Tony Smith wrote:
>>> Compare the
>>> cost of that new hybrid with the cost /difference/ between 
>>>       
>> the gas my 
>>     
>>> old civic will use compared to the new hybrid. [...]
>>>       
>> I remember a while back one of the presenters at the local 
>> SAE chapter meeting mentioned that storing the braking energy 
>> as compressed air achieves up to 70% efficiency, compared to 
>> only 20% for batteries. I do not recall the reason why 
>> hybrids are still using batteries. Safety? Difficult to 
>> achieve smooth acceleration?
>>
>> Best regards,
>>
>> Vitaliy 
>>     
>
>
> Energy density.
>
> Battery don't hold much power, but bottles of air contain even less.
>
> Tony
>
>   
I looked into compressed air as well, for storing household energy. The 
pressures must be incredibly
high before compressed air becomes useful, but once the pressures are 
high, air works wonders. For
example, it is the ONLY way to start large diesels (as in marine 
vessels). But to be useful in the
storage of energy, it seems to generate a lot of useless heat when 
compressing, and cold when
decompressing (sounds like old Volkswagen air conditioner, doesn't it..?).

Years ago, as a young engineer from TI, I was sent to monitor some TI 
seismic equipment on board
seaborne seismic vessels. The schemes used a method of generating 
explosions called an "AIR GUN".
It was a high-pressure air cable attached to a gadget that was capable 
of releasing a HUGE bubble
of air quickly, which caused a shock wave that hammered the rock in the 
ocean floor. These high
pressures were generated by stout three-stage , water-cooled air 
compressors on board the seismic
boat. The amount of energy released  with the bubble was remarkable; 
fish within 200' were killed
by the shock wave.

For me in 2002, the idea was to build a house in the western desert of 
the US, self-sufficient, with wind generator
and batteries for light storage, and use compressed air for long-term 
storage. For safety, the compressed
air tanks had to be buried deeply underground. The reason is that in the 
US Western desert, wind speeds
are high for several months of the year, then low for several months, 
and excess wind power would run
compressors to store excess power. I think it is feasible for a house, 
but NOT feasible for a vehicle, because
(1) an accident could result in a disastrous explosion, and (2) extra 
weight would be needed to make the tanks
strong enough to withstand 2000psi+..

It was a failure because there is almost NO available western lands to 
buy; US Indian tribes own all the land.

--Bob

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