Compressed Air Energy Storage: Things to Know

compressed air energy storage

Here’s everything you need to know about compressed air energy storage (CAES).

Numerous socioeconomic advantages and environmental advantages come with energy storage. Numerous methods can be used to store energy. Energy can be stored using various methods, such as capacitors, pumped hydro storage, and superconducting magnetic energy storage.

To learn more about compressed air energy storage, read this article.

You may be interested in Thermal Energy Storage and Battery Energy Storage. You can check out more information we have on 16 Best Energy Storage Companies in 2022.

What is Compressed Air Energy Storage (CAES)?

Compressed air energy storage (CAES) is a more than 40-year-old technological idea. In order to meet peak demand and provide load following while preserving a constant capacity factor in the nuclear power industry, compressed air energy storage, or CAES, was seriously investigated in the 1970s.

Since the late 1970s, compressed air energy storage (CAES) technology has been offered for sale. Over 24 years have passed since the successful operation of one commercial demonstration CAES plant, and 11 years have passed since the successful operation of another.

The siting, economic viability, and design of numerous additional CAES plants have also been studied (EPRI, 2002).

Figure 1 explains the fundamental operation of compressed air energy storage (CAES), and the introduction picture above is an artist’s conception of a CAES plant coupled with a wind farm.

Compressed air energy storage is a general term that describes the technology’s fundamental operation. A compressed air energy storage plant can compress air and store the compressed air in an underground cavern when there is too much electricity on the grid (for example, due to high power delivery during periods of low demand).

compressed air energy storage

When demand is high, it is possible to recover energy by releasing the stored air.

Due to the fact that low-cost electricity is produced during periods of low demand while high-cost electricity is created during periods of high demand, storing energy is strongly influenced by the economic advantages the technology offers in addition to the environmental benefits it offers.

The technology also supports the energy market and has positive socioeconomic effects.

We have introduced other compressed-air products:

How Does Compressed Air Energy Storage Work?

Regarding their applications, compressed air energy storage (CAES) facilities are largely comparable to pumped-hydro power plants.

The ambient air or another gas is compressed and stored under pressure in an underground cavern or container in a CAES plant, as opposed to pumping water from a lower to an upper pond during times of excess power.

When electricity is needed, heated and expanded pressurized air is used to power a generator by an expansion turbine.

The unique feature of compressed air storage is that the air strongly warms up during compression from atmospheric pressure to approximate storage pressure. 1,015 psia (70 bar). Normal multistage air compressors use inter- and after-coolers to lower discharge temperatures to 300/350°F (149/177°C) and cavern air injection temperatures to 110/120°F (43/49°C).

So, during the compression process or after it, a cooler in between removes the heat of compression.

The high-pressure air is then heated in combustors using natural gas fuel to make up for the loss of this heat energy during the expansion turbine power generation phase, or alternatively, the heat from a combustion gas turbine exhaust is used in a recuperator to warm the incoming air prior to the expansion cycle. 

Methods to Compress Air

There are two methods that are commonly used to compress air to store energy:

Diabatic CAES Method

The compression of the combustion air in these plants is separate from and independent from the actual gas turbine process, so in theory, they are just regular gas turbines. The two main advantages of this approach are consequently produced.

Since the compression stage typically consumes about two-thirds of the turbine’s capacity, the CAES turbine can produce three times as much energy for the same amount of input of natural gas when the compression stage is not present.

Depending on whether the waste heat is utilized to warm the air in a recuperator, this reduces the specific gas consumption and the associated carbon dioxide emissions by 40 to 60%. About 80% of the power is converted into power. 42% without and 55% with waste heat utilization.

During off-peak hours or when local energy demand exceeds the supply of renewable energy, less expensive excess energy can be used in place of compressing the air with valuable gas.

Both of the aforementioned plants use single-shaft machines, where the compressor-motor/ generator/gas turbine are all mounted on the same shaft and connected by a gearbox. Other conceptual CAES plant designs will mechanically separate the turbine-generator unit and the motor-compressor unit.

In terms of the permitted input power and output power, this enables modular expansion of the plant. CAES plants of different sizes based on cavern storage volume and pressure are possible.

This is accomplished by using conventional gas turbine exhaust heat energy to warm the high-pressure air prior to expansion in an air-bottoming cycle.

Adiabatic Method

If the heat of compression is recovered and used to reheat the compressed air during turbine operations, there is no longer a requirement to burn additional natural gas to warm the decompressed air, which results in significantly higher efficiencies of up to 70%.

Feasibility of Compressed Air Energy Storage (CAES) and Operational Necessities

The CAES technology idea has been around for more than 40 years, as was previously mentioned. In the vicinity of Huntorf, Germany, the first and oldest CAES facility in the world has been in operation since 1978.

The 290 MWe Huntorf plant serves industrial customers in northwest Germany primarily for cyclic duty, ramping duty, and as a hot spinning reserve.

compressed air energy storage

The variable power from numerous German wind turbine generators has recently been leveled with success by this plant. A 110 MWe plant was built in the US and has been in operation since 1991 near McIntosh, Alabama.

In Norton, Ohio, the United States, a third CAES facility is being considered. With a 2700 MWe capacity, this facility will be the largest ever, compressing air to 1500 pounds per square inch (psi) in an active limestone mine located 2200 feet below the surface.

Other CAES plants have been planned, investigated, and/or designed but never built for a number of different reasons (EPRI, 2002). Several examples are:

  1. A 1050 MWe CAES plant using salt cavern geology formations for air storage was proposed for development in the Donbas region of Russia during the Soviet era. The development of air storage’s subterranean geology was started. The construction was, however, stopped when the Soviet Union fell.
  2. A 3 x 100 MWe CAES facility in Israel using fractured hard rock aquifers was among the CAES facilities for which plans had been developed.
  3. At the Viendan site, a pumped hydroelectric plant was built by Luxembourg and has a 100 MWe CAES plant that shares an upper reservoir for a water compensation system with it.
  4. A 220 MWe hard rock-based plant is being built under a contract with Soyland Electric Cooperative. When the project was abandoned due to non-technical considerations, plant engineering, the drilling and analysis of the cavern sample, and the purchase of all major equipment had been made.

The examples above demonstrate that CAES technology is unquestionably past the developmental stage, even though the majority of projects were not finished. The technology can also create large-scale energy storage systems with capacities of up to 1000 MWe.

Several Key Features and Limitations of Compressed Air Energy Storage

  1. The CAES technology is easily adaptable to particular site conditions and economics.
  2. CAES is a tested technology that can be offered by a variety of suppliers at competitive prices.
  3. Black start is a capability of CAES plants (more on this below). The McIntosh and Huntorf plants both have the ability to use black-start when necessary.
  4. Plants built by CAES start up quickly. A CAES plant can quickly reach its maximum capacity if run as a hot spinning reserve. The Huntorf and McIntosh plants require approximately 5 minutes to restart in an emergency due to cold weather. Their normal startup times are about 10 to 12 minutes

According to the 2002 EPRI study, utility planners’ lack of awareness of this option is most likely to blame for the currently limited market penetration of this technology.

In addition, utilities are likely to view the underground geology as a risk issue. In addition, very few engineers are aware that CAES sites are actually fairly typical. In accordance with the EPRI study from 2002, suitable CAES sites are present in about 80% of the country.

These factors contribute to the underutilization of the market potential for CAES.

Conclusion: Compressed Air Energy Storage

An approach to storing energy produced at one time for use later is compressed air energy storage (CAES). At the utility scale, the energy produced during times of low energy demand (off-peak) can be released to meet times of high demand (peak load).

A large-scale, low-cost, long lifespan and established operation experience are just a few of CAES’s standout qualities.

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