Abstract:The energy storage system (ESS) is becoming an important component in power systems to mitigate the adverse impact of intermittent renewable energy resources and improve power grid reliability and efficiency. However, storage devices driven by different technologies can have specific grid impacts. This special section is dedicated to reflecting the latest progress and technologies in ESS, focusing on the key issues in operation, control, reliability impact and market value of multi-type grid-scale energy storage devices. There are 12 papers resented in this special section, 1 of which reviews challenges and progresses of ESS technology, 5 of which discuss the battery energy storage (BES); 2 of which are centered on compressed air energy storage (CAES), 2 of which focus on pumped hydro storage (PHS); 2 of which study the market issue with ESS. In summary, these papers comprehensively review current progresses and clearly reveal technical challenges in ESS research. We hope this section will serve as an introduction for future research aiming at promoting technical development and fostering practical utilization of ESS in power systems.

Abstract:As a flexible power source, energy storage has many potential applications in renewable energy generation grid integration, power transmission and distribution, distributed generation, micro grid and ancillary services such as frequency regulation, etc. In this paper, the latest energy storage technology profile is analyzed and summarized, in terms of technology maturity, efficiency, scale, lifespan, cost and applications, taking into consideration their impact on the whole power system, including generation, transmission, distribution and utilization. The application scenarios of energy storage technologies are reviewed and investigated, and global and Chinese potential markets for energy storage applications are described. The challenges of large-scale energy storage application in power systems are presented from the aspect of technical and economic considerations. Meanwhile the development prospect of global energy storage market is forecasted, and application prospect of energy storage is analyzed.

Abstract:As an effective approach of implementing power load shifting, fostering the accommodation of renewable energy, such as the wind and solar generation, energy storage technique is playing an important role in the smart grid and energy internet. Compressed air energy storage (CAES) is a promising energy storage technology due to its cleanness, high efficiency, low cost, and long service life. This paper surveys state-of-the-art technologies of CAES, and makes endeavors to demonstrate the fundamental principles, classifications and operation modes of CAES. Critical subsystems of CAES are elaborated exhaustively. The application prospects and further research directions are summarized to promote the popularization of CAES in smart grid and energy internet.

Abstract:In order to cut greenhouse-gas emissions and increase energy security, the European Commission stimulates the deployment of intermittent renewable energy sources (IRES) towards 2050. In an electricity system with high shares of IRES implemented in the network, energy balancing like storage is needed to secure grid stability and smooth demand satisfaction. Pumped hydro storage (PHS) is at this moment the best option for large scale storage. Switzerland has strong ambitions to further develop their PHS sector and become the battery of Europe. In this research, the potential of the Swiss PSH plants is explored, whilst taking inflow into the upper reservoirs of the PHS plants into consideration. To simulate electricity imbalance, Germany is used as a case study. Germany already has a high penetration of IRES and has plans to increase installed IRES capacity. By using an energy planning model (PowerPlan), three future scenarios of the German electricity system were designed, each with a different set of IRES installed (solar, mixed and wind). Results show that the Swiss battery ambition offers most benefits to a wind-oriented scenario, reducing both shortages as well as surpluses. Water inflow in Swiss PHS-reservoirs is of minor importance when looking at security of supply, although it was shown that the solar-scenario profits more from inflow in terms of system stability. However, a potential conflict was observed in the solar-scenario between the need for electricity storage and the storage of natural inflow, resulting in more surpluses in the system when inflow was taken into account.

Abstract:The battery energy storage system (BESS) is regarded as one of the most promising address operational challenges caused by distributed generations. This paper proposes a novel multi-stage sizing model for utility-scale BESS, to optimize the BESS development strategies for distribution networks with increasing penetration levels and growth patterns of dispersed photovoltaic (PV) panels. Particularly, an integrated model is established in order to accommodate dispersed PVs in short-term operation scale while facilitating appropriate profits in long-term planning scale. Clusterwise reduction is adopted to extract the most representative operating scenarios with PVs and BESS integration, which is able to decrease the computing complexity caused by scenario redundancy. The numerical studies on IEEE 69-bus distribution system verify the feasibility of the proposed multi-stage sizing approach for the utility-scale BESS.

Abstract:To utilize heat and electricity in a clean and integrated manner, a zero-carbon-emission micro Energy Internet (ZCE-MEI) architecture is proposed by incorporating non-supplementary fired compressed air energy storage (NSF-CAES) hub. A typical ZCE-MEI combining power distribution network (PDN) and district heating network (DHN) with NSF-CAES is considered in this paper. NSF-CAES hub is formulated to take the thermal dynamic and pressure behavior into account to enhance dispatch flexibility. A modified DistFlow model is utilized to allow several discrete and continuous reactive power compensators to maintain voltage quality of PDN. Optimal operation of the ZCE-MEI is firstly modeled as a mixed integer nonlinear programming (MINLP). Several transformations and simplifications are taken to convert the problem as a mixed integer linear programming (MILP) which can be effectively solved by CPLEX. A typical test system composed of a NSF-CAES hub, a 33-bus PDN, and an 8-node DHN is adopted to verify the effectiveness of the proposed ZCE-MEI in terms of reducing operation cost and wind curtailment.

Abstract:Grid-scale battery energy storage systems (BESSs) are promising to solve multiple problems for future power systems. Due to the limited lifespan and high cost of BESS, there is a cost-benefit trade-off between battery effort and operational performance. Thus, we develop a battery degradation model to accurately represent the battery degradation and related cost during battery operation and cycling. A linearization method is proposed to transform the developed battery degradation model into the mixed integer linear programming (MILP) optimization problems. The battery degradation model is incorporated with a hybrid deterministic/stochastic look-ahead rolling optimization model of wind-BESS bidding and operation in the real-time electricity market. Simulation results show that the developed battery degradation model is able to effectively help to extend the battery cycle life and make more profits for windBESS. Moreover, the proposed rolling look-ahead operational optimization strategy can utilize the updated wind power forecast, thereby also increase the wind-BESS profit.

Abstract:Battery energy storage system (BESS) is one of the effective technologies to deal with power fluctuation and intermittence resulting from grid integration of large renewable generations. In this paper, the system configuration of a China’s national renewable generation demonstration project combining a large-scale BESS with wind farm and photovoltaic (PV) power station, all coupled to a power transmission system, is introduced, and the key technologies including optimal control and management as well as operational status of this BESS are presented. Additionally, the technical benefits of such a large-scale BESS in dealing with power fluctuation and intermittence issues resulting from grid connection of large-scale renewable generation, and for improvement of operation characteristics of transmission grid, are discussed with relevant case studies.

Abstract:Isolated energy systems in archipelagos are characterized for having a great dependence on fossil sources due to isolation and territorial fragmentation. The island of La Palma is situated on the northwest of the Canary Islands, and its electric system is very small. Sustainability policies planned by local authorities are aimed to increase the share of renewable energies and the reduction of fossil energies. However, intermittence and the concentration of unmanageable renewable energies in few locations may hinder the operation of the system. In order to solve these problems, energy storage plays an essential role. The aim of this paper is to analyse the effects of the introduction of two possible alternatives as a way of energy storage: pumped hydro storage and electric vehicles. For this, we use a simulation model adapted to the features of La Palma, considering different scenarios. Results show that, in the most favourable scenario, the installation of an additional 25 MW from renewables (more than double the current power), supported by 20 MW of pumped hydro storage and a fleet of 3361 electric vehicles, would allow the current share of renewables to increase from 11% (in 2015) to 49%. Furthermore, this would mean a 26% reduction in CO2 emissions, 10% in costs of generated kWh and 19% in energy dependence.

Abstract:Energy storage (ES) has been considered as the key source of flexibility to support the integration of renewable energy. Previous studies have demonstrated the substantial system cost savings by the deployment of ES, including both investment and operation of generation, transmission and distribution infrastructure. However, this societal benefit may not be realized if industry actors do not have a viable business case to appropriately capture these multiple value streams. In this context, this paper investigates the value that ES may deliver to its owner over two specific business cases in a 2030 UK system. Firstly, the application of large-scale ES in the wholesale market is analysed. It is demonstrated that the optimal allocation of ES to provide multiple services is the key element for ES to become competitive in the electricity market. In the second business case, this paper analyses the value of kilowattscale ES combined with roof photovoltaic (PV) system in the household and community level. The study shows that multiple service provision of ES through advanced pricing schemes, for example time-of-use (ToU) tariff and dynamic distribution use of system (DUoS), lead to higher value and the coordination in the community level could further justify the application of domestic ES.

Abstract:Hydrogen as an energy carrier represents one of the most promising carbon-free energy solutions. The ongoing development of power-to-gas (PtG) technologies that supports large-scale utilization of hydrogen is therefore expected to support hydrogen economy with a final breakthrough. In this paper, the economic performance of a MW-sized hydrogen system, i.e. a composition of water electrolysis, hydrogen storage, and fuel cell combined heat and power plant (FCCHP), is assessed as an example of hydrogen-based bidirectional electrical energy storage (EES). The analysis is conducted in view of the Danish electricity spot market that has high price volatility due to its high share of wind power. An economic dispatch model is developed as a mixed-integer programming (MIP) problem to support the estimation of variable cost of such a system taking into account a good granularity of the technical details. Based on a projected technology improvement by 2020, sensitivity analysis is conducted to illustrate how much the hydrogen-based EES is sensitive to variations of the hydrogen price and the capacity of hydrogen storage.

Abstract:This paper presents a method for reliability evaluation of a hybrid generation system of wind and tidal powers with battery energy storage. Such a system may widely exist in coastal areas and islands in the future. A chronological multiple state probability model of tidal power generation system (TPGS) considering both forced outage rate (FOR) of the TPGS and random nature of tidal current speed is developed. In the evaluation of FORs of TPGS and WPGS (wind power generation system), the delivered power related failure rates of power electronic converters for TPGS and WPGS are considered. A chronological power output model of battery energy storage system (BESS) is derived. A hybrid system of tidal and wind generation powers with a BESS is used to demonstrate the effectiveness of the presented method. In case studies, the effects of various parameters on the system reliability are investigated.

Abstract:A day-ahead optimal scheduling method for a grid-connected microgrid based on energy storage (ES) control strategy is proposed in this paper. The proposed method optimally schedules ES devices to minimize the total operating costs while satisfying the load requirements of cold, heat, and electricity in microgrids. By modeling the operating cost function of each stage, the proposed method is able to adapt to different types of electricity markets and pricing mechanisms. The technical characteristics of ES, such as self-discharge and round-trip effi- ciency, are considered in the control strategy with a multistage process model. An improved dynamic programing method is used to solve the optimization model. Finally, case studies are provided to illustrate the application process and verify the proposed method.

Abstract:Climate change is mainly attributed to the burning of fossil fuels. To solve the problem, current inhabitants have to dispense with fossil fuels as a source of power. It has been demonstrated that this can be secured before 2050 by transitioning to renewable sources of energy. Massive energy storage (MES) incorporated into long distance high voltage direct current (HVDC) transmission systems is the key technology for the transition. This paper describes the current state-of-the-art in electricity grid configurations. It demonstrates how MES, and other back-up local electricity storage schemes represent a natural way of buffering electricity consumers from the intermittency of inherent in the primary renewable systems. Consequently, it can solve the base-load issues and facilitate a global transition to 100% renewable energy sources over the next fifteen to twenty years.

Abstract:This paper presents a simplified zero-dimensional mathematical model for a self-humidifying proton exchange membrane (PEM) fuel cell stack of 1 kW. The model incorporates major electric and thermodynamic variables and parameters involved in the operation of the PEM fuel cell under different operational conditions. Influence of each of these parameters and variables upon the operation and the performance of the PEM fuel cell are investigated. The mathematical equations are modeled by using Matlab–Simulink tools in order to simulate the operation of the developed model with a commercial available 1 kW horizon PEM fuel cell stack (H-1000), which is used for the purposes of model validation and tuning of the developed model. The model can be extrapolated to higher wattage fuel cells of similar arrangements. New equation is presented to determine the impact of using air to supply the PEM fuel cell instead of pure oxygen upon the concentration losses and the output voltage when useful current is drawn from it.

Abstract:Traditional outage model for the power equipment usually focus on the behavior of the equipment under random factors, and the availability of the power equipment in system analysis is usually confined to the steady value. However, this model may be inaccurate in the short term analysis, where the transient process of availability has not ended yet. Furthermore, the power equipment in the short term analysis might be influenced by both random factors and deterministic factors, yet the impact of deterministic factors cannot be completely reflected in the traditional outage model. Based on the above issues, a Markov-based transient outage model is proposed in this paper, which describes the deterioration and repair process of an equipment. Both the corrective maintenance and preventive maintenance are concerned in the model. The preventive maintenance in the model is considered as deterministic event, in which the start time and duration are both scheduled. Meanwhile the corrective maintenance and the unexpected failure are modeled as random events. The transient state probability and availability of equipment under preventive maintenance is derived. The effect of deterministic events on the availability of equipment is analyzed on numerical tests. The proposed model can be used in the short-term reliability assessment and maintenance scheduling in actual systems.

Abstract:This paper employs an efficacious analytical tool, adaptive simplified human learning optimization (ASHLO) algorithm, to solve optimal power flow (OPF) problem in AC/DC hybrid power system, considering valve-point loading effects of generators, carbon tax, and prohibited operating zones of generators, respectively. ASHLO algorithm, involves random learning operator, individual learning operator, social learning operator and adaptive strategies. To compare and analyze the computation performance of the ASHLO method, the proposed ASHLO method and other heuristic intelligent optimization methods are employed to solve OPF problem on the modified IEEE 30-bus and 118-bus AC/DC hybrid test system. Numerical results indicate that the ASHLO method has good convergent property and robustness. Meanwhile, the impacts of wind speeds and locations of HVDC transmission line integrated into the AC network on the OPF results are systematically analyzed.

Abstract:There are many types of tidal current power generation devices, and it is necessary to make comprehensive evaluation of tidal current power generation devices in order to provide valuable reference for the improvement of their performance indexes. On the basis of the analysis of the tidal current power generation device performance indexes, the hierarchical model for comprehensive evaluation of device performance is given in this paper. By normalizing the membership matrix elements based on fuzzy comprehensive evaluation model, all the values of the matrix elements are restrained in the range of 0.0 to 1.0, hence the complexity of the calculations is reduced. Vector similarity is used to determine the expert weights which reflect the knowledge and experience of the experts. This paper presents an improved method for rank correlation analysis, and calculates the comprehensive weight value and the final evaluation results of tidal current power generation devices. The presented method improves the credibility of the evaluation. In the end, measured data of two units of tidal current power generation devices are evaluated in the paper, and the effectiveness of the presented method is verified.