A review on underwater compressed air energy storage

压缩空气储能技术是目前储能技术的研究热点之一。水下压缩空气储能利用水的静压特性实现压缩空气的等压存储,具有系统效率较高、受地形限制小、储能规模灵活可变的特点,尤其适合于海上风能等可再生能源的规模化存储。本文简要介绍了压缩空气储能技术的工作原理与发展,通过对比分析阐明了水下压缩空气储能所具有的优势,全面分析了水下压缩空气储能技术的研究进展,对采用柔性储能包的水下压缩空气储能技术进行了重点分析,并对水下压缩空气储能系统开发的关键技术进行了总结和展望。     

Technical principle of compressed air energy storage system

压缩空气储能被公认为是一种比较适合大规模系统的储能技术.本文对压缩空气储能的技术原理和发展现状进行了简要讲解,包括工作原理,工作过程,关键技术,发展现状,应用领域等.     

An exergy analysis of a traditional compressed air energy storage system

压缩空气储能技术是具有较大发展前景的大规模储能技术之一,具有广阔的发展前景。使用Aspen Plus软件以传统压缩空气储能系统为例进行流程模拟,运用分析方法对模拟结果进行热力性能分析。分析结果表明,燃烧室的损失是系统各设备损失中最大的。同时还对压缩空气储能系统各个组成部件的运行效率与储能系统的损失之间的关系进行了敏感性分析,分析结果表明,对系统效率影响最大的参数为燃烧室效率,最小的参数为膨胀透平绝热效率。     

Energy,exergy, and sensitivity analyses of underwater compressed air energy storage in an island energy system

An underwater compressed air energy storage (UWCAES) system is integrated into an island energy system. Both energy and exergy analyses are conducted to scrutinize the performance of the UWCAES system. The analyses reveal that a round‐trip efficiency of 58.9% can be achieved. However, these two analyses identify different directions for further improvement. The heat exchangers, expanders, compressors, electric motors, and generators account for the most exergy destruction. A sensitivity analysis is also conducted to investigate the importance of different input parameters on the round‐trip exergy efficiency of the UWCAES system. The results of both local and global analyses show that the round‐trip exergy efficiency is most sensitive to the isentropic efficiency of the expanders and compressors, and the efficiencies of the electric motors and generators. The impacts of the heat exchangers, the self‐discharge rate of the air accumulator, the inner diameter of the pneumatic pipelines, and the insulation thickness of the hot‐oil tank on the round‐trip exergy efficiency are shown to be highly nonlinear.     

Design and thermodynamic analysis of compressed air energy storage system

压缩空气储能技术具有提升风能与太阳能等可再生资源电能质量的潜力,通过此项技术实现间歇性与不稳定性可再生电力的有效储存,进而在电网负荷高峰期以优质电力的形式稳定输出.结合热力学分析方法设计了储能功率56.58 MW,释能输出功率154.76 MW的压缩空气储能系统.在释能阶段透平机组配置上,参照GE 9171E燃机布置第二级透平入口参数,并以其812.41 K高温烟气余热提供第一级透平工质所需全部热量,无需为第一级透平配备专门燃烧器.在此思路下设计的压缩空气储能系统,热耗可降低至3783.96 kJ/(kW·h),储能系统的能量转换效率也高达56.11%.     

Techno-economic analysis of compressed air energy storage power plant

压缩空气储能系统被认为是最具发展前景的大规模电力储能技术之一,具有广阔发展前景。本文建立了压缩空气储能系统的技术经济性计算模型,并针对蓄热式压缩空气储能系统应用于工业用户的情景,在有无补贴的两种计算条件下,进行了技术经济性分析。研究结果表明,在无补贴条件下,系统内部收益率为16.3%,投资回收期为9.2年;计算补贴时,系统内部收益率为23.8%,投资回收期为6.2年。同时本文还对该系统进行了盈亏平衡、敏感性等不确定性分析,找出影响系统经济性的敏感因素;并得出政策扶持对提高压缩空气储能电站的财务收益水平和抗风险能力具有重要的作用。本文的研究可以为压缩空气储能系统的研究和工程应用提供理论参考和工程指导。     

A compressed air energy storage system for wind power generation in western Inner Mongolia

内蒙古自治区陆上风能资源总储量达到了1380 GW,其中技术可开发量为380 GW,几乎占全国风电资源的一半.风力发电负荷已经占到内蒙古电网负荷的20%以上.针对这种情况,对大规模风电并入内蒙古电网进行了研究.在此研究基础之上,为了更有效的利用风电资源,设计了一台压缩空气储能电站.该压缩空气储能电站可以利用风电场夜晚的弃风电量进行储热,为白天的运行提供部分热源.最后,从热耗率,充电比与发电效率三方面对压缩空气储能电站进行了分析,研究结果表明,更高的储气压力和更大的储气容量能够得到更好的发电效率.     

Performance investigation of a novel near-isothermal compressed air energy storage system with stable power output

As one of the grid-scale energy storage technologies, compressed air energy storage (CAES) is promising to facilitate the permeability of renewable energies. By integrating CAES into renewable sources, the fluctuation and intermittence of renewable energies could be effectively restrained. Among various CAES system configurations, isothermal CAES (I-CAES) is considered as a most competitive technology with expected high efficiency. However, most of the existing I-CAES systems have trouble in keeping a stable power output. To address this issue, a novel near-isothermal CAES system is proposed in this article to acquire a near stable power output. Imitating the concept of hydraulic accumulator, a two pressure vessels structure is employed to maintain the gas pressure stable during discharging. Besides, the turbine power output can be controlled by adjusting the liquid flow rate of the Pelton turbine under this near constant pressure condition. Based on the system transient model and economic model, the system components transient behavior, parametric analysis, off-design performance analysis and economic evaluation issues are also conducted. Results show that system round trip efficiency (RTE) with 61.42% and energy density (ED) with 0.2015 kWh/m³ can be achieved under design condition. In the discharge process, the gas pressure in vessel varies in a small range, from 68 to 72 bar, which is relatively stable. The power output from Pelton turbine can be maintained around 1 kW. Meanwhile, the initial pressure, the pipe diameter, and the spraying flow rates of circulating pumps have significant effects on system RTE and ED. Furthermore, the Pelton turbine power output level can be adjusted by adding jets number, and the higher storage pressure can make the power output unsteady.     

Dynamic characteristics and operation strategy of the discharge process in compressed air energy storage systems for applications in power systems

In the context of the rapid development of large-scale renewable energy, large-scale energy storage technology is widely considered as the most effective means of improving the quality and security of electricity. In the existing energy storage technology, advanced adiabatic compressed air energy storage (AA-CAES) technology has broad application prospects because of its advantages of low pollution, low investment, flexible site selection, and large capacity. However, the lack of an in-depth understanding of the dynamic characteristics of CAES systems has severely limited the development of system design and control strategy, resulting in a lack of commercial operation of large-scale CAES systems. This paper describes the design and implementation of a CAES plant and its controller for applications in the distribution network level. The dynamic mathematical models of AA-CAES were established and a feasible control strategy for the grid-connected process was developed to analyze the dynamic characteristics of the system in the discharge stage. The work done in this study provided a data reference for the deep understanding of the dynamic characteristics of AA-CAES, system design, and control strategy in the industry.     

Multi‐criteria algorithm‐based methodology used to select suitable domes for compressed air energy storage

Storing energy allows both the efficiency and availability of renewable energy to be increased, thus dissociating actual from expected generation and from consumption demands. Compressed air energy storage (hereinafter ‘CAES’) enables the efficient and cost‐effective storage of large amounts of energy, achieving a capacity of over 100 MWh. There are several geological structures that can be used as CAES, among which the use and construction of salt domes are particularly noteworthy. However, there is a high exploration risk associated with subsurface exploration. To this end, it is advisable to establish a detailed schedule to select and characterize structures, with the purpose of minimizing the aforementioned risk. Multi‐criteria algorithms can be used to establish a hierarchy of the alternatives and to identify the structures with the greatest potential with an objective approach. The analytic hierarchy process method is used in this paper as the selection algorithm, which is based on identifying and assessing criteria and weighting each criterion. In accordance with the analytic hierarchy process method, the goal was divided into a series of different level criteria, defining a breakdown structure of the problem to select salt domes. This paper defines a structure hierarchization method that allows the objective establishment of the areas with the highest potential for CAES, considering both technical and socioeconomic factors. Therefore, a supporting decision‐making method may be established to reduce the exploration risk associated with underground structures. Copyright © 2017 John Wiley & Sons, Ltd.     

基于压缩空气储能的新型冷热电联供系统性能研究

为了解决用户负荷需求在时间上的变动和传统冷热电联供（Combine Cooling, Heating & Power, CCHP）系统大部分时间处于非设计工况下运行导致系统的能源利用效率较低的问题,提出了一种耦合压缩空气储能系统（Compressed Air Energy Storage system, CAES）和蓄热装置的新型CCHP系统（CAES based CCHP system,CAES CCHP）,建立系统的热力学模型,在给定的充、放电工作条件下对CAES CCHP系统的热力学性能进行分析,并对影响该系统性能的CAES压气机压缩比、透平进气口压力、流经CAES的烟气质量流量3个关键参数进行敏感性分析。研究结果表明：CAES CCHP系统能实现冷热电灵活调控,且系统的CAES功转换效率为57.41%,一次能源利用率、一次节能率及火用效率分别为76.22%,24.84%和31.97%,比传统的CCHP系统分别提高10.97%,18.15%和7.58%。     

Analysis of diabatic compressed air energy storage systems with artificial reservoir using the levelized cost of storage method

A detailed analysis has been carried out to assess the thermodynamic and economic performance of Diabatic Compressed Air Energy Storage (D‐CAES) systems equipped with above‐ground artificial storage. D‐CAES plant arrangements based on both Steam Turbine (ST) and Gas Turbine (GT) technologies are taken into consideration. The influence of key design quantities (ie, storage pressure, turbine inlet pressure, turbine inlet temperature) on efficiency, capital and operating costs is analysed in detail and widely discussed. Finally, D‐CAES design solutions are compared with Battery Energy Storage (BES) systems on the basis of the Levelized Cost of Storage (LCOS) method. Results show that the adoption of D‐CAES can lead to better economic performance with respect to mature and emerging BES technologies. D‐CAES ST based solutions can achieve a LCOS of 28 €cent/kWh, really close to that evaluated for the better performing BES system. Interesting LCOS values of 20 €cent/kWh have been attained by adopting D‐CAES plant solutions based on GT technology.     

Economics of compressed air energy storage to integrate wind power: A case study in ERCOT

Compressed air energy storage (CAES) could be paired with a wind farm to provide firm, dispatchable baseload power, or serve as a peaking plant and capture upswings in electricity prices. We present a firm-level engineering-economic analysis of a wind/CAES system with a wind farm in central Texas, load in either Dallas or Houston, and a CAES plant whose location is profit-optimized. With 2008 hourly prices and load in Houston, the economically optimal CAES expander capacity is unrealistically large – 24 GW – and dispatches for only a few hours per week when prices are highest; a price cap and capacity payment likewise results in a large (17 GW) profit-maximizing CAES expander. Under all other scenarios considered the CAES plant is unprofitable. Using 2008 data, a baseload wind/CAES system is less profitable than a natural gas combined cycle (NGCC) plant at carbon prices less than $56/tCO₂ ($15/MMBTU gas) to $230/tCO₂ ($5/MMBTU gas). Entering regulation markets raises profit only slightly. Social benefits of CAES paired with wind include avoided construction of new generation capacity, improved air quality during peak times, and increased economic surplus, but may not outweigh the private cost of the CAES system nor justify a subsidy.     

Operating characteristics of constant-pressure compressed air energy storage (CAES) system combined with pumped hydro storage based on energy and exergy analysis

Energy storage systems are becoming more important for load leveling, especially because of the widespread use of intermittent renewable energy. Compressed air energy storage (CAES) is a very promising method for energy storage because CAES relies on existing technologies, is less expensive, and easier to site and permit, as compared to pumped hydro storage. But, in the case of CAES employing hard rock caverns or man-made air vessels, although the smallest possible cavern volume is desirable in order to minimize the construction cost and optimize utilization of the given space, the operating pressure range in the cavern must be limited in order to reduce the deterioration in efficiency of the CAES system at off-design conditions. In this paper, a new constant-pressure CAES system combined with pumped hydro storage was studied to address the current problem associated with the conventional CAES systems. An energy and exergy analysis of the novel CAES system was performed in order to understand the operation characteristics of the system according to several different compression and expansion processes; we then examined the effects of the height of the storage cavern and heat transfer between two media (air, water) and the cavern on the performance of the novel CAES system.     

Techno‐economic study of compressed air energy storage systems for the grid integration of wind power

Integrating variable renewable energy from wind farms into power grids presents challenges for system operation, control, and stability due to the intermittent nature of wind power. One of the most promising solutions is the use of compressed air energy storage (CAES). The main purpose of this paper is to examine the technical and economic potential for use of CAES systems in the grid integration. To carry out this study, 2 CAES plant configurations: adiabatic CAES (A‐CAES) and diabatic CAES (D‐CAES) were modelled and simulated by using the process simulation software ECLIPSE. The nominal compression and power generation of both systems were given at 100 and 140 MWe, respectively. Technical results showed that the overall energy efficiency of the A‐CAES was 65.6%, considerably better than that of the D‐CAES at 54.2%. However, it could be seen in the economic analysis that the breakeven electricity selling price (BESP) of the A‐CAES system was much higher than that of the D‐CAES system at €144/MWh and €91/MWh, respectively. In order to compete with large‐scale fossil fuel power plants, we found that a CO₂ taxation scheme (with an assumed CO₂‐tax of €20/tonne) improved the economic performance of both CAES systems significantly. This advantage is maximised if the CAES systems use low carbon electricity during its compression cycle, either through access to special tariffs at times of low carbon intensity on the grid, or by direct coupling to a clean energy source, for example a 100‐MW class wind farm.     

Thermal storage in an air conditioning system with dual energy storage unit

在自行搭建的双蓄能实验平台上进行了制冷兼蓄热实验研究,对比了制冷兼蓄热模式和一般制冷模式,探讨了不同冷冻水流量和不同风机盘管风量对机组性能的影响.实验结果表明:蓄热对机组制冷端的影响很小,但是由于回收了大量的冷凝热,使得机组的综合能效比得到大幅提高,因此蓄热对空调节能具有较大作用.此外,在制冷兼蓄热模式下,冷冻水流量或风机盘管风量越大,机组的综合能效比越大,当风量为1033 m³/h,冷冻水流量为972 L/h时,机组综合能效比高达7.06.     

Baseload wind energy: modeling the competition between gas turbines and compressed air energy storage for supplemental generation

The economic viability of producing baseload wind energy was explored using a cost-optimization model to simulate two competing systems: wind energy supplemented by simple- and combined cycle natural gas turbines (“wind+gas”), and wind energy supplemented by compressed air energy storage (“wind+CAES”). Pure combined cycle natural gas turbines (“gas”) were used as a proxy for conventional baseload generation. Long-distance electric transmission was integral to the analysis. Given the future uncertainty in both natural gas price and greenhouse gas (GHG) emissions price, we introduced an effective fuel price, p_NGeff, being the sum of the real natural gas price and the GHG price. Under the assumption of p_NGeff=$5/GJ (lower heating value), 650 W/m² wind resource, 750 km transmission line, and a fixed 90% capacity factor, wind+CAES was the most expensive system at ¢6.0/kWh, and did not break even with the next most expensive wind+gas system until p_NGeff=$9.0/GJ. However, under real market conditions, the system with the least dispatch cost (short-run marginal cost) is dispatched first, attaining the highest capacity factor and diminishing the capacity factors of competitors, raising their total cost. We estimate that the wind+CAES system, with a greenhouse gas (GHG) emission rate that is one-fourth of that for natural gas combined cycle plants and about one-tenth of that for pulverized coal plants, has the lowest dispatch cost of the alternatives considered (lower even than for coal power plants) above a GHG emissions price of $35/tC_equiv., with good prospects for realizing a higher capacity factor and a lower total cost of energy than all the competing technologies over a wide range of effective fuel costs. This ability to compete in economic dispatch greatly boosts the market penetration potential of wind energy and suggests a substantial growth opportunity for natural gas in providing baseload power via wind+CAES, even at high natural gas prices.     

Thermodynamic analysis of a novel compressed carbon dioxide energy storage system with low-temperature thermal storage

Research projects on new electrical energy storage (EES) systems are underway because of the role of EES in balancing the electric grid and smoothing out the instability of renewable energy. In this paper, a novel compressed carbon dioxide energy storage with low-temperature thermal storage was proposed. Liquid CO₂ storage was employed to increase the storage density of the system and avoid its dependence on geological formations. Low-temperature thermal energy storage technology was utilized to recycle the heat of compression and reduce the challenges to system components. The system configuration was introduced in detail. Four evaluation criteria, the round trip efficiency (RTE), exergy efficiency (η_Ex), thermal efficiency (η_TE), and energy density (ρ_E) were defined to show the system performance. Parametric analysis was carried out to examine the effects of some key parameters on system performance and the genetic algorithm was adopted for system optimization. The calculated results show that, for the novel EES under the basic working condition, its RTE is 41.4%, η_TE is 59.7%, η_Ex is 45.4%, and ρ_E is 15 kWh m⁻³. The value of ρ_E increases with the increasing pump outlet pressure for a fixed value of pressure ratio, and the changes of RTE, η_TE, and the total exergy destruction of the system (E_D,total) with pump outlet pressure are complicated for different values of pressure ratio. When both pressure ratio and pump outlet pressure are high, the values of RTE and ρ_E can be maximized whereas the value of E_D,total can be minimized. Besides, no matter how pump outlet pressure and pressure ratio change, the exergy destruction of the system mainly come from compressors and regenerators, which accounts for about 50% of the total exergy destruction.     

Performance comparison of different combined heat and compressed air energy storage systems integrated with organic Rankine cycle

Compressed air energy storage (CAES) is promising to enable large‐scale penetration of renewable energies (REs). However, conventional diabatic CAES (D‐CAES) depends largely on fossil fuels, while adiabatic CAES (A‐CAES) is limited in output power. To conquer these disadvantages, concept of combined heat and CAES (CH‐CAES) is proposed in this paper. The proposed system couples an electric heater with conventional A‐CAES. During charging, electricity storage transforms from pure compression to partly relying on Joule heating. The stored heat in an electric heater will be used to boost turbine inlet temperature during discharging. Consequently, system charge/discharge capacity can be improved without enlarging cavern size, raising cavern pressure, and producing greenhouse gases. This paper discusses three types of CH‐CAES systems with different electric heater installation positions. Off‐design performance analysis for each system is conducted on the basis of turbomachinery (compressors, turbines, and the pump) characteristic maps and heat exchangers off‐design models. Performance comparison is conducted between these three CH‐CAES systems (called Mode II, III, and IV for simplification) and the conventional A‐CAES system (Mode I). Control strategies are also given in this paper. Results show that the EVR (energy generated per unit volume of storage) increases with participation of an electric heater, while the RTE (system roundtrip efficiency) slightly decreases. Mode I has the highest RTE. The largest EVR appears in Mode III where the electrical heater is in series with the intercooler and after cooler. Mode II is a compromise solution to achieve both relatively high RET and EVR when the electrical heater is installed in series only with the intercooler. Mode IV with a paralleling electrical heater has great flexibility to adapt different user demands. The integration of the ORC has a positive effect on system RTE and EVR.     

基于相变储能的太阳能空气源热泵系统的研究

针对由天气变化导致太阳能利用不稳定和寒冷地区热泵性能低的问题,文章介绍了一种基于相变储能的太阳能空气源热泵系统,该系统能够根据气象情况灵活切换4种供暖模式,大大减少了系统耗电量。文章通过独特设计的储能冷凝器,不仅可以调节太阳能空气源热泵系统能量分配,改善太阳能空气源热泵系统制热量和建筑热负荷之间不平衡的供需关系、提高太阳能利用率,还可以提高空气源热泵低温性能,快速恢复供暖,从而实现提高太阳能空气源热泵系统整体性能的目的。文章以石家庄农村某户为研究对象进行研究,研究结果表明,太阳能空气源热泵系统供暖效果较好,太阳能空气源热泵系统COP最大值为5.19,节能环保效益十分明显。