Compressed Air Energy Storage Plant Research Articles

A thermo-hydro-mechanical damage model for lined rock cavern for compressed air energy storage

Large-scale compressed air energy storage (CAES) technology is regarded as an effective way to alleviate the instability of electricity generated from renewable sources such as wind and solar power, which involves the expensive construction of underground caverns to store highly pressurized and high-temperature compressed air. This study documents mechanical behavior and gas permeability of granite under temperature-pressure synchronous cyclic loading, and the response of the surrounding rock to Thermo-Hydro-Mechanical-Damage (THMD) evolution. Firstly, physical experiments were conducted to examine mechanical property and gas permeability evolutions of granite due to temperature-pressure synchronous cyclic loading. Based on these experiments, equations describing the damage evolution of granite were deduced. Subsequently, using these equations in combination with a thermo-hydro-mechanical coupled model of porous media with two-phase fluid flow, a sophisticated computational routine for the thermo-hydro-mechanical-damage analysis of underground gas storage caverns was developed. Lastly, numerical simulations were conducted to study heat transfer, two-phase seepage, and mechanical response of a CAES cavern under operating conditions. Under low to medium pressure and high-temperature synchronous cyclic loading, granite exhibited a significant variation in elastic modulus and compressive strength. Also, its permeability showed a substantial increase due to damage evolution. After two months of operation, prominent heat transfer was observed in the surrounding rock, particularly in the region extending to approximately 10 m from the inner surface of the cavern, exceeding the range of gas leakage diffusion within the cavern. The plastic zone of surrounding rock is distributed above the cavern's roof and below its bottom. Moreover, areas with higher damage are concentrated in the surrounding rock near the cavern's side walls. These findings contributed to our understanding of the behavior of granite in the context of CAES technology and provided valuable insights for the design and operation of gas storage caverns. The development of the THMD model offered a valuable tool for investigating stress and deformation characteristics of the lining and surrounding rock in CAES plants.

Efficiency-Driven Iterative Model for Underwater Compressed Air Energy Storage (UW-CAES)

The competitiveness of large-scale offshore wind parks is influenced by the intermittent power generation of wind turbines, which impacts network service costs such as reserve requirements, capacity credit, and system inertia. Buffer power plants smooth the peaks in power generation, distribute electric power when the wind is absent or insufficient, and improve the capacity factor of wind parks and their profitability. By substituting the variable pressure storage with an underwater variable volume air reservoir and reducing the wastage of compression heat using liquid Thermal Energy Storage (TES), which eliminates the combustor, the plant design allows overcoming the most common drawbacks of CAES plants. Underwater Compressed Air Energy Storage (UW-CAES) plants are investigated with a thermodynamic model to drive the power plant design toward efficiency maximization. Functional maps, constrained on the plant pressure ratio and the number of compressor/turbine phases with inter-refrigerated/inter-heating phases, are drawn by solving the model iteratively for the heat exchangers’ effectiveness to meet the target turbine discharge temperature, selected in advance to avoid unfeasible mathematical solutions.

Performance Analysis of a Diabatic Compressed Air Energy Storage System Fueled with Green Hydrogen

The integration of an increasing share of Renewable Energy Sources (RES) requires the availability of suitable energy storage systems to improve the grid flexibility and Compressed Air Energy Storage (CAES) systems could be a promising option. In this study, a CO2-free Diabatic CAES system is proposed and analyzed. The plant configuration is derived from a down-scaled version of the McIntosh Diabatic CAES plant, where the natural gas is replaced with green hydrogen, produced on site by a Proton Exchange Membrane electrolyzer powered by a photovoltaic power plant. In this study, the components of the hydrogen production system are sized to maximize the self-consumption share of PV energy generation and the effect of the design parameters on the H2-CAES plant performance are analyzed on a yearly basis. Moreover, a comparison between the use of natural gas and hydrogen in terms of energy consumption and CO2 emissions is discussed. The results show that the proposed hydrogen fueled CAES can effectively match the generation profile and the yearly production of the natural gas fueled plant by using all the PV energy production, while producing zero CO2 emissions.

Creep properties and constitutive model of salt rocks under a slow cyclic loading path

The construction of compressed-air energy storage (CAES) plants using the huge space created by salt rock mining is a key means of optimizing China's energy structure. The creep properties of salt rock are vital parameters for ensuring the long-term, stable operation of CAES plants. According to the operation mode of CAES plants, creep tests were conducted on salt rock under the influence of slow loading and unloading. The results indicated that the slow loading and unloading history locally changed the creep development process but did not affect the overall creep process. Additionally, the steady state creep rate of the salt rock depended mainly on the magnitude of external stress. Moreover, the creep test was monitored simultaneously using acoustic emission (AE) technology, and the distribution of the AE absolute energy during the initial loading phase and steady state creep phase satisfied the power law. To more accurately describe the creep characteristics of the salt rock under the influence of slow loading and unloading, a full-process creep constitutive model of salt rock was constructed using state variable, fracture expansion factor, and unloading factor.

Comparison of the characteristics of compressed air energy storage in dome-shaped and horizontal aquifers based on the Pittsfield aquifer field test

Most studies have suggested that aquifers with anticlinal structures are the most favorable structures for compressed air energy storage (CAES) in aquifers because of their trapping ability, but this limits the potential locations for CAES plants, as horizontal aquifers are very common only in offshore areas rich in wind power. The comparison of the characteristics of CAES in dome-shaped and horizontal aquifers can help in understanding the quantitative differences between them. In this study, based on Pittsfield aquifer field test strata and parameters, the characteristics of CAES in dome-shaped and horizontal aquifers were investigated using a numerical simulation method by establishing two comparable conceptual models of a dome-shaped aquifer and a horizontal aquifer. Reasonable matches between the monitored data and simulated results were obtained for the initial air bubble development period of the Pittsfield aquifer field test. Comparisons of the initial air bubble, air cycling performance and energy recovery efficiency were carried out with the same calculation settings for the dome-shaped and horizontal aquifers. In the initial air bubble development period, when the same air volume was injected into the dome-shaped and horizontal aquifers, the radius of the air–water interface in the horizontal aquifer was 16.7% larger than that in the dome-shaped aquifer. In the air cycling period, an isothermal cycle type with a constant injection and production air pressure was designed. The energy recovery efficiency of CAES in aquifers is calculated in terms of the concept of exergy. In the case of isothermal compressor work and ignoring the energy loss in the compressor system, the energy recovery efficiency of the horizontal aquifer can reach approximately 80% of that in the dome-shaped aquifer. The effects of wellbore injection/production length and circulation mode on the performance of CAES in both aquifers were investigated. Wellbore injection/production length has obvious impacts on air mass flow rates during initial air bubble development and subsequent cycling, and a longer wellbore injection/production length can provide greater capacity. A comparison between the daily and weekly circulation periods in the dome-shaped and horizontal aquifers showed that the daily circulation has an efficiency advantage at the same energy storage scale, and the energy recovery efficiency of the horizontal aquifer in the weekly circulation can reach approximately 74% of that of the dome-shaped aquifer. In addition, a constant flow rate injection/production gas daily cycle mode was investigated, and the results showed that this mode has higher energy recovery efficiency than the constant pressure cycle mode, and the horizontal aquifer can reach 88.39% of the efficiency of the dome-shaped aquifer. The comparison of the characteristics of CAES in dome-shaped and horizontal aquifers shows that horizontal aquifers may be a potential choice for the storage media of CAES in the case that there are no suitable aquifers with anticlinal structures in offshore areas.

Stability of lower limit of air pressure in abandoned coal mine roadways during long-term CAES

Power supply instability in the grid has been exacerbated by the rapid development of new energy generation methods. Notably, large-scale energy storage is the most practical solution to this problem. Meanwhile, in China, an effective method of reusing the increasing number of abandoned coal mines is urgently required. Accordingly, building compressed air energy storage (CAES) plants along the roadways of abandoned coal mines can serve as a viable energy storage method while repurposing these mines. This study examined the effect of the lower limit of air pressure (LLAP) on the stability of coal mine roadways in CAES applications by considering an ongoing pilot CAES coal mine in Chongqing, China. The findings indicate that the LLAP has a positive correlation with the roadway stability provided the frequency of air injection/extraction and upper limit of air pressure are constant. Over 10 years of CAES operation, a higher LLAP corresponds to less overall deformation of the roadway and top slab subsidence, and smaller plastic zone volume. Furthermore, the first main principle stress also decreases as the LLAP increases. According to the findings of this paper, the LLAP for the actual operation of CAES should be adjusted upwards as appropriate, which help to improve the geological stability of CAES roadways.

Creep–fatigue mechanical characteristics of salt rocks under triaxial loading: An experimental study

Salt rock is a sedimentary rock that is widely distributed in the crust. Since salt rock has a low permeability, rheological behavior, and self-healing characteristics, it has been extensively exploited for subsurface energy storage and waste disposal. The construction of compressed air energy storage (CAES) facilities using salt caverns for solution mining is a practical solution to achieve carbon peaking and carbon neutrality goals worldwide. The stability of the salt cavern surrounding rock is critical to the function of a CAES plant. Considering the triaxial stress condition of the rock surrounding such underground salt caverns, a number of triaxial creep–fatigue mechanics tests were performed on salt rock using an MTS815 mechanical testing device. The creep–fatigue damage to the salt rock was examined under various confining pressures and stress levels. The main research results and conclusions are as follows. First, the triaxial creep–fatigue stress–strain curves show a similar tendency to classical triaxial fatigue results: the strength and ultimate deformation of salt rocks increase as the confining pressure increases. Second, in contrast to typical fatigue test results, the residual strain before the high-stress plateaus is larger than that after the plateaus during a creep–fatigue test. However, as the confining pressure increases, this disparity decreases. Third, fatigue loading increases creep deformation, and this effect weakens when the confining pressure increases. Fourth, the residual strain differential before and after the high-stress plateau increases together with the stress level, and the contribution of creep strain increases correspondingly. Last, as the confining pressure increases, the salt rock behavior transitions from a brittle response to a fully ductile response. A high confining pressure prevents relative sliding between the salt rock particles. Thus, the effect of confining pressure on the creep–fatigue mechanical behavior of the salt rock reaches a threshold.

A unified framework for the thermo-economic optimisation of compressed-air energy storage systems with solid and liquid thermal stores

Compressed-air energy storage is an attractive option for satisfying the increasing storage demands of electricity grids with high shares of renewable generation. It is a proven technology that can store multiple gigawatt hours of electricity for hours, days and even weeks at a competitive cost and efficiency. However, compressed–air energy storage plants need to be designed carefully to deliver these benefits. In this work, a consistent thermo-economic optimisation framework is applied to assess the performance and costs of different compressed–air energy storage configurations across different scales. Special attention is paid to the thermal energy stores, with both solid packed-bed stores and liquid stores examined as viable options for advanced compressed–air energy storage plants and different storage materials proposed for both options. The comprehensive thermo-economic optimisation, considering different system layouts, thermal energy storage technologies and storage materials, and system scales is a key novelty of the presented work. A configuration with two packed–bed thermal energy stores using Basalt as the storage material is found to perform best, achieving an energy capital cost of 140 $/kWh, a power capital cost of 970 $/kW and a roundtrip efficiency of 76% at a nominal discharge power of 50 MW and a charging / discharging duration of 6 h. The best-performing liquid storage material is solar salt, which is associated with an energy capital cost of 170 $/kWh and a power capital cost of 1,230 $/kW. Systems with liquid thermal energy stores however are found generally to perform worse than systems with packed–bed thermal energy stores both in terms of cost and efficiency across all scales.

A Novel Analysis of Energy Density Considerations and Its Impacts on the Cost of Electrical Energy Storage (EES) Plants

Geological restrictions and the low energy density of compressed air energy storage (CAES) plants constitute a technical and economic barrier to the enablement of variable and intermittent sustainable sources of energy production. Liquid air energy storage (LAES) and pumped thermal energy storage (PTES) systems offer a promising pathway for increasing the share of renewable energy in the supply mix. PTES remains under development while LAES suffers from low liquefaction unit efficiency, although it is at a higher technology readiness level (TRL) than PTES. The most significant element of large-scale EES is related to the discharge features of the power plants, especially the energy storage unit. Here, a novel multi-aspect equation, based on established codes and thermodynamic principles, is developed to quantify the required storage capacity to meet demand consistent with the design parameters and operational limitations of the system. An important conclusion of the application of the multi-aspect equation shows that liquid air storage systems instead of compressed air would reduce the space required for storage by 35 times. Finally, a cost equation was introduced as a function of the required storage volume. Calculations have demonstrated that the use of the novel cost equation, in lieu of the old one-aspect cost equation, for an LAES power plant with a production capacity of about 50 MW makes the costs of installing liquid air storage tanks against the total expenditure of the power plant about six times higher than what was reported in earlier research.

Integration of geological compressed air energy storage into future energy supply systems dominated by renewable power sources

Compressed air energy storage in geological porous formations, also known as porous medium compressed air energy storage (PM-CAES), presents one option for balancing the fluctuations in energy supply systems dominated by renewable energy sources. The strong coupling between the subsurface storage facility and the surface power plant via the pressure of the compressed air, which directly determines the amount of energy stored and the power rates achievable, requires the consideration of the fluctuating supply and demand of electric power, the specific technical design of the compressed air energy storage plant and the subsurface storage processes to determine achievable power rates, storage capacities and overall performance. In this paper, we present subsurface storage designs using a set of future energy system scenarios with different fractions of renewable energy supply and technical options for the power plant. Our findings indicate that the PM-CAES systems can supply 115 MW of electric power and between 12.1 GWh and 49.9 GWh of electric energy for up to 429 h, thus offering grid-scale power storage capacity. The storage design is robust against variations in future energy system scenarios and different power plant configurations, with efficiencies between 0.54 and 0.67 and energy densities between 0.12 and 0.28 kWh per kilogram of stored air. The storage design can be improved further by using horizontal instead of vertical wells, which also reduces induced pressure increases in the storage formation. This study for the first time provides a complete framework for assessing achievable storage rates and capacities for PM-CAES based on detailed forecasts of future energy systems, the geological and geotechnical setting as well as engineering aspects of the compressed air energy power plant.

On the possibility of using an industrial steam turbine as an air expander in a Compressed Air Energy Storage plant

Small/medium size CAES systems (1–10 MW) could be efficiently and successfully employed for off-grid and self-consumption applications and for the delivery of ancillary services on the lower grid levels. A critical issue affecting the feasibility of such systems is related to the availability of efficient and affordable air expanders. Taking into consideration that typical CAES applications are characterized by inlet pressure levels in the range of 40–60 bar, an attractive opportunity to reduce development efforts and investment costs is to resort to the consolidated steam turbine engineering practice. In the present paper, the possibility of using existing building blocks developed to assemble industrial steam turbines to arrange air expanders for CAES applications is explored. A general model for off-design calculation capable of simulating, for a given turbine geometry, steam and air operations as well, has been developed and applied to a case study. On the basis of available information about an existing industrial steam turbine, a possible arrangement for an air expander has been set up and investigated. Results have evidenced a performance loss in terms of both power output and efficiency with respect to steam operations. Nevertheless, the air expander behavior in a wide range of operation can be considered satisfactory. Therefore, the use of industrial steam turbines technology might be considered interesting for the applications under consideration.

Process improvements and multi-objective optimization of compressed air energy storage (CAES) system

Intermittency and high cost were the main barriers to the large-scale commercialization of renewable energy decades ago. The cost of renewable energy has decreased dramatically in the last decade. The intermittency of renewable energy, however, remains a serious challenge to be overcome. Compressed Air Energy Storage (CAES) is widely considered to be a promising energy storage technology at utility-scale and receives increasing attention from both academic and industrial communities. In this study, two novel CAES systems are proposed and a thorough investigation and comparison of the thermodynamic performance of both conventional and novel CAES systems have been performed. The turbine inlet temperature and the maximum cavern storage pressure are identified as the bottlenecks of CAES plants. The round-trip efficiency and energy density are chosen as the conflicting objectives. Pareto fronts are obtained based on the simulation-based multi-objective optimization framework developed in this study. The energy density of a diabatic CAES plant is within the range between 4.24 and 11.58 kWh/m3, while that value becomes 1.28–7.96 kWh/m3 for a conventional adiabatic CAES system. The novel two-pressure level adiabatic CAES system can improve the round-trip efficiency by at least 3.5% compared with the conventional adiabatic CAES system. The novel indirect heating diabatic CAES system can improve the round-trip efficiency by at least 2%. The Pareto fronts can be a useful tool for the grassroot design or retrofit of a CAES plant. Solutions to improve the CAES system performance have been proposed based on the optimization results of this study.

Advanced Adiabatic Compressed Air Energy Storage design and modelling accounting for turbomachinery performance

Energy storage plants are going to become a strategic asset in electric grids. This statement is confirmed looking at the increasing shares of renewables composing the energy portfolio of several nations. Therefore the power demand and production mismatches, caused by the intermittent nature of renewables, must be reconciled. Many energy storage solutions are available but Advanced Adiabatic Compressed Air Energy Storage (AA-CAES) plants have potentials similar to pumped hydro systems (PHS). A physical model was developed in Matlab-Simscape to simulate the dynamics of AA-CAES plants, implementing temperature-dependent air properties, efficiency maps for turbomachinery and realistic power ramps. Furthermore, start-up and shut-down phases and energy consumption during idle periods were accounted for. The model embeds a 1D Fortran code to model the detailed behaviour of a packed-bed TES. The grid-to-grid performance of an AA-CAES plant was determined and the assumptions implemented to take into account real turbomachinery behaviour are presented.

A MILP Model for Revenue Optimization of a Compressed Air Energy Storage Plant with Electrolysis

Energy storage, both short- and long-term, will play a vital role in the energy system of the future. One storage technology that provides high power and capacity and that can be operated without carbon emissions is compressed air energy storage (CAES). However, it is widely assumed that CAES plants are not economically feasible. In this context, a mixed-integer linear programming (MILP) model of the Huntorf CAES plant was developed for revenue maximization when participating in the day-ahead market and the minute-reserve market in Germany. The plant model included various plant variations (increased power and storage capacity, recuperation) and a water electrolyzer to produce hydrogen to be used in the combustion chamber of the CAES plant. The MILP model was applied to four use cases that represent a market-orientated operation of the plant. The objective was the maximization of revenue with regard to price spreads and operating costs. To simulate forecast uncertainties of the market prices, a rolling horizon approach was implemented. The resulting revenues ranged between EUR 0.5 Mio and EUR 7 Mio per year and suggested that an economically sound operation of the storage plant is possible.

Adiabatic compressed air energy storage technology

Adiabatic compressed air energy storage technology

Self-Scheduling Models of a CAES Facility Under Uncertainties

This paper presents two mathematical formulations to represent uncertainties in self-scheduling models of a price-taker Compressed Air Energy Storage (CAES) facility. The proposed model is from the point of view of the plant owner participating in the energy, spinning, and idle reserve markets. The first described formulation is based on Robust Optimization (RO) and the second one is based on Affine Arithmetic (AA) techniques, which are both range arithmetic methodologies, and consider the thermodynamic characteristics of the CAES facility for a more realistic representation. The implementation of both methods are tested, validated and compared with each other and with Monte Carlo Simulations (MCS) using prices from the Ontario market. From the simulation results, it can be observed that both methods have some similarities, presenting lower computational burden compared with MCS, and demonstrate the advantage of applying the proposed models for CAES plant owners to hedge against price uncertainties.

Simulation and Modeling of Hybrid Fuel Storage System using Compressed Air Energy Storage

In the present work, Hybrid fuel storage system of compressed air is an extensive technology that provides long duration energy storage. It is encouraged in balancing the large scale penetration of intermittent and dispersed sources of power. Such as wind and solar power into electric grids .The existing Compressed air energy storage (CAES) plants utilize natural gas as fuel. In this project we are replacing the natural gas with the composition of air (15 bar), copper oxide (5-20%), and water (50%). validated with the results obtained using Computational Fluid Dynamics (CFD) analysis. Modeling of energy storage tank is done in Computer Aided Three Dimensional Interactive Application (CATIA) software, mesh has been created using ANSYS workbench software and Analysis is done in Fluent Software. The composition is sent from the inlet of the energy storage tank and temperatures are varied like 298k, 373k, 423k, and 473k. Velocities are also varied like 15m/s, 25m/s, 35m/s, 45m/s. This hybrid fuel storage deals with phase change material by using water and copper by heating at different temperatures to get the energy and re-utilized. This device is applicable for renewable energy application to avoid the heat losses new technique of energy saving in suitable forms. This has the lead to the emergence of fuel storage as a management of energy and allowing it to various levels of energy storage. In many parts of the world this storage of energy plays an important role and a new technique of energy saving in suitable forms. This has the lead to the emergence of fuel storage as a management of energy and allowing it to various levels of energy storage.

Salt Cavern Exergy Storage Capacity Potential of UK Massively Bedded Halites, Using Compressed Air Energy Storage (CAES)

The increasing integration of large-scale electricity generation from renewable energy sources in the grid requires support through cheap, reliable, and accessible bulk energy storage technologies, delivering large amounts of electricity both quickly and over extended periods. Compressed air energy storage (CAES) represents such a storage option, with three commercial facilities using salt caverns for storage operational in Germany, the US, and Canada, with CAES now being actively considered in many countries. Massively bedded halite deposits exist in the UK and already host, or are considered for, solution-mined underground gas storage (UGS) caverns. We have assessed those with proven UGS potential for CAES purposes, using a tool developed during the EPSRC-funded IMAGES project, equations for which were validated using operational data from the Huntorf CAES plant. From a calculated total theoretical ‘static’ (one-fill) storage capacity exceeding that of UK electricity demand of ≈300 TWh in 2018, filtering of results suggests a minimum of several tens of TWh exergy storage in salt caverns, which when co-located with renewable energy sources, or connected to the grid for off-peak electricity, offers significant storage contributions to support the UK electricity grid and decarbonisation efforts.

Investigation of a combined heat and power (CHP) system based on biomass and compressed air energy storage (CAES)

Compressed air energy storage (CAES), owing to low geographical limitation, high reliability, and negligible environmental impact, has attracted attention in recent years, hybridizing with different types of renewable energies. Contrary to the other renewable energies such as solar and wind, biomass does not depend on the region's weather condition and is more reliable than other renewables, making it a promising solution for sustainable development. Therefore, a novel combined heat and power system based on biomass gasification, CAES, and gas turbine power plant is introduced in the present research and analyzed by using ASPEN PLUS. Three different kinds of biomass materials, including wood chips, green waste, and municipal solid waste are considered, and the effects of critical parameters on system performance are precisely investigated. The results showed that the syngas composition has no significant impact on the variation of steam and air temperature. However, the air temperature has a considerable indirect effect on the char split fraction. Comparing the effect of biomass materials on efficiency shows that Green waste is the least efficient material, while the MSW offers the highest total efficiency, and the highest power plant efficiency can be obtained by using the wood chips to produce syngas fuel. Consequently, the gasifier's maximum efficiency is obtained at a temperature of 960℃ and steam to biomass ratio of 1.

Overview of current compressed air energy storage projects and analysis of the potential underground storage capacity in India and the UK

Compressed air energy storage (CAES) is an established and evolving technology for providing large-scale, long-term electricity storage that can aid electrical power systems achieve the goal of decarbonisation. CAES facilities often utilise large underground storage caverns to ensure high capacity systems. This results in the need of locations with suitable geological features to develop a CAES plant. This paper examines recent and ongoing large-scale CAES projects and presents candidate methods of storing high pressure air using underground features. An assessment of the overall potential for CAES in India is presented by examining its geological features and locations with the greatest potential for CAES plants are determined. This is combined with an analysis of the renewable electricity generation potential in India to identify candidate areas for renewable generation and CAES integrated systems. Up to 1.05% of Indian land area is deemed suitable for CAES plant development and if fully utilised would be sufficient to meet the energy storage needs of India, however, practically a very small fraction of the total suitable land that could be developed so other competing energy storage technologies should be considered. Conversely, the UK possesses a very good potential for CAES, enough to greatly exceed necessary energy storage, owing to the abundance of salt beds not present in India. For CAES to garner serious consideration in India, aquifer storage based CAES needs to be demonstrated.