Optimal economic-emission performance of fuel cell/CHP/storage based microgrid

In this paper, optimal heat and power dispatch of the fuel cell (FC) and combined heat and power (CHP) based microgrid (MG) in grid-connected mode is studied in the presence of demand response program (DRP). Considering cost and emission minimization has turned this study to a multi-objective problem. Multiple generating and storing units such as FC, CHP, power-only unit, boiler, battery storage system, and heat buffer tank are considered in investigated MG. Also, demand response program has been modeled, and the effects of such programs on the load profile have been discussed. The DRP transfers some amount of load from peak periods to other periods which flats the load curve and minimizes total cost and emission of the MG. To solve the multi-objective optimization problem, the Pareto solutions are generated by using the compromising programming, then, optimal solution is chosen by implementing the fuzzy satisfying approach. In comparison with other methods, the proposed method has reduced the set of efficient solutions to a more reasonable size without demanding any information about the decision making parameters. Finally, the problem is solved in two cases as with and without DRP to clarify the impact of DRP on MG scheduling.     

Optimization of a thermal storage unit combined with a biomass boiler for heating buildings

The performance of a boiler with a built-in thermal storage unit is presented. The thermal storage unit is an insulated water tank that absorbs surplus heat from the boiler. The stored heat in the thermal storage unit makes it possible to heat even when the boiler is not operating, thus increasing the heating efficiency. A system with three components is described. The model of the system and the mathematical model were made using the TRNSYS program package and a test reference year (TRY). The degree of efficiency, which optimizes the thermal storage volume and the heating power of the boiler, was determined. The thermal storage must also ensure that the heat is stored at the highest possible exergy level, and complete mixing of the water is a condition for optimizing the thermal storage. The matching of the boiler’s heating capacity with the thermal storage unit ensures a supply of heat even when the boiler is not operating.     

Risk-constrained scheduling of a CHP-based microgrid including hydrogen energy storage using robust optimization approach

Recently, the integration of various energy resources, including renewable generation and combined heat and power (CHP) units in microgrids, has created the opportunity of off-grid operation with a suitable range of reliability. This paper presents an optimization model to schedule an islanded MG with various resources, including CHP, photovoltaic (PV), and boiler, as the primary energy provision sources besides electric battery storage, thermal storage and hydrogen energy system (HES). The HES has the power-to-hydrogen (P2H) and hydrogen-to-power (H2P) modes, which increases the flexibility of the scheduling. The uncertainty management is the most essential task in the CHP-based MGs scheduling problem, since the power and heat productions are interrelated and can result in economic losses without enough deliberations. Hence, this paper proposes the robust optimization approach (ROA) to cope with the uncertainties associated with the PV production and electric and heat load demands. The robust counterparts are applied to the deterministic problem to create a tractable adjustable robust framework. The problem is structured as a mixed-integer linear programming (MILP) handled by the General Algebraic Modeling System (GAMS) using CPLEX solver. The results verified the effectiveness of the proposed robust counterparts in managing the associated risk. The results illustrated a conscious scheduling strategy under robust conditions. However, the more preserved decisions are taken, the higher operational cost is realized. In this regard, the increment of robustness level from the lowest value (deterministic condition) to the highest value (conservatism condition) increased the operation cost by about 43.29%.     

Stochastic heat storage problem—solved by the progressive hedging algorithm

In the present study, a problem concerning operation of a heat storage tank in connection with a combined heat and power (CHP) plant is considered. The heat storage is used to supply the district heating system when the CHP plant is producing electric power alone and also to redistribute optimally over time the required heat production. Stochasticity is assumed attached to the future power production, and it is assumed that accurate predictions of the future heat consumption are available. A receding horizon idea is used. The problem is solved by the Progressive Hedging Algorithm (PHA), a recently developed method to deal with multi-period optimization problems under uncertainty. The application of the method is explained in detail.     

Independent thermal storage power station with molten salt:Technology and evaluation

储能电站可解决可再生能源间歇性和不稳定性的问题,满足常规电力系统和区域能源系统效率,安全性和经济性的迫切需要.本文提出了一种新的蓄热电站技术----独立熔盐蓄热电站,进行了独立熔盐蓄热电站原理的介绍,概念设计和技术经济评价.结果表明:独立熔盐蓄热电站初期投资很低,仅为6152.88元/kW,投资回收期短,在3年以内.独立熔盐蓄热电站占地面积小,可建在城市中实现热电联供,总能效率可由单纯发电的30%提高到80%以上.     

计及风光不确定性的新能源虚拟电厂多时间尺度优化调度

针对中国西北地区新能源消纳问题,该文聚合风力发电、光伏发电、光热电站、电储能装置组成虚拟电厂（VPP）,提出一种基于鲁棒随机优化理论的新能源虚拟电厂多时间尺度优化调度策略。首先对风力发电、光伏发电、光热电站与电储能装置进行数学描述,在此基础上建立VPP多时间尺度优化调度模型。在日前调度层中,以VPP运行效益最大为目标,依据风光日前预测出力建立日前优化调度模型;在时前调度层中,以VPP运行成本最小为目标,根据风光时前预测出力建立时前调度修正模型。同时,为了衡量风电、光伏发电出力不确定性对系统的运行影响,建立VPP随机优化调度模型。仿真结果验证该模型可提高运行效益与新能源消纳能力。     

热电联产机组储热罐最佳容量的确定方法

为解决“风热冲突”下储热罐的容量选择问题,以热电联产机组整个采暖期为研究对象,引入特征日概念,对配置储热罐后的热电机组建立了逐小时的运行模型。分别以机组深度调峰空间的增量、全年总收益和10年净现值为目标函数,寻找储热罐容量的最优值。结果表明,热负荷越高储热罐的最佳容量也越大,同时机组配置储热罐后所能获得的深度调峰空间也越大;不考虑初投资时,以全年总收益为目标的储热罐最优容量约为820 MW;在考虑初投资后,以10年净现值为目标的储热罐最优容量约为430 MW,容量几乎减半。     

分区蓄热水箱应用于太阳能热泵中的蓄放热分析

针对冬季太阳能辐射弱且不稳定的特点,提出一种应用于太阳能热泵的分区蓄热水箱,以水泵驱动蓄热水箱循环区与蓄热区的热量传递,并运用热力学原理对水箱循环区与蓄热区的运行状况进行模拟,分析了水箱两区在不同水泵体积流量下的逐时温度变化并与整体式水箱进行对比。结果表明,分区蓄热水箱克服了整体式水箱的热惰性,启动灵活,能在较短时间内达到热泵运行的理想温度,显著提高了系统的性能。     

Experimental results of a sensible heat storage system for residential and light commercial application

This paper presents the performance results for a sensible heat storage system. The system under study operates as an air source heat pump which stores the compressor heat of rejection as domestic hot water or hot water in a storage tank that can be used as a heat source for providing building heating. Although measurements were made to quantify space cooling, space heating, and domestic water heating, this paper emphasizes the space heating performance of the unit. The heat storage system was tested for different indoor and outdoor conditions to determine parameters such as heating charge rate, compressor power, and coefficient of performance (COP). The thermal storage tank was able to store a full charge of heat. The rate of increase of storage tank temperature increased with outdoor temperature. The heating rate during a charge test, best shown by the normalized rate plots, increased with evaporating temperature due to the increasing mass flow rate and refrigerant density. At higher indoor temperature during the discharge tests, the rate of decrease of storage tank temperature was slower. Also, the discharge heating rate decreased with time since the thermal storage tank temperature decreased as less thermal energy became available for use. Copyright © 1999 John Wiley & Sons, Ltd.     

考虑碳捕集利用与可再生能源的低碳综合能源系统配置优化研究

为实现传统工业部门的低碳转型,构建了集成可再生能源、电锅炉、储热以及碳捕集利用与封存（CCUS）装备的低碳综合能源系统,并提出了经济和低碳双重导向下的系统配置优化方法。应用粒子群优化算法求解获得各设备的最优配置容量及典型场景下的最优调度方案,并选取乙烯工业进行案例分析。结果表明：通过引入CCUS和可再生能源装备,系统碳排放减少了57.50%,年总成本增加15.92%;当碳价高于109.61元/t时,低碳综合能源系统具有经济和低碳双重优势。     

基于AA-CAES的冷热电三联产系统的热经济性分析

为了研究储热罐内热量的分配和利用对先进绝热压缩空气储能系统性能的影响,提高系统在可再生能源并网应用中的效率与经济性,提出5种热量分配方案。采用数值模拟的方法,比较系统5种方案下的热力学与经济学特性,并研究关键参数对不同方案下系统性能的影响。结果表明：热量分配比越大,循环效率越高,而年利润率越小。对于5种热量分配方案,循环效率和年利润率随储气室最大压比的增大均存在最小值,且存在最佳的换热器效能,使得循环效率和年利润率具有最大值。压缩机入口温度的变化对5种热量分配方案的循环效率和年利润率的影响各不相同。系统年利润率随着燃料价格的升高而减少,而随着产品价格的升高而增加。     

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.     

考虑风电不确定性的电热系统经济调度

随着风电等新能源大规模并网,其出力的不确定性给电力系统日前调度带来很大挑战。传统的研究方法多是假设风电功率预测误差服从某种概率分布,但风电功率预测误差受到多种因素影响,概率分布模型无法准确描述其特性。为此,采用基于神经网络的组合预测方法对风电功率误差进行建模,再将预测的风电误差加入到包含热电机组、火电机组、风电、储热装置和电锅炉的热电联合优化调度模型中,最后以实际的10机系统为例进行仿真,分析了风电预测误差对机组出力、风电消纳及调度成本的影响。结果表明,与传统方法相比,所建模型可减少机组燃煤成本与旋转备用成本,降低了经济调度成本,提高了风电消纳水平。     

A new type of phase change heat storage tank in solar energy combination system

介绍了一种新型笼屉式相变蓄热水箱,通过实验测试对比分析相变蓄热水箱与普通蓄热水箱对太阳能组合系统的太阳能保证率及系统能效比的影响。实验表明：同等水箱容积,使用相变蓄热水箱时太阳能集热系统的小时集热量为普通蓄热水箱的3.7倍,相变蓄热水箱有利于提高太阳能保证率及系统能效比。在太阳能辐照强度相似的情况下,相变蓄热水箱会使太阳能保证率平均提高72%,使系统能效比平均提高26%。同时相变蓄热水箱可减少夜间水箱上部的热损失,使水箱上部水温降减少50%。     

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.     

Experimental study on laboratory scale Totalized Hydrogen Energy Utilization System using wind power data

The renewable energy source like wind energy generates electric power with intermittent nature. Hydrogen energy system can help to solve the fluctuation problem of the wind power. Totalized Hydrogen Energy Utilization System (THEUS) consists of a Unitized Reversible Fuel Cell (URFC), a hydrogen storage tank, and other auxiliary components. Wind power is inherently variable; the URFC will be subjected to a dynamic input power profile in water electrolyzer mode operation. This paper describes the THEUS operation and performance at different variations in intermittent wind power. The performance of the THEUS was evaluated in water electrolyzer and fuel cell mode operation. The stack efficiency, system efficiency, and system efficiency including heat output from the URFC were presented at each operation. The total efficiency of the URFC and THEUS were also investigated. The maximum total efficiency of the URFC and THEUS were 53% and 66%, respectively.     

Thermal-fluid-solid coupling of electric heat storage device based on wind power absorption

电网调峰能力不足，弃风问题严重，已成为我国风力发电规模进一步扩大的瓶颈。通过配置蓄热装置参与风电调峰，改变传统“以热定电”的约束模式，是解决我国大量弃风问题的一个趋势。提高电热蓄能装置效率及优化蓄热装置分布对于实现有效调峰具有重要意义。本文针对固体电蓄热装置内流动、传热、应力等现象，建立了热-流-固多场三维耦合传热数学模型，采用流-固耦合传热模型将难以确定的热流边界转化为系统内部边界，分析固体电蓄热装置温度场及应力场分布，并对比三种不同孔隙率、电热丝排布方式对蓄热装置温度分布均匀性及热膨胀量的影响。研究结果对提高固体电蓄热装置的效率以及电网调峰具有一定的参考价值。     

电热锅炉蓄热在空调采暖系统中的应用

介绍了电热锅炉蓄热的意义、系统形式及原理，在实例中对系统设计提出了新思路，并介绍了电热锅炉及蓄热槽的选型。     

Experimental investigation and performance analysis on a solar adsorption cooling system with/without heat storage

A solar adsorption cooling system which can be switched between a system with heat storage and a system without heat storage was designed. In the system with heat storage, a heat storage water tank was employed as the link between the solar collector circulation and the hot water circulation for the adsorption chillers. However, the heat storage water tank was isolated in the system without heat storage, and the hot water was directly circulated between the solar collector arrays and the adsorption chillers. It was found that the inlet and outlet temperatures for the solar collector arrays and the adsorption chillers in the system without heat storage were more fluctuant than those of the system with heat storage. Also found was that the system with heat storage operated stably because of the regulating effect by the heat storage water tank. However, under otherwise similar conditions, the cooling effect of the system without heat storage was similar to that of the system with heat storage. Compared with the system with heat storage, the system without heat storage has the advantages of higher solar collecting efficiency as well as higher electrical COP.     

Thermodynamic and economic analysis of heat storage application in co‐generation systems

The possibility of improvement of the energy performance and economic feasibility of a CHP plant by the use of hot water storage tank is analysed in the paper. An energy balance of a system consisting of a CHP module, a peak boiler and a heat storage unit has been built and the storage efficiency has been defined. Heat transfer in storage tanks and its influence on the energy balance is discussed. A numerical model of heat transfer in the storage tank is presented. The thermodynamic and economic optimum of the tank volume for a sample co‐generation plant has been found. It has been eventually proved that the installation of a heat storage unit provides reduction of fuel consumption in the system. Copyright © 2004 John Wiley & Sons, Ltd.