In article ,
wmbjk wrote:

A source of mechanical energy can directly drive a compressor head,
saving the extremely inefficient conversions to electricity and back.
Compressed air is easy and economical to store in large volumes and is
free from the chemical hazards of batteries. Useable service life of
compressed air tanks is much higher than batteries as well.

Wind driven compressor - storage tank - air motors? Could be OK if
one had a really windy site, lots of surplus pressure vessels, and a
plenty of rotor diameter. To get an idea of the diameter versus work
produced, check out the size and pumping rates of Bowjon well pumps.

Ya know, you could probably make this work with a little creativity.
Find a compressor that's happy running at any speed between near-zero
and max, (good luck) then rig up a speed governor and a CVT (variable
pulleys would probably be the most practical). Arrange it so that the
governor keeps the windmill turning at optimal speed, and varies the
compressor speed depending on how much energy is available from the
wind. So, light wind, slow compressor, heavy wind, fast compressor.
Unload it through a small restriction when the system's full, so it can
keep the windmill moving, but control its speed. You wouldn't need an
oversized rotor to deal with the torque at high compressor outlet
pressures since the CVT would adjust for that on the fly.
For the tanks, get some pressure protection valves. These work sort
of like check valves, but only open at so many PSI, like 60 or so, and
with no pressure drop through the valve once open. Some are pre-set,
others are adjustable. Set to above your expected working pressure (by
that I mean whatever you set the outlet regulator to) and below your
maximum tank pressure. Just above working pressure is probably best.
Hook it up as compressor- valve- small tank- valve- large tank-
valve- large tank-... Then, for the outlet of all the tanks, regular
check valves to a common manifold and then the regulator.
The result you'd have is a pressure buildup time proportional to the
small tank up to the pressure where the protection valve opens, after
that it'll be proportional to the total volume of first and second until
second is full, then second plus third, and so on. But when using air
your pressure fall would be proportional to the entire system's volume
(or at least the volume of the tanks currently charged up) as the
manifold would always pull from the highest-pressure tank first.
Kind of complex, but would ensure that you have lots and lots of air
available at highest pressure, and your system would be arbitrarily
expandable simply by adding additional tanks at the end of your chain
without hurting buildup time. And with a moderate wind and
appropriately sized first tank, you'd have a good buildup time for when
you actually need highest pressure.
You could even eliminate the unloader scheme if you just stick a
pressure pop off valve at the end of the chain. Or just keep adding
bigger tanks until you can never fill the final one. (:

ASCII Diagram:

Compressor----T1--ppValve--T2--ppValve--T3----pop-off valve
| | | or more tanks
Check Check Check
| | |
v v v
Regulator-------------------------------------
|
v
Out

Probably couldn't run a sandblaster on it, but an impact, grinder,
nailer, or drill would be doable. Could probably even handle the fridge
idea someone mentioned earlier without trouble.
And if you outpace the system on occasion you would be able to
augment it with an engine or electric compressor that runs when you use
a whole lot of air and let the windmill keep the system topped off
otherwise.

--
B.B. --I am not a goat! thegoat4 at airmail dot net
http://web2.airmail.net/thegoat4/