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Storing Renewable Energy through Air Compression

written by: Swagatam • edited by: Lamar Stonecypher • updated: 9/25/2013

Rechargeable batteries probably can be considered the best power-storing devices for various forms of renewable energy, but compressed air energy storage is also promising and should not be overlooked. Unlike batteries these systems are cheaper, lighter, and, most importantly, permanent.

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    It’s not surprising to see history repeat itself yet again. Long ago before oil was discovered, our ancestors largely depended on and exploited various renewable resources and forces of nature and could very skillfully harness solar, wind, and gravitational energy to their benefit (although not very efficiently.)

    When man struck oil, everything changed rapidly, as this particular natural resource had tremendous potential and could be converted into huge and efficient power sources.

    Armed with this resource the process of modernization looked obvious and grew at very fast pace. Almost unimaginable happenings like industrialization, power vehicles, and electricity through the burning of fossil fuel could now be conceived and become an indispensable part of our life.

    However, we slowly started realizing the grim fact that this type of natural resource was not permanent and was being exhausted at an alarming rate, almost by 1% every year. Moreover, burning oil resulted in the emission of dangerous CO and CO2 gases, giving rise to the threatening greenhouse effect.

    This message was not a pleasant one and scientists desperately started concentrating on more sustainable means of energy. Although harnessing wind and solar energy remained a priority among the researchers, these resources need to be used instantly as they are created, on the spot, and also are not consistently available. Therefore, more efficient recoverable storage of wind and solar energy was needed before these technologies could logically advance.

    Methods of compressed air energy storage looked promising and of late are being effectively devised for storing various forms of energy by compressing air inside specialized tanks.

    Here, a stream of air is forced or stuffed inside the tank through a valve mechanism using some external power source until the tank can take no more. The inlet valve mechanism makes it sure that the forced air once inside the chamber is restricted from reversing out from the same passage.

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    High Pressure Air Tank - Construction and Efficiency

    Typical Compressed Air Energy Storage High Pressure Tank, Image  

    A typical air pressure storage tank is comprised of the following components:

    Air Receiver: Basically this is the chamber or the tank that accepts and stores the compressed air. It’s either made of high grade steel or carbon fiber to enable withstanding extreme pressures. It’s normally cylindrical in shape to optimize maximum amount of storage.

    However, no matter how sturdy the body of the tank may be, the material may have certain physical limitations and needs to be both protected and to provide warning before the parameters reach the breakdown limits.

    Pressure Gauges or the Pressure Indicators: With the parameters being so critical, a physical monitoring device becomes essential. A pressure gauge is a precision instrument fitted and integrated externally to high pressure tanks to measure the internal pressure of the enforced air exerted over its walls. The personnel responsible for checking the correct pressure of the tank keep a constant watch over this device and may be prompted to take the necessary precautions to avoid a possible mishap. The meter or the gauge provides a direct display of the involved pressure in the standard unit: “pressure per square inch" or psi in short.

    Safety Relief Guard or Valve: The device is introduced to guard the tank in case the above pressure control schemes fail. This outlet valve is permitted to open only through one outward direction when subjected to certain specified high pressures, enabling instant release and normalization of the internal tank air pressure.

    The mechanism inside the valve of such tanks is adjusted such that it operates at a certain pressure which may be considered dangerous and gives off the excess gas to relieve the tank enclosure from exceeding pressures. Once the pressure comes to tolerable limits, the valve shuts, maintaining the required pressure level inside the tank.

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    Pioneering Efforts

    Car Powered by Compressed Air, Image  

    Among researchers, some "optimists" predict that within the next 30 years almost 99% of earth’s fossil fuel content will be used. This news has certainly created quite a panic in the automobile industry. Scientists are thus compelled to find alternatives to replace oil used in motor cars through means that must be powerful, cheap, and renewable.

    In the recent past French engineers were successful in accomplishing the mission by effectively using compressed air for powering vehicles (CATS.)

    In the system, light weight tanks made up of composite carbon fiber filled with compressed air are used. The engine of the vehicle is driven by the power of the released compressed air into a second generation flywheel/piston mechanism. The release of the compressed air can be controlled by the driver himself through sophisticated instrumentation.

    Once the air pressure inside the tank becomes exhausted, it can be replenished through external electrically charged air compressors. Each filling may provide at least 125 Km of continuous travel for a two-seater vehicle; attempts are being made to further improve this. Here, since no combustion is involved, the entire process becomes highly eco-friendly, silent and with minimum wear and tear.

    In some countries compressed air power is also being used in producing electricity in conjunction with the normal methods of utility (Compressed Air Energy Storage CAES Power Plant in McIntosh, Alabama.) Here, during off-peak hours the generated energy is stored in underground mines in the form of compressed air, which is released back to assist in the production of electricity during peak demand hours.

    When it comes to the storing of solar and wind power, we normally look toward rechargeable batteries, which can be very effectively used to store the various renewable energy sources by first converting them into electricity. Though more efficient, batteries are not permanent, they degrade fast and ultimately require a replacement, and therefore become a relatively costlier means of power storage. Also as they degrade, their efficiency also declines proportionately.

    Contrary to this compressed air energy storage methods look more interesting as these are simpler, uncomplicated, and offer a permanent solution for storing renewable energies.

    The procedures involved are simple too; solar heat can be first used to heat water inside an enclosed chamber. The gradual expansion of water will create a high pressure inside the chamber with increasing temperature, and this generated high pressure may be appropriately channelized, transferred, and stored inside high pressure storage tanks.

    Similarly wind mills can be easily mechanized to move the piston of an air pump whose resultant output power can be fed and converted into pressurized stored energy inside tanks for future usage.

    References:

    Google Books

    Discovery Channel

    Dresser-Rand (CAES provider of Alabama installation)

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