Compressed Air

More than just hot air: Could adiabatic compressed air energy storage save the planet?

An emerging technology called Adiabatic-Compressed Air Energy Storage (A-CAES) uses industrial air compressors to generate heated air, heat exchangers to extract the heat energy, and large underground tanks to store the pressurized cold air before remixing at the surface.
More than just hot air: Could adiabatic compressed air energy storage save the planet?

By Michael Pollick | Wealth of Geeks | Associated Press

The search for a clean energy supply with no reliance on fossil fuels and an estimated lifespan of 50+ years may have ended with one of the most basic ingredients on the planet: compressed air. An emerging technology called Adiabatic-Compressed Air Energy Storage (A-CAES) uses industrial air compressors to generate heated air, heat exchangers to extract the heat energy, and large underground tanks to store the pressurized cold air before remixing at the surface.

Companies such as Canada’s Hydrostor are exploring ways to implement A-CAES technology on a scale large enough to produce clean turbine-generated electricity for entire regions currently served by fossil fuel-burning utility companies. While a form of compressed air energy storage has existed for decades, it currently relies on fossil fuels to compensate for heat loss during remixing and distribution stages.

The goal is to make A-CAES systems as self-sufficient as possible, with excess heat energy being reintroduced as a power source for the air compressors. Once this technological challenge is met, A-CAES may become the latest source of clean energy.

How A-CAES technology works

A conventional household air compressor uses an electric motor to force air into a reinforced metal tank, where it can be stored and released for power washing, spray painting, pneumatic tools, or other common projects. The industrial air compressors used in A-CAES operations, however, force external air supplies into vast underground storage tanks. Compressed air becomes extremely hot, and this heat passes through exchangers, which extract it from the air itself.

The generated heat and the pressurized cold air are stored in separate underground units, often existing mines or cave systems. The heat and compressed air are then remixed with water before returning to the surface as power sources. The compressed air can be used to produce electricity through turbines, and the heat energy can be used to generate steam.

Current A-CAES technology is not 100% efficient since there is some energy loss in the storage process, and additional energy in the form of fossil fuels may still be required. The current efficiency of A-CAES systems is estimated at 93.6%, according to a study by ScienceDirect.

Is A-CAES currently a viable option?

While A-CAES shares many of the same promising benefits as geothermal energy, the technological challenges have proven extremely difficult to overcome. Air compressors require energy to function, and a successful A-CAES facility would need to install an array of large commercial models. Any energy savings realized by the compressed air heat exchange might be offset by the cost of operating the air compressors themselves.

Two vital stages in the A-CAES process, heat exchange and compressed air storage, are still largely unproven commercially. An ideal location for an A-CAES facility would need to include enough open spaces underground for regulated compressed air storage, a reliable water source, and the infrastructure to deliver the generated energy to a power grid.

Hydrostor currently has a binding contract with Australian mining company Perilya to construct a large-scale A-CAES facility near New South Wales, but the project still faces a number of technological and logistical challenges.

Paul Rasmussen, Hydrostor’s Vice-President of Integration, said: “By leveraging the existing mine investment and infrastructure, this partnership enables us to improve project delivery timeframe since we can build the underground air storage cavern much faster, with reduced setup costs and a better understanding of the geology at the site.”

Hydrostor also has plans to build two A-CAES facilities in California, but those projects are also facing logistical and legal challenges.

Would an A-CAES system work on a smaller scale?

While most discussions about implementing an A-CAES system involve large-scale operations, there is also the possibility of smaller applications using CAES technology as an alternative to chemical batteries or other energy storage methods. Instead of storing compressed air in vast underground facilities, a micro-scale CAES system could store it above ground in reinforced tanks. The heated air often wasted in large-scale CAES applications can be used more efficiently in a smaller CAES array.

The clean heat energy produced by a small-scale CAES system may only be enough to power a few homes at best, but it would still be a viable solution for those who prefer to live off-grid or seek to reduce their monthly utility bills.

Could A-CAES technology really save the planet?

There are some valid criticisms in the scientific and energy production communities about the future of A-CAES technology as a viable alternative for energy storage. Theoretically, A-CAES could eliminate or significantly reduce the need for fossil fuels for electricity production. The heat generated by compressing air is a natural by-product, and the process would take advantage of this otherwise wasted resource. However, the scale and efficiency of mechanical heat exchangers need to be improved substantially.

The location of future A-CAES facilities would also be a consideration since creating new underground storage spaces could be cost-prohibitive or require significant time and resources. Deactivated mines and natural cave systems may be prime locations for the technology, but they may not be structurally or logistically feasible. There are still several issues that will need to be addressed before A-CAES-powered utility plants become a regular part of the landscape.

This article was produced by Media Decision and syndicated by Wealth of Geeks.