Grid Services Research Articles

Low-Cost and High Rate Na-FeCl2 Batteries for Large Scale Energy Storage Applications

Developing battery systems that are inexpensive, enduring, and safe is essential for integrating renewable energy sources such as solar and wind power into the electricity grid and providing valuable grid services such as frequency regulation, peak shaving, and arbitrage. In this regard, Na-based batteries are promising candidates because they use naturally abundant sodium (Na) as the charge carrier, which can potentially reduce the materials cost and support multiple energy storage applications. Among various Na-based batteries developed to date, thorough investigations have been done on high-temperature (~300°C) Na-metal halide (Na-MH) batteries, which offer long cycle life and superior safety. In particular, the tubular sodium-nickel chloride (Na-NiCl2 or Zebra) battery has been commercialized and found wide application in the telecom and oil/gas industries. However, the high operating temperature and cost of the Zebra battery has hindered its further market penetration. Considering constraints of the Ni-based cell chemistry, it is highly desirable to develop an alternate cathode for Na-MH batteries towards next-generation energy storage applications. This pursuit, unsurprisingly, led us to the Fe/NaCl cathode. In this study, we present an advanced Na-FeCl2 battery with unprecedented high-rate performance and low cost for stationary energy storage applications. Operated at an extremely high current density of 33.3 mA/cm2 at 190°C, the cell can output 74% of its total capacity—a capacity retention double that of IT Na-NiCl2 cells. The origin of the high rate capability of Na-FeCl2 batteries was elucidated by means of comprehensive phase/structure analysis and electrochemical/electroanalytical characterizations. Moreover, Fe particle pulverization originating from liquid-phase reactions was determined to be the major source of capacity fading during long-term cycling. Accordingly, we designed a unique cathode with Ni additive, which delivered a high discharge specific energy density of over 295 Wh/kg for 200 cycles at C/5 with almost no capacity fading.

Impact of cell balance on grid scale battery energy storage systems

With the adoption of Lithium ion battery systems for grid scale storage, a better understanding of how these systems behave is becoming necessary in order to optimise their performance. Providing different grid services results in different types of power delivery — frequency response services result in varying depth, low power cycles, whereas other services such as arbitrage result in sustained delivery, generally at a higher power. The battery systems being used consist of a large number of cells where the variation and imbalance of these can cause operational issues. Using observed data from a grid connected 2MW / 1MWh battery system these issues are presented in this paper and a hypothesis is given. The observations are recreated under lab conditions using two different types of battery module allowing analysis at cell level. The results confirm the variation in cell behaviour at upper and lower states-of-charge and methods to mitigate are proposed.

Dynamic Response Analysis on a 9 Kw Vrfb Test Facility

An industrial-scale Vanadium redox flow battery test facility (IS-VRFB) in operation at the Electrochemical Energy Storage and Conversion Laboratory of University of Padua aims at exploring the technological developments from VRFB laboratory testbeds to grid scale VRFB systems. The 40-cell 600-cm2 active-area stack and two 550-L tanks provide a power of 9 kW and an energy 27 kW h. An AC/DC bidirectional static converter that controlled by the battery management system (BMS) provides the electric power conditioning during charge and discharge with currents up to 75 A and a variable passive load allows high-current discharges up to 600 A. The plant is fully instrumented with electrical and thermo-fluid dynamic probes and the in-house LabVIEW-based BMS provides acquisition, processing and control functions. Since VRFBs are capable of fast response times and can provide fast grid services, such as frequency regulation, it is quite important characterizing their transient behavior. Nerveless, extensive experimental campaigns for investigating the fast response of a large-scale VRFB systems, are largely missing, especially in term of fast time-domain analysis. This presentation is an early contribution in such regard, in view of real large-scale applications of the VRFB technology. Two different time intervals involving different phenomena occurring in the cell have been analysed. Initially, the first 20 ms after battery powering were acquired using an oscilloscope with a sample rate of 2 GHz. Secondly, the first 120 s were explored by means of the BMS acquisition system a sampling rate of 0.8 Hz. In order to widely explore the fast response capability, different conditions were examined by varying state of charge (SOC), flow rate (Q), and current (I). The oscilloscope analyses revealed a “peak transient” time interval during which both current and voltage undergo large variations, up to 50%. During this interval, lasting few milliseconds, no reliable current and voltage value can be provided by the battery. In the longer timescale, different behaviors occurred depending on the Q, SOC, and I. The higher Q and SOC, the shorter the transient before a steady-state condition was achieved, with both current and voltage constant in time (Fig.1a). Preliminary analysis demonstrated the suitability of the model of Fig.1b to predict the stack dynamic response. Modelling resorted to experimental data obtained from a multichannel Electrochemical Impedance Spectroscopy (EIS) analyzer, tailored for IS-VRFB and capable of operating in the range 0-20 kHz with bias currents up to 400 A.

H∞ Control of Wrim Driven Flywheel Storage System to Ride-Through Grid Voltage Dips

Flywheel Energy Storage Systems (FESSs) are commonly integrated with wind farms to help them to provide many grid services, including frequency control, voltage control, and power smoothing. Although such systems are not concerned by the severe grid code requirements, their ability to ride-through voltage dips is important to ensure better stability of the power grid. In this paper, the authors propose a robust H∞ current controller for a Wound Rotor Induction Machine (WRIM) based FESS during grid voltage dips. The proposed H∞ controller decreases the negative effects of voltage dips in the WRIM system, such as the rotor over-currents and the active power oscillations. On the other hand, it also guarantees the robustness in the presence of parameter perturbation. The proposed controller is designed using a modified mixed-sensitivity H∞ technique to take into consideration grid disturbances and parameter perturbation. Finally, simulations are made in MATLAB/Simulink using SimPowerSystems to verify the effectiveness of the H∞ controller under grid voltage dips with WRIM parameter perturbation. The simulation results show that the proposed H∞ controller can improve the stability of the WRIM based FESS subject to grid voltage dips and guarantee the robustness with parameter perturbation.

Plug-in Electric Vehicles for Grid Services Provision: Proposing an Operational Characterization Procedure for V2G Systems

Plug-in electric vehicles (PEVs) are expected to play a role as power grid ancillary service providers through vehicle-to-grid (V2G) chargers, enabling higher levels of renewable electricity penetration. However, to fully exploit the storage capacity of PEVs and fast responsiveness, it is crucial to understand their operational characteristics. This work proposes a characterization procedure for V2G systems providing grid services. It extends the existing literature on response time, AC/DC conversion and reactive power assessment. Illustrative results were obtained by implementing the procedure using a Nissan Leaf battery electric vehicle (BEV) connected to a remotely operated commercial V2G CHAdeMO charger. The V2G system was characterized as having a relative inaccuracy and variability of response inferior to 3% and 0.4%, respectively. Its average communication and ramping times are 2.37 s and 0.26 s/kW, respectively. Its conversion efficiency and power factor both showed degradation in the power values below 50% of the charger’s nominal power. Moreover, the proposed visualizations revealed that: i) the V2G system implements power requests for the DC power flow; ii) the power factor control algorithm was nonoperational; and iii) the acquired data can leverage statistical models that describe the operation of V2G systems (which is of extreme value for researchers and operators).

Analysis of Key Security Technologies for Power Dispatch Control System of Power Dispatch Support System

The scale of China’s power grid is continuously expanding, the amount of collected data is increasing rapidly, and data processing and analysis services are developing towards clustering. Therefore, at present, task management in a stand-alone mode faces severe challenges in ensuring the high efficiency and reliability of distributed tasks. Information security risks in cyberspace can cause fatal threats to smart grid entities through the destruction of grid dispatching control systems and communication networks. Security check is one of the application functions of intelligent power dispatching control system. It is an important security defense line to ensure the stable operation of power grid and provides security check service for power grid dispatching plan and power grid operation. The existing operation and maintenance management mode of the power grid dispatching control system is distributed, and the data of each system and unit is not effectively integrated and connected, and lacks overall consideration. Based on the development history of power grid dispatching automation, this paper comprehensively analyzes the current status of the overall structure of the power grid dispatching system, and summarizes the key technology innovations and application effects.

Communication bandwidth prediction based on smart distribution grid service level

Aiming at the problem that the bandwidth utilization of current current service bandwidth calculation method is not high, a bandwidth calculation method based on queuing theory is proposed. From the perspective of macro service security level, different levels of bandwidth prediction are performed for services of different security levels. The bandwidth prediction model for different levels of service processing is built. Finally, based on the bandwidth prediction model, the optimal transmission efficiency bandwidth prediction calculation method for the service node queuing theory is proposed, and the example of the typical distribution electric information collection service of the national grid is adopted. Compared with the current elastic coefficient bandwidth prediction method, the effectiveness of the proposed method is verified.

Rural Electrification: Practical Exposition of Hybrid Solar PV-Wind for Grid Integrated Power Systems in India

Reliable electric power supply is still remained a major problem in rural India. Off grid renewable sources of energy have been applied in the last few years to increase reliability but not succeeding to be realistic because of too high energy costs compared to the national grid. Grid Integrated Minigrids with Storage (Grid Integrated Mini Grids) have potential to provide reliable power supply at reasonably priced by combining Mini-Grids and National Grid services. This research paper analyzed different aspects of the GRID INTEGRATED MINI GRIDS practicability. The feasibility of the use of hybrid - solar Photovoltaic (PV) systems and wind in Grid Integrated Minigrids

Smart control of BESS in PV integrated EV charging station for reducing transformer overloading and providing battery-to-grid service

Uncontrolled charging demand in an electric vehicle charging station (EVCS) can potentially result in the overloading of the grid coupling transformer that will affect the transformer’s lifetime. This paper proposes a smart coordinated control of photovoltaic (PV) and battery energy storage system (BESS) integrated in an EVCS in order to avoid transformer overloading. BESS is designed to provide the additional EV power demand which is greater than the transformer’s rated capacity and thus reduce transformer overloading. In addition, the smoothing control of PV power output when PV output is lower than a threshold value is incorporated in the control method. Also, BESS which is used to provide grid services i.e battery to grid (B2G) is also incorporated in the designed smart control when the energy selling price is attractive to the BESS operator. Considering a single point connection type, B2G can only be implemented when there is no EV demand. Furthermore, B2G and battery recharging power is maintained within the transformer’s rated capacity to avoid overloading during their particular services. Two different sizes of BESS and transformer capacity are considered to demonstrate the overloading of transformer for a particular time of the day. A small EVCS with integrated PV-BESS in a residential area and food center is simulated to validate the efficacy of the proposed coordinated control technique. Simulation results demonstrate that the integrated BESS with the proposed control method effectively minimizes transformer overloading during all the studied network operating conditions. Moreover, BESS successfully smooths out PV power output, provide grid service and recharge the battery within the defined rated transformer capacity and thus avoids transformer overloading while satisfying design constraints.

Leveraging concentrating solar power plant dispatchability: A review of the impacts of global market structures and policy

Concentrating solar power (CSP) integrated with thermal energy storage delivers flexible and dispatchable power, which is an increasingly valuable quality as electricity systems integrate growing penetrations of variable renewable energy. Valuing and compensating CSP's dispatchability and flexibility requires electricity market structures and policies that appropriately remunerate generation during high-value portions of the day. We review previous analyses of CSP economics and deployment, and we find that continued CSP growth will require valuation mechanisms that appropriately compensate for CSP's flexibility during both plant design and plant operation. We then review market structures that drive CSP operations and dispatch in jurisdictions where CSP is being developed, with perspectives from Spain, Chile, Australia, Morocco, South Africa, the United States, China, and the United Arab Emirates (Dubai). Despite broad agreement that CSP's dispatchability provides value to electricity grids, countries' policies for remunerating and leveraging such dispatchability varies widely. As deployment of CSP and variable renewable energy grows, it will be increasingly important to redesign current integration policies to signal the delivery of CSP's grid services more appropriately.

Repurposed electric vehicle battery performance in second-life electricity grid frequency regulation service

Repurposing of electric vehicle (EV) batteries for a “second life” in electricity grid applications is a potential dual solution for extending the value of these high-quality batteries beyond EV service while reducing the capital cost of grid-scale energy storage. Given the diversity among EV batteries in terms of size, shape, chemistry, performance, and thermal management, it is expected that the practicality and performance of different brands and models will vary in a second-life application. To develop this energy storage technology, common EV battery types must be characterized and ranked according to their performance in different grid services. This experimental study evaluates six different EV batteries with different EV use histories for performance in electricity grid frequency regulation (FR) service using a novel methodology based on the protocol developed by Sandia National Laboratories. For each battery, the applied FR power signal is scaled to greater magnitudes in sequential tests to evaluate trends in energy efficiency and thermal performance. It is found that dc energy efficiency of EV batteries in FR service is primarily influenced by positive active material type and ranges from 92% (NCA) to 99% (NMC) for mid-range FR power magnitudes. Batteries featuring active air or active liquid thermal management are found to maintain safe operating temperatures at substantially higher FR power magnitudes compared to passive thermal management. The results are used to rank the tested EV batteries for commercial performance in second-life FR service, with practical consideration of the trade-offs between metrics in relation to different potential project constraints.

Sustainable and Resilient Distribution Systems With Networked Microgrids [Point of View

Grid modernization calls for increasing requirements of electric grid operation with enhanced sustainability and resilience [1] . In particular, distribution grids serve as a critical venue to bridge bulk upstream transmission and generation systems and a large number of downstream end users on the customer side, playing a significant role in modern electric grids for multiple purposes (e.g., renewable energy integration, power flow distribution, and end-user power quality enhancement) [2] . Under a normal grid operation condition, the increasing penetration level of renewable energy sources imposes new challenges on conventional distribution grid infrastructure (e.g., protection malfunction [3] and voltage violation [4] ); on the other hand, in an extreme grid operation scenario, it is urgently needed to restore grid services after severe power outages, such as those caused by natural disasters [5] . In particular, for critical infrastructures, an efficient grid service restoration strategy should be implemented to avoid further damage over an extended period of time.

Flexible Converters for Meshed HVDC Grids: From Flexible AC Transmission Systems (FACTS) to Flexible DC Grids

Flexible Alternating Current Transmission Systems (FACTS) have achieved to enhance the flexibility of modern AC power systems, by providing fast, reliable and controllable solutions to steer the power flows and voltages in the network. The proliferation of High Voltage Direct Current (HVDC) transmission systems is leading to the opportunity of interconnecting several HVDC systems forming HVDC Supergrids. Such grids can eventually evolve to meshed systems which interconnect a number of different AC power systems and large scale offshore wind (or other renewable sources) power plants and clusters. While such heavily meshed systems can be considered futuristic and will not certainly happen in the near future, the sector is witnessing initial steps in this direction. In order to ensure the flexibility and controllability of meshed DC grids, the shunt connected AC-DC converters can be combined with additional simple and flexible DC-DC converters which can directly control current and power through the lines. The proposed DC-DC converters can provide a range of services to the HVDC grid, including power flow control capability, ancillary services for the HVDC grid or adjacent grids, stability improvement, oscillation damping, pole balancing and voltage control. The present paper presents relevant developments from industry and academia in the direction of the development of these converters, considering technical concepts, converter functionalities and possible integration with other existing systems. The paper explores a possible vision on the development of future meshed HVDC grids and discusses the role of the proposed converters in such grids.

Should I Stay Or Should I Go? The importance of electricity rate design for household defection from the power grid

The cost declines of solar and storage technologies have led to concerns about customers disconnecting from utility service and self-supplying electricity. Prior research addressing this issue focused on average electricity tariffs, solar profiles, and demand without considering detailed customer heterogeneity. This paper fills the gap by analyzing how electricity tariffs that shift cost recovery away from variable charges towards fixed charges influence a customer’s decision to disconnect from utility service. A linear optimization model is developed to size an off-grid solar/storage system. Technology cost and reliability parameters of the optimization model are then adjusted to calculate a range of off-grid costs. Unique rate structure information for over 2000 utilities in the United States is then used to compare grid costs to off-grid costs. The results show limited ability for solar/storage systems to economically substitute for grid services. However, 1% of households might disconnect from utility service in a scenario that accounts for future off-grid costs and updated tariff designs. We find that 3% of households in the Southwest and California have private economics that favor defection in this scenario, rising to as much as 7% in Hawaii. Grid defection could increase from 1% to 7% of United States households in a slightly reduced reliability scenario. These results indicate that utilities and regulators seeking to limit rooftop solar adoption by lowering variable charges face a significant possibility that the corresponding increase in fixed charges could lead to inefficient grid defection.

Coordinated Market Design for Peer-to-Peer Energy Trade and Ancillary Services in Distribution Grids

A novel peer-to-peer (P2P) market design is proposed in this work for the distribution grid level. Envisioning that the grid constraints violations are the major challenge for P2P energy sharing, we propose these to be handled through the ancillary service (AS) market. By calculating the decomposable distribution locational marginal prices (DLMPs), the essential price signals of procuring ASs can be recovered to determine the grid usage prices (GUPs) to each P2P transaction. Hence, the GUPs, due to their decomposable properties, act as incentive signals for the P2P market to support the grid operation in terms of loss reduction, voltage support and congestion management. The proposed market design comprises i) an interactive market design of P2P trade & AS and, ii) a fully distributed peer-centric market-clearing model for P2P energy trade. The duality analysis provides the composition of market equilibrium prices of P2P trading and their interpretations. The case studies demonstrate the effectiveness of the proposed P2P trade to support grid operational objectives.

Providing Grid Services With Heat Pumps: A Review

Abstract The integration of variable and intermittent renewable energy generation into the power system is a grand challenge to our efforts to achieve a sustainable future. Flexible demand is one solution to this challenge, where the demand can be controlled to follow energy supply, rather than the conventional way of controlling energy supply to follow demand. Recent research has shown that electric building climate control systems like heat pumps can provide this demand flexibility by effectively storing energy as heat in the thermal mass of the building. While some forms of heat pump demand flexibility have been implemented in the form of peak pricing and utility demand response programs, controlling heat pumps to provide ancillary services like frequency regulation, load following, and reserve have yet to be widely implemented. In this paper, we review the recent advances and remaining challenges in controlling heat pumps to provide these grid services. This analysis includes heat pump and building modeling, control methods both for isolated heat pumps and heat pumps in aggregate, and the potential implications that this concept has on the power system.

Thermal Energy Storage for Grid Applications: Current Status and Emerging Trends

Thermal energy systems (TES) contribute to the on-going process that leads to higher integration among different energy systems, with the aim of reaching a cleaner, more flexible and sustainable use of the energy resources. This paper reviews the current literature that refers to the development and exploitation of TES-based solutions in systems connected to the electrical grid. These solutions facilitate the energy system integration to get additional flexibility for energy management, enable better use of variable renewable energy sources (RES), and contribute to the modernisation of the energy system infrastructures, the enhancement of the grid operation practices that include energy shifting, and the provision of cost-effective grid services. This paper offers a complementary view with respect to other reviews that deal with energy storage technologies, materials for TES applications, TES for buildings, and contributions of electrical energy storage for grid applications. The main aspects addressed are the characteristics, parameters and models of the TES systems, the deployment of TES in systems with variable RES, microgrids, and multi-energy networks, and the emerging trends for TES applications.

Economic optimization and potential analysis of fuel cell vehicle-to-grid (FCV2G) system with large-scale buildings

The popularization of fuel cell electric vehicles (FCV) is an important measure for solving the global carbon emission reduction problem. However, the overall cost of FCV and the production cost of fuel hydrogen are relatively high, so FCV promotion is slow. Considering that FCV has the characteristics of near-zero carbon emission and high endurance, which is suitable for the vehicle-to-grid (V2G) system, this paper hoped to provide a boost for the promotion of FCV by analyzing the economic potential of the FCV2G system. Firstly, a large-scale commercial building in Japan was selected as the research target and the agent of vehicles to provide a V2G service for the power grid. Then the Monte Carlo simulation method was used to simulate the visiting time and condition of the vehicles. Secondly, the discharge model was established. Combined with the carbon emission price and self-elasticity coefficient of the discharge price, the overall economic optimization model was established. Then, the genetic algorithm was used to optimize the model. With continuous importing of FCVs, the overall economic benefit was improved. Finally, a sensitivity analysis was carried out on the six parameters of daily electricity price, battery cost, fuel cell cost, carbon emission price, power grid carbon emission and hydrogen cost. It was concluded that FCV2G has good economic benefits and high development potential, and the economic benefits of FCV2G will continue to increase with the passage of time.

Forecasting the future scale of vehicle to grid technology for electric vehicles and its economic value as future electric energy source: The case of South Korea

With the world seeking ways to cope with climate change, the interest in and demand for electric vehicles are increasing as part of the efforts to resolve the issue of fine dust, especially in South Korea. The Korean government has consistently announced plans to promote electric vehicles as a means of transportation by providing benefits such as subsidies for electric vehicle purchase and expansion of charging infrastructure. Meanwhile, as electric vehicles continue to grow in number, the energy industry has become attentive to its role as a resource for power generation through vehicle to grid technology. This study analyzes electric vehicle consumer preferences using the discrete choice experiment (DCE) and found that there exists a clear nested structure in Korean consumers’ choice of vehicle. The study also estimates the amount of vehicle to grid electricity supply in the power market and calculates not only national but also individual economic benefit of electric vehicle owners participating in vehicle to grid services based on the estimated amount of electricity supplied. The results of scenario analysis indicate that the estimated electric vehicle supply in Korea will be about 560,000 units cumulatively and that the vehicle to grid electric vehicle power supply scale will reach 1.81 GW by 2030. The estimation shows that the economic benefit of vehicle to grid at the national power market level is 50.9 billion KRW per year, while the economic benefit at an individual level (per vehicle) is 104,151 KRW.

The SIMPLE Framework for deploying containerized grid services

The Worldwide LHC Computing Grid (WLCG) currently has about 170 sites. In order to support WLCG workloads, each site has to deploy and maintain a number of possibly complex grid services. Quite often, site managers require assistance of WLCG experts, for example when new software versions need to be deployed. Modern configuration management (e.g. Puppet, Ansible), container orchestration (e.g. Docker Swarm, Kubernetes) and containerization technologies (e.g. Docker, Podman) can help make such activities more lightweight by means of packaging sensible configurations of grid services and providing simple mechanisms to distribute and deploy them across the infrastructure available at a site. This article describes the SIMPLE project: a Solution for Installation, Management and Provisioning of Lightweight Elements. The SIMPLE framework leverages modern infrastructure management tools to deploy containerized grid services, such as popular compute elements (e.g. HTCondor, ARC), batch systems (e.g. HTCondor, Slurm), worker nodes, etc. Its architecture follows principles of sustainability, scalability and extensibility. We describe how system administrators can use the framework, as well as the first results, featuring the migration of computing resources to HTCondor at 2 sites. We conclude with an outlook on further developments.