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Compressed Air Energy Storage

Lee Layton, P.E.


Course Outline

This course begins with an overview of the concept of using compressed air to store electrical energy and the plants currently in operation are reviewed.  Next, the various methods to store compressed air are discussed.  This is followed by a detailed look at how a compressed air storage plant operates and the different types of designs that are available.  Finally, the advantages and disadvantages of compressed air energy storage is discussed.

This course includes a multiple-choice quiz at the end, which is designed to enhance the understanding of the course materials.

Learning Objective

After taking this course you should,

Intended Audience

This course is intended for electrical engineers and others who want to understand how compressed air energy storage power plants work.

Benefit to Attendees

There are very few practical methods to store large volumes of electrical power and compressed air energy storage is one of the more economical options.  In this course, you will learn how compressed air can be used to “store” electrical energy and how the various types of compressed air energy storage plants operate.

Course Introduction

Large quantities of electrical energy cannot be stored.  Since the advent of the electric power industry, engineers have looked for ways to store energy for consumption at a later time.  At the present, we really have only practical two choices to store energy; Pumped Storage Hydro-electric power or Compressed Air Energy Storage (CAES).  Pumped hydro is very site-specific and very little new pumped hydro sources have come on line in the last decade.   Compressed Air Energy Storage, or CAES, is one of the few practical methods to store energy. 

Compressed Air Energy Storage (CAES) is the term given to the technique of storing energy as the potential energy of a compressed gas. Usually it refers to air pumped into large storage tanks or naturally occurring underground formations.

While the technique has historically been used to provide the grid with a variety of ancillary services, it is also gaining attention as a means of addressing the intermittency problems associated with wind turbine electrical generators.  When energy is available, it is used to run air compressors which pump air into the storage cavern. When electricity is needed, it is expanded through conventional gas turbine expanders. Note that some additional energy (typically natural gas) is used during the expansion process to ensure that maximum energy is obtained from the compressed air (albeit as much as 67% less gas than would be used for an equivalent amount of electricity using gas turbine generators without CAES).

In CAES systems, electricity is used to compress air during off-peak hours when low-cost generating capacity is available.  Electricity is cheapest in the middle of the night and by running air compressors, air can be pumped into a cavern or vessel.  In the daytime, when the price of electricity is expensive, the compressed air is preheated with the heat generated and stored during compression and then used to help power a turbine.

For power plants with energy storage in excess of approximately 100 MWh or five hours of storage, the compressed air is most economically stored underground in salt caverns, hard rock caverns, or porous rock formations. A CAES plant with underground storage must be built near a favorable geological formation. Above ground compressed air storage in gas pipes or pressure vessels is practical and cost effective for storage plants with less than about 5 hours of capacity, however some above ground systems with up to about 10 hours of storage may be economically attractive depending on plant design and site conditions.

CAES is less complex and cheaper to construct and operate than a combined cycle.  Energy arbitrage is a large value driver of a CAES plant, as it uses cheaper off-peak power combined with minimal fuel, to provide on-peak power, usually at a significant spark margin to the market clearing on-peak price.  CAES provides exceptional ancillary service value, as its speed and flexibility allow for area regulation, synchronized spinning, non-synchronized reserve and other ancillary services.

In this course, we will look at some of the technical aspects of compressed-air storage systems, including storage options and the state of the art in CAES designs.  In Chapter One we look at the Huntorf and McIntosh plants in more detail as well as a few of the planned projects for the future.  Chapter Two discusses the storage options for CAES systems, and Chapter Three delves into CAES designs.  Finally, Chapter Four reviews the advantages and disadvantages of Compressed-Air Energy Storage systems.

Course Content

This course content is in the following PDF document:

Compressed Air Energy Storage

Please click on the above underlined hypertext to view, download or print the document for your study. Because of the large file size, we recommend that you first save the file to your computer by right clicking the mouse and choosing "Save Target As ...", and then open the file in Adobe Acrobat Reader. If you still experience any difficulty in downloading or opening this file, you may need to close some applications or reboot your computer to free up some memory.

Course Summary

Based on the experience gained with the operation of the McIntosh and Huntorf plants, the industry has found that:  CAES plants can be built within estimated costs and schedule; the plants confirmed the expected high efficiency, reliability, availability; the plants have competitive economics; the underground storage caverns can be developed using well-established techniques; underground storage reservoirs can achieve negligible leak rates. In fact, no air leakage has been measured at either the Huntorf or McIntosh plants since they were commissioned, and; CAES plants can be constructed using commercially available equipment; mainly components developed for the combustion turbine and oil/gas industries over that last 50 years.

Compressed Air Energy Storage systems are well suited as a companion to intermit energy sources such as wind and solar.  They also complement large base-load nuclear plants and offer an effective method to store vast amounts of power for later consumption.

Quiz

Once you finish studying the above course content, you need to take a quiz to obtain the PDH credits.

DISCLAIMER: The materials contained in the online course are not intended as a representation or warranty on the part of PDH Center or any other person/organization named herein. The materials are for general information only. They are not a substitute for competent professional advice. Application of this information to a specific project should be reviewed by a registered architect and/or professional engineer/surveyor. Anyone making use of the information set forth herein does so at their own risk and assumes any and all resulting liability arising therefrom.