetric cells, as a function of temperature. Figure 1

Concrete based molten salt storage tanks

High-temperature molten salt mixtures such as chloride-based salts have been widely investigated in recent years as alternate thermal energy storage media since they can enable higher temperature power cycles with higher thermodynamic efficiencies in concentrated solar power plants. They can also be used to decarbonize industrial processes requiring high-grade heat for industries located in electrical grids with increasing penetration of intermittent renewable energy. However, molten salts in general, and chloride salts in particular, are highly corrosive towards metals and thus require special stainless steel grades for storage tank construction. These grades, such as nickel-based alloys, can be up to four times more expensive than a regular grade stainless steel. Therefore, the primary cost driver for high-temperature chloride salts is the tank material instead of the salt itself which limits the commissioning of high-temperature thermal energy storage plants. Until now, a low-cost tank material which can effectively overcome the problems associated with molten salts operating above 670 °C has not been reported. In this work, we present low-cost engineered concrete-based thermal energy storage tanks for molten salts capable of operating at high temperatures even in corrosive environments. The engineered concrete composites are developed using commercially available additives and coatings. Tank prototypes, filled with moderate-temperature nitrate salts, are rigorously tested under thermal cycling conditions to demonstrate that the tanks can effectively withstand thermal shocks experienced during daily salt charge/discharge cycles. Moreover, salt diffusion through the porous concrete walls is shown to be suppressed by using external coatings. Finally, the compatibility of engineered composites with high-temperature chloride salts is qualitatively evaluated under a high-flux solar simulator.

Voltage profile assessment in smart distribution grids considering BESS and communication network failures

• Sequential monte carlo simulation for assessing voltage profile of smart grids. • modeling failures in the BESS systems and the communication network (CN). • BESS optimization models for day ahead scheduling and voltage profile correction. • The results shows that communication failures have impact on the voltage profile. Battery energy storage systems (BESSs) are expected to play a major role in voltage control of smart distribution grids (SDGs) due to the high penetration of intermittent renewable energy. However, neither these devices nor the communication infrastructure needed for their control, are fully reliable. Due to this, BESS unavailability might occur, degrading voltage profile. This paper presents a new fixed-time sequential Monte Carlo simulation for assessing indices of SDGs’ long-duration voltage variations (LDVVs) considering both failures in BESS systems and in the communication network (CN). Results show that these failures have significant impact on the LDVV indices of the SDG.

Distributionally Robust Unit Commitment With Flexible Generation Resources Considering Renewable Energy Uncertainty

As the penetration of intermittent renewable energy increases in bulk power systems, flexible generation resources, such as quick-start gas units, become important tools for system operators to address the power imbalance problem. To better capture their flexibility, we proposed a two-stage distributionally robust unit commitment framework with both regular and flexible generation resources, in which the unit commitment decisions for flexible generation resources can be adjusted in the second stage to accommodate the renewable energy intermittency. In order to tackle this challenging two-stage distributionally robust mixed-binary model, to which traditional separation algorithms won’t apply, we designed a revised integer L-shaped algorithm with lift-and-project cutting plane techniques. In comparison to the traditional distributionally robust unit commitment, the proposed approach can reduce the system cost through an improved flexible resource quantification in the modeling.

A Supervised-Learning Assisted Computation Method for Power System Planning

To achieve a low-carbon economy, the comprehensive planning of the early retirement of coal-fired power plants (CFPPs), the construction of renewable energy plants, and the investment in energy storage systems (ESSs) are critical. However, the nonlinear characteristic of the alternating current power flow (ACPF) brings difficulties in solving the long-term planning problem efficiently. Hence, in this article, a learning and optimization integrated framework is presented to help the power sector to reach the emission reduction goal economically while guaranteeing system security and reliability. First, the electricity network transition from the fossil fuel-dominated system to the low-carbon-oriented system is planned. Then, a data-driven method is utilized to regress the power flows, and a method is proposed to integrate the data-driven model into an optimization problem to alleviate the heavy computational burden. Because the penetration of intermittent renewable energy is high in a low-carbon energy system, the security and reliability of the planning decisions are verified in the second level by the N-1 security check. Simulation results reveal that the data-driven method can calculate power flows more accurately than direct current power flow (DCPF) and linearized ACPF models. Also, the supervised-learning method can help reduce computing time. The proposed planning model is verified on the IEEE 30-bus system. Through case studies, it can be concluded that our proposed method can reach the low-carbon goals with the lowest cost, and reliability can be ensured at the same time. Because of the coordinated retirement of CFPPs and the proper planning of ESS, the planned electricity system can cope with uncertainties better.

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).

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).

Multi-objective co-optimization of the guide vane closure law and rotor inertia in pumped-storage power system

Improving the transition safety and stability of pumped-storage hydropower plants supports the penetration of intermittent renewable energy into the grid. This paper presents the multi-objective optimization of the guide vane closure law and rotor inertia to reduce the rotational speed, water hammer pressure, and draft-tube vacuum by adopting genetic algorithms and a one-dimensional method of characteristic during load rejection transients. To reduce the increase in rotational speed to indirectly suppress pressure pulsations, a co-optimization of the guide vane closure law and rotor inertia is proposed. Results suggest that the above-mentioned co-optimization scheme can significantly reduce the increase in the rotational speed, water hammer pressure, and draft-tube vacuum and suppress the influence of pressure pulsations on the extreme pressure heads at the volute inlet and draft-tube inlet. Additionally, it can significantly reduce the transformation number of operation modes during pump-turbine load rejection transients.

Integrated capacity configuration and control optimization of off-grid multiple energy system for transient performance improvement

The off-grid multiple energy system offers a promising way for energy supply due to its advantages of independency, multi energy co-generation, high efficiency and local utilization of renewable energy. A key issue of the off-grid multiple energy system is the operating performance during the dynamic transition because it is isolated from the utility grid. The conventional steady-state configuration methods ignore the significant impact of configuration scheme on the transient performance of the multiple energy system, which can easily lead to poor dynamic performance, thus are not suited for the off-grid multiple energy system with high penetration of intermittent renewable energy. It is necessary to consider the closed-loop dynamic control behavior of the system early in the configuration stage. To this end, this paper proposes a novel integrated capacity configuration and control optimization method of the multiple energy system, in which both the economic costs and closed-loop dynamic performance are fully considered. The multi-parametric programming is applied to construct a design-perceptive predictive tracking controller to bridge the gap between configuration and dynamic operation of the system. Case study on a typical off-grid combined heat and power multiple energy system shows that the proposed approach can reduce the dynamic thermal and electrical deviations of the multiple energy system by 84.45% and 28.11% respectively at the expense of only 1.86% increase of total economic costs. In-depth validations are carried out under extreme weather conditions and low carbon requirements, which further demonstrate the effectiveness and applicability of the proposed approach.

A Data Driven Approach for Day Ahead Short Term Load Forecasting

This paper aims to develop an evolutionary deep learning based hybrid data driven approach for short term load forecasting (STLF) in the context of Bangladesh. With the lapse of time, the power system is getting complex. Penetration of intermittent renewable energy (RE) into the grid, changing prosumer load pattern with the need of demand side management (DSM) has thrown a challenge for dynamic power system operation and control. Load forecasting plays a significant role in this dynamic operation and control. In addition, it directly affects the future planning of network expansion, unit commitment and economic energy mix for power market. Day ahead short-term forecasting is very crucial for day to day operation. As such, various conventional and modified methods have been used over time for short-term prediction. Nevertheless, the existing approaches like age old statistical methods, artificial intelligence (AI), machine learning (ML), deep learning (DL) techniques alone cannot provide effective accuracy all the time. Hence, an integrated genetic algorithm (GA)-bidirectional gated recurrent unit (Bi-GRU) hybrid data driven technique (GA-BiGRU) is proposed in this work. The developed method is validated in Bangladesh power system (BPS) network by providing day ahead forecasting of electrical load of the whole country. Besides, the performance of the prediction model is compared with some existing approaches such as long short-term memory network (LSTM), gated recurrent unit (GRU) and integrated genetic algorithm-gated recurrent unit (GA-GRU) in terms of mean absolute performance error (MAPE) and root mean squared error (RMSE). The outcome gives an indication of better forecasting accuracy of proposed GA-BiGRU evolutionary DL technique compared to others.

Operational Probabilistic Power Flow Analysis for Hybrid AC-DC Interconnected Power Systems with High Penetration of Offshore Wind Energy

With increasing penetration of intermittent renewable energy, power systems are facing great pressures in real-time operation and control. Minutes ahead short-term static risk assessment using the probabilistic power flow (PPF) can help system operators detect potential over-limit risks in advance and take preventive measures in time. However, current probability models of renewable power outputs lack enough adaption and efficiency in operational stage, and the PPF formulation also neglects the effects of control system and tie line power exchange of large power systems. This paper establishes a systematic operational PPF scheme for hybrid AC-DC interconnected power systems with offshore wind energy integration. An adaptive probabilistic modeling and fast update method is proposed to model multiple time-varying offshore wind power outputs. Considering different responses of control systems and AC/DC tie line power exchanges, a novel hybrid PPF is proposed to reflect power flow uncertainty more robustly and accurately. The above techniques are validated on a modified IEEE 30 bus system and the whole scheme is applied to the short-term static risk assessment of a real system in Southern China. The results show that our proposed scheme can well meet online calculation requirements, and can also achieve a more realistic characterization of operational PPF.

What can be learned from the French partial nuclear shutdown of 2016?

The penetration of intermittent renewable energies in the electricity mixes impact the wholesale price. In the absence of electricity storing capacities at reasonable costs, the back-up of the intermittent renewable energies is ensured by fossil or nuclear power plants. In 2016 the French Nuclear Safety Authority has ordered the shutdown of a large part of nuclear units for safety reasons. This paper analyses the impact of such a decision both on the evolution of the whole-sale price of electricity and on the French commercial balance. Although the resulting mix from the partial shutdown of the nuclear power plants was able to produce the electrical energy consumed, it was unable to keep up with demand. This has resulted in a very sharp increase in the price of electricity on the spot market and in massive electricity imports at peak times. Moreover the carbon electricity footprint produced in France is much lower than the one pro-duced by its neighbors. Consequently, the nuclear partial shutdown has a negative climatic impact resulting in a deterioration of the citizen welfare. Thus, the French experience of 2016 teaches us that in the absence of electricity storage facilities, there is no point in trying to re-duce the share of nuclear and fossil fuels in the electricity mix. If the policymakers want to do so, they must ensure that massive electricity storage facilities are present and promote electrici-ty demand flexibility on a large scale. This study highlights also the divergence that can exist between the interest of the nuclear producer (higher revenues) and the collective interest (lower welfare and negative impact on the trade balance).

Solid Oxide Cell Technology for Supply, Recovery, and Storage Energy

Fuel Cell Energy, Inc. (FCE) is advancing the current state of Solid Oxide Fuel Cell (SOFC) technology towards commercial deployment for efficient and nonpolluting generation of electric power from natural gas and biomass derived fuels. Additionally, FCE is utilizing the same solid oxide cell and stack technology in electrolysis of steam for production of hydrogen from renewable sources and other electric power sources, such as nuclear power plants during the curtailment periods. Additionally, FCE’s SOFC technology has shown to be a viable technology for storage of energy by cyclic charge and discharge operation.FCE’s SOFC technology is based on anode supported thin electrolyte planar cell platform chosen for its higher power density at reduced operating temperature (700-800°C). Traditional materials, such as Ni/YSZ anodes, YSZ electrolytes and perovskite cathodes have been utilized in a basic cell structure. Research and development focus has been placed on developing better electrochemical functional areas at both cathode/electrolyte and anode/electrolyte interfaces. This was achieved through material advancements, microstructure optimization, and manufacturing process integration.The solid oxide stack is comprised of planar solid oxide fuel cells with glass ceramic seals and sheet metal, bipolar plate interconnects; and has a mix of internal and external gas manifolds. Each cell is a 0.30 mm thick annular (donut shaped), cell with 81 cm2 active area made in a process consisting of tape casting, screen printing, and firing cell components. The full height stack consists of 350 repeat units and a set of non-repeat parts. A repeat unit includes one ceramic cell, inner and outer seals, and a metallic interconnect which incorporates flow fields for both fuel and oxidant. Non-repeat parts include the end plates, manifolds, and compression components. The stack is capable of producing 7kW power when fueled with natural gas, biogas, hydrogen, or other fuels. The same stack is capable of operating at higher power density in electrolysis mode, producing 25 kg/day hydrogen with 36 kW power input.FCE’s SOFC system design philosophy is based on using factory-assembled stack building blocks, which in turn may be used to fabricate larger multi-stack modules for applications in centralized natural gas and coal fueled power plants. An attractive pathway to deployment of SOFC systems is through near-term market opportunities in natural gas fueled distributed generation (DG) applications. FCE is planning to take the advantage of the scalability, modularity, and fuel flexibility of the SOFC technology to transition the technology from small (sub-MW) systems to megawatt class power plants for distributed generation, and ultimately (through aggregation of fuel cell modules) to large stationary power plants for base-load utility applications using coal and/or natural gas fuel.FCE has recently designed, fabricated, and tested a 200kW natural gas fueled packaged system. This autonomous unit is an outdoor rated power system with capabilities for both grid-connection as well as island operation.Electricity storage is a growing need given the increasing penetration of intermittent renewable sources of solar and wind. Traditional battery storage technology uses rare materials that could pose sourcing challenges and depletion with widespread adoption. Hydrogen based energy storage is the only practical way to store the GWh of energy that will need to be stored to enable significant penetration of intermittent renewable energy on the electricity grid. Another advantage of hydrogen based energy storage is that once hydrogen is stored it can be used to make power, or exported for another use such as vehicle fueling or industrial uses.

Comparison of two storage units for a sustainable off‐grid climate refuge shelter

AbstractConsidering the broad range of applications, efficient retrieval and storing electrical energy methods are still challenging. Besides the load variations, the ever‐increasing intermittent renewable energy penetration into the grid system has witnessed the system complexities. In off‐grid applications, energy storage can balance electricity consumption and electricity generation to avoid voltage and frequency deviations. This research paper focuses on the energy management of an off‐grid climate refuge system used for hot and arid locations with a system comparison for two routes of different storage techniques, namely flywheels and a lithium‐ion battery. The proposed system can generate its power from photovoltaics and provide cooling and other auxiliaries through vapor compression cycle and water misting units with an operation of about 16 hours (ie, from 7:00 am to 11:00 pm) on the weekdays and 12 hours on the weekends. A comparison of levelized costs is conducted for the evaluation using HOMER software. The annual energy production by solar photovoltaics for the proposed system is 20 MWh, and the annual consumption is 16 MWh. The photovoltaic‐battery storage system has shown the lowest cost of electricity, corresponding to 0.761 $/kWh, and net present cost of $66 238 and is optimum in all sensitivity analysis cases.

The Covid-19 shock on a low-carbon grid: Evidence from the nordics

I investigate how the Covid-19 epidemic affected consumption and prices in a part of the Nordic electricity market that has a high penetration of intermittent renewable energy: Denmark and the southernmost part of Sweden. In sharp contrast to studies of other regions, I find no overall drop in consumption in this region. However, the distribution of consumption shifted away from peak hours. Nonetheless, prices dropped significantly, with a decline that started well before the imposition of societal restrictions in Denmark. Periods where wind power covered all of local load saw prices collapse towards zero with little variance under the Covid-19 epidemic. The results have important policy implications. Energy-only markets may fail to provide sufficient investment incentives for renewable energy when penetrations of such generation are already high. Policies and technologies that shift load from peak to non-peak times may further erode market incentives.

High-Throughput Electrochemical Characterization of Aqueous Organic Redox Flow Battery Active Material

Aqueous Organic Redox Flow Batteries (AORFBs) have emerged as promising and 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 over Li-ion batteries for stationary storage due to their potentially low-cost active materials, their inherent non-flammability, and the intrinsic decoupling of energy and power capacities in the flow battery design. Recent work has 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. For accurately determining molecular fade rates, the importance has been known since 2018 of potentiostatic holds in order to avoid artifacts caused by drifts in internal resistance; additionally the utility of volumetrically unbalanced, compositionally-symmetric cell configurations to distinguish molecular fade from membrane crossover has been known [1]. However, some reports continue to use purely galvanostatic cycling to characterize molecular stability, leading to unreliable accounts of molecular fade rates.An in-depth study comparing previously published redox-active organic molecules [2-8] has been performed using the symmetric cell protocol. True capacity fade rates as functions of concentration and pH are evaluated in a high-throughput setup using high-precision coulometry. Collectively, these results highlight the relevance of electrochemical techniques to understand molecular degradation in AORFBs. By accelerating the screening process of candidate molecules for AORFBs and ensuring rigorous assessment of battery performance, these techniques are expected to more rapidly advance good candidates for long lifetime RFB designs, capable of enabling 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] E. S. Beh, D, De Porcellinis, R. L. Gracia, K. T. Xia, R. G. Gordon, and M. J. Aziz, “A Neutral pH Aqueous Organic-Organometallic Redox Flow Battery with Extremely High Capacity Retention,” ACS Energy Letters, 2, 639 (2017).[3] 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).[4] 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).[5] M.-A. Goulet, L. Tong, D. A. Pollack, D. P. Tabor, S. A. Odom, A. Aspuru-Guzik, E. E. Kwan, R. G. Gordon, and M. J. Aziz, “Extending the Lifetime of Organic Flow Batteries via Redox State Management,” Journal of the American Chemical Society, 141, 8014 (2019).[6] J. Luo, W. Wu, C. Debruler, B. Hu, M. Hu, and T. L. Liu, “A 1.51 V pH Neutral Redox Flow Battery towards Scalable Energy Storage,” Journal of Materials Chemistry A, 7, 9130 (2019).[7] 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).[8] S. Jin, E. M. Fell, L. Vina-Lopez, Y. Jing, P. W. Michalak, R. G. Gordon, and M. J. Aziz, “Near Neutral pH Redox Flow Battery with Low Permeability and Long-Lifetime Phosphonated Viologen Active Species,” Advanced Energy Materials, 2000100, (2020).

Analytic assessment of the power system frequency security

Recently, with the increased intermittent renewable energy penetration, many power grids have been incorporated into a large-scale long-distance UHV AC–DC hybrid system. In the actual grid, power disturbances, such as DC blocking faults and trip-off of wind turbines, often occur, resulting in power shortages and large frequency fluctuations. However, the existing approaches to assess the system frequency security are not reliable. This paper proposes an analytic formula for the system frequency response based on a generic system frequency-response (SFR) model, which can be applied to modern large-scale power systems. First, a generic SFR model with a reasonable structure is designed according to the parameter determination strategy. Second, according to the transfer function in the model, the time-domain analytic formula of the frequency response is obtained by realizing the inverse Laplace transform. Moreover, four main indexes are established to represent the characteristics of the frequency dynamic process in different periods, and these indexes are qualitatively and quantitatively analysed. Finally, the New England 10-unit 39-bus power system and East China Power Grid are considered to demonstrate the key features of the proposed method. The results show that the proposed analytic assessment method can be effectively adopted in several applications.