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[en] The low efficiency of existing CAES systems is due to large energy losses during the air compression process. This could be remedied by building an adiabatic CAES system, where the heat of compression is stored and subsequently used during the expansion process in the turbine. An energy and exergy analysis of A-CAES is presented in this article. A dynamic mathematical model of an adiabatic CAES system was constructed using Aspen Hysys software. The volume of the CAES cavern is 310000 m3 and the operation pressure inside the cavern ranges from 43 to 70 bar. Thermal oil was used as the working medium in thermal energy storage system. The temperature in the hot oil tank was 300 °C and in the cold oil tank 80 °C. Simulations of processes of loading and unloading of compressed air storage were performed and then places where exergy destruction occurs were identified. The biggest exergy destruction occurs in the compressors (276.191 MWh/cycle in total) and turbines (190.394 MWh/cycle in total). Major destruction of exergy was also reported at control valve V2 (103.688 MWh/cycle). Round trip efficiency of the system is 50%. - Highlights: • An adiabatic compressed air energy storage system using thermal oil is proposed. • Analysis of energy efficiency of adiabatic CAES was presented. • Exergy destruction and exergy losses have been pointed out.
[en] This paper presents a framework for optimally allocating storage technologies in a power system. This decision support tool helps in quantitatively answering the questions on “where to and how much to install” considering the profits from arbitrage opportunities in a co-optimized electricity market. The developed framework is illustrated on a modified IEEE (Institute of Electrical and Electronics Engineers) 24 bus RTS (Reliability Test System), and the framework finds the optimal allocation solution and the revenues storage earns at each of these locations. Bulk energy storage, CAES (compressed air energy storage) is used as the representative storage technology, and the benefits of optimally allocated storage integration onto the grid are compared with transmission expansion solution. The paper also discusses about system-level indicators to identify candidate locations for economical storage ventures, which are derived based on the optimal storage allocation solution; and applies the market price based storage venture indicators on MISO (Mid-continental Independent System Operator) and PJM (Pennsylvania-New Jersey-Maryland Interconnection) electricity markets. - Highlights: • Storage optimal allocation framework based on high-fidelity storage dispatch model. • Storage with transmission addresses energy and ancillary issues under high renewables. • Bulk storage earns higher revenues from co-optimization (∼10× energy only market). • Grid offers distributed opportunities for investing in a strategic mix of storage. • Storage opportunities depend on cross-arbitrage, as seen from MISO (Mid-continental Independent System Operator) and PJM (Pennsylvania-New Jersey-Maryland Interconnection) markets
[en] Electricity storage (ES) has the potential of offering several energy system benefits but different technologies also offer different services which can be traded on different markets. In this study, a combined assessment methodology is proposed, enabling a benchmark comparison of stationary electricity storage technologies for different time and system scales, considering their technical, economic and environmental performance. The results show that for short time scale (0.01 h), battery stands out with an advantage in terms of levelised costs, while Advanced Adiabatic (AA-) and Isothermal (I-) Compressed Air Energy Storage (CAES) have relatively low life cycle Greenhouse Gas (GHG) emissions. For the medium time scale (4.5 h), I-CAES shows the best performance for small scale systems, while for large scale systems, Pumped Hydro Storage (PHS) and AA-CAES show best performance. In our long time scale (seasonal) scenario, Power-to-gas-to-power (P2G2P) has lower levelised costs due to low or avoided investment for storage of gas, but higher GHG emissions than other technologies. If existing reservoirs can be utilized for PHS, it can be economically competitive to P2G2P for seasonal storage. However, storage capacity required for seasonal storage should also be taken into account, for which P2G2P has more flexibility. - Highlights: • Stationary electricity storage assessment combining techno-economic and life cycle assessment. • Current and future performance variations, type and price of electricity stored were considered. • Performances of storages were investigated under different time- and system-scales. • Storage technologies perform quite differently based on applications and the electricity stored. • Recommendations were made in terms of preference of technologies for different applications.
[en] A simulation model consisting of wind speed, wind turbine and AA-CAES (advanced adiabatic compressed air energy storage) system is developed in this paper, and thermodynamic analysis on energy conversion and transfer in hybrid system is carried out. The impacts of stable wind speed and unstable wind speed on the hybrid system are analyzed and compared from the viewpoint of energy conversion and system efficiency. Besides, energy conversion relationship between wind turbine and AA-CAES system is investigated on the basis of process analysis. The results show that there are several different forms of energy in hybrid system, which have distinct conversion relationship. As to wind turbine, power coefficient determines wind energy utilization efficiency, and in AA-CAES system, it is compressor efficiency that mainly affects energy conversion efficiencies of other components. The strength and fluctuation of wind speed have a direct impact on energy conversion efficiencies of components of hybrid system, and within proper wind speed scope, the maximum of system efficiency could be expected. - Highlights: • A hybrid system consisting of wind, wind turbine and AA-CAES system is established. • Energy conversion in hybrid system with stable and unstable wind speed is analyzed. • Maximum efficiency of hybrid system can be reached within proper wind speed scope. • Thermal energy change in hybrid system is more sensitive to wind speed change. • Compressor efficiency can affect other efficiencies in AA-CAES system
[en] This paper presents the findings from a multi-objective genetic algorithm optimization study on the design parameters of an underwater compressed air energy storage system (UWCAES). A 4 MWh UWCAES system was numerically simulated and its energy, exergy, and exergoeconomics were analysed. Optimal system configurations were determined that maximized the UWCAES system round-trip efficiency and operating profit, and minimized the cost rate of exergy destruction and capital expenditures. The optimal solutions obtained from the multi-objective optimization model formed a Pareto-optimal front, and a single preferred solution was selected using the pseudo-weight vector multi-criteria decision making approach. A sensitivity analysis was performed on interest rates to gauge its impact on preferred system designs. Results showed similar preferred system designs for all interest rates in the studied range. The round-trip efficiency and operating profit of the preferred system designs were approximately 68.5% and $53.5/cycle, respectively. The cost rate of the system increased with interest rates. - Highlights: • UWCAES system configurations were developed using multi-objective optimization. • System was optimized for energy efficiency, exergy, and exergoeconomics • Pareto-optimal solution surfaces were developed at different interest rates. • Similar preferred system configurations were found at all interest rates studied
[en] PV (Photovoltaic) plants are widely used to produce power in either large or small scales all around the world. In addition, CAES (compressed air energy storage) system has attracted considerable attention as one of the most efficient candidates for large scales energy storage applications in the recent years. In this work, detailed energy and exergy analysis of a 100 MWp (megawatt peak) grid connected PV plant equipped with a CAES system is carried out. The PV plant is assumed to be located in Brazil. The formulations related to the first and the second laws of thermodynamic for all components as well as detailed solar engineering formulations for both the PV farm and the solar heating unit are presented. The performance of the power plant is comprehensively investigated for one entire year in real circumstances. The results revealed that the energy and exergy efficiencies of the CAES system are very close and vary from 35% up to 65% during the year. Also, the annual average exergy and energy efficiencies of the power plant are calculated to be 17.9% and 16.2%, respectively. - Highlights: • This article presents a thorough thermodynamic analysis on a PV farm equipped with a CAES unit. • Energy performance of all components in the system are investigated. • Exergy analysis formulation for of all components in the system is given. • Energy and exergy destruction origins are found and reported. • Detailed energy and exergy efficiency report for the power plant and its subsystems is presented
[en] Renewable energy generation is expected to continue to increase globally due to renewable energy targets and obligations to reduce greenhouse gas emissions. Some renewable energy sources are variable power sources, for example wind, wave and solar. Energy storage technologies can manage the issues associated with variable renewable generation and align non-dispatchable renewable energy generation with load demands. Energy storage technologies can play different roles in each of the step of the electric power supply chain. Moreover, large scale energy storage systems can act as renewable energy integrators by smoothing the variability. Compressed air energy storage is one such technology. This paper examines the impacts of a compressed air energy storage facility in a pool based wholesale electricity market in a power system with a large renewable energy portfolio
[en] Decreasing fuel consumption in compressed air energy storage (CAES) system is a general trend for conserving energy and protecting the environment. Waste heat recovery is an interesting technology to compact energy storage system. However, CAES system has a low thermal efficiency when using low grade waste heat as heat source directly. In this paper, an integrated energy system consisting of a CAES system and a precooling system (PC-CAES) is proposed to decrease the energy consumption of compression train in the charging process, and enhance the round trip efficiency (RTE) of the system. Air conditioner is utilized as pre-cooler to precool the inlet air of compressor and five refrigerants are investigated. The thermodynamic analysis is performed by using steady-state mathematical model and thermodynamic laws. The calculation results show that the RTE of the proposed PC-CAES system is improved by more than 3% than that of the conventional CAES system and more economical than CAES with additional compression stages. Meanwhile, a parametric analysis is also carried out to evaluate the effects of several key parameters on the system performance of two CAES systems. - Highlights: • A novel CAES system combined with pre-cooler is introduced. • Proposed PC-CAES is more compact than A-CAES by using free waste heat. • Air conditioner is utilized as pre-cooler to precool the inlet air of compressor. • Efficiency improvement is achieved via cool down the compressor inlet air temperature.
[en] Many countries worldwide have committed themselves to reducing the rate in which they emit greenhouse gasses. These emissions are the major driver behind human induced global warming. Renewable electricity implementation is one way of reducing the amount of greenhouse gas emissions. However, this transition is also accompanied by some problems. The intermittency of renewables demands for a more flexible electricity system. In existing electricity systems this lack of flexibility already leads to load balancing issues increasing costs and threatening energy security. Large scale storage facilities could provide the needed flexibility. This paper focuses on the economic and environmental system consequences of the application of power-to-gas, pumped hydro storage and compressed air energy storage in an electricity system at different wind power penetration levels. The study shows that the application of large scale energy storage techniques results in economic costs reducing effects on the electricity system. These are highest for pumped hydro storage, followed by the cost reducing effects of compressed air energy storage and power-to-gas. The impact on the fuel use and the emissions is less obvious. In some scenarios, the application of storage even resulted in an increase of the fuel use and the emissions. - Highlights: • We studied the effects of adding three storage techniques to an electricity system. • We modelled: Power-to-gas, pumped hydro storage and compressed air energy storage. • Storage is used for optimizing the operational costs of the electricity system. • The economic system benefits were highest when applying pumped hydro storage. • The application of storage not always resulted in environmental system benefits
[en] Electricity generated from renewable wind sources is highly erratic due to the intermittent nature of wind. This uncertainty of wind power can lead to challenges regarding power system operation and dispatch. Energy storage system in conjunction with wind energy system can offset these effects, making the wind power controllable. Moreover, the power spectrum of wind power exhibits that the fluctuations of wind power include various components with different frequencies and amplitudes. Thus, the hybrid energy storage system is more suitable for smoothing out the wind power fluctuations effectively rather than the independent energy storage system. A hybrid energy storage system consisting of adiabatic compressed air energy storage (A-CAES) system and flywheel energy storage system (FESS) is proposed for wind energy application. The design of the proposed system is laid out firstly. The A-CAES system operates in variable cavern pressure, constant turbine inlet pressure mode, whereas the FESS is controlled by constant power strategy. Then, the off-design analysis of the proposed system is carried out. Meanwhile, a parametric analysis is also performed to investigate the effects of several parameters on the system performance, including the ambient conditions, inlet temperature of compressor, storage cavern temperature, maximum and minimum pressures of storage cavern. - Highlights: • A wind-hybrid energy storage system composed of A-CAES and FESS is proposed. • The design of the proposed hybrid energy storage system is laid out. • The off-design analysis of the proposed system is carried out. • A parametric analysis is conducted to examine the system performance