[LINK] Compressed Air Hybrids [WAS plug-in-hybrid-vehicles and grids]

Karl Auer kauer at biplane.com.au
Mon Sep 7 22:41:32 AEST 2009

On Mon, 2009-09-07 at 16:38 +1000, David Boxall wrote:
> In stop-start driving, the energy isn't stored for long, so heat loss 
> isn't the issue it might otherwise be.

Er - yes it is. "Ye canna break the laws of physics, Captain!". Either
you don't store much energy, or you have a problem containing it, and a
gas under pressure (more energy stored) is hotter than a gas not under
pressure (energy released). You have to deal with both an extreme heat
issue during storage and an extreme cooling issue during release.

Unless you are storing very little energy, of course - but we are
talking about sufficient energy stored as compressed gas to power a car,
and presumably for some useful distance - this is not a SCUBA tank we're
talking about.

I'm not sure why you say stop-start driving means energy is not stored
for long.

>  The air tanks are carbon fibre, 
> which is light and fails (in an accident, for example) by tearing. 
> There's no explosion, as there can be with batteries in that situation.

Not sure on this point. When a container holding very high pressure
"goes" (and I think we are talking multiple thousands of bar here) I
suspect it goes in a big way.

> With no batteries or secondary electric drive train, compressed air 
> hybrids are lighter than battery-electric, which makes for greater 
> efficiency.

Greater efficiency while using a massively inefficient energy storage
system? No, not convinced.

> Transport will reply on liquid fuels for the foreseeable future, at 
> least for longer distances. Those fuels may not be fossil, but we'll 
> need to make the best of them. The potential of a fully-programmable 
> combustion cycle is intriguing indeed.

I think it is an unfortunate distraction that delays the inevitable
re-education of the motoring public to the realities of a world where we
just don't have the luxury of burning stuff to make energy.

Regards, K.

Karl Auer (kauer at biplane.com.au)                   +61-2-64957160 (h)
http://www.biplane.com.au/~kauer/                  +61-428-957160 (mob)

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