Here's an old concept - a car powered by compressed air. Powered by an air motor, it is a dependable piece of technology. Air motors are used for everything from the drills in dentists offices (not the tube connected to the drills) to the torque wrenches in the brake shop with that distinctive 'brrt-brrt' sound. The problem? Where does compressed air come from? Sure air is free, but compressing it to high pressure is not. This is the 2nd time I've seen Hot Air highlight the compressed air-powered car. The first time was back in May of 2009.From Hot Air yesterday: Video: The "Air Pod". The video from CNN:
The air powered car has the same drawback as the fuel cell minus the technological limitations. In the fuel cell, you have to manufacture the hydrogen, which is energy intensive. In the air-powered car, the pressure of the air has to be converted via a compressor. The problem is, it takes more energy to pressurize air than you will ever get out of the pressurized air itself. It's that inconvenient conservation of energy principle. You know - energy can neither be created nor destroyed.
For one thing, the pressure would have to be extremely high to pack enough energy into a small volume. An adiabatic/isentropic compressor would theoretically (assuming a reversible process thereby pushing the 2nd law to the limit) yield be about 70% efficiency. Realistically, let's say closer to 60%. That's just to get the compressed gas. When the pressure is discharged from the air motor onboard, that's going to be about 60% of that. So 60% of 60% is 36%. In addition, there will be losses in the transmission, driveshaft, parasitic losses, etc. You're now down in the 20's (let's just say 25% for the sake of argument), which incidentally is where spark-ignition internal combustion vehicles reside.
Worse yet though is that the roughly 25% efficiency ignores where the electricity originally comes from - mostly coal. Coal power plants are themselves only about 33% efficient. Plus transmission losses and that 25% energy efficiency is now itself only 25% of the original coal energy. The true efficiency of the compressed air-powered vehicle is an abysmal 6%. SIX PERCENT! Electric cars like the Chevy Volt (not withstanding the ludicrous EPA rating) are themselves about 25% overall efficient, mainly because their method of storage of electric energy - chemical potential in batteries rather than pressure potential in gas - is far more efficient in charging and discharging (85-90%).
The environmental benefits of air-powered cars have no basis in science. Ed Morrissey ends his piece with this:
The air powered car has the same drawback as the fuel cell minus the technological limitations. In the fuel cell, you have to manufacture the hydrogen, which is energy intensive. In the air-powered car, the pressure of the air has to be converted via a compressor. The problem is, it takes more energy to pressurize air than you will ever get out of the pressurized air itself. It's that inconvenient conservation of energy principle. You know - energy can neither be created nor destroyed.
For one thing, the pressure would have to be extremely high to pack enough energy into a small volume. An adiabatic/isentropic compressor would theoretically (assuming a reversible process thereby pushing the 2nd law to the limit) yield be about 70% efficiency. Realistically, let's say closer to 60%. That's just to get the compressed gas. When the pressure is discharged from the air motor onboard, that's going to be about 60% of that. So 60% of 60% is 36%. In addition, there will be losses in the transmission, driveshaft, parasitic losses, etc. You're now down in the 20's (let's just say 25% for the sake of argument), which incidentally is where spark-ignition internal combustion vehicles reside.Worse yet though is that the roughly 25% efficiency ignores where the electricity originally comes from - mostly coal. Coal power plants are themselves only about 33% efficient. Plus transmission losses and that 25% energy efficiency is now itself only 25% of the original coal energy. The true efficiency of the compressed air-powered vehicle is an abysmal 6%. SIX PERCENT! Electric cars like the Chevy Volt (not withstanding the ludicrous EPA rating) are themselves about 25% overall efficient, mainly because their method of storage of electric energy - chemical potential in batteries rather than pressure potential in gas - is far more efficient in charging and discharging (85-90%).
The environmental benefits of air-powered cars have no basis in science. Ed Morrissey ends his piece with this:
Still, if it's cheap enough (CNN doesn't mention the price), it might not be a bad option for the densest urban areas and singles who live there.Who's going to pay for all of the electricity of which only a small percentage will get you around? An electric vehicle would be better. Put a plastic chassis around a golf cart for Pete's sake!
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