Current application situation and development prospect of physical energy storage technologies

作为可再生能源并网的关键技术,可再生能源的高速发展也带动了储能产业的发展和成熟。物理储能技术,发展历史长,技术较为成熟,部分已实现商业化运作;以抽水蓄能为代表,是电网调峰的主力,也在储能市场容量中占据着绝对份额。但无论是传统抽水蓄能,还是压缩空气储能都对环境、地理地质条件有较高的要求,极大地制约了这些技术的普遍推广和应用。因此物理储能也经历着应用模式的变革、传统技术向新兴技术转化的过程。虽然抽水蓄能、压缩空气储能和飞轮储能三种物理储能技术在原理、应用领域、安装容量以及未来发展趋势上各不相同, 但作为战略新兴技术,都需要技术的突破、政策和资金的支持以及更多的市场应用机会。     

Bulk energy storage potential in the USA, current developments and future prospects

Stored energy can provide electricity during periods of high demand, as currently demonstrated with bulk storage systems such as pumped hydro storage (PHS), which accounts for only 2.5% of the current installed base load in the USA. Sites for future developments have become less available, and environmental siting issues, as well as high costs have stopped further prospects. This paper looks at the potential beyond PHS, with bulk storage systems such as compressed air energy storage (CAES) flow-batteries and 1 MW flywheel systems that can provide system stability/support at the grid, substations and distributed level. Current developments in bulk energy storage will be reviewed as well as some storage project developments incorporating wind energy and the impact on base-loaded coal and natural gas fired GT combined cycle plants. The large potential and the economic benefits for energy storage in the US will be examined.     

A review of marine renewable energy storage

Marine renewable energies are promising enablers of a cleaner energy future. Some technologies, like wind, are maturing and have already achieved commercial success. Similar to their terrestrial counterparts, marine renewable energy systems require energy storage capabilities to achieve the flexibility of the 21st century grid demand. The unique difficulties imposed by a harsh marine environment challenge the unencumbered rise of marine renewable energy generation and storage systems. In this study, the fundamentals of marine renewable energy generation technologies are briefed. A comprehensive review and comparison of state‐of‐the‐art novel marine renewable energy storage technologies, including pumped hydro storage (PHS), compressed air energy storage (CAES), battery energy storage (BES), hydrogen energy storage (HES), gravity energy storage (GES), and buoyancy energy storage (ByES), are conducted. The pros and cons, and potential applications, of various marine renewable energy storage technologies are also compiled. Finally, several future trends of marine renewable energy storage technologies are connoted.     

Modeling and simulation of compressed air storage in caverns: A case study of the Huntorf plant

An accurate dynamic simulation model for compressed air energy storage (CAES) inside caverns has been developed. Huntorf gas turbine plant is taken as the case study to validate the model. Accurate dynamic modeling of CAES involves formulating both the mass and energy balance inside the storage. In the ground reservoir based storage bed, the heat transfer from the ground reservoir plays an important role in predicting the cavern storage behavior and is therefore taken into account. The heat transfer coefficient between the cavern walls and the air inside the cavern is accurately modeled based on the real tests data obtained from the Huntorf plant trial tests. Finally the model is validated based on a typical daily schedule operation of the Huntorf plant. A comparison is also made with the results obtained from adiabatic and isothermal assumptions inside the cavern to gain further insights. Such accurate modeling of cavern dynamics will affect the design of the cavern storage beds for future explorations.     

Thermodynamic analysis of CAES/TES systems for renewable energy plants

A thermodynamic analysis is presented for an energy storage system without combustion and including thermal recuperation (adiabatic compressed air energy strong (CAES)). The storage volume is optimized and a system layout with thermal storage (TES) and variable configuration is designed. The proposed system is simulated in order to have a first estimate of its energy recovery efficiency.     

Energy and exergy analysis of a micro-compressed air energy storage and air cycle heating and cooling system

Energy storage systems are becoming more important for load leveling, especially for widespread use of intermittent renewable energy. Compressed air energy storage (CAES) is a promising method for energy storage, but large scale CAES is dependent on suitable underground geology. Micro-CAES with man-made air vessels is a more adaptable solution for distributed future power networks. In this paper, energy and exergy analyses of a micro-CAES system are performed, and, to improve the efficiency of the system, some innovative ideas are introduced. The results show that a micro-CAES system could be a very effective system for distributed power networks as a combination that provides energy storage, generation with various heat sources, and an air-cycle heating and cooling system, with a energy density feasible for distributed energy storage and a good efficiency due to the multipurpose system. Especially, quasi-isothermal compression and expansion concepts result in the best exergy efficiencies.     

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%.     

The value of compressed air energy storage in energy and reserve markets

Storage devices can provide several grid services, however it is challenging to quantify the value of providing several services and to optimally allocate storage resources to maximize value. We develop a co-optimized Compressed Air Energy Storage (CAES) dispatch model to characterize the value of providing operating reserves in addition to energy arbitrage in several U.S. markets. We use the model to: (1) quantify the added value of providing operating reserves in addition to energy arbitrage; (2) evaluate the dynamic nature of optimally allocating storage resources into energy and reserve markets; and (3) quantify the sensitivity of CAES net revenues to several design and performance parameters. We find that conventional CAES systems could earn an additional $23 ± 10/kW-yr by providing operating reserves, and adiabatic CAES systems could earn an additional $28 ± 13/kW-yr. We find that arbitrage-only revenues are unlikely to support a CAES investment in most market locations, but the addition of reserve revenues could support a conventional CAES investment in several markets. Adiabatic CAES revenues are not likely to support an investment in most regions studied. Modifying CAES design and performance parameters primarily impacts arbitrage revenues, and optimizing CAES design will be nearly independent of dispatch strategy.     

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.     

New technology and possible advances in energy storage

Energy storage technologies may be electrical or thermal. Electrical energy stores have an electrical input and output to connect them to the system of which they form part, while thermal stores have a thermal input and output. The principal electrical energy storage technologies described are electrochemical systems (batteries and flow cells), kinetic energy storage (flywheels) and potential energy storage, in the form of pumped hydro and compressed air. Complementary thermal storage technologies include those based on the sensible and latent heat capacity of materials, which include bulk and smaller-capacity hot and cold water storage systems, ice storage, phase change materials and specific bespoke thermal storage media.     

A review of large‐scale electrical energy storage

This paper gives a broad overview of a plethora of energy storage technologies available on the large‐scale complimented with their capabilities conducted by a thorough literature survey. According to the capability graphs generated, thermal energy storage, flow batteries, lithium ion, sodium sulphur, compressed air energy storage, and pumped hydro storage are suitable for large‐scale storage in the order of 10's to 100's of MWh; metal air batteries have a high theoretical energy density equivalent to that of gasoline along with being cost efficient; compressed air energy storage has the lowest capital energy cost in comparison to other energy storage technologies; flywheels, super conducting magnetic storage, super capacitors, capacitors, and pumped hydro storage have very low energy density; compressed air energy storage, cryogenic energy storage, thermal energy storage, and batteries have relatively high energy density; high efficiencyin tandem with high energy density results in a cost efficient storage system; and power density pitted against energy density provides a clear demarcation between power and energy applications. This paper also provides a mathematical model for thermal energy storage as a battery. Furthermore, a comprehensive techno‐economic evaluation of the various energy storage technologies would assist in the development of an energy storage technology roadmap. Copyright © 2015 John Wiley & Sons, Ltd.     

压缩空气储能技术现状与发展趋势

在分析传统压缩空气储能（CAES）技术的工作原理和技术特点的基础上,介绍了压缩空气储能技术的发展,包括非绝热压缩空气储能技术（D-CAES）、绝热压缩空气储能技术（A-CAES）、液化空气储能技术（LAES）和超临界压缩空气储能技术（SC-CAES）等,并给出了评价不同系统性能的技术参数。以国际上第一座压缩空气储能电站——德国Huntorf电站的运行参数和相关情况为例,分析了D-CAES技术的应用情况;对压缩空气储能技术在美国及其他国家和地区的应用和发展现状进行分析。通过对比不同的压缩空气储能技术方案,分析了A-CAES、LAES、SC-CAES及LCES储能系统的先进性、竞争优势与不足,分析了未来CAES技术的发展趋势。     

Commercial and research battery technologies for electrical energy storage applications

Developing green energy solutions has become crucial to society. However, to develop a clean and renewable energy system, significant developments must be made, not only in energy conversion technologies (such as solar panels and wind turbines) but also regarding the feasibility and capabilities of stationary electrical energy storage (EES) systems. Many types of EES systems have been considered such as pumped hydroelectric storage (PHS), compressed air energy storage (CAES), flywheels, and electrochemical storage. Among them, electrochemical storage such as battery has the advantage of being more efficient compared to other candidates, because it is more suitable in terms of the scalability, efficiency, lifetime, discharge time, and weight and/or mobility of the system. Currently, rechargeable lithium ion batteries (LIBs) are the most successful portable electricity storage devices, but their use is limited to small electronic equipment. Using LIBs to store large amounts of electrical energy in stationary applications is limited, not only by performance but also by cost. Thus, a viable battery technology that can store large amounts of electrical energy in stationary applications is needed. In this review, well-developed and recent progress on the chemistry and design of batteries, as well as their effects on the electrochemical performance, is summarized and compared. In addition, the challenges that are yet to be solved and the possibilities for further improvements are explored.     

The thermodynamic effect of thermal energy storage on compressed air energy storage system

With the increasing penetration of renewable energy into energy market, it is urgent to solve the problem of fluctuations of renewable energy sources (RES). Energy storage technology is regarded as one method to cope with the unstable nature of RES. One of these technologies is compressed air energy storage (CAES), which is a modification of the basic gas turbine technology. Electric power supplied by CAES can meet peak-load requirement of electric utility systems. Because there is heat waste in the existing CAES systems during compression process, fossil fuels are used to improve the expansion work to generate peak power. In order to avoid the use of fuels and keep high efficiency of system, CAES system with thermal energy storage (TES) is designed to capture and reuse the compressed air heat. This paper uses a thermodynamic model of a CAES system with TES to analyze the effect of TES on system efficiency. Besides, this paper evaluates the influence of temperature and pressure on the utilization of heat in TES. Results show that even when power efficiency reaches maximum, there is still a proportion of thermal energy left in TES for other use. Meanwhile, the utilization of heat in TES can be affected by pressure in the air storage chamber. With appropriate selection of pressure limits, the utilization of compressed air heat can be optimized.     

Thermo-economic analysis and sizing of a PV plant equipped with a compressed air energy storage system

Photovoltaic (PV) farms are widely used around the world to provide required electricity. Compressed air energy storage (CAES) system has been already proposed for energy storage applications in large scales. In this work, employing a CAES unit equipped with an ancillary solar heating system for a large scale PV farm in Brazil is proposed. A PV farm with 100 MWp (megawatt peak) capacity is proposed to be built in the most suitable point within Brazil. The sizing of the CAES unit and the solar heating system, which has not been investigated, along with selecting the best power sales strategy for the power plant, which has been always a challenge for renewable energy source power plants, are carried out emphasizing energy-economic considerations. In order to prove the proficiency of the proposal, the performance of the power plant and energy storage unit is assessed over a sample year. In order to have a comprehensive economic analysis, Net Present Value (NPV) method is employed and all the possible uncertainties in the system have been taken into account.     

Dynamic simulation of air storage–based gas turbine plants

Cavern storage is a proven energy storage technology, capable of storing energy in the form of compressed air inside a cavern. The Huntorf plant and the Alabama plants use this technology to store electrical energy during the off‐peak load hours by compressing the air inside a cavern and then using this compressed air during gas turbine operation to generate electricity during peak load demand hours. The advantage of doing this is that it increases the efficiency of gas turbine operation while meeting the grid generation and the load balance. The operation of a typical compressed air energy storage (CAES)–based gas turbine plant involves the operation of several components, including the compressor, the cavern storage, the combustor, the turbine, and so on. The dynamics of the plant as a whole depends on the performance of the individual components. The focus of this article is to develop a Simulink‐based models for each of the individual components, which can then be assembled appropriately to design an entire CAES plant. As an illustration, a case study for the Huntorf CAES plant is presented with the developed models. A typical daily operation of the Huntorf plant is simulated and compared with the reported Huntorf plant data. The model accurately captures the reported dynamics of the cavern storage. In addition, the reported quantities like the compressor power consumption, the turbine power generation, and the temperature at different junctions of the CAES plant match well with the simulated results. Copyright © 2011 John Wiley & Sons, Ltd.     

Performance of a small‐scale compressed air storage (CAS)

The use of renewable energy, such as wind and solar, has significantly increased in the last decade. However, these renewable technologies have the limitation of being intermittent; thus, storing energy in the form of compressed air is a promising option. In compressed air energy storage (CAES), the electrical energy from the power network is transformed into a high‐pressure storage system through a compressor. Then, when the demand for electricity is high, the stored high‐pressure air is used to drive a turbine to generate electricity. The advantages of CAES are its high energy density and quality, and for being environmentally friendly process. In the existing facilities of University of Auckland, New Zealand, air cavern is not available; thus, a high‐pressure tank is used to store the compressed air, which could provide an excellent opportunity for small size applications. There is a limited literature available on the temperature and pressure profiles in a typical high‐pressure tank during charging and discharging processes. Therefore, this research investigates how temperature and pressure inside a high‐pressure tank change during charging and discharging processes. It will provide a better understanding for heat transfer in such system. Furthermore, it will provide the necessary information needed for the designing of an efficient small‐scale CAES. In this work, air is compressed to a maximum pressure of 200 bar and stored into a 2 L tank, which is fully fitted with a pressure transducer and a thermocouple suitable for high‐pressure measurements. The charging and discharging process is theoretically modeled, and the results are compared with the experimental measurements, showing a good agreement. The heat balance on the system is used to validate the steady‐state condition, while dynamic analysis is used to predict the transient change of compressed air and tank wall temperatures. The theoretical modeling is undertaken by solving the differential equations describing the transient change in temperature of both air and tank wall. The results of this study show that air temperature rises from 24°C to 60°C at 100 bar and from approximately 17°C to over 60°C at 200 bar. During discharging process, air temperature drops from ambient to 5°C at starting pressure of 100 bar and to ?20°C at starting pressure of 200 bar.     

Temperature and pressure variations within compressed air energy storage caverns

In the present work, the thermodynamic response of underground cavern reservoirs to charge/discharge cycles of compressed air energy storage (CAES) plants was studied. During a CAES plant operation, the cyclical air injection and withdrawal produce temperature and pressure fluctuations within the storage cavern. Predictions of these fluctuations are required for proper cavern design and for the selection of appropriate turbo-machinery. Based on the mass and energy conservation equations, numerical and approximate analytical solutions were derived for the air cavern temperature and pressure variations. Sensitivity analyses were conducted to identify the dominant parameters that affect the storage temperature and pressure fluctuations and the required storage volume. The heat transfer at the cavern walls was found to highly affect the air temperature and pressure variations as compared to adiabatic conditions. In essence, heat transfer reduces the temperature and pressure fluctuations during cavern charge and discharge and effectively leads to a higher storage capacity. Additionally, for realistic conditions, in each cycle, few percents of the injected energy are lost by conduction into the rocks. The principal thermal property that governs the heat transfer process is the rock effusivity. To reduce the required storage volume preference must be given to sites of rocks that have the largest thermal effusivity. Lower injected air temperatures also reduce the required storage volume, but increase the cooling costs. The injected temperature can also be used to control the cycle temperature extreme limits. It is evident from the results that the storage pressure ratio has a dominant effect on the required storage volume and should preferably range between 1.2 and 1.8.     

System behaviour of compressed-air energy-storage in Denmark with a high penetration of renewable energy sources

In 2005, wind power supplied 19% of the 36 TWh annual electricity demand in Denmark, while 50% was produced at combined heat-and-power plants (CHP). The installed wind-turbine capacity in Western Denmark exceeds the local demand at certain points in time. So far, excess production has been exported to neighbouring countries. However, plans to expand wind power both in Denmark and in its neighbouring countries could restrain the export option and create transmission congestion challenges. This results in a need to increase the flexibility of the local electricity-system. Compressed-Air Energy-Storage (CAES) has been proposed as a potential solution for levelling fluctuating wind-power production and maintaining a system balance. This paper analyses the energy-balance effects of adding CAES to the Western Danish energy-system. Results show that even with an unlimited CAES plant capacity, excess power production is not eliminated because of the high percentage of CHP production. The optimal wind-power penetration for maximum CAES operation is found to be around 55%. The minimum storage size for CAES to fully eliminate condensing power plants operation in the optimized system is over 500 GWh, which corresponds to a cavern volume of around 234 Mm³ at an average pressure of 60 bar. Such a storage size would be technically and economically unfeasible. The analysis, however, did not include the potential role of a CAES plant in regulating the power services.     

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.