Compressed Air Energy Storage: Types, systems and applications
The intermittency of renewable energy sources is making increased deployment of storage technology necessary. Technologies are needed with high round-trip efficiency and at low cost to allow renewables to undercut fossil fuels. The cost of lithium batteries has fallen, but producing them comes with a substantial carbon footprint, as well as a cost to the local environment. Compressed air energy storage (CAES) uses excess electricity, particularly from wind farms, to compress air. Re-expansion of the air then drives machinery to recoup the electric power. Prototypes have capacities of several hundred MW. Challenges lie in conserving the thermal energy associated with compressing air and leakage of that heat, materials, power electronics, connection with the power generator, and grid integration. This comprehensive book provides a systematic overview of the current state of CAES technology. After an introduction to motivation and principles, the key components are covered, and then the principal types of systems in the order of technical maturity: diabatic, adiabatic, and isothermal. Experts from industry write about their experiences with existing major systems and prototypes. Economic aspects, power electronics and machinery, as well as special systems for offshore applications, are dealt with. Researchers in academia and industry alike, in particular at energy storage technology manufacturers and utilities, as well as advanced students and energy experts in think tanks will find this work valuable reading.
Inspec keywords: renewable energy sources; pricing; power markets; energy storage; compressed air energy storage
Other keywords: heat transfer; thermal energy storage; power generation economics; design engineering; compressed air energy storage; thermodynamics; renewable energy sources; power markets; pricing
Subjects: Direct energy conversion and energy storage; Conference proceedings; Energy resources and fuels; Energy storage; Power system management, operation and economics; Energy resources; General electrical engineering topics
- Book DOI: 10.1049/PBPO184E
- Chapter DOI: 10.1049/PBPO184E
- ISBN: 9781839531958
- e-ISBN: 9781839531965
- Page count: 285
- Format: PDF
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Front Matter
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1 The current status and future perspectives of compressed air energy storage
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It is trite to say that energy storage is essential for furthering renewable energy by stabilizing the supply and demand. It is also cliche to point out that compressed air energy storage (CAES) is a promising means for energy storage. To highlight but a few of the multitude of recent publications on CAES, Tan et al. present a comprehensive review concerning various energy storage technologies for empowering smart grid. CAES is also one of the most promising energy storage means in the harsh marine environment. Guo et al. discuss the promise and challenges of utility-scale CAES in aquifers. A regional review of CAES for northern China is compiled by Tong et al. and Mahmoud et al. compare and contrast the three main mechanical energy storage options, flywheel, pumped hydro, and CAES. They conclude that flywheel is best suited for short-duration applications. For longer durations, pumped hydro has the efficiency while CAES provides a faster start-up. For good environmental stewardship, adiabatic or isothermal CAES is recommended. In short, the case for CAES is clear. It is expected to ramp up its importance as we march forward to harness progressively greener energy.
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2 An overview of CAES
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Energy storage systems as a part of energy secure supply have the ability to take up a certain amount of energy, store it in a storage medium for a suitable period of time, and release it in a controlled manner after a certain time delay. Large-scale mechanical storage of electric power is currently almost exclusively achieved by pumped-storage hydroelectric power stations. In the area of electrochemical storage, different technologies are currently in various stages of research, development, and demonstration of their suitability for large-scale electrical energy storage. Thermal energy storage technologies are based on the storage of sensible heat, exploitation of phase transitions, adsorption/desorption processes, and chemical reactions. In thermo-mechanical energy storage systems like compressed air energy storage (CAES), energy is stored as compressed air in a reservoir during off-peak periods, while it is used on demand during peak periods to generate power with a turbo-generator system. In the following chapter, after introduction of system key components, timeline development and progress of CAES from different point of view is discussed. Such plants can offer significant benefits in terms of flexibility in matching a fluctuating power demand, particularly when coupled with renewable sources. Storing energy when it's made and releasing it when it's needed helps keep the grid reliable and paves the way for introducing intermittent renewables like wind and solar to the mix. CAES is NOT "a mature technology." Also, it is not "a single technology." There is huge scope for further learning and further cost reduction.
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3 Isothermal compressed air energy storage
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Isothermal compressed air energy storage (I-CAES) technology is considered as one of the advanced compressed air energy storage technologies with competitive performance. I-CAES has merits of relatively high round-trip efficiency and energy density compared to many other compressed air energy storage (CAES) systems. The main challenge is to realize high-efficiency heat transfer for charging and discharging in order to keep the air temperature almost constant, thus, to achieve the isothermal or near-isothermal compression and expansion. In this chapter, the general concept of I-CAES was introduced, and its thermodynamic cycle was illustrated. The research progress of I-CAES was reviewed. Both I-CAES system configuration and performance, and key components performance were reviewed. A new isothermal expander was further designed for I-CAES. The specific reciprocating expander with a high-pressure ratio was developed and its adiabatic expansion characteristics were measured by the authors' group. We further proposed a quasi-isothermal expansion process using water injection into the expander cylinder. Modelling was developed and validated by the experimental results of the adiabatic expander, which was also extended to simulate the quasi-isothermal process by introducing water-air direct heat transfer equations. Simulation results showed that when spraying tiny water droplets into the cylinder, the specific work generated was improved compared with that of the adiabatic expansion under the same air mass flow rate. While the temperature difference between inlet and outlet was decreased substantially, and the cylinder size was more compact. The influence of water/air mass flow rate ratio and the inlet temperature on the expander performance was also studied.
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4 Improving the efficiency of A-CAES systems by preconditioning discharge air stream
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This chapter explores the effects of variations in cavern air quality on the overall performance of adiabatic compressed air energy storage (A-CAES) systems. Components of A-CAES systems interact in dynamic ways and often have compounding effects. This chapter analyses the effect of variations in these parameters on the performance of A-CAES systems by thermodynamic simulation of a 100 MW plant with three stages of expansion. For a fair comparison in between generated models, the atmospheric condition, the volume of the hot thermal store, and the efficiency of expanders were fixed for all cases. Simulations were performed for systems with cavern pressures between 4 and 8 MPa, where the ratios between hot water mass flow and air mass flow were between 0.65 and 0.85. The obtained result shows that the maximum reachable power and efficiency in the considered ranges are 117 MW and 80.3%, respectively. Also, the maximum and the minimum accessible energies are 482 and 324 MWh, respectively, with corresponding discharge durations of 4.5 and 3.4 h. The optimum performance of the system was observed when the ratio of hot water to air mass flow was 0.8. Moreover, this work revealed that every 25% increase in humidity percentage can increase the total expander power by about 0.1%. The output of this work can also be used for the management of the thermal systems according to the cavern air property.
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5 Technical feasibility analysis of compressed air energy storage from the perspective of underground reservoir
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This chapter is intended to discuss the potential and challenges of large-scale commercialization of CAES by analysing the technical issues associated with the underground reservoir. We also conducted a case study of the CAES in Ontario, Canada, where the salt cavern is used for the energy storage.
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6 Comprehensive overview of compressed air energy storage systems
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Compressed air energy storage (CAES) is a technology employed for decades to store electrical energy, mainly on large-scale systems, whose advances have been based on improvements in thermal management of air compression and expansion stages through adiabatic and nearly isothermal processes. Recently, small-scale CAES (SS-CAES) systems have also been applied as an alternative to replace batteries in autonomous systems and in distributed generation applications with renewable sources. These systems require compact and efficient power stages, with remarkable presence of power electronics. In this context, this chapter presents a comprehensive overview about some CAES and SS-CAES systems and describes their operating principles, as well as information regarding energy density, efficiency, cost, limitations, and challenges to be overcome in order to make them attractive solutions.
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7 Compressed air energy storage systems, towards a zero emissions in electricity generation
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In the fight against climate change, the electricity sector is involved in the promotion of renewable sources. These technologies, free of CO2 emissions in their electricity generation process, suffer from a low load factor. This requires expensive backup systems for the power grid to guarantee supply. To increase the availability of these resources, the concept of 'massive energy storage' arises, considering chemical storage in the form of hydrogen, pumping water, or storage of compressed air in the subsurface. This chapter will review the concepts of this latest technology, gathering the concept of compressed air storage taking advantage of obsolete infrastructure and a novel alternative to thermal energy management. The viability of this technology depends on an adequate use of the thermal energy exchanged in the compression and expansion processes, which allows an increase in the overall efficiency of the process and an improvement in the competitiveness, compared to other mass storage solutions.
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8 Compressed air energy storage system dynamic modelling and simulation
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The compressed air energy storage (CAES) system is a very complex system with multi-time-scale physical processes. Following the development of computational technologies, research on CAES system model simulation is becoming more and more important for resolving challenges in system pre-design, optimization, control and implementation. In this chapter, five types of simulation model for CAES system and components have been explained and compared based on the discharging process of the CAES. Principles for choosing suitable model methods targeting different purposes for CAES system have been described, and a novel data-driven dynamic simulation approach for the complex system is demonstrated. The result shows that the data-driven simulation approach can reduce computational cost sharply and may help build CAES system-level real-time simulation in the future.
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9 Application of compressed air energy storage systems in a day-ahead dispatch schedule under demand response and renewable obligation
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In this chapter, a combined day-ahead dispatch schedule for compressed air energy storage (CAES) systems with renewable energy sources (RESs) under demand response and renewable obligation is presented. The model uses CAES systems to overcome the uncertainty related to wind and photovoltaic (PV) energy systems. The proposed model is applied to a renewable obligation policy which ensures that a certain percentage of the energy generated comes from RESs. In order to participate in the day-ahead market, CAES systems are integrated with RES generators, and demand response is used for deferring flexible demand from peak electricity price period to low-price periods. The proposed model uses real data from a large-scale demand response programme which allows the system operator to directly control the participation of electric water heaters from the substation level. The effectiveness of the proposed model is tested on a modified IEEE 30-bus system and the results show that the CAES systems can help in increasing the RES penetration and improve profitability.
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10 Direct air capture and wind curtailment: a technology-based business approach for the US market
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As the grids are continually modernized and integrate higher amounts of renewable energy sources, further deployment of renewables could bring further abrupt reduction in wind-based electricity generation, also known as wind curtailment. The electricity markets are able to economically and technically lay the foundations to facilitate further penetration (by massively offering negative prices via demand response); however, since independent power producers (and subsequently wind manufacturers) need a stable growth and profitable plan not dependent on each market's marginal prices, the pressure from the industry on establishing another system based on negative emissions will also grow. Direct air capture (DAC) could play that role in the immediate future. It is widely accepted that curtailment will continue to be present, but in order its rate to fall, investments are needed, especially in the markets where wind farms are not meeting the majority of electricity demand, and there is still a long way, such as the Chinese and the US markets. In this work, a business and technology-based analysis for the US market points out the political decisions required for such a long and decisive step.
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11 Exergy analysis of a small-scale trigenerative compressed air energy storage system
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Trigenerative compressed air energy storage (T-CAES) capitalizes on the heat of the compression process, something that is often wasted in more conventional compressed air energy storage (CAES) approaches. A T-CAES system with a 4 kW compressor and 2 kW turbine is thermodynamically analyzed in this study. Exergy analyses performed on each component in the system identify specific areas for improvement. It is found that, under actual conditions, more than half of the total exergy destruction is caused by the accumulator and about a quarter of the destruction is caused by the pressure regulator and turbine. Further, the pressure regulator, accumulator, and turbine offer 66%, 27%, and 32% of individual component recoverable exergies, respectively. These recoveries can improve the overall exergy efficiency of the system by 35%.
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12 Offshore systems
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Compressed air energy storage (CAES) systems can be designed such that the air is stored underwater and at high pressures in lightweight reinforced balloons called energy bags [1,2]. This chapter shows an offshore device, Buoyancy Engine, that effectively harnesses the resultant buoyant force acting on an inflated energy bag by converting the upward vertical thrust of the bag (when released) to torque with the help of a rack-and-pinion gear system. Similar to lifting bags for salvaging objects from the sea, the energy bag works by rising a certain distance through the water column during the generation stage. The system was designed such that a rack gear is attached to the energy bag at its base. The rack gear is also in mesh with a pinion gear at a given point along its length. An energy bag filled with the stored compressed air is allowed to float during the buoyancy engine operation, pulling along the rack gear, thereby causing torque to be generated in the pinion gear because the rack and pinion gears are in mesh. Furthermore, the pinion gear's torque is transferred through a shaft to an electric generator designed to be a quick-start, variable speed and protected in a waterproof housing anchored at the bottom of the sea. The design achieves a positive network output by considering the ascent speed and the resultant forces acting on the submerged energy bag linked to a rack gear in mesh with a pinion gear. This design's calculations showed that the pinion gear produced high torque at a low angular speed for sufficient electrical power to be produced in the generator. By appropriately tuning the short-term electrical power towards higher voltages, the electricity can be used in a purpose-built electric arc furnace [3] to instantly heat a eutectic mixture of molten salts to high temperatures of over 550°C [3,4]. For an adiabatic CAES system, some of the heat energy stored in the molten salt can be utilised along with the harnessed heat of compression in multiple generation stages to heat up the stored air for higher work output. Furthermore, similar to a concentrated solar thermal plant, the molten salt can be used as a heat transfer fluid to slowly generate electricity in a coupled heat engine such as a steam turbine [4].
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Back Matter
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