Compressed Air as energy storage mechanism

[Miclar99]

A challenge facing all wind turbines is matching the electricity generating components to an energy source, wind, which is highly variable. Most small wind turbines use a variable speed generator or alternator that produces dirty power. An inverter is then used to make it into utility grade electricity. Inverters are expensive, $3k to $15k for a small to medium size wind turbine.

The Melecca idea is to capture the energy of the wind and store it as compressed air. Then use the energy in the compressed air to create utility grade electricity because a generator could be powered at a constant speed.

Specifically, have a wind turbine drive an air compressor (probably a screw compressor designed to run at low RPMs) which would fill a tank (maybe a 660 gallon tank to 200psi) and then use an air motor to drive a generator (maybe a 10hp motor driving a 5kw induction generator at a constant speed).

The objective is not to capture more energy than a traditional wind turbine, but to produce utility grade electicity more cost effectively.

Is this a good idea?

 

[dcasto]

You are still driving a small generator which needs a governor to control Hertz. The air motor will have to to have some controls to compensate for the changeing inlet air pressure. So same the "dirty" electricity problem.

The screw compressor will be about 50% efficient and the turbine generator about 60%, so you'll only get about 30% of the energy out. I believe that new Inverters that can sync the electricity from the alternator to line are cheap and reliable.

On a larger scale, the DOE is investigating using underground cavaties to store air under pressure wfor peak shaving. The compressors would run at 81% effiecient and the turbines at 75%, overall 60% efficiency.

 

[crjones]

Air motors are fairly inefficient. Also screw compressors are inefficient at slow speeds, they rely on speed to setup the sealing between rotors and housing and 200psig will exceed most single stage screw compressors.

 

[zdas04]

Details. If the screw turns too slowly then you put step-up gears and worry about starting torque. I think that with a whole lot of design decisions, there are ways to take this idea to a reasonable place on the effeciency curve.

It is similar to the idea of driving a pump with the wind turbine to pump water to the top of a hill and then using that potential difference to drive a water turbine, but it doesn't require a hill.

I'd be really thorough in the analysis of the kind of compressor, size pressure vessel, and vessel operating pressure. Would multiple turbines share the pressure vessel and genereator or would each be stand-alone? It's all just details. Good luck with it.

David

 

[pmover]

having been part of the design team for a CAES facility, it boils down to what power can be bought vs sold. the Norton project was quite the project and challenge which involved some brilliant engineer and scientests

see:

http://en.wikipedia.org/wiki/Compressed_air_energy_storage

there are other websites pertaining to the Norton plant as well - search via google.

undoubtedly, the air storage capacity will need to be large enough to suffice the power demand. the 660 gal tank at 200-psi is a small amount of air storage; thus power demand must be relatively minor as well.

lastly, the location will need wind a good percentage of the time.

good luck!
-pmover