xxxxx
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compressed air to store energy
for various electrical generation systems such as wind for a one family home some sort of energy storage is needed for times of no wind. i was
thinking about compressing air which then would push a piston in a machine similar to an internal combustion engine only powed by compressed air,
which would turn an electrical generator. for a conventional air tank such as a large oxgen tank for welding, air would be stored at 3000 psi.
presumably this would be more environmentally friendly than lead acid bateries and probably would have more "charge-discharge" cycles. i was
wondering how much compressed air would it take to match the energy in a 12 volt 400 amp-hour lead acid battery and would this be practical in terms
of operation with removing water vapor from the air and the efficiency of return.
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not_important
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Remember that compressing a gas heats it, that heat leaking away represents lost energy. While you can absorb heat from the surrounds during the
expansion phase, it takes fancy heat exchangers to get a decent rate.
Another thing to consider is the charge/discharge characteristics. While most batteries have a fairly constant voltage and maximum current over most
of their charge range, compressed gases and capacitors have a exponential decay curve.
Because of the heat loss, compressed gas is more efficient with very large storage volumes, taking advantage of the cube/square relationship between
volume and surface. This is less critical if the storage is being used to load level over a short time period, or in similar short term storage.
For a cubic meter gas at STP, the energy stored in isothermal mode is very roughly 110 kjoules times the natural log of the compression ratio.
might be of interest:
http://www.eere.energy.gov/de/cs_energy_storage.html
http://www.doc.ic.ac.uk/~matti/ise2grp/energystorage_report/...
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chemrox
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Every approach I can think of would be equipment intense. Especially preventing or capturing heat leakage. I wondered about storing E in a solar
pond .. again .. realizing energy from slight temperature changes would take highly sophisticated equipment...batteries are constantly being improved
thanks to aerospace and I still think batteries are the best bet. Better than storage though is two way metering. You're still on the grid but you
get credit for what you make. Still, I like the idea of being off the grid.
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Twospoons
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For a more environmentally friendly solution, look up Vanadium Redox batteries. Uses V in H2SO4 - on both sides of a PEM. Capacity is only limited
by the size of the electrolyte storage tanks. There are several other redox systems too - notably Cerium/Zinc, which has a mixed Ce/Zn electrolyte,
and selective catalysts on the reaction membrane.
Helicopter: "helico" -> spiral, "pter" -> with wings
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evil_lurker
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Ever run any air tools?
To answer your question, it would take as much hot air as george bush and all of congress put together over the last 6 years to run a 5000W generator
for one hour.
Not all chemicals are bad. Without chemicals such as hydrogen and oxygen, for example, there would be no way to make water, a vital ingredient in
beer.
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16MillionEyes
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I don't know if anyone else has heard of this but there's actually a car engine that runs on compressed air. It might be useful to you to look it up (
I don't have links, I saw it on Discovery) and figure out how it actually works. What's really impressive about this system is that the car actually
reached a maximum speed of 90m/h. Really good for compressed air.
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guy
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I heard of this method from my professor; he said he wasn't sure if people were actually doing it but he said it might be a good idea.
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franklyn
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Compressed air is an excellent transmitter of power and actually predates
electricity in this regard. Pneumatics offer advantages over a short range
where high power and light weight are requirements such as for hand tools.
Due to the very low energy density , unrealistically large storage volume is
needed for anything more than a brief run time. Commercial compressors
have a tank which only serves as a buffer for the pulses from the compressor
which turns on frequently as the storage tank is drained.
Sopplemental heating of the air supply provides only a small improvement.
The distribution of natural gas through pipes from a one gas field to another
is perhaps the exception. Gas from one source is often stored underground
at another location in the natural gas bearing stratum obviating the need
for tanks.
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Mr. Wizard
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Why carry those heavy bulky tanks? Here is a link to a liquid nitrogen vehicle.
http://www.washington.edu/alumni/columns/dec97/car4.html
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