You have a good point there -- I omitted it because I don't know how much those compressors go for, because a regular gas station also requires a similar initial investment (underground tank, pump, island), and these costs get amortized over a few years.

I think fixnair was referring to the compressed air that comes in those tall metal cylinders, and that obviously wouldn't be practical, but compressed air at fill-up stations should be a lot cheaper than that.

 

Here is an example of just how expensive compressed air is. A 5 HP radial piston air motor requires approximately 150 SCFM to run at rated speed and load. An air compressor large enough to provide that amount of air would have to be powered by a 30 HP electric motor.
And when you consider the cost of electricity to operate that 30 HP compressor, It is a considerable sum. Here in arid central California farming is big business and water is hard to come by. All the irrigation water comes from wells sometimes 150 feet deep. It is cheaper to drive these water pumps with a 125 HP diesel engine rather than an equivelant electric motor. So much cheaper that the farmer can afford to buy a new engine every year with the savings in electricity and still be ahead of the game.


Steve Bark

 

Converting one kind of energy to another always involves losses. The well pump example is perfect. Burn fuel oil to boil water into steam in order to spin a turbine which is attached to an alternator. Transform the voltage high enough for long distance transmission, then transform it down again to a usable voltage for an electric motor that drives a pump. Or, burn fuel oil in an internal combustion engine to drive a pump.

Jim

 

Absolutely correct.

I actually saw this technology on the Discovery Channel special "Futurecars". I couldn't believe it, but they actually gave the impression that you could put a compressor on the vehicle that would make for a perpetual motion car. My roommate and I (we're both engineers) were laughing on the floor.

I think the company does actually say that the car needs to be refilled. Sounds like they've made it have some sort of regen braking as well. Still, you'll never run forever on one tank of air. It is impressive that they have gotten as far as they have. I think that they need to be more forthcoming with the calculations and specifics of what the costs ($, emissions, and energy) of producing the compressed air. They treat the car as the whole system, when we really need to analyze the whole solution (car, fuel production, fuel delivery, etc), as is done for other alternatives like ethanol, butanol, biodeisel, hydrogen, etc. Several in this thread have said similar things.

In short, it's an interesting technology and company to watch, but no magic bullet to solve all our problems.

-Jim

 

It all comes down to converting one form of energy into another. I don't buy into the regenerative braking providing much savings. I don't see putting a compressor capable of delivering 4000 psig into the car. The weight would kill the concept.

So, as stated above, you burn fossil fuels, raise steam, spin a turbine, spin a generator, send electricity to the grid, spin an electric motor that spins a compressor, the compresses air spins the motor in the car that spins the wheels. I don't see how this can be more effiecent that an internal combustion engine, or even a plug in rechargable electric car.

 

Would it not be possible to use the city water supply. To turn a turbine to run the compressor? The water goes back in the system and is never diminished or polluted. There would be no elc's invalved. Except what is pumping the water already there.

 

There is no free lunch. To run a turbine that would compress the air would drop the pressure in the water system. So, you would just end up running the pumps that feed the system more.

 

More efficient, possibly not. However, there is a significant advantage over a plug-in electric car. Namely, (according to this company's claim) you could drive 120 miles, then fill up in 3 minutes and drive another 120 miles. That's not something any electric can do at this point. The only way I can imagine that currently is if you could go to a "refilling station" and have them swap out your batteries and reload a new set every "tank". We can't charge storage batteries that quickly. Gasoline obviously has an even better edge in this category (you can drive 300 miles in many vehicles, then refill in 3 minutes, and drive another 300).

Gasoline also doesn't have a positive well-to-wheel energy balance. From looking for ethanol numbers last year, I found a few sources that said it only returns 80% of the energy spent in getting it to the pump.

Also, what a perfect application for renewable electricity. Many people fault renewables for not addressing peak load (ie, grid-tied solar with no storage makes electricity and puts it on the grid, but can't necessarily solve a peak problem, so you still rely on fossils). And they don't always address transportation needs. If instead a renewable source sat there compressing air for later delivery and use in a car, that could be a pretty good solution. Obviously, the economics would have to be worked out. And it could be that at this point you can't deliver compressed air direct from a renewable source to beat gasoline at $2.50/gallon. I'd like to see the numbers. If Democrats push through carbon caps, it may start to make a whole lot of economic sense (not saying I'm for this platform, but it is a reality we may have to deal with).

-Jim

 

You are certainly correct about the length of time it takes to recharge being a problem for the plug in electric car.

 

Energy can not be created nor distroyed! When I was in middle school I came up with the design of a electric motor driving the generator and then the generator in turn drives the motor....and a seperate winding on the generator is used to provide power for external items. Well..the design was enough to stump teachers.....it would never work in real life...just because of the energy law...cant be created nor distroyed!...you would also have heat lose...friction...etc....

 

I think that it would be practical to use a light weight pump and air storage tank to "help" get the car moving once it has stoped, You could use the energy from braking to pump up the pressure .If the air pressure could just get you moving it would have to save fuel

 

Hydraulic fluid works much better than any air pump. Hydraulic stop/start systems are being experimented with at this time. They really are only practical on stop/start vehicles like a garbage truck or mail truck.

 

Hadnt thought about liquid pressure power. True only a small amount of compressed hydo fluid can store alot of energy

 

You can't compress liquids. That is why you pressure test vessels with water instead of air. If the vessel fails the test full of water, there is a small pop and the water drains out, If a vessel fails full of air, there is a major explosion. Liquids under pressure don't store any energy. They can transmit energy as in a hydraulic ram, but not store it.

 

I watched the "fuel" episode of future cars tonight. The fact that they closed posing the posibility that the air car could lead to a perpetual motion machine pretty much said it all. The entire show was full of a great deal of wishful thinking.