Frequency control by the PV station in electric power systems with hydrogen energy storage

The rapid growth of renewable energy capacity, in particular photovoltaic systems, is creating challenges associated with changing the rate of transient processes in the power system. This is due to the approach PV systems are connected to the grid using power converters and the absence of a rotating mass in the PV power plant. One of the most pressing challenge is the participation of PV stations in the process of frequency control in power systems, including in emergency modes. Simultaneously with PV power plants, it is efficient to use energy storage systems, including hydrogen ones. This is due to the fact that it is possible to obtain hydrogen for such energy storage systems using excess energy from PV power plants. The article proposes to solve the problem of frequency regulation in the power system by using an algorithm that allows to control the frequency in the power system using a synthetic inertia block of PV station, including at different levels of insolation and temperature of PV panels. The robustness of the proposed algorithm allows it to be used at different levels of power generated by the PV station, as well as in emergency modes.     

Impact of renewable generation unit on stability of power systems

Nowadays, the development of the electric power system is associated with the penetration of power generation units based on renewable energy sources and operated with energy storage systems. However, the operation of such generation units changes and complicates the processes in the electric power system, which determines the need for a number of studies and analyses. This paper presents the results of assessing the impact of the operation of photovoltaic plants on the static stability of the electric power system. To achieve the goal, the EUROSTAG software was used. The results of studies of normal and post-emergency modes of electric power system with the different penetration level of generation units are presented, power system stability coefficients of active power and voltage are determined, damping properties of electric power system based on the calculation of the transient damping coefficient of the damping process are estimated.     

Retailer energy management of electric energy by combining demand response and hydrogen storage systems,renewable sources and electric vehicles

The increasing pollution caused by conventional cars and the problems caused by the use of fossil fuels have drawn the attention of researchers and manufacturers to the design of cars that use clean fuels. Electric vehicles connected to the network have a significant impact on reducing environmental pollution and transportation costs, especially in big cities. The cost of supplying loads to subscribers in the distribution network also includes generation and transmission costs. These costs are directly related to the intelligence of the distribution network and the total amount of energy of electric vehicles. The contribution of each generation unit and each transmission line must be calculated to determine the generation and transmission costs. In this research, in order to maximize the profit of the parking lot owner, improve voltage drop and load factor, a comprehensive framework for optimal energy management in a parking lot is presented, which can provide a method to control the charging of electric vehicles, in addition to meeting the needs of their owners, only as a series of controllable loads that they need to receive electrical energy to charge their batteries. In the next step, considering the inherent characteristic of electric cars, i.e. having a battery, and looking at them as a series of storage resources that can return the electric energy in their battery to the grid if necessary, a method to simultaneously control their charging and discharging is provided. In the final step of the paper, it is assumed that hydrogen storage systems will also enter the circuit, and thus, a comprehensive method for energy management is proposed. Finally, the linearized model of demand response and the proposed scheme along with the modeling of hydrogen storage and electric vehicles are considered to be part of contribution to improve the operation and economic situation of the network.     

Research on optimal confguration of hybrid energy storage capacity for wind-solar generation system

储能系统可以有效解决微电网中分布式可再生能源特别是风光互补发电的间歇性、波动性以及“源”与“荷”错位的问题。不同储能技术在响应时间、容量规模、技术成熟度及成本等方面各有特点,两种或多种储能技术耦合将可以更有效地满足用电系统的技术性和经济性的要求。针对电力用户对分布式可再生能源的利用情况,本文提出一种由压缩空气储能、锂电池和超级电容器组成的混合储能系统,建立了三种储能的数学模型,针对其不同的特性,提出了基于二次移动平均滤波的储能系统功率分配方法和基于连续性运行的容量优化配置方法。基于某个实际的用户负荷进行了案例分析,得到了混合储能系统的功率和容量配置结果,并分析了其运行特性。研究表明,在分布式可再生能源微电网中,多种储能技术耦合既能充分发挥每种储能的优势,又可以通过相互配合弥补各自的劣势,这对于可再生能源的充分利用和满足用电负荷的严苛需求具有重要的作用和意义,在分布式能源利用领域具有较好的工程应用前景。     

Modeling of hydrogen and electrical energy storages in wind/PV energy system on the Lake Baikal coast

The paper presents a research on a green power supply system (producing no carbon dioxide and other harmful emissions) in the area of Baikal Lake, for the maximum loads of 10 kW and 100 kW. The system includes photovoltaic converters, wind turbines, batteries for electric energy storage and a system for hydrogen production, storage and energy use. Calculations based on the optimization mathematical model demonstrated the efficiency of the combined use of wind and solar energy in the considered areas, as well as the simultaneous storage of electric energy and hydrogen. The electric energy storage is most efficient for short-term time intervals whereas an increase in the duration of continuous energy “standstills” up to several days makes the storage of hydrogen more cost-effective.     

Electrode and electrolyte materials for electrochemical capacitors

Among different electric energy storage technologies electrochemical capacitors are used for energy storage applications when high power delivery or uptake is needed. Their energy and power densities, durability and efficiency are influenced by electrode and electrolyte materials however due to a high cost/performance ratio; their widespread use in energy storage systems has not been attained yet.Thanks to their properties such as high surface area, controllable pore size, low electrical resistance, good polarizability and inertness; activated carbons derived from polymeric precursors are the most used electrode materials in electrochemical capacitors at present. Other electrode materials such as shaped nano-carbons or metal oxides are also investigated as electrode materials in electrochemical capacitors, but only as useful research tools.Most commercially used electrochemical capacitors employ organic electrolytes when offering concomitant high energy and high power densities. The use of aqueous based electrolytes in electrochemical capacitor applications is mainly limited to research purposes as a result of their narrow operating voltage. Recent studies on room temperature ionic liquids to be employed as electrolyte for electrochemical capacitor applications are focused on fine tuning their physical and transport properties in order to bring the energy density of the device closer to that of batteries without compromising the power densities.In this paper a performance analysis, recent progress and the direction of future developments of various types of materials used in the fabrication of electrodes for electrochemical capacitors are presented. The influence of different types of electrolytes on the performance of electrochemical capacitors such as their output voltage and energy/power densities is also discussed.     

储能技术在冷热电三联供系统中的研究现状与应用

冷热电三联供（CCHP）系统是利用一次能源或可再生能源发电,并通过多种余热回收设备高效利用余热,建立在能源的综合梯级利用基础上的产能系统。用户负荷动态变化及可再生能源输出不稳定会导致冷热电联供系统供、需侧能量不匹配,储能技术可有效解决该问题。本文总结了CCHP系统中储能技术类型及其研究现状,阐明了CCHP系统中电能储存和热能储存技术的应用方式。指出在传统能源与可再生能源相结合、供能系统越发复杂化的能源发展态势下,系统特性、配置优化和对不同场景制定出运行策略是储能技术与CCHP集成系统未来的研究方向。     

Managing peak loads in energy grids: Comparative economic analysis

One of the key issues in modern energy technology is managing the imbalance between the generated power and the load, particularly during times of peak demand. The increasing use of renewable energy sources makes this problem even more acute. Various existing technologies, including stationary battery energy storage systems (BESS), can be employed to provide additional power during peak demand times. In the future, integration of on-board batteries of the growing fleet of electric vehicles (EV) and plug-in hybrid electric vehicles (PHEV) into the grid can provide power during peak demand hours (vehicle-to-grid, or V2G technology).This work provides cost estimates of managing peak energy demands using traditional technologies, such as maneuverable power plants, conventional hydroelectric, pumped storage plants and peaker generators, as well as BESS and V2G technologies. The derived estimates provide both per kWh and kW year of energy supplied to the grid. The analysis demonstrates that the use of battery storage is economically justified for short peak demand periods of <1 h. For longer durations, the most suitable technology remains the use of maneuverable steam gas power plants, gas turbine,reciprocating gas engine peaker generators, conventional hydroelectric, pumped storage plants.     

Algorithm for optimal pairing of res and hydrogen energy storage systems

The global climate and environmental crisis dictate the need for the development and implementation of environmentally friendly and efficient technical solutions, for example, generation based on renewable energy sources. However, the annually increasing demand for electricity (according to the forecasts of the U.S. Energy Information Administration, the amount of energy consumed for the period 2006–2030 will increase by 44 %) cannot be fully provided by alternative energy. The main reason is not so much the high cost of these technologies, like unstable power generation, which determines the need for an additional reserve of regulated power.The solution to this problem can be the combined use of generation based on renewable energy sources with energy storage units of large capacity. Currently, a promising direction is the use of excess electricity for the production of hydrogen and its further accumulation in hydrogen storage. In this case an additional energy can be generated using industrial fuel cells (electrochemical generators) to compensate for the power shortage.At the same time, the distinctive advantage of hydrogen energy storage systems lies in the ability to accumulate a large amount of energy for long periods of time. This fact makes it possible to increase the reliability of the functioning of the electric power system, to provide power supply with a sufficiently long interruption (in case of faults) or allocation for isolated operation.With an increase in the unit capacity and the share of renewable generation in the total installed capacity, researches that aimed to systematic analysis of the impact of the implemented generation unit and the energy storage system on the parameters of the mode of the electric power system become more relevant. There are a number of tasks can be noted related to determining the optimal location and size of the generation unit and energy storage systems being implemented in terms of reducing power losses and maintaining an appropriate voltage level in the nodes of the electric power system. In this article, a variant of solving the optimization task for a typical 15-bus IEEE scheme is presented by means of software calculation using the bubble sorting method. To achieve this goal, the following tasks were solved: the objective function, which indicates the optimal location and size of the generation unit, and constraints, for example, the available deviation of voltage level, were formed; the software implementation of the algorithm for calculating power flows and power losses using the bubble sorting method was carried out. The results of the work of the program code for two scenarios are presented: for instance, installation of one renewable generation unit with a different range of possible capacities, and are compared with the data obtained in the MATLAB/Simulink software package.     

Coordinated control of a hybrid type 3 wind turbine and hydrogen energy storage model to provide efficient frequency control

The growing share of generation from wind farms is becoming one of the challenges in maintaining the sustainability of electric power systems. System operators approve requirements for the participation of such plants in frequency and power regulation, but they do not contain requirements for specific technologies in the control of wind turbines. There are several methods of frequency and power control, which are implemented by additional control systems, the implementation of underload mode, extraction of hidden inertia, the use of energy storage devices, etc. Each of these methods has both advantages and disadvantages. In this paper we consider the combined coordinated control of type 3 wind turbines using kinetic energy and energy from hydrogen storage to provide the best frequency response in order to minimize the negative factors. A digital-analog-physical model of type 3 wind turbine is used as a model, which allows to reproduce the whole range of transients most accurately and avoid the limitations of strictly numerical simulation.     

Autonomous WPP/HPP power system operating modes study

Today, there are centralized and decentralized energy supply areas world-wide. Centralized energy supply is provided by united energy grids which cover most habitable areas; they incorporate several types of power sources with centralized control system. Decentralized energy supply areas cover territories disconnected from power grid, and they incorporate only one type of power source.Autonomous diesel power plants (DPP) are nowadays used mainly to power decentralized consumers and consumer groups. DPP basic disadvantages are power production high cost, diesel fuel nonregenerability, greenhouse gas emission and environmental pollution. The possibility of power supply by autonomous power systems combining wind power plants (WPP) and hydro power plants (HPP) as alternative to diesel generation due to hydraulic energy storage advantages has been considered.Autonomous WPP/HPP power system is a combination of WPP, HPP with water-storage reservoir, automatic control system and switchgear, combined by power, infrastructural and data connections. Hydrogen energy storage is considered to be the second energy storage.HPP water-storage reservoir parametrization procedure considering operating specificity of HPP and WPP as a part of power system with hydraulic and hydrogen energy storage has been suggested. Mathematical models for operating modes of WPP, HPP and storage reservoir have been developed, which consider resources, technical and technological features of their performance in decentralized power supply system. Technique for determining storage reservoir backup volume with allowance for wind conditions parameters, WPP features and storage reservoir configuration have been suggested. Method of day-ahead WPP power calculation in solving problem of operational planning of power system operating modes has been suggested. Simulation of WPP/HPP power system operating modes with seasonal-storage reservoir and hydrogen energy storage have been carried out.The suggested techniques could be used for solving design problems to substantiate decentralized power supply system parameters in remote and isolated areas, as well as for evaluating energy efficiency of replacing the existent decentralized power supply systems on the basis of DPP using imported diesel fuel by environmentally safe systems on the basis of local energy resource – wind energy and hydraulic energy. The suggested techniques are also focused on solving problem of power system operating modes for operational planning.     

孤网运行微电网中混合储能管理与控制策略研究

对孤网运行风光互补微电网电压频率控制和混合储能功率分配问题提出了混合储能管理控制策略,该策略将混合储能中锂电池设定恒功率和压频电源两种模式,对超级电容器采用电压/频率控制。锂电池作恒功率电源时,根据发电预测和负荷预测结果平复系统波动;超级电容器则依据电压/频率控制补偿系统实时功率缺额,保障微电网稳定运行。为此在MATLAB/SIMULINK中搭建了仿真模型,进行了孤网运行、能量分析、模式切换三次仿真,结果表明该策略正确。     

Novel method for setting up the relay protection of power systems containing renewable energy sources and hydrogen energy storage systems

Integration of renewable energy sources (RES) together with energy storage systems (ESS) changes processes in electric power systems (EPS) significantly. Specifically, rate of change and the lowest values of operating conditions during the emergencies are got influenced. Such changes can cause incorrect actions of relay protection (RP) as it was designed and adjusted with no regard for influence of RES and ESS. Detailed research on processes during the different normal and abnormal modes in both EPS and primary transducers and also in RP devices should be done to take preventive actions. To do this research mathematical modeling based on detailed and authentic models of all elements including RP should be used. HRTSim (which was developed by authors) software for simulating EPS provides the opportunity to create such models of EPS of any size without simplifications and limits. Using of this instrument together with detailed mathematical models of RP which were developed before provided the opportunity to investigate them rigorously in RES-integrated EPS. Settings providing adequate action of RP in certain conditions were performed as a result of this investigation. Fragments of these investigations are performed in this paper. Results of these investigations would be useful for designing new methods and tools of RP adjustment.     

Time dependent model of a complex PV water pumping system

A complex time-dependent solar water pumping system is analysed in this paper. Several existing models (e.g. for the PV cell, the battery and the assembly electric motor—centrifugal pump) are used. New models are proposed for PV array and water storage tank operation. The system has two main operating modes, which depend on the level of the incident solar global irradiance. The mathematical model consists of systems of eight or five ordinary differential equations, as a function of the operating mode. Using a water storage tank improves the stability of PV pumping system operation. The mechanical power stored in the water tank is rather constant during the year. The fraction of collected solar energy that is stored in the water’s gravitational energy is higher during the winter months, during the cloudy days and around sunrise and sunset. It is smaller during the summer months, during the clear sky days and in the middle of the day. The fraction of the power supplied by the battery that is stored in the gravitational energy of water is almost constant during the year.     

Hydrogen-based systems for integration of renewable energy in power systems: Achievements and perspectives

This paper is a critical review of selected real-world energy storage systems based on hydrogen, ranging from lab-scale systems to full-scale systems in continuous operation. 15 projects are presented with a critical overview of their concept and performance. A review of research related to power electronics, control systems and energy management strategies has been added to integrate the findings with outlooks usually described in separate literature. Results show that while hydrogen energy storage systems are technically feasible, they still require large cost reductions to become commercially attractive. A challenge that affects the cost per unit of energy is the low energy efficiency of some of the system components in real-world operating conditions. Due to losses in the conversion and storage processes, hydrogen energy storage systems lose anywhere between 60 and 85% of the incoming electricity with current technology. However, there are currently very few alternatives for long-term storage of electricity in power systems so the interest in hydrogen for this application remains high from both industry and academia. Additionally, it is expected that the share of intermittent renewable energy in power systems will increase in the coming decades. This could lead to technology development and cost reductions within hydrogen technology if this technology is needed to store excess renewable energy. Results from the reviewed projects indicate that the best solution from a technical viewpoint consists in hybrid systems where hydrogen is combined with short-term energy storage technologies like batteries and supercapacitors. In these hybrid systems the advantages with each storage technology can be fully exploited to maximize efficiency if the system is specifically tailored to the given situation. The disadvantage is that this will obviously increase the complexity and total cost of the energy system. Therefore, control systems and energy management strategies are important factors to achieve optimal results, both in terms of efficiency and cost. By considering the reviewed projects and evaluating operation modes and control systems, new hybrid energy systems could be tailored to fit each situation and to reduce energy losses.     

Methodological approach to the study of the electro-hydrogen system in Northeast Asia

The article proposes a methodological approach to the development of the tools for studying the international electro-hydrogen system creation in Northeast Asia. The term "hydrogen carrier" was introduced and its definition was given. The resource, economic and technological prerequisites for the development of the unified regional infrastructure to produce, transfer, transform and utilise both electricity and "hydrogen carriers" for consumers of energy services are considered.The author points out the need for a comprehensive consideration of technological, economic, social and political factors when developing such a complex technical system, which affects the diverse actors' interests. In order to create mutual understanding and balance the stakeholders’ interests, the tool to evaluate the efficiency of such a system is necessary. The use of mathematical models is becoming one of the most vital and widespread techniques employed for this purpose. Thereby, the article deals with the structure and the development stages of a regional electro-hydrogen model for Northeast Asia.The review of models that address the issues of hydrogen technologies and renewable energy integration into energy supply systems is given. The main types of models used to describe such technical and economic systems are identified and it is concluded that the development of a two-level modelling system is necessary. The production and transport models at the upper (international) level should be the core of the proposed models system. At the lower level (the "green hydrogen carriers" production), the models of optimal resource management are required to determine the composition and parameters of the technological equipment.Step-by-step development of the modelling system is proposed. The first stage is the simplest scenario where only solar and wind energy is considered as an energy source. At this stage, it is possible to weed out inefficient technologies and identify targeted technologies and mechanisms for multilateral regional cooperation. The second stage should balance the interests of the actors and stakeholders. Here, the traditional renewable energy (biomass, hydro and pumped storage) along with carbon (thermal) and nuclear power generation, as well as other ("carbon") hydrogen technologies will become available for consideration. The final, third stage of the research tools development, will require separate accounting of "green" and "carbon" energy to consider certification mechanisms and energy pricing when building the international hydrogen system in Northeast Asia.In conclusion, the structure of the first stage production and transport model is described. This model will allow estimating the comparative effectiveness of different electric and hydrogen technologies to deliver green energy to consumers in the Northeast Asian economies.     

An updated review of energy storage systems: Classification and applications in distributed generation power systems incorporating renewable energy resources

The demand of electric energy is increasing globally, and the fact remains that the major share of this energy is still being produced from the traditional generation technologies. However, the recent trends, for obvious reasons of environmental concerns, are indicating a paradigm shift towards distributed generation (DG) incorporating renewable energy resources (RERs). But there are associated challenges with high penetration of RERs as these resources are unpredictable and stochastic in nature, and as a result, it becomes difficult to provide immediate response to demand variations. This is where energy storage systems (ESSs) come to the rescue, and they not only can compensate the stochastic nature and sudden deficiencies of RERs but can also enhance the grid stability, reliability, and efficiency by providing services in power quality, bridging power, and energy management. This paper provides an extensive review of different ESSs, which have been in use and also the ones that are currently in developing stage, describing their working principles and giving a comparative analysis of important features and technical as well as economic characteristics. The wide range of storage technologies, with each ESS being different in terms of the scale of power, response time, energy/power density, discharge duration, and cost coupled with the complex characteristics matrices, makes it difficult to select a particular ESS for a specific application. The comparative analysis presented in this paper helps in this regard and provides a clear picture of the suitability of ESSs for different power system applications, categorized appropriately. The paper also brings out the associated challenges and suggests the future research directions.     

Stored energy control for long-term continuous operation of an electric and hydrogen hybrid energy storage system for emergency power supply and solar power fluctuation compensation

In order to realize a large-capacity stand-alone emergency power supply that enables highly reliable and high-quality power supply at the time of a large-scale natural disaster and enables effective use of solar power generation, we proposed an electric and hydrogen hybrid energy storage system (HESS). It is composed of an electric double-layer capacitor bank, fuel cell, electrolyzer, and hydrogen storage (buffer gas tank and metal hydride). In an emergency, this HESS is expected to supply power for loads together with photovoltaics panels for a long time. In usual time, it should not only cooperate with external electricity grids to convert unstable photovoltaic output power into reliable power supply, but also maintain sufficient stored energy in case of emergency. To realize the continuous operation of the HESS in both emergency and usual time, we proposed an electric double-layer capacitor's state-of-charge feedback control method and a hydrogen energy feedback control method, coordinating an energy management method based on Kalman filter algorithm. An experiment and a simulation demonstrated the operations of a 10-kW scale model HESS in emergency and usual time mode, respectively. The demonstrations verified the correct performance of the proposed HESS with the proposed control methods and enabled the continuous operation of the HESS.     

Operation modes for partially failed vanadium redox battery (VRB) energy storage systems

围绕全钒电池系统在部分失效条件下如何保持正常运行全面展开实验验证与理论分析.从电池系统结构组成角度分析了导致全钒电池系统失效的若干情况,并借助实验模拟和实验数据统计分析,总结归纳出全钒电池系统在部分失效条件下的运行特性,从而提出采用降额定功率与倍额定功率两种部分失效运行模式.研究证实该两种运行模式对系统运行效率无显著影响,是实现全钒电池储能系统在部分失效紧急情况下仍能保持正常运转的合理操作.