Friday, April 26

Compressed Air Energy Storage: Compressed Air & Renewable Energy

We commonly talk about the amount of electricity, or energy, it takes to operate compressed air systems. It is true that electricity is the largest cost to operating compressed air, but it is also true that compressed air can be used for renewable energy! Let’s take a look at how compressed air can be used for renewable energy in the following blog post:

Where Does Renewable Energy Originate?

The following are three major types of renewable energy sources and technologies as defined by The Department of Energy:

Wind Turbines

Wind energy is a form of renewable energy that utilizes wind and wind turbines to generate electricity. These wind turbines activate when wind passes through them, causing them to rotate like a fan. These rotating propellers activate a generator to spin, thus supplying electricity.

Solar Panels

Solar power is a form of renewable energy that utilizes sunlight and solar panels to generate electricity. Solar panels and similar technologies absorb sunlight being shone down on Earth. This sunlight creates electromagnetic radiation. Photovoltaic panels or mirrors collect, concentrate, and convert this solar radiation, converting it into electricity.

Hydropower (water)

Hydropower is a form of renewable energy that utilizes water and dams to generate electricity. These dams or other diversion structures collect and alter the flow of natural bodies of water. The kinetic energy from flowing water fuels turbines and generators to convert this kinetic energy into electricity.

Compressed Air Energy Storage

Air compressors can be used to create pressurized air that is then stored and used later in its pressurized state. This is called compressed air energy storage (CAES). This stored pressurized air is considered stored energy, as it is taken out of storage and immediately used in various functions. There are currently very few CAES systems worldwide, but the fact that the technology has been discovered and exists means there are lots of possibilities for compressed air and the future of powering our world.

The Process:

Renewable energy is generated (generally originating from wind turbines) and powers a motor to drive the air compressor.
The air compressor does its usual job: it pulls the energy and air in to compress it. This creates pressurized air. During the compression process, heat is also generated and released from the compressor. This leaves cooler pressurized air that leaves the compressor.
The released heat may be stored in a thermal energy storage system for other usage or rejected.
The cooled, pressurized air is then sent underground to storage tanks where it is stored in its pressurized state.
When this pressurized air, or energy, is needed, it gets released through a heating system to expand the cold compressed air for use.
The expanded air begins to spin expansion turbines. A generator is then engaged to convert the spinning motion of the turbines into electricity to travel to electrical grids for use.

Management of Thermal Energy

The excess heat that is created during the compression process is then decompressed to remove the heat. There are 3 types of storage systems and processes for this compression and decompression process dealing with the excess heat (step 3 in the previous process flow):

Adiabatic: Adiabatic energy storage systems store the heat that was produced during the compression process and release it out into the environmental air as it decompresses it. The excess heat can either be stored in solids or liquids.
Diabatic: Diabatic energy storage uses intercoolers to dissipate the heat into air waste, rather than storing it. As this heat becomes waste, the compressed air that needs to be decompressed to be released from storage requires additional heat to assist in the process. This is when natural gas is many times added to re-heat the compressed air. These systems tend to be less efficient.
Isothermal: Isothermal storage systems are currently only used in smaller scale systems that already obtain highly efficient equipment. They achieve a near-perfect heat exchange with the environment but cannot be used on large-scale systems due to the unavoidable amount of heat loss that occurs.

Compressed Air Storage Methods

The compressed air we are discussing is stored underground in a variety of storage system types. It can often be stored in already existing natural reservoirs. The following are the two main types of underground CAES systems:

Constant Volume Storage: Constant volume storage systems are systems consisting of physical boundaries, like walls, that can store the pressurized air. These systems have a constant, or set, volume of storage space, but the air pressure within the space is variable. Examples include caves, mines, natural reservoirs, or man-made systems, like pipelines.
Constant Pressure Storage: Constant pressure storage systems are the opposite of constant volume storage systems. These systems maintain a constant, or set, air pressure, while the volume of the storage is variable. These systems are many times constructed from large bags that are stored underground, many times deep in the ocean to utilize hydrostatic pressure that the ocean generates. These systems tend to cost more.

Environmental Sustainability Implications of Compressed Air Energy Storage

Of course, the use of compressed air energy storage systems has great environmental sustainability benefits, including the following:

Conservation and reusability of natural resources.
Contributes to a carbon-free energy environment.
Safe, long-duration energy storage.
Absorbs excess energy during low demand, rather than wasting it.
Ability to restore operations without external power in the case of power failure.

Other benefits:

Economical systems for long-duration energy storage.
Long system lifetime.
Constant technological advances are being discovered.
Increases off-peak output.
Faster startup times without increasing power requirements.

The Cost of Compressed Air Energy Storage

For larger-scale energy usage, like providing electricity to energy grids, CAES is more affordable than alternative storage systems like thermal energy, lithium battery storage, pumped hydropower, etc. Because these systems utilize existing natural resources and structures, the installation cost is generally lower as well. According to an article by Green Tech Media, CAES creates a capital cost of about $1,500 per Kw which is relatively affordable compared to the cost per Kw of other energy storage systems.

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Our compressed air experts look forward to meeting you to discuss your equipment and support needs. Please contact us directly at (262) 695-7000 with any questions or to schedule service for your system moving forward.

Sources

Compressed Air Energy Storage. (n.d.). https://www.energy.gov/sites/default/files/2023-07/Technology Strategy Assessment - Compressed Air Energy Storage_0.pdf

Oberkirch, A. (2023, August 31). How compressed air is used for renewable energy. Quincy Compressor. https://www.quincycompressor.com/compressed-air-energy-storage-renewable/#:~:text=With%20compressed%20air%20energy%2C%20the%20electricity%20produced%20by,so%20it%20can%20be%20used%20as%20electricity%20again.

Pester, P. (2022, March 15). How to store Renewable Energy. LiveScience. https://www.livescience.com/renewable-energy-storage

Schirber, M. (2008, June 4). How compressed air could power the future. LiveScience. https://www.livescience.com/4955-compressed-air-power-future.html

Seamus, G. Professor of Dynamics. (2022, September 13). Let’s store solar and wind energy – by using compressed air. The Conversation. https://theconversation.com/lets-store-solar-and-wind-energy-by-using-compressed-air-103183

Weisbrod, K. (2021a, December 1). Inside clean energy: Here’s how compressed air can provide long-duration energy storage. Inside Climate News. https://insideclimatenews.org/news/02122021/inside-clean-energy-compressed-air-energy-storage/

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