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It sounds like a good idea: Use electricity to compress air, stuff it in a tank and use the power expelled by the air's release to power a vehicle. Seems like a good idea, certainly a lot easier to understand than nano-constructed cathodes on a lithium ion cell. And several companies have been actively attempting to build cars powered by conpressed air for quite some time. We at EcoGeek have been excited about them. The two biggest of these companies are MDI, a French company and Tata Motors, India's largest car company.
But I have bad news. Today, here at EcoGeek, we are declaring the air car dead. It's a question of physics, every conversion from one type of energy to another decreases efficiency. With battery electric vehicles, energy is converted into electricity and electricity is converted to motion. With air cars, energy is converted into electricity, electricity into compressed air and then compressed air into motion. Because of this, compressed air cars will always be less efficient than electric vehicles.
Even more problematic, no air car has ever been developed that can reach highway speeds and no air car has even been demonstrated to have a range of more than 10 kilometers. Promises were made, and with the entrance of Tata Motors to the fray, we thought there might be some truth to the claims.But Tata's goal of a 2008 release of an air car has, obviously, not been met. In 2009, Tata stated that the short range of the cars and issues with keeping them from freezing up (when compressed air is decompressed, temperatures drop dramatically) were proving them impractical.
So, I'm sorry my friends, we're all going to have to be happy with the much more technologically confusing (though also much more efficient) battery electric vehicles. The good news is, with the Leaf and the Volt already hitting the road, that's one technology that definitely isn't vaporware.
More on the disadvantages of air cars.
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written by "Crunchy" Steve Jay, September 01, 2010
You've missed out CRUCIAL steps in the electric car which bring it back into line with the air car.
Electricity at "the socket" is converted into a chemical potential (charging), that chemical potential is converted into electricity and that electricity is converted into motion. Just as many steps.
The air car, being lower, more consistently mechanical technology has several construction and disposal advantages, too. (Lower tech waste, more recyclable when worn out, fewer filthy chemical processes to produce the energy storage system.)
Electric cars have a torque advantage over compressed air cars, so there's been little incentive to make EVs smaller and lighter, which is still the best way to make a car more energy efficient. For example, my 1970s mini moke with a normally aspirated medium compression engine had way better fuel economy than my Holden Barina with electronic injection. Both had a similar sized engine, and the Barina had a very efficient engine, but the Moke weighed half as much.
So, at this stage, while air cars may not be gaining popularity like electrics, it has more to do with major car manufacturer marketing than being greener. Now, don't get me started on lithium batteries and how green they are not ;-)
Electricity at "the socket" is converted into a chemical potential (charging), that chemical potential is converted into electricity and that electricity is converted into motion. Just as many steps.
The air car, being lower, more consistently mechanical technology has several construction and disposal advantages, too. (Lower tech waste, more recyclable when worn out, fewer filthy chemical processes to produce the energy storage system.)
Electric cars have a torque advantage over compressed air cars, so there's been little incentive to make EVs smaller and lighter, which is still the best way to make a car more energy efficient. For example, my 1970s mini moke with a normally aspirated medium compression engine had way better fuel economy than my Holden Barina with electronic injection. Both had a similar sized engine, and the Barina had a very efficient engine, but the Moke weighed half as much.
So, at this stage, while air cars may not be gaining popularity like electrics, it has more to do with major car manufacturer marketing than being greener. Now, don't get me started on lithium batteries and how green they are not ;-)
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written by karthik, September 02, 2010
Maybe the air compression technology could be used for motorcycles or three wheelers which are used for public transport in developing countries??
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written by karthik, September 02, 2010
Or maybe this technology cannot be used as a stand alone. It can only be used to be combine with other technologies to make that that technoloy more efficient....if not in automotive, atleast in other sectors.
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written by Jerry, September 02, 2010
There ARE several obstacles to overcome with air cars that are unique to them and not other renewables, such as engine freezing up. Might I add that when gas powered engines were coming into play, many very similar obstacles also came up and were overcome. Gas engines heated up just as dramatically or more than air engines cool down, and engine design (and other designs like water cooling) took many years, indeed decades, to adapt. Range was also limited, but more efficiency and more abundance of gas led to much increased range and more practical designs.
Also, it is not necessarily less efficient than an all-electric. Compressed air can be made easily and sustainably through many sources like solar and wind, without the need for fancy batteries, inverters, etc. They can have simpler materials involved, giving a lower footprint of production, and have more easily managed and recyclable waste at the end stage. Compressed air can in theory do as much work coming out as was imbued it going into the tank. The trick is: can we harvest it effectively?
You may be right that the air car is dead as electrics have come so far. But I'm inclined to agree with the responder above that this is not due to an intrinsic deficiency of air as a power source but rather from a capital/political and marketing perspective of the big auto manufacturers.
Also, it is not necessarily less efficient than an all-electric. Compressed air can be made easily and sustainably through many sources like solar and wind, without the need for fancy batteries, inverters, etc. They can have simpler materials involved, giving a lower footprint of production, and have more easily managed and recyclable waste at the end stage. Compressed air can in theory do as much work coming out as was imbued it going into the tank. The trick is: can we harvest it effectively?
You may be right that the air car is dead as electrics have come so far. But I'm inclined to agree with the responder above that this is not due to an intrinsic deficiency of air as a power source but rather from a capital/political and marketing perspective of the big auto manufacturers.
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written by M Cooper, September 02, 2010
I alway thought a compressed air car would be more efficient if you could use wind turbines to compress the air directly (i.e. connect the turbine to the compressor with no electricity being involved).
This would remove the lossy conversions of mechanical to electrical energy and back again. Electricity and air both suffer transmission losses, but air would be easier to store in large quantities and this is important for an intermittant energy source like wind. Furthermore, storing compressed air is efficient, whereas storing electricity incurs additional conversion losses in the battery.
This would remove the lossy conversions of mechanical to electrical energy and back again. Electricity and air both suffer transmission losses, but air would be easier to store in large quantities and this is important for an intermittant energy source like wind. Furthermore, storing compressed air is efficient, whereas storing electricity incurs additional conversion losses in the battery.
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written by Deki, September 02, 2010
There is no official information that they gave up (http://www.mdi.lu/english/actualite.php)
I like idea...
I like idea...
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written by BenHead, September 02, 2010
Took the words right out of my mouth, Crunchy Steve. Clearly batteries ARE more efficient than compression, but they're not NECESSARILY so.
Event ultracaps, which DO keep the energy as electrical potential, aren't NECESSARILY more efficient: the devil's always in the details.
Event ultracaps, which DO keep the energy as electrical potential, aren't NECESSARILY more efficient: the devil's always in the details.
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written by Jarko, September 02, 2010
Yep, the air car is just a bunch of hot air.
And it's not because of marketing ...it's physics. The air car will never be efficient enough...engineers/scientists were telling us this years ago, but some people (like the ones here) didn't want to believe it.
And there might be the same number of conversion steps in a battery vs. air car. BUT not all conversion are equal. It's not that simple.
And it's not because of marketing ...it's physics. The air car will never be efficient enough...engineers/scientists were telling us this years ago, but some people (like the ones here) didn't want to believe it.
And there might be the same number of conversion steps in a battery vs. air car. BUT not all conversion are equal. It's not that simple.
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written by Charlie, September 03, 2010
The energy density per kilogram of compressed air is about twice that of a lead acid battery and a bit less than a lithium battery (assumes ultra-lightweight carbon fiber composite type 4 tank, and 350 bar/ 5000psi pressure).
The problem is that batteries and electric motors are much more efficient than air motors and high pressure compressors.
It is very difficult to make efficient air motors that operate over a wide range of input pressures. Most difficult is the 5000psi high pressure stage. MDI avoids this by first reducing the pressure to 20 bar / 290psi using a pressure regulator. This wastes about 1/2 of the stored energy, eliminating any joule/kg energy density advantage compared to lead acid batteries.
If MDI finally, after 10 years of promising production "next year", delivers a car, it will most likely have a range around 100km/60 miles.
Recharging can be very fast if you have a large tank of 5000 psi air sitting around. Otherwise, you must have a noisy, hot, high maintenance compressor similar to that found at scuba dive shops.
Hopefully, MDI will at some point change their business model of one based on selling franchises and licenses and raising investment money, and finally actually build and sell a vehicle.
I'm not holding my breath.
The problem is that batteries and electric motors are much more efficient than air motors and high pressure compressors.
It is very difficult to make efficient air motors that operate over a wide range of input pressures. Most difficult is the 5000psi high pressure stage. MDI avoids this by first reducing the pressure to 20 bar / 290psi using a pressure regulator. This wastes about 1/2 of the stored energy, eliminating any joule/kg energy density advantage compared to lead acid batteries.
If MDI finally, after 10 years of promising production "next year", delivers a car, it will most likely have a range around 100km/60 miles.
Recharging can be very fast if you have a large tank of 5000 psi air sitting around. Otherwise, you must have a noisy, hot, high maintenance compressor similar to that found at scuba dive shops.
Hopefully, MDI will at some point change their business model of one based on selling franchises and licenses and raising investment money, and finally actually build and sell a vehicle.
I'm not holding my breath.
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written by tgp, September 04, 2010
Based on current battery technologies, Im still inclined to be more optimistic with compressed air.
1. batteries discharge over time while tanks (assuming no leaks), will keep their pressure indefinitely.
2. current batteries degrade over time, whether used or not. You still will have to buy new batteries. It's not just the number of charging but the natural degradation of the chemicals. I have yet to see these new nanotubes though and see how they truly affect battery performance.
3. While lithium is incredibly abundant in nature, unfortunately, other RARE METALS are used in the manufacture of these batteries. Which I believe are currently not recyclable. Yet.
4. Lead acid batteries are 97% recyclable so far. But still very heavy.
5. Compression technologies are easier to create simply by changing their physical and mechanical designs compared to innovations of batteries.
In the final analysis, though the air car seems like a dream, it still remains an excellent concept that is currently limited by design.
1. batteries discharge over time while tanks (assuming no leaks), will keep their pressure indefinitely.
2. current batteries degrade over time, whether used or not. You still will have to buy new batteries. It's not just the number of charging but the natural degradation of the chemicals. I have yet to see these new nanotubes though and see how they truly affect battery performance.
3. While lithium is incredibly abundant in nature, unfortunately, other RARE METALS are used in the manufacture of these batteries. Which I believe are currently not recyclable. Yet.
4. Lead acid batteries are 97% recyclable so far. But still very heavy.
5. Compression technologies are easier to create simply by changing their physical and mechanical designs compared to innovations of batteries.
In the final analysis, though the air car seems like a dream, it still remains an excellent concept that is currently limited by design.
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written by Gene, September 05, 2010
Hank,
Maybe, instead of Electric to air, it should be air to electric? It would seem to me that Compressed air would be great for charging a battery or capacitor. But I'm not any kind of physicist.
Maybe, instead of Electric to air, it should be air to electric? It would seem to me that Compressed air would be great for charging a battery or capacitor. But I'm not any kind of physicist.
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written by Adam St. John, September 07, 2010
The same argument may also be applied to fuel cells.
Energy -> hydrogen / hydrogen storage method => Converted back to electricity by fuel cell -> motion.
Just sayin...
Energy -> hydrogen / hydrogen storage method => Converted back to electricity by fuel cell -> motion.
Just sayin...
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written by Niels, September 09, 2010
Frankly the whole idea of using compressed air to drive a vehicle is a load of crap. As an engineer I know that typically 8% of the energy used to create compressed air goes into compressed air and the rest into waste heat (80% of the electrical energy going into the compressor itself is released as waste heat, other losses are from electricity distributed to the compressor and from the electricity production itself). Of course you could recover heat and all that stuff, but it won't create more compressed air per kWh going into the compressor.
Knowing this (and in the industry, compressed air is known as one of the most expensive energy carriers), it would make no sense whatsoever, economically or physically to use compressed air to propel a car or any other vehicle.
Knowing this (and in the industry, compressed air is known as one of the most expensive energy carriers), it would make no sense whatsoever, economically or physically to use compressed air to propel a car or any other vehicle.
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written by Gordo, September 16, 2010
Why not recognise the facts before wasting any more energy and ink on this topic. Some of us know that the incansdescent light is dead. 3% light 97% heat? Compressed air car is a close second. 12% air 88% waste heat and that's only going in. It's pretty much the same coming out (and it freezes). Why carry a tonne of batteries around in a car that struggles for range and economy? Let's have a think about making the electricity on board then we can forget the compressed air and the battery?
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written by Glen McDiarmid, September 16, 2010
IMO, compressed air technology is still in its infancy. I've been following it for years, and have come up with a few ideas myself. Check these out:
1. Instead of using the pressure of compressed air to create kinetic energy, use the decrease in temperature to cool down one side of a thermovoltaic cell. The other side is positioned to be a heat sink for an electric motor that drives the vehicle. It's a fact that (from memory) only one sixth of the energy of compressed air is available when using the pressure. The remainder is "wasted" as cold. Obviously, we will be using the "waste" heat from the electric motor and the "waste" cold from the compressed air, to create electricity when and where needed. By using a series of thermovoltaic cells, we can sap out a major proportion of the energy that is possible to be gotten from the compressed air.
2. Step (1) above increased efficiency of conversion. Next let's tackle the storage problem. As someone above described, it's possible to store 5000 PSI in a tank. If we had two of these each with 1000 litre capacity, then we'd be able to drive twice as far right? Okay, so now let's make one of them 5 percent larger. And during manufacture, let's place the smaller tank inside the larger one. Fill the outer tank with 5000 PSI, and fill the inner tank with 10000 PSI. It's the strength of the walls of each tank that limits how much pressure can be stored. The walls of the outer tank sense 5000 PSI. Same with the inside tank. So now for 5 percent more volume taken up in the car, we've got 95 percent more energy. But let's not stop there. Let's add a few more tanks, and give the vehicle 1000 KM range. That's plenty for sure.
3. Distribution: use multiple pipes, use pressure multiple pressure sensors to detect if/when a pipe bursts. Shut off supply to that pipe and let the others take up the slack.
4. Where do we get it? Forget about using electricity to compress air. Use temperature differences, a series of electronically controlled valves, and a series of concentric cylinders (somewhat similar to (1) above) and you've got a solid state air compressor. It basically works like this: heat the inside of cylinder (A) and the outside of cylinder (B), while you cool the outside of cylinder (A) and the inside of cylinder (B). If the cylinders start with equal volume and pressure, this will move air from (A) into (B). Reverse, and allow (A) to draw air from ambient, while (B) moves air into (C) and so forth. (A) is the outermost cylinder, whilst (Z) is innermost. With each step comes a pressure difference. The temperature difference can be derived from whatever source you like. OTC, solar, industrial waste, whatever.
5. Where do we store it? For mass storage, anchor a large flexible container to the bottom of the ocean, where the pressures are multiple tons per square inch. Pump air into container. Container increases in size so that equal pressures exist inside and outside of said container walls. Dangers? My answer:
"Big bubbles, no troubles".
1. Instead of using the pressure of compressed air to create kinetic energy, use the decrease in temperature to cool down one side of a thermovoltaic cell. The other side is positioned to be a heat sink for an electric motor that drives the vehicle. It's a fact that (from memory) only one sixth of the energy of compressed air is available when using the pressure. The remainder is "wasted" as cold. Obviously, we will be using the "waste" heat from the electric motor and the "waste" cold from the compressed air, to create electricity when and where needed. By using a series of thermovoltaic cells, we can sap out a major proportion of the energy that is possible to be gotten from the compressed air.
2. Step (1) above increased efficiency of conversion. Next let's tackle the storage problem. As someone above described, it's possible to store 5000 PSI in a tank. If we had two of these each with 1000 litre capacity, then we'd be able to drive twice as far right? Okay, so now let's make one of them 5 percent larger. And during manufacture, let's place the smaller tank inside the larger one. Fill the outer tank with 5000 PSI, and fill the inner tank with 10000 PSI. It's the strength of the walls of each tank that limits how much pressure can be stored. The walls of the outer tank sense 5000 PSI. Same with the inside tank. So now for 5 percent more volume taken up in the car, we've got 95 percent more energy. But let's not stop there. Let's add a few more tanks, and give the vehicle 1000 KM range. That's plenty for sure.
3. Distribution: use multiple pipes, use pressure multiple pressure sensors to detect if/when a pipe bursts. Shut off supply to that pipe and let the others take up the slack.
4. Where do we get it? Forget about using electricity to compress air. Use temperature differences, a series of electronically controlled valves, and a series of concentric cylinders (somewhat similar to (1) above) and you've got a solid state air compressor. It basically works like this: heat the inside of cylinder (A) and the outside of cylinder (B), while you cool the outside of cylinder (A) and the inside of cylinder (B). If the cylinders start with equal volume and pressure, this will move air from (A) into (B). Reverse, and allow (A) to draw air from ambient, while (B) moves air into (C) and so forth. (A) is the outermost cylinder, whilst (Z) is innermost. With each step comes a pressure difference. The temperature difference can be derived from whatever source you like. OTC, solar, industrial waste, whatever.
5. Where do we store it? For mass storage, anchor a large flexible container to the bottom of the ocean, where the pressures are multiple tons per square inch. Pump air into container. Container increases in size so that equal pressures exist inside and outside of said container walls. Dangers? My answer:
"Big bubbles, no troubles".
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written by John Cossham, September 16, 2010
I think this probably proves the author wrong
http://www.youtube.com/watch?v=uVIwropRMME
but of course, I could be wrong...
Watch and make up your own mind!
http://www.youtube.com/watch?v=uVIwropRMME
but of course, I could be wrong...
Watch and make up your own mind!
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written by Mike D, September 16, 2010
How about electric cars without a lot of batteries? Instead, highways will have power strips in the middle of each lane, and a sensor could be lowered from the underneath of the car to contact it and draw power. That way the car would need only minimal batteries (to drive short distances, or change lanes, etc), but be able to drive unlimited miles on these "powered" roadways. We'd save a fortune on car cost and battery weight. And centralized power sources would be more efficient than everyone needing hundreds of lbs of batteries. Obviously there are drawbacks - cost of installation and infrastructure, and risk of electricution - but I'm sure there could be solutions to these obstacles. Maybe the power strip has a hard plastic covering that slides aside when a sensor is close. Any thoughts?
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written by Poly Endrasik, September 17, 2010
OK, I admit that I am not an engineer type but I always wondered why you couldn't use the compressed air to pressurizer hydralic fluid and power hydralic motors which I understand are much more efficient. You cycle back and forth between reservoir and pressure chamber to minimize oil (weight), Since it was said air engines are prone to freeze up (something I didn't know till now) and hydralic motors generate hot "oil" then there should be a thermal cancellation effect if done right. I am probably missing some major engineering facts why it wouldn't work but that my two-cents anyway. OH, the hydralic motors could be used to repressurize the air under braking too.
Have a great day all.
Have a great day all.
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written by Bernard, September 18, 2010
The current thermal engine car has energy efficiency around 10%, computed by many independant studies (OECD,...).
Compressed air and battery car are almost on par, both being at least 2 times more efficient than thermal engine car.
But compressed air is a lot cheaper, because batteries use a lot of natural ressources to make them : compressed air will allow more people to save energy.
With a car battery at 15000€ every 5 years, you can pay 7500 full tanks of air for airpod at 2€/filling (being pessimistic), that is 750 000km (at 100km/filling).
But the main advantage is not on the road, but at home : the small cost of air tank allow you to have some tanks at home (and at work...) that solar panels and wind turbine can fill in when sun and wind are available. In France, this would be 20% saving on electricity centralised production and distribution, and 19,6% saved on VAT...
Compressed air and battery car are almost on par, both being at least 2 times more efficient than thermal engine car.
But compressed air is a lot cheaper, because batteries use a lot of natural ressources to make them : compressed air will allow more people to save energy.
With a car battery at 15000€ every 5 years, you can pay 7500 full tanks of air for airpod at 2€/filling (being pessimistic), that is 750 000km (at 100km/filling).
But the main advantage is not on the road, but at home : the small cost of air tank allow you to have some tanks at home (and at work...) that solar panels and wind turbine can fill in when sun and wind are available. In France, this would be 20% saving on electricity centralised production and distribution, and 19,6% saved on VAT...
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written by adenilsom, October 06, 2010
eu acho que os poderosos do petroleo deram um bilhão pro cara que inventou o carro a ar desistir do projeto ou mesmo ameaçaram a familia dele ja que o mundo e movido pelo petroleo e não e do interese dos poderosos do petroleo que voce deixe de abastecer as bonbas de gasolina A retomada do conceito deu-se em meados da década de 1990, também por pioneirismo da GM que fabricou o EV1, seguida pela Ford (Think e Ranger), Honda (EV Plus), e Toyota (RAV4). Todos esses modelos eram vendidos apenas através de leasing, custando entre 250 e 600 dólares mensais. No início da década atual, entretanto, todas as montadoras resolveram retirá-los de circulação e, por força do mesmo sistema de leasing, exigiram que os consumidores os devolvessem.
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Pity about the air cars, though. That'd've been awesome. And I'm pretty sure there's a rule about double contractions somewhere in the Big Grammar Bible.