Compressed Air Energy Research Articles

Simulation-Based Hybrid Energy Storage Composite-Target Planning with Power Quality Improvements for Integrated Energy Systems in Large-Building Microgrids

In this paper, we present an optimization planning method for enhancing power quality in integrated energy systems in large-building microgrids by adjusting the sizing and deployment of hybrid energy storage systems. These integrated energy systems incorporate wind and solar power, natural gas supply, and interactions with electric vehicles and the main power grid. In the optimization planning method developed, the objectives of cost-effective and low-carbon operation, the lifecycle cost of hybrid energy storage, power quality improvements, and renewable energy utilization are targeted and coordinated by using utility fusion theory. Our planning method addresses multiple energy forms—cooling, heating, electricity, natural gas, and renewable energies—which are integrated through a combined cooling, heating, and power system and a natural gas turbine. The hybrid energy storage system incorporates batteries and compressed-air energy storage systems to handle fast and slow variations in power demand, respectively. A sensitivity matrix between the output power of the energy sources and the voltage is modeled by using the power flow method in DistFlow, reflecting the improvements in power quality and the respective constraints. The method proposed is validated by simulating various typical scenarios on the modified IEEE 13-node distribution network topology. The novelty of this paper lies in its focus on the application of integrated energy systems within large buildings and its approach to hybrid energy storage system planning in multiple dimensions, including making co-location and capacity sizing decisions. Other innovative aspects include the coordination of hybrid energy storage combinations, simultaneous siting and sizing decisions, lifecycle cost calculations, and optimization for power quality enhancement. As part of these design considerations, microgrid-related technologies are integrated with cutting-edge nearly zero-energy building designs, representing a pioneering attempt within this field. Our results indicate that this multi-objective, multi-dimensional, utility fusion-based optimization method for hybrid energy storage significantly enhances the economic efficiency and quality of the operation of integrated energy systems in large-building microgrids in building-level energy distribution planning.

Design and evaluation of integrated energy system combining solar energy and compressed-air energy storage

A new integrated energy system (IES) has been proposed by combining the cooling, heating, and power generation (CCHP) system coupled with PV/T and compressed air energy storage (CAES). Based on the developed control operation strategy, rigorous system modeling and dynamic simulation are carried out by TRNSYS to determine the integrated operation effect of each subsystem. Energy utilization efficiency and annual value of costs were adopted to assess the benefits of the system. A building in Gansu Longnan area is selected as a study case. The study results show that the proposed system can meet the building load demand well. The PV efficiency and thermal efficiency are 0.17 and 0.19, respectively. The gas ratio of CAES storage tank is 0.94, which is safe and stable. In addition, the energy utilization is maximum when the internal combustion engine proportioning capacity is 30 % of the maximum heat load, which is 89.13 %. The annual value of the cost is 2.49 × 107 RMB during 40 years of operation.

Impact of demand growth on the capacity of long-duration energy storage under deep decarbonization

Abstract The weather-dependent uncertainty of wind and solar power generation presents a challenge to the balancing of power generation and demand in highly renewable electricity systems. Battery energy storage can provide flexibility to firm up the variability of renewables and to respond to the increased load demand under decarbonization scenarios. This paper explores how the battery energy storage capacity requirement for compressed-air energy storage (CAES) will grow as the load demand increases. Here we used an idealized lowest-cost optimization model to study the response of highly renewable electricity systems to the increasing load demand of California under deep decarbonization. Results show that providing bulk CAES to the zero-emission power system offers substantial benefits, but it cannot fully compensate for the 100% variability of highly renewable power systems. The capacity requirement of CAES increases by ≤33.3% with a 1.5 times increase in the load demand and by ≤50% with a two-times increase in the load demand. In this analysis, a zero-emission electricity system operating at current costs becomes more cost-effective when there is firm power generation. The least competitive nuclear option plays this role and reduces system costs by 16.4%, curtails the annual main node by 36.8%, and decreases the CAES capacity requirements by ≤80.7% in the case of a double-load demand. While CAES has potential in addressing renewable variability, its widespread deployment is constrained by geographical, societal, and economic factors. Therefore, if California is aiming for an energy system that is reliant on wind and solar power, then an additional dispatchable power source other than CAES or similar load flexibility is necessary. To fully harness the benefits of bulk CAES, the development and implementation of cost-effective approaches are crucial in significantly reducing system costs.

Comparative techno-economic evaluation of energy storage technology: A multi-time scales scenario-based study in China

Energy storage technology is a crucial means of addressing the increasing demand for flexibility and renewable energy consumption capacity in power systems. This article evaluates the economic performance of China's energy storage technology in the present and near future by analyzing technical and economic data using the levelized cost method. Through a comparative analysis of different energy storage technologies in various time scale scenarios, we identify diverse economically viable options. Sensitivity analysis reveals the possible impact on economic performance under conditions of near-future technological progress. The application analysis reveals that battery energy storage is the most cost-effective choice for durations of <2 h, while thermal energy storage is competitive for durations of 2.3–8 h. Pumped hydro storage and compressed-air energy storage emerges as the superior options for durations exceeding 8 h. This article provides insights into suitable energy storage technologies for China's energy structure development in the present and near future.

Experimental study on permeability evolution of sandstone under cyclic loading

The permeability of a rock mass affects the site selection and construction of underground high-pressure gas storage for compressed-air energy storage. This study investigates the permeability evolution of sandstone under high-pressure gas during the cycle of confining and axial pressures. Nitrogen permeation tests were conducted at different inlet pressures using the steady-state method. The initial steady-state flow, seepage in the circulation, and steady-state flow after circulation were measured continuously in three stages. The effects of the loading and unloading rates and load-holding time on the seepage flow were analyzed. The results indicate that the flow rate and displacement changed with periodic changes in the axial and confining pressures during the cycle. The higher the inlet pressure, the greater was the difference between the peak and trough of the flow in the cycle, and the greater was the difference between the flow after the cycle and the initial flow. When the inlet pressure was 10 MPa, the steady-state flow rate increased from 284 ml/min to 336 ml/min (18%). When the inlet pressure was 2 MPa, the evolution range of the seepage flow in the sample was similar for different load-holding times. The loading and unloading rates had a significant influence on the flow waveform in the circulation process but little influence on the wave height. With an increase in the number of cycles, the porosity of the samples first decreased rapidly and then increased slowly. This study provides a reference for construction and operation of compressed-air energy-storage systems.

Measurements and Modelling of the Discharge Cycle of a Grid-Connected Hydro-Pneumatic Energy Storage System

Hydro-pneumatic energy storage is a form of compressed-air energy storage that can provide the long-duration storage required for integrating intermittent renewable energies into electrical power grids. This paper presents results based on numerical modelling and laboratory tests for a kilowatt-scale HPES system tested at the University of Malta. This paper presents measurements of the discharge cycle, in which energy stored in compressed air within a pressure vessel is hydro-pneumatically converted back into electricity via a Pelton turbine and fed into the national electricity grid. The tests were conducted using a hydraulic turbine operated under different fixed-turbine rotational speed settings, with the pressure being allowed to decrease gradually during the HPES system’s discharge cycle. The system’s overall efficiency accounted for flow losses, turbine inefficiencies, and electrical losses. The tests showed that this efficiency was practically independent of the compressed-air pressure of specific water turbine runner speeds, despite the water turbine operating at fixed speeds. A numerical model developed in MATLAB Simulink (R2022a) was also presented for use simulating the hydraulic performance of the system during the discharge cycle. The model used secondary loss coefficients for the hydraulic circuit and derived velocity coefficients from computational fluid dynamics (CFD) for the Pelton turbine nozzle. We achieved very good agreement between the predictions based on numerical modelling and the measurements taken during laboratory testing.

Mitigation of Renewable Energy Source Production Variability in Residential Stock through Small-Scale Gas–Liquid Energy Storage Technology Application

Despite renewable energy source integration being a well-established requirement in international policies, energy systems still face some unresolved issues, including the intermittence of production. To tackle this problem, a viable solution could comprise the off-peak storage of electricity production excess, to be consumed later during peak-load hours. The transition from the diffuse pattern of centralized generation to the distributed model, involving energy communities, suggests an additional aspect to manage: the spatial constraints of systems for domestic applications. Compressed-air energy storage represents a promising Power-to-Power technology for small-scale energy integration. This study proposes the application of a gas–liquid energy storage system (GLES) in a residential building, using renewable energy excess from a photovoltaic (PV) array. The performance of the proposed system, whose operation involves the compression of the gaseous mass through a piston operated by mineral oil, was evaluated through energy analysis performed simulating the devices and their coupling with the load profiles of the building. The thermodynamic model of storage was validated using data from an experimental campaign on a prototype. A sensitivity study, acting on the features of the system, such as the compression rate and vessel size, allowed us to compare the absorbed PV energy excess, the coverage of the building energy demand during the expansion phase, and the electrical efficiency of a daily cycle. The results obtained, together with the related economic analysis, were used to quantify the market potential of the proposed solution, to be exploited as a mechanical alternative to conventional electric batteries in dwellings.

Prospects of Hydrogen Application as a Fuel for Large-Scale Compressed-Air Energy Storages

A promising method of energy storage is the combination of hydrogen and compressed-air energy storage (CAES) systems. CAES systems are divided into diabatic, adiabatic, and isothermal cycles. In the diabatic cycle, thermal energy after air compression is discharged into the environment, and the scheme implies the use of organic fuel. Taking into account the prospects of the decarbonization of the energy industry, it is advisable to replace natural gas in the diabatic CAES scheme with hydrogen obtained by electrolysis using power-to-gas technology. In this article, the SENECA-1A project is considered as a high-power hybrid unit, using hydrogen instead of natural gas. The results show that while keeping the 214 MW turbines powered, the transition to hydrogen reduces carbon dioxide emissions from 8.8 to 0.0 kg/s, while the formation of water vapor will increase from 17.6 to 27.4 kg/s. It is shown that the adiabatic CAES SENECA-1A mode, compared to the diabatic, has 0.0 carbon dioxide and water vapor emission with relatively higher efficiency (71.5 vs. 62.1%). At the same time, the main advantage of the diabatic CAES is the possibility to produce more power in the turbine block (214 vs. 131.6 MW), having fewer capital costs. Thus, choosing the technology is a subject of complex technical, economic, and ecological study.

Application of Auxetic Tubular Structure in Flow Control of the Throttle Valve

Compressed-air energy storage and other energy storage technologies play crucial roles in the use of renewable energy sources. As a key component in energy storage technology, the throttle valve plays an important role in throttling and reducing the pressure. The proposed method incorporates a throttle valve without relative motion based on the auxetic tubular structure. The fundamental principle of the method is to exploit the elastic deformation characteristics of the auxetic tubular structure to achieve flow control. When the structure is subjected to tension or compression, its diameter changes, thereby altering the dimensions of the valve, and regulating the flow rate. To assess the efficacy of the proposed method, a geometrical analysis is conducted. A prototype of the flow control device, incorporating an auxetic tubular structure, is fabricated using 3D printing technology. Experimental tests substantiate the performance of the proposed flow control method, demonstrating excellent linearity and repeatability. The results of this study indicate the potential applications of this method in throttling, further highlighting the importance and feasibility of the utilization of elastic deformation in auxetic structures as a method to achieve predictable motion.

The Implications of Ontario’s Historical Oil and Gas Drilling and Abandonment Practices for Abandoning Orphan and Legacy Wells

Oil and gas exploration in Ontario began in the mid-1800s, leading to the first oil well drilled in 1858 and the first commercial gas well drilled in 1889. These early discoveries kicked off a boom of exploration and development drilling activity, but well records were not mandatory until 1919 after the introduction of the Natural Gas Act R.S.O.1918, c. 12. The Ontario Bureau of Mines estimated 10,000 operating oil wells in the province at the turn of the 20th century, but there are only records for approximately 1,500 wells. By 1970 there were an estimated 50,000 wells drilled in the province though there are only records for 27,000 wells, indicating there may be tens of thousands of unrecorded or lost wells in southwestern Ontario. Wells that are not properly plugged are a conduit for fluid movement, including brine, natural gas, oil, and hydrogen sulphide, to move from the subsurface to the surface. Historical well abandoning regulations required wells to be plugged with inferior materials including wood, clay, and rubble. Cement was not the standard plugging material until 1964. There are orphaned and legacy wells leaking natural gas and sulphur water (groundwater containing dissolved sulphate and hydrogen sulphide) creating a risk to public safety. Orphaned and legacy wells are also a risk for subsurface energy projects including geological storage of carbon dioxide, hydrogen, and compressed air energy, because the wells may provide a pathway for injected fluids to return to the surface. This study reviews well construction, legislation, and abandonment practices in Ontario beginning in 1858 and identifies five factors impacting the plugging and abandonment of orphaned and legacy wells.Further work is required to locate unreported or lost wells and to develop new techniques to permanently plug wells to limit gas leakage, reduce greenhouse gas emissions, and improve public and environmental safety.

A Review of Potential Electrochemical Applications in Buildings for Energy Capture and Storage.

The integration of distributed renewable energy technologies (such as building-integrated photovoltaics (BIPV)) into buildings, especially in space-constrained urban areas, offers sustainable energy and helps offset fossil-fuel-related carbon emissions. However, the intermittent nature of these distributed renewable energy sources can negatively impact the larger power grids. Efficient onsite energy storage solutions capable of providing energy continuously can address this challenge. Traditional large-scale energy storage methods like pumped hydro and compressed air energy have limitations due to geography and the need for significant space to be economically viable. In contrast, electrochemical storage methods like batteries offer more space-efficient options, making them well suited for urban contexts. This literature review aims to explore potential substitutes for batteries in the context of solar energy. This review article presents insights and case studies on the integration of electrochemical energy harvesting and storage into buildings. The seamless integration can provide a space-efficient source of renewable energy for new buildings or existing structures that often have limited physical space for retrofitting. This work offers a comprehensive examination of existing research by reviewing the strengths and drawbacks of various technologies for electrochemical energy harvesting and storage, identifying those with the potential to integrate into building skins, and highlighting areas for future research and development.

Numerical and experimental investigation of static shaft Wankel expander for compressed-air energy storage

Compressed air energy storage (CAES) is a promising technology for storing mechanical and electrical energy using the gas power cycle. The expansion device is a critical component of the CAES that determines the overall performance of the system. Standard Wankel expander (SWE) is one of the volumetric expanders which has several advantages including low vibration, ability to produce high power output, low manufacturing cost and less moving parts. However, SWE requires valves for timing the inlet and outlet flow and a balancing system to ensure reliable operation. Static shaft Wankel expander (SSWE) is an attractive solution to enable valves’ removal and the need for balancing system. This paper presents a detailed experimental and numerical investigation of an SSWE performance at various operating pressures and temperatures for CAES application. An advanced computational fluid dynamic simulation model taking into account the dynamic motion of the SSWE and utilising real gas air properties. A compressed air test rig was constructed and instrumented with temperature, flow rate, pressure and torque sensors. Experimental testing at temperatures 20 °C to 80 °C and pressures of 1.5 bara to 3 bara was conducted and compared to the CFD simulations results. Correlations were developed for the friction power loss. Experimental results showed that the developed SSWE can produce power output of 504 W at 80 °C and 3 bara and its isentropic efficiency reached 71 % at 60 °C and 2 bara.

A Cogeneration-Coupled energy storage system utilizing hydrogen and methane-fueled CAES and ORC with ambient temperature consideration enhanced by artificial neural Network, and Multi-Objective optimization

The increasing demand for energy in both commercial and residential sectors poses a pressing challenge, driving the ongoing quest for sustainable and virtually limitless energy resources. As nations become increasingly reliant on energy, the need to enhance energy system efficiency while curbing costs and reducing greenhouse gas emissions, particularly CO2 from fossil fuel combustion, becomes imperative. This paper presents a thermodynamics modeling, economic assessment, and optimization of a multigenerational module that utilizes compressed-air energy storing and polymer electrolyte membrane electrolysis with methane and hydrogen fuels, with a case study focused on Munich, Germany. Using EES, a system comprising of a modified organic Rankine cycle, gas turbine, PEM electrolyzer, and CAES unit was modeled. The combustion chamber was used to exploit methane and a combination of methane and hydrogen. The performance of the suggested module under these two scenarios was evaluated using multi-objective optimization to select the optimal scenario based on TOPSIS. In this study, we conducted 700 runs and obtained data on seven inputs. To derive a mathematical function from this data, we employed an Artificial Neural Network (ANN). This function was subsequently integrated into a multi-objective optimization system, allowing us to optimize the desired objectives. It was determined that Scenario 1 was the best choice for lowering the cost rate, reducing CO2 emissions, and optimizing energy round-trip effectiveness (ERTE). The highest exergy destruction rates were observed in the gas turbine, combustion chamber, and recuperator of the suggested system. The cost rates for ORC, CAES, and PEM electrolyzer were the highest according to the economic evaluation of the proposed module. Moreover, the gas turbine had the highest price. The study assessed the power demand of a building and evaluated the efficiency of the proposed power supply system. Additionally, an investigation was conducted in Munich, Germany, to examine how the system's performance is influenced by daily changes the annual variation in the environment temperature. The results revealed that the exergy destruction rates for the charging and discharging units were identified as 1706.38 kWh and 3019.31 kWh, respectively. additionally, based on the economic analysis, the total cost rate for the proposed energy production system was projected to be 68.073 USD per hour. The subsystems were ranked in the following order of costs: CAES > ORC > PEM electrolyzer. Additionally, within the specified system equipment, the gas turbine equipment exhibited the highest cost rate.

Compressed Air Energy Storage as a Battery Energy Storage System for Various Application Domains: A Review

The recent increase in the use of carbonless energy systems have resulted in the need for reliable energy storage due to the intermittent nature of renewables. Among the existing energy storage technologies, compressed-air energy storage (CAES) has significant potential to meet techno-economic requirements in different storage domains due to its long lifespan, reasonable cost, and near-zero self-decay. When viewed as a battery system, the key performance metrics of CAES, like energy density (ED), round trip efficiency (RTE), and the depth of discharge (DoD), have poor values when compared with other battery technologies in similar domains. This prevents CAES from transitioning to a state-of-the-art form of energy storage. This paper reviews the transition of CAES concepts from carbonized to carbonless types of CAES, along with different single-objective optimization strategies and their effects on the overall system’s performance. It was discovered that competing performance metrics attributes cause single-objective optimization to have trade-offs that worsen at least one other preferred metric. The topology limitations of the generic CAES design were noted to prevent its use in different domains. To ensure that the optimal convergence of subsystem parameters is retained during charging and discharging periods, a suitable topology and subunit combinations for different domains are necessary. Possible options for solving these problems are identified so that the effects of the trade-offs imposed by optimization are either suppressed or eliminated.

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.

Гравитационная транспортная система: принципы построения и управления

The paper considers the principle of constructing a gravitational transport system designed for container transportation of the technological materials. It proposes a scheme of the transport system providing the container shuttle motion between the stations. A scheme is developed, and description of the stations operation principle is presented being a part of the transport system; the compressed air energy is used there to provide transport container with the potential energy ensuring its motion along the transport route under the gravity influence. The proposed station scheme makes it possible to consider the station as a functionally complete module forming the basis for possible development of the extended transport systems with various configurations. An algorithm for the station functioning was developed that implemented the processes of sending and receiving a container. A microprocessor system for managing the station mechanisms is proposed, which controls the sensor signals state and generates control signals for the compressed air distributors. A computer model of the control system was designed and developed to debug algorithms for controlling the transport system stations. The considered schemes and algorithm are intended to develop the technological transport lines.

Experimental Study: The Effect of Pore Shape, Geometrical Heterogeneity, and Flow Rate on the Repetitive Two-Phase Fluid Transport in Microfluidic Porous Media.

Geologic subsurface energy storage, such as porous-media compressed-air energy storage (PM-CAES) and underground hydrogen storage (UHS), involves the multi-phase fluid transport in structurally disordered or heterogeneous porous media (e.g., soils and rocks). Furthermore, such multi-phase fluid transport is likely to repeatedly occur due to successive fluid injections and extractions, thus, resulting in cyclic drainage-imbibition processes. To complement our preceding study, we conducted a follow-up study with microfluidic pore-network devices with a square solid shape (Type II) to further advance our understanding on the effect of the pore shape (aspect ratio, Type I: 5-6 > Type II: ~1), pore-space heterogeneity (coefficient of variation, COV = 0, 0.25, and 0.5), and flow rates (Q = 0.01 and 0.1 mL/min) on the repetitive two-phase fluid flow in general porous media. The influence of pore shape and pore-space heterogeneity were observed to be more prominent when the flow rate was low (e.g., Q = 0.01 mL/min in this study) on the examined outcomes, including the drainage and imbibition patterns, the similarity of those patterns between repeated steps, the sweep efficiency and residual saturation of the nonwetting fluid, and fluid pressure. On the other hand, a higher flow rate (e.g., Q = 0.1 mL/min in this study) appeared to outweigh those factors for the Type II structure, owing to the low aspect ratio (~1). It was also suggested that the flow morphology, sweep efficiency, residual saturation, and required pressure gradient may not severely fluctuate during the repeated drainage--imbibition processes; instead, becoming stabilized after 4-5 cycles, regardless of the aspect ratio, COV, and Q. Implications of the study results for PM-CAES and UHS are discussed as a complementary analysis at the end of this manuscript.

Techno-Economic Analysis and Optimization of a Compressed-Air Energy Storage System Integrated with a Natural Gas Combined-Cycle Plant

To address the rising electricity demand and greenhouse gas concentration in the environment, considerable effort is being carried out across the globe on installing and operating renewable energy sources. However, the renewable energy production is affected by diurnal and seasonal variability. To ensure that the electric grid remains reliable and resilient even for the high penetration of renewables into the grid, various types of energy storage systems are being investigated. In this paper, a compressed-air energy storage (CAES) system integrated with a natural gas combined-cycle (NGCC) power plant is investigated where air is extracted from the gas turbine compressor or injected back into the gas turbine combustor when it is optimal to do so. First-principles dynamic models of the NGCC plant and CAES are developed along with the development of an economic model. The dynamic optimization of the integrated system is undertaken in the Python/Pyomo platform for maximizing the net present value (NPV). NPV optimization is undertaken for 14 regions/cases considering year-long locational marginal price (LMP) data with a 1 h interval. Design variables such as the storage capacity and storage pressure, as well as the operating variables such as the power plant load, air injection rate, and air extraction rate, are optimized. Results show that the integrated CAES system has a higher NPV than the NGCC-only system for all 14 regions, thus indicating the potential deployment of the integrated system under the assumption of the availability of caverns in close proximity to the NGCC plant. The levelized cost of storage is found to be in the range of 136–145 $/MWh. Roundtrip efficiency is found to be between 74.6–82.5%. A sensitivity study with respect to LMP shows that the LMP profile has a significant impact on the extent of air injection/extraction while capital expenditure reduction has a negligible effect.

Investigation of synergistic integration and optimization in combining compressed-air energy storage and a gas turbine

It is very important to guarantee performance synergy when combining two sub-systems. This study investigated combinations of compressed air energy storage systems (CAESs) and a gas turbine (GT) while considering various design factors. These factors included the CAES type, CAES capacity, and air injection flow rate, which were not considered in previous studies. The feasibility of various integration scenarios was evaluated, and the best scenario with the highest synergistic effect was obtained through an optimization method. When using a conventional CAES (C-CAES), the combined system was undesirable. When using an adiabatic CAES (A-CAES) or regenerative A-CAES, the combined system outperformed the standalone operation. When the flow ratio of the GT and A-CAES was 1:1.33, the percentage increases in net power and generated energy were 31.5 % and 12.6 %, respectively, and the roundtrip efficiency increased by 3.4 %p. When the flow ratio of GT and regenerative A-CAES was 1:0.88, the percentage increases in net power and generated energy were 31.3 % and 20.6 %, respectively, and the roundtrip efficiency was improved by 2.2 %p. This study provides the best synergistic integration between a CAES and GT for the first time by fully considering various scenarios, including thermal and mass integrations.

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.