Two-stage stochastic-based scheduling of multi-energy microgrids with electric and hydrogen vehicles charging stations,considering transactions through pool market and bilateral contracts

In order to mitigate greenhouse gas emissions and improve energy efficiency, sustainable energy systems such as multi-energy microgrids (MEMGs) with the high penetration of renewable energy resources (RES) and satisfying different energy needs of consumers have received significant attention in recent years. MEMGs, by relying on renewable resources and energy storage systems along with energy conversion systems, play an essential role in sustainability of energy supply. However, renewable energies are uncertain due to the intermittent nature of solar and wind energy sources. Thus, optimal operation of the MEMGs with the consideration of the uncertainties of RES is necessary to achieve sustainability. In this paper, risk constrained scheduling of a MEMG is carried out with the presence of the PV, wind, biomass, electric vehicles (EVs) and hydrogen vehicles (HVs) charging stations, combined heat and power (CHP), boiler, hydrogen electrolyzer (HE), cryptocurrency miners (CMs), electrical, thermal and hydrogen storage systems, responsive demands. From the trading and business model side, the proposed MEMG optimized operation relies on bilateral contracts between producers and consumers and pool electricity markets. A two-stage stochastic programming method is used for considering the uncertainties of electrical, thermal and hydrogen demands, EV and HV charging stations load, CM load, PV and wind power, and the price of electricity purchased from the pool market. The proposed mixed integer linear programming (MILP) model is solved using the CPLEX solver in GAMS which guarantees to achieve a globally optimal solution. The results show that due to the certain prices of bilateral contracts, the possibility of transaction by bilateral contracts decreases the risk metric CVaR by 50.42%. The simulation results demonstrate that risk of high operation costs while considering flexibility sources, such as storages and demand response (DR) programs, is decreased by 5.45% and 4.6%, respectively. As far as operation costs are concerned, results reveal that using renewable resources decreases operation costs by 34.47%. Moreover, the operation cost is reduced by 5.94% and 4.57% in the presence of storage units and DR programs, respectively. In the same way, storages and DR programs decrease cost of purchased electricity by 13.47% and 14.46%, respectively.     

Integration of hydrogen storage system and wind generation in power systems under demand response program: A novel p-robust stochastic programming

Penetration of renewable energy sources (RESs) in power systems increase all over the world to overcome current challenges, most importantly environmental issues. Beside advantages of RESs, their integration into the power systems have imposed various challenges considering uncertain and intermitted power output. To cope with these challenges, utilizing energy storage systems with renewable energy sources alongside the demand response (DR) programs are considered as reliable solutions. On the other hand, in an uncertain environment, minimizing worst-case cost or regret is counted as an important criterion to evaluate operation of any system under uncertain parameters. Therefore, in this paper, optimal operation of power systems is solved under penetration of wind turbines, hydrogen storage system, and DR programs in an uncertain environment. To guarantee robust operation of the system under the worst-case scenario, a novel stochastic p-robust optimization method (SPROM) is proposed which combines both stochastic programming and robust optimization approaches where minimizes the worst-case cost or regret level. The performance of the developed model is evaluated considering a six-bus test system under two cases as stochastic optimization (SO) and SPROM. Obtained results show that the maximum regret level is reduced considerably using the proposed SPROM comparing with pure stochastic method.     

Comparing electricity,heat and biogas storages’ impacts on renewable energy integration

Increasing penetration of fluctuating energy sources for electricity generation, heating, cooling and transportation increase the need for flexibility of the energy system to accommodate the fluctuations of these energy sources. Controlling production, controlling demand and utilising storage options are the three general categories of measures that may be applied for ensuring balance between production and demand, however with fluctuating energy sources, options are limited, and flexible demand has also demonstrated limited perspective. This article takes its point of departure in an all-inclusive 100% renewable energy scenario developed for the Danish city Aalborg based on wind power, bio-resources and low-temperature geothermal heat. The article investigates the system impact of different types of energy storage systems including district heating storage, biogas storage and electricity storage. The system is modelled in the energy systems analyses model energyPRO with a view to investigating how the different storages marginally affect the amount of wind power that may be integrated applying the different storage options and the associated economic costs. Results show the largest system impact but also most costly potential are in the form of electricity storages.     

Discharge dynamics of coupled fuel cell and metal hydride hydrogen storage bed for small wind hybrid systems

In small hybrid wind systems, excess wind energy is stored for later use during the deficit power generation. Excess wind energy can be stored as hydrogen in a metal hydride storage bed and reused later to generate power using a fuel cell. This paper deals with the discharge dynamics of the coupled fuel cell and metal hydride storage bed during the power extraction. Thermal coupling of the fuel cell and metal hydride bed is also discussed. The waste heat generated in the fuel cell is removed using a water coolant. The exit fuel cell coolant stream is passed through the metal hydride storage bed to supply the necessary heat required for desorption of hydrogen from the bed. This will also lead to a reduction in the load on the radiator. The discharge dynamics and the thermal management of the coupled system are demonstrated through a system simulation model developed in Matlab/Simulink platform.     

应用于平抑风功率的燃氢燃气轮机储能系统控制策略研究

储能技术可用于提高风电并网能力,因此其储能系统及控制策略成为研究热点。提出将燃氢燃气轮机作为储能系统主要部分,低通滤波器结合模糊控制作为其平抑风功率的控制策略。通过设定储氢罐容量,对15台1.5 MW风机的历史风功率数据进行了处理。结果表明：低通滤波器结合模糊控制能有效平抑风功率至限制值,实现平抑指标,并得到储氢罐容量的设置限制;可实现储能时燃气轮机不工作,耗能时燃气轮机工作,当储氢罐容量为0.017 m³时,燃气轮机输出功率为0.1 MW。在将燃气轮机作为平抑风功率的储能系统时,需将燃气轮机的启停控制作为今后的研究重点。     

Stochastic security-constrained operation of wind and hydrogen energy storage systems integrated with price-based demand response

Because of highly increasing energy consumption, environmental issues and lack of common energy sources, the use of renewable energy sources especially wind power generation technology is increasing with significant growth in the world. But due to the variable nature of these sources, new challenges have been created in the balance between production and consumption of power system. The hydrogen energy storage (HES) system by storing excess wind power through the technology of power to hydrogen (P2H) and delivering it to the electricity network through hydrogen-based gas turbine at the required hours reduces not only wind alternation but can play an important role in balancing power production and consumption. On the other hand, power consumers by participating in demand response (DR) programs can reduce their consumption at peak load or wind power shortage hours, and increase their consumption at low-load or excess wind power hours to reduce wind power spillage and system energy cost. This paper proposes a stochastic security constrained unit commitment (SCUC) with wind energy considering coordinated operation of price-based DR and HES system. Price-based DR has been formulated as a price responsive shiftable demand bidding mechanism. The proposed model has been tested on modified 6-bus and 24-bus systems. The numerical results show the effect of simultaneous consideration of HES system and price-based DR integrated with wind energy on hourly generation scheduling of thermal units. As a result there is some reduction in wind generation power spillage and daily operation cost.     

Assessing wind uncertainty impact on short term operation scheduling of coordinated energy storage systems and thermal units

Renewable resources, especially wind power, are widely integrated into the power systems nowadays. Managing uncertainty of the large scale wind power is often known as one of the most challenging issues in the power system operation scheduling. Additionally, energy storage systems (ESSs) have been widely investigated in the power systems owing to their valuable applications, especially renewable energy smoothing and time shift. In this paper, a stochastic unit commitment (UC) model is proposed to assess the impact of the wind uncertainty impact on ESSs and thermal units schedule in UC problem. Wind uncertainty is modeled based on the two measures. First, the wind penetration level is changed with respect to the basic level. Second, the wind forecasting error is modeled through a normal probability distribution function with different variances. The ESSs are modeled based on several technical characteristics and optimally scheduled considering different levels of the wind penetration and forecasting accuracies. The proposed formulation is a stochastic mixed integer linear programming (SMILP) and solved using GAMS software. Simulation results demonstrate that the wind uncertainty have a considerable impact on operation cost and ESSs schedule while proposed optimum storage scheduling through the stochastic programming will reduce the daily operational cost considerably.     

Design and evaluation of PV-wind hybrid system with hydroelectric pumped storage on the National Power System of Egypt

National and international policies encourage increased penetration of solar and wind energy into electrical networks in order to reduce greenhouse gas emission. Solar radiation and wind speed variations complicate the integration of wind and solar generation into power systems and delay the transition of these sources from centralized to distributed energy sources. The increased penetration of nontraditional energy sources into the electric grid stimulates the demand for large capacities in the field of energy storage. A mathematical model, which describes the operation of a proposed hybrid system, including solar PV, wind energy, and a pumped storage hydroelectric power plant is developed in this paper. This hydropower plant utilizes seawater as a lower reservoir, and only a tank has to be built in order to reduce the installation cost of the storing system. The pumped storage power plant used for compensation of the variation of the output energy from the PV and wind power plants by discharging water from the upper reservoir, which is previously pumped in the case of surplus energy from PV and wind turbine power plants. The impact of the proposed system on the grid utility is investigated in accordance with the values of energy exchange (deficits and surpluses of energy) between the considered hybrid system and the grid. The optimum design is determined by the pump and turbine capacities, upper reservoir volume, and the volume of water left in the tank for emergencies. Different scenarios of the optimum operations are presented for analysis. The results obtained from the examined scenarios indicate the ability of such a hybrid energy system to reduce the exchange of energy with the grid. This paper indicates the technical feasibility of seawater pumped-storage hydropower plant for increasing the Egyptian national grid’s ability to accept high integration of renewable energy sources.     

The value of energy storage in optimal non-firm wind capacity connection to power systems

Wind is a variable and uncontrollable source of power with a low capacity factor. Using energy storage facilities with a non-firm connection strategy is the key to maximum integration of distant wind farms into a transmission-constrained power system. In this paper, we explore the application of energy storage in optimal allocation of wind capacity to a power system from distant wind sites. Energy storage decreases transmission connection requirements, smoothes the wind farm output and decreases the wind energy curtailments in a non-firm wind capacity allocation strategy. Specifically, we examine the use of compressed air energy storage (CAES) technology to supplement wind farms and downsize the transmission connection requirements. Benders decomposition approach is applied to decompose this computationally challenging and large-scale mixed-integer linear programming (MILP) into smaller problems. The simulation results show that using energy storage systems can decrease the variation of wind farms output as well as the total cost, including investment and operation costs, and increase the wind energy penetration into the power system.     

风电与储能联合运行的碳减排效果

在全球能源危机和环境污染的背景下,风电—储能联合运行系统对电力行业的节能减排有重大影响。将风电和储能变量同时引入供给函数均衡模型来模拟风电—储能联合运行系统提供的基荷电量,并在此基础上通过情景分析分别估算了发电企业在风电系统、储能系统及风电—储能联合运行系统3种情景下的污染气体排放量。结果表明,各发电企业在利益最大化目标的驱使下将不断增加储能量,使得联合运行系统比单独的风电或储能系统具有更高的排放量,且排放量的大小受储能容量的影响。     

Hydrogen energy storage system in a Multi‒Technology Microgrid:technical features and performance

The features and performance of a hydrogen energy storage system included in the microgrid powering a plant for advanced green technologies is presented. The microgrid is powered by a 730–kW photovoltaic source and four energy storage systems. The hydrogen storage system consists of a water demineralizer, a 22.3–kW alkaline electrolyzer generating hydrogen, its AC–DC power supply, 99.9998% hydrogen purifier, 200-bar compressor, 200–L gas storage cylinders, a 31.5–kW proton–exchange–membrane fuel cell running on hydrogen, its DC–AC power conditioning system. The whole system is housed in three containers provided with anti–salt filters to remove brine. The whole system is controlled by the microgrid system supervisor. Operative tests at nominal power show that the round-trip efficiency of the hydrogen energy storage system at full power is ca. 10% in a pure electric operation and ca. 24% in a heat cogeneration operation. At half power these values reduce to 9.5% and 18%, respectively.     

Optimal management of hydrogen storage in stochastic smart microgrid operation

This paper presents an energy management and reserve scheduling scheme in order to optimally operate a 17-bus Low Voltage (LV) grid-tied microgrid, powered by photovoltaics, a wind turbine and a Fuel Cell (FC) utilizing on site hydrogen production and storage. Since high Renewable Energy Resources (RES) penetration is assumed, the expected deviations due to their intermittency are accounted for by the reserve provision by the FC system, in order to deviate as little as possible from the scheduled energy demand injected by the upstream grid. All these are incorporated into the operating cost of the microgrid assuming penalization of unscheduled power injections from the grid. The intermittency of RES and load are incorporated in the model by assuming known probability density functions for the forecasting errors. Then, energy and reserve scheduling is performed utilizing the Harmony Search algorithm in order to minimize the expected operating costs of the examined system by optimal reserve and energy provision from the stored/generated hydrogen. For that purpose, hourly optimizations are performed for a given year to assess the value on-site hydrogen generation and FC technologies add to microgrid operation and Distributed Generation (DG) in general. The purpose is to prove the use of hydrogen storage systems in effective uncertainty balancing. The hydrogen storage system appears to effectively counter the intermittency of renewables in moderate penetration, reducing the uncertainty costs. In higher renewable penetrations, due to uncertainty being already accounted for by the storage, the benefits of the RES penetration are even greater.     

The role of hydrogen in high wind energy penetration electricity systems: The Irish case

The deployment of wind energy is constrained by wind uncontrollability, which poses operational problems on the electricity supply system at high penetration levels, lessening the value of wind-generated electricity to a significant extent. This paper studies the viability of hydrogen production via electrolysis using wind power that cannot be easily accommodated on the system. The potential benefits of hydrogen and its role in enabling a large penetration of wind energy are assessed, within the context of the enormous wind energy resource in Ireland. The exploitation of this wind resource may in the future give rise to significant amounts of surplus wind electricity, which could be used to produce hydrogen, the zero-emissions fuel that many experts believe will eventually replace fossil fuels in the transport sector. In this paper the operation of a wind powered hydrogen production system is simulated and optimised. The results reveal that, even allowing for significant cost-reductions in electrolyser and associated balance-of-plant equipment, low average surplus wind electricity cost and a high hydrogen market price are also necessary to achieve the economic viability of the technology. These conditions would facilitate the installation of electrolysis units of sufficient capacity to allow an appreciable increase in installed wind power in Ireland. The simulation model was also used to determine the CO₂ abatement potential associated with the wind energy/hydrogen production.     

Role of hydrogen in future North European power system in 2060

The Balmorel model has been used to calculate the economic optimal energy system configuration for the Scandinavian countries and Germany in 2060 assuming a nearly 100% coverage of the energy demands in the power, heat and transport sector with renewable energy sources. Different assumptions about the future success of fuel cell technologies have been investigated as well as different electricity and heat demand assumptions. The variability of wind power production was handled by varying the hydropower production and the production on CHP plants using biomass, by power transmission, by varying the heat production in heat pumps and electric heat boilers, and by varying the production of hydrogen in electrolysis plants in combination with hydrogen storage. Investment in hydrogen storage capacity corresponded to 1.2% of annual wind power production in the scenarios without a hydrogen demand from the transport sector, and approximately 4% in the scenarios with a hydrogen demand from the transport sector. Even the scenarios without a demand for hydrogen from the transport sector saw investments in hydrogen storage due to the need for flexibility provided by the ability to store hydrogen. The storage capacities of the electricity storages provided by plug-in hybrid electric vehicles were too small to make hydrogen storage superfluous.     

Optimal day-ahead energy planning of multi-energy microgrids considering energy storage and demand response

Due to the environmental and economic advantages of combined heat and power (CHP) units, their use in power grids has expanded. The entry of CHP into power systems increases the complexity of the economic power flow problem. This complexity is due to the introduction of multiple constraints into problem. A mere electricity supply is not optimal in today's networks, and energies such as heat, power and gas must be planned and managed simultaneously as an energy hub. Therefore, in this paper, an intelligent multi-energy microgrid (MG) consisting of power generation units, CHP units and gas units is modeled for day-ahead energy management (DAEM). The economic distribution problem focuses on the amount of power generation, heat and gas of the units in the system. In contrast, the total generation cost of the system is minimized, and all the equality and inequality constraints of the problem are observed. The proposed microgrid includes various energy-dependent equipment such as CHP units, gas boilers, electricity-to-gas units, power and heat storage units and electric heat pumps. Also, price-based load management was included to reduce costs due to the transfer of information between the consumer and the generator in the context of smartization. Since the above problem is difficult to solve due to various constraints and decision parameters, a newly developed optimization method based on water flows was proposed. The simple movement of water flows on the ground is efficient and optimal and always follows the shortest and fastest path to reach the deepest point. In the proposed algorithm, simple movements of water in routing, a change of direction and even the creation of rapids and vortices were simulated as various mathematical operators. Finally, the proposed model and method were examined in different scenarios. The numerical outcomes demonstrated that, the proposed modeling framework is superior to hub-based multi-carrier microgrid models in terms of power system security. The sensitivity of operational expenses to changes in initial values of energy storage systems (ESS) and thermal storage system (TSS) is proved that the cost of operation reduces as the baseline values of ESS and TSS are reduced to 0.2% of the maximum capacity. Because DAEM performance is less flexible when the primary values are reduced by 0.2% of the maximum value, the system running expenses increase marginally.     

Pumped storage in systems with very high wind penetration

This paper examines the operation of the Irish power system with very high levels of wind energy, with and without pumped storage. A unit commitment model which accounts for the uncertainty in wind power is used. It is shown that as wind penetration increases, the optimal operation of storage depends on wind output as well as load. The main benefit from storage is shown to be a decrease in wind curtailment. The economics of the system are examined to find the level at which storage justifies its capital costs and inefficiencies. It is shown that the uncertainty of wind makes the option of storage more attractive. The size of the energy store has an impact on results. At lower levels of installed wind (up to approximately 50% of energy from wind in Ireland), the reduction in curtailment is insufficient to justify building storage. At greater levels of wind, storage reduces curtailment sufficiently to justify the additional capital costs. It can be seen that if storage replaces OCGTs in the plant mix instead of CCGTs, then the level at which it justifies itself is lower. Storage increases the level of carbon emissions at wind penetration below 60%.     

基于蚁狮算法的风电集群储能容量配置优化方法

随着风电渗透率提高,风电并网对电网安全稳定运行影响更加显著。风电配备储能可有效改善风电出力波动性和不确定性,增强可调度性。该文建立以风电集群联合储能系统售电收益最高为优化目标的模型,采用蚁狮算法算法进行求解,得到风电集群功率备用、储能功率和容量最优配置方案,对比蚁狮算法、遗传算法和粒子群算法优化结果,分析储能电池单位成本和寿命对优化结果影响。最后以中国东北某风电集群作为算例,验证了所提算法与模型的有效性。     

Large-scale integration of wind power into the existing Chinese energy system

This paper presents the ability of the existing Chinese energy system to integrate wind power and explores how the Chinese energy system needs to prepare itself in order to integrate more fluctuating renewable energy in the future. With this purpose in mind, a model of the Chinese energy system has been constructed by using EnergyPLAN based on the year 2007, which has then been used for investigating three issues. Firstly, the accuracy of the model itself has been examined and then the maximum feasible wind power penetration in the existing energy system has been identified. Finally, barriers have been discussed and suggestions proposed for the Chinese energy system to integrate large-scale renewable energy in the future. It is concluded that the model constructed by the use of EnergyPLAN can accurately simulate the Chinese energy system. Based on current regulations to secure grid stability, the maximum feasible wind power penetration in the existing Chinese energy system is approximately 26% from both technical and economic points of view. A fuel efficiency decrease occurred when increasing wind power penetration in the system, due to its rigid power supply structure and the task of securing grid stability, was left primarily to large coal-fired power plants. There are at least three possible solutions for the Chinese energy system to integrate large-scale fluctuating renewable energy in the long term: Redesigning the regulations to secure grid stability by means of diversifying the participants, such as including hydropower and CHP plants; integrating large-scale heat pumps combined with heat storage devices to satisfy district heat demands and developing electric vehicles to promote off peak electricity utilisation.     

Techno-economic analysis of RES & hydrogen technologies integration in remote island power system

The main objective of the present study is the integration of hydrogen technologies as an energy storage medium in a hybrid power system. The existing power system of the island of Milos, which is based on fossil fuel generators and a small wind park, is assessed in the context of this paper. System level simulation results, from both technical and economic point of view, are presented for the currently existing and the proposed island's hybrid power system. The latter integrates a higher number of wind turbines and hydrogen technologies as energy storage medium, and the two system architectures are being compared taking into account not only technical and economic parameters but also Green House – Gas (GHG) emissions, fossil fuels consumption and Renewable Energy Sources (RES) penetration increase. Moreover, a sensitivity analysis has been performed in order to determine the contribution of hydrogen technologies equipment costs; with the cost of energy produced (COE) being the critical parameter. Results show that COE for the proposed power system is higher than the existing one, but on the other hand GHG emissions and fossil fuel consumption are significantly reduced. In addition, RES penetration increases dramatically and the sensitivity analysis indicates that a further reduction in hydrogen technologies equipment and subsidy on wind turbine costs would make RES & Hydrogen-based systems economically competitive to the existing power system of the island.     

A wind-hydrogen energy storage system model for massive wind energy curtailment

With wind energy penetration rate increasing, wind energy curtailment turns severe in some wind farms nowadays and new wind farm construction trends to aggregate this situation. Therefore the need for massive energy storage technology such as “Power to gas” is growing. In this study, a model of integrating curtailed wind energy with hydrogen energy storage is established based on real time data in term of 10 min avg. throughout a whole year in a wind farm. Two wind/hydrogen production scenarios via water electrolysis are given and the influence exerted on payback period by electrolyser power and hydrogen price is talked in tandem as well as the model validity is specified in the conclusion section. Our results further stress the importance of hydrogen energy storage technology on addressing wind energy curtailment and disclose some regularities from an economical perspective.