How good is compressed air power?

Yes, I know, it only moves the problem from polluting car engines to producing electricity - but hey, at least here in Quebec we get most of our electricity from hydroelectric barrage, which are a magnitude less polluting. I also know that the real solution involve a massive re-engineering of our car-based society, but…

What I want to know is: how efficient and environmentally sound is this technology compared to other alternatives out there?

I must not be understanding something. The site continuously trumpets “zero-emission compressed air power”, yet shows a schematic with a “constant volume combustion chanber”, and discusses running off of “petrol, LNP, and even diesel”.

It is a somewhat confusing website, and seems to offer no real detailed explanation of how the cars work. I will suspend judgement, as a result, except to say that by definition any combstion source that emits a greenhouse gas should not really be termed a “zero emission vehicle” anymore, IMO.

Every conversion of energy from one form to another brings inefficiency. For conventional internal combustion engines, we are converting fuel (gas/diesel/CNG/Propane/etc.) directly into motive power, with a big loss on that conversion. With electric cars, we go from burning fuel to motive power, then add:
-the losses for generation (sizable ~50%)(less for fuel cells: direct fuel to electricity),
-transmission (getting the power across the power lines; not nearly as sizeable, but reasonably big),
-conversion to chemical energy (charging the battery, small loss),
-conversion back to electrical power (discharging the battery, small loss)
-transforming this electrical power back into motive power (about 10% loss, 5-6% with expensive, premium efficiency motors).
You do gain a little energy back with regenerative braking, which turns motive power back into electricity, instead of motive power into heat, like conventional auto brakes.

With this compressed air system, we convert fuel to motive power to electricity(big loss ), transmitted over power lines (more loss) to motive power (10% loss), to drive an air compressor (another sizeable loss), then to storage (negligible loss), and finally to motive power. Aside from the additional losses, consider the following:

-The cited page says that the compressed air is 4500 psi (about 300 times normal atmospheric pressure, or atm), with a capacity of 3200 feet[sup]3[/sup] (I assume this is at standard atmosphere, ~15 ft[sup]3[/sup]). It takes serious equipment to compress air this much. Your garden variety air compressor that you can buy at your local hardware store generates about 150 psi (10 atm).

-A standard SCUBA tank holds about 70 ft[sup]3[/sup] at 3000 psi. To store 3200 ft[sup]3[/sup] at 4500 psi, it would take about 30 regular SCUBA tanks (assuming that they could hold 4500 psi, which they can’t, for normal use). That’s a lot of SCUBA tanks for that little car to haul around.

-There is a lot of energy stored in that much compressed air. When released all at once (like with a burst air tank), it could do a LOT of damage. In researching this response, I found this site. If a gas tank is defective, it will leak fuel, which may burn (over a relatively long period of time), if ignited. If a 4500 psi air tank is defective, it will burst, releasing all of its energy over a short time (small fraction of a second). This will send pieces of the tank all over at a high speed.

The only advantage I see is that all of the pollution happens at the power plant, where it can be controlled a lot better than at the tailpipe. This system actually is less efficient than electric vehicles. It also suffers from a problem that I associate with electric vehicles: It makes people feel a lot better about using their vehicle, without actually reducing global pollution (much), and while using more energy than they would have if they would have if they would’ve driven a good, modern gasoline powered (or diesel, even better, efficiency-wise) vehicle.


Re-reading my response (preview, preview, preview), I lumped in the loss for fuel to motive power in the 50% loss for generation. This is the approximate loss for fuel to generated electricity.

It is the jump from fuel to motive power that is the big loss (about 45%). The loss for generation is about 10%(of the remaining energy). This equals about 50% loss from fuel to electricity.

I agree with Anthracite that the web site is least misleading, possibly a snow job. It calls them “compressed air” powered vehicles. But click on “engine”, and you find:

It AIN’T running on compressed air, and untreated exhaust pollutant levels “lower than those of a conventional engine fitted with a catalyst” AIN’T zero.

It may be a clever and praiseworthy idea (or may not), but the marketing job is misleading as hell.

We can also find this: