The growth of renewable power generation is experiencing a remarkable surge worldwide. According to the U.S. Energy Information Administration (EIA), it is projected that by 2050, the share of wind and solar in the U.S. power-generation mix will reach 38 percent, which is twice the proportion recorded in 2019. The incorporation of Compressed Air Energy Storage (CAES) into renewable energy systems offers various economic, technical, and environmental advantages.
Image Credit: disak1970/Shutterstock.com
What is Compressed Air Energy Storage?
By 2030, it is anticipated that renewable energy sources will account for 36 percent of global energy production. Energy storage systems will be instrumental in attaining this objective. Mechanical storage systems stand out among the available energy storage methods due to their reduced investment expenses, prolonged lifetimes, and increased power/energy ratings. Notably, commercialized large-scale Compressed Air Energy Storage (CAES) facilities have arisen as a prominent energy storage solution.
Since the late 1970s, (CAES) technology has been commercially available. This energy storage system functions by utilizing electricity to compress air during off-peak hours, which is then stored in underground caverns. When energy demand is elevated during the peak hours, the stored compressed air is released, expanding and passing through a turbine to generate electricity.
How Does Compressed Air Energy Storage Work?
As per an article published in Energies, the CAES system follows the conventional three-phase model of a conventional gas turbine, encompassing charging, storing, and discharging.
In the charging phase, CAES makes use of off-peak and cost-effective electricity to compress ambient air. The compressed air is then stored in a dedicated pressurized reservoir, which can be either an underground cavern or an aboveground tank, typically maintained at a pressure of 40-80 bar.
During the discharge phase, the elastic potential energy stored in the compressed air is harnessed. The compressed air is drawn from the reservoir, heated, and subsequently expanded in a turbine train at high pressure and temperature. This expansion process generates electricity that can be fed back into the grid.
Traditional Compressed Air Energy Storage System Configurations
CAES technology encompasses different types, including adiabatic systems and diabatic systems. The key distinction between these configurations lies in how they handle the heat generated during the compression process.
The diabatic CAES systems are the first-generation technology. In these systems, ambient air is compressed using a compressor train. The compression process generates waste heat, which is then dissipated to the surrounding environment through intercoolers. During the discharge phase, fuel is combusted to heat the air before its expansion in the turbines. This combustion process allows for the generation of electricity during peak demand periods.
The adiabatic configuration of CAES has been under development since the late 1970s, aiming to address the limitations of diabatic CAES. This particular compressed air energy storage system focuses on effectively capturing and storing the waste heat generated during compression. The stored heat is then recycled to elevate the turbine inlet temperature of the compressed air during the discharge phase. As a result, the adiabatic CAES system aims to reduce or even eliminate the reliance on fossil fuels, offering a more sustainable energy storage solution.
Recent Developments in Novel Configurations of CAES
In addition to the adiabatic and diabatic configurations, two other types of CAES systems have been proposed: isothermal CAES (I-CAES) and supercritical CAES.
The primary objective of I-CAES is to maintain stable compression and expansion temperatures of the compressed air during the charging and discharging processes, respectively. This is achieved by implementing a quasi-isothermal process.
On the other hand, supercritical CAES involves compressing the air to a supercritical thermodynamic state, where the waste heat generated during compression is recovered and stored in a thermal energy storage system. The compressed air is then liquefied and stored in a dedicated cryogenic tank. During the discharge phase, the liquid air is re-gasified, heated using the stored thermal energy, and subsequently expanded through a turbine train to generate electricity, which can be supplied back to the grid. This process has an efficiency of around 68%.
Components and Operational Necessities
- The primary components of a conventional CAES plant cycle include a motor/generator with pulleys on both ends (to engage/disengage it to/from the compressor train, expander train, or both).
- Multistage air compressors with intercoolers, which reduce the required power during the compression cycle, and an aftercooler, which reduces the required storage volume play a vital role in energy storage.
- The next component is the control system for an expander train composed of high- and low-pressure turbo-expanders with burners between stages.
- Accessories (fuel storage and management, refrigeration systems, mechanical systems, power systems, and heat exchangers).
- Storage of pressurized air underground or aboveground, including piping and fixings.
Advantages
CAES is utilized to improve high-demand preservation, thus decreasing the electrical grid's burden. This enables energy providers to supply adequate power for the entire service area without producing additional energy during peak demand. CAES, when implemented on a lesser scale, can reduce reliance on the electrical infrastructure, thus decreasing energy costs and maintenance costs.
It can store energy for several hours to days, assuring a consistent power supply during periods of high demand or when intermittent resources are not producing. The use of CAES as a supplementary energy source contributes to the enhancement of power grid stability during periods of excessive electrical demand. In addition, these systems require relatively little upkeep compared to other methods.
Limitations and Challenges
Despite such advantageous features, compressed air energy storage falls short owing to certain challenges and limitations. The scarcity of appropriate geological formations for underground caverns may hinder the extensive application of CAES. A viable geographical location is required for the integration of CAES with the energy production source. Additionally, compressing the air followed by the expansion processes in CAES systems leads to losses of energy due to thermal dispersion, thereby reducing overall efficiency.
Even in the presence of such challenges, all over the world, CAES projects are underway. The Chinese Academy of Sciences' Institute of Engineering Thermo-physics recently activated a 100 MW compressed air energy storage facility in Zhangjiakou, Hebei province. The facility is comprised of a multistage, high-load compressor, an expander, and a supercritical heat storage and heat exchanger with outstanding efficiency.
Market Assessment
CAES appears to be a natural fit with the wind farms presently under construction. This is because CAES can operate on a brief enough time scale to balance out variations in the power grid that are triggered by wind fluctuations. The future market potential for compressed air energy storage (CAES) systems is substantial. Experts have published a report in Allied Market Research stating that the global compressed air energy storage market was worth $4 billion in 2021 and is expected to reach $31.8 billion by 2031, expanding at a compound annual growth rate (CAGR) of 23.6% from 2022 to 2031. This is primarily because renewable energies are anticipated to gain market influence in the foreseeable future.
Cost and Performance Assessment of CAES
It is anticipated that CAES will dominate the energy storage market. According to calculations done by Pacific Northwest National Laboratory, a 1000MW CAES plant incurs the following costs:
| |
High Estimate
|
Point Estimate
|
Low Estimate
|
|
Cavern Storage ($/kWh)
|
$ 16.44
|
$ 6.31
|
$ 2.47
|
|
CAES Capital ($/kW)
|
$1167
|
$1061
|
$955
|
|
Total Installed Cost ($/kWh)
|
$97.97
|
$112.41
|
$133.14
|
|
Fixed O&M ($/kW-year)
|
$8.84
|
$9.83
|
$10.80
|
|
RTE (%)
|
52
|
52
|
52
|
|
Calendar Life Years
|
60
|
60
|
60
|
Table Depicting Costs and Performance Parameters of 1000 MW CAES system Source: Pacific Northwest National Library https://www.pnnl.gov/compressed-air-energy-storage-caes
References and Further Reading
Allied Market Research, 2023. Compressed Air Energy Storage: Global Opportunity Analysis and Industry Forecast, 2021 - 2023. [Online]
Available at: https://www.alliedmarketresearch.com/compressed-air-energy-storage-market-A31889
Compressed Air Systems, 2023. 5 Benefits of Compressed Air Energy Storage. [Online]
Available at: https://www.compressedairsystems.com/
Pacific Northwest National Laboratory, 2023. Compressed Air Energy Storage (CAES) Cost and Performance Database. [Online]
Available at: https://www.pnnl.gov/compressed-air-energy-storage-caes
UN Climate Technology Center and Network, 2023. Compressed Air Energy Storage (CAES). [Online]
Available at: https://www.ctc-n.org/technologies/compressed-air-energy-storage-caes
Borri E. et. al. (2022). Compressed Air Energy Storage—An Overview of Research Trends and Gaps through a Bibliometric Analysis. Energies. 15(20):7692. Available at: https://doi.org/10.3390/en15207692
Rabi AM, Radulovic J, Buick JM. (2023). Comprehensive Review of Compressed Air Energy Storage (CAES) Technologies. Thermo. 3(1):104-126. Available at: https://doi.org/10.3390/thermo3010008
Disclaimer: The views expressed here are those of the author expressed in their private capacity and do not necessarily represent the views of AZoM.com Limited T/A AZoNetwork the owner and operator of this website. This disclaimer forms part of the Terms and conditions of use of this website.