Compressed Air Energy Storage (CAES)

Published on July 12th, 2017 | by Tina Casey

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Ruh-Roh: New Texas Wind Energy Storage System Should Make Coal Nervous (And Natural Gas, Too)

July 12th, 2017 by  

There goes Texas again. European researchers are talking up the advantages of compressed air energy storage, and a Houston startup called Apex-CAES has already jumped the gun with big plans for a new compressed air system near the city of Palestine, Texas. If all goes well with the first system Apex has plans for more, and Texas can kiss its fleet of aging coal power plants good-bye.

The rise of compressed air energy storage (CAES) also complicates the picture for natural gas power plants and large scale lithium-ion battery storage, so let’s take a look and see what’s going on with that.

Compressed Air Energy Storage, Texas Style

The key factor making CAES economical in Texas is the state’s booming wind industryApex explains that it will take advantage of low cost (as in, practically free sometimes) off-peak power from wind turbines spinning at night.

Cheap wind power, and the state’s unified wholesale electricity market, provide Apex with the price differential that will turn a profit.

Low cost natural gas also factors in, since the system requires compressed air to be heated during peak demand periods and other times (more on that in a minute). According to Apex, though, CAES is more economical than conventional gas power plants, and uses far less gas.

Here’s the breakdown on emissions from Apex:

CAES energy production results in 40% fewer emissions per MWh than a combined cycle gas turbine, and its ancillary service production yields 98% fewer emissions per MWh.

Apex also points out that the system does not transfer energy from fuel to steam, so it requires “a fraction” of the water used in conventional power plants.

That should make natural gas stakeholders nervous. Right now cheap natural gas is the driving force pushing coal out of the power generation market, but low cost wind and solar are beginning to compete with gas in some areas, and the U.S. Department of Energy is working toward a grid modernization strategy that includes a growing share of renewables.

Compressed air storage could give renewables the edge they need to start claiming bigger chunks of the power market and accelerate the transition out of fossil fuels.

That could make lithium-ion battery stakeholders nervous, too. According to Apex, the cost advantages of CAES over large scale Li-ion arrays are significant:

Cost of storage for CAES is $18/kWh, versus $435/kWh for a lithium-ion battery.

CAES operating life of more than 30 years is three times that of a lithium-ion battery, resulting in dramatically lower annualized costs.

One additional advantage is that CAES is essentially an underground operation. Apex anticipates that surface “disturbance” can be kept as low as 10 acres for a 317 megawatt CAES system.

CAES: “The Ultimate Demand Response Provider”

Apex points out that the basic technology has a long track record of reliability, although according to the company there are only two CAES plants currently in operation, one in Huntorf, Germany and the McIntosh plant in Alabama.

Using the McIntosh plant as a model, Apex will use Siemens equipment with the aim to meet or beat that level of performance.

The concept is simple. During off-peak hours, electricity from the grid is used to power an underground electric air compression system.

When called upon to generate electricity, the compressed air is moved out of storage and heated to expand it (that’s where the natural gas comes in). The heated air is used for powering an expansion turbine, which in turn powers a generator.

The system is both an ancillary service provider (ancillary refers to services like frequency control, which are needed for grid balance) and the “ultimate demand response provider” because the compressors can be called into service instantly.

Texas Rules, Others Drool

The Houston Chronicle points out that underground energy storage is a familiar field in Texas, so its a natural fit for the nation’s first CAES plant in 37 years (the McIntosh plant went into operation in 1981).

The plant will take advantage of the Bethel salt dome, which already has a track record of underground energy storage in the form of natural gas.

Here’s a rundown from the Chronicle:

Located near five existing natural gas storage caverns, the compressed air would spin turbines rated at 317 megawatts, capable of generating 15,000 megawatt-hours of electricity over two days without a recharge…

The Chronicle also notes that the system’s ability to provide ancillary services enhances the company’s chance of turning a profit, since such the Texas grid manager ERCOT pays a premium for such services.

And, Chronicle has more bad news for both Li-ion and natural gas stakeholders:

Compressed air has both a price and operational advantage over batteries. Salt caverns are cheaper than lithium-ion batteries, and the system can fill the cavern with air while generating electricity. You can’t charge and discharge a battery at the same time.

Operators can easily and quickly adjust output to match the needs of the grid – unlike with a natural gas turbine. In many ways, compressed air storage operates like a hydroelectric dam.

Meanwhile over in Europe, back in March CleanTechnica took note of a pan-European R&D project for compressed air energy storage systems:

Compressed air storage is in no way a “new” concept, but scientists from all over Europe, working under the auspices of the RICAS 2020 research project, are investigating the possibility of storing large amounts of compressed air in disused caverns and tunnels as large-scale storage sites.

Have at it, guys.

Apex was gearing up to start construction on the Bethel Energy Center as early as 2014, but put the project on hold until this year.

It seems that things are back on track. Apex is raising $500 million to build the plant and expects commercial operation to begin in 2020.

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Image: via Apex.


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About the Author

specializes in military and corporate sustainability, advanced technology, emerging materials, biofuels, and water and wastewater issues. Tina’s articles are reposted frequently on Reuters, Scientific American, and many other sites. Views expressed are her own. Follow her on Twitter @TinaMCasey and Google+.



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