Are compressed-air-powered cars practical?

December 30, 2008 by Walter Schneider.

A friend sent to us some information on compressed-air-powered cars.  Those are being produced and being put on the market in India.  A search for “compressed-air-powered cars” provides about 1,200 entries on the search-return list.  Here is the first of the entries on the list:

Air-Powered Car Coming to U.S. in 2009 to 2010 - Zero Pollution …
22 Feb 2008 … A New York-based startup wants to make the first air-powered car to hit US roads a $17800, 75-hp equivalent, 96-mph, four-door version of …

The price range of the Indian compressed-air-powered cars is from about $3,000 to $17,000, depending on size of a car and the number of passengers it is designed to carry.

At first glance, the idea to use compressed air to power cars is great, but I have a couple of concerns, one easily explained, the other requiring a lot more words.

1. If a tank containing that compressed air explodes, would that cause less damage than having a terrorist explode a car bomb?

It can take less than gallon of gasoline to blow up a house, but when a gasoline tank leaks, that is not necessarily a catastrophe, unless the conditions are right, not even if a gasoline tank splits wide open.  If the equivalent amount of energy in the form of compressed air is released all at once, that would instantaneously kill the occupants of the car that carried it, plus it would possibly kill everything for some distance around.  It would destroy much property in the vicinity of the car that exploded.

2. Ethanol is more than joke, it is a scam.  Ethanol consumes almost twice as much energy for its production than it contains.  Therefore it also causes far more pollution than it is said to save.  Furthermore, the production of Ethanol is taxpayer subsidized.  In addition, it caused food prices to rise enormously and thereby caused an increase of starving people in the world. Comparable issues come into play with cars powered by electrical energy that has been stored in batteries and with compressed-air-powered cars.  Neither of the latter alternative energy sources would have the devastating consequences for poor people that ethanol has.  After all, the corn required to tank up a family car with ethanol just once could feed a family for a whole year.

However, what is used for energy to power those compressors that put compressed air into cars?  I have no idea on the efficiency of the compressors and of the engines that use compressed air.

The reality of that is that to propel a car requires energy.  That is a considerable amount of energy.  The energy used to compress air to the required pressure must equal the energy used by the car plus the energy wasted by the car plus the energy wasted in compressing the air.

That would be about equivalent to the energy required to power a car with electrical energy from a battery (energy wasted by the battery charger when charging a battery, plus energy lost in the transition from electrical to chemical energy in the battery when it is being charged, plus energy lost when converting chemical energy in the battery to electrical energy in the car’s electrical motor, plus the energy lost in the electric motor that drives the car, plus energy lost in the transmission, plus the energy required to propel the car.)  All of those losses are somewhat compensated for by using kinetic energy from decelerating and braking to produce chemical energy stored in the car’s battery, but that process, too, suffers from conversion losses.  All of those losses are quite considerable.  Only about ten percent or a bit more of the electrical energy for use by battery-powered cars  that is injected at the generating source into the transmission and distribution network will actually result in putting and keeping the car in motion.

Where does the energy for compressing air come from?  What are the total energy requirements, plus all of the applicable energy losses, to put a car into motion and keeping it moving?  Will each service station have a fossil-fuel-powered compressor, or will that compressor be using electrical energy from the network (with transmission and distribution losses that are very similar to those in the case of battery-powered cars)?

Furthermore, battery-powered cars recover some of the kinetic energy generated by decelerating or braking, to convert it to chemical energy that is stored in their batteries, thereby reducing the overall energy losses of those cars a bit.  However, I see nothing comparable along those lines in the descriptions of air-powered cars.

Without examining all of those issues it is not possible to determine whether compressed-air-powered cars are more efficient or cheaper as far as energy consumption goes than battery-powered cars are.  Anyone wishing to make a profit from the production or sale of compressed-air-powered cars is not likely to tell anyone about peripheral costs of the generation and distribution of energy required for converting and storing of that energy in the form of compressed air.

There is no question that as far as the engineering and production of air-powered cars is concerned, air-powered cars will not only be cheaper to produce and to dispose of, but their production and ultimate disposal will be far more environmentally-friendly.

I have great doubts that the overall energy requirements (including all of the losses of energy at the various stages of transporting energy and the applicable conversion processes) of either air-powered or battery-powered cars will be able to compete with or come close to the relatively low cost of the transportation, distribution and consumption of energy used by fossil-fuel-powered cars.

So far there is no cheaper or more effective way to store, distribute and use energy for cars than in the form of the chemical energy contained in fossil fuel.

Lastly, the bottom line: What will the cost be per km of driving for the three different solutions that need to be compared.  Cost subsidies such as those used for the production of ethanol come out of tax revenues and require taxpayers to pay higher taxes.  There is no such thing as a free lunch.  Not only that, but the government will want to collect the taxes it presently derives from fossil-fuel consumption.   The production and use of compressed air will have to be taxed to an extent that produces at least the amount of tax revenues collected from the use of fossil fuels.

Battery-powered cars may cause the electricity rates to go up.  Existing distribution networks require massive upgrading if more than one household in every seven will use battery chargers to charge the batteries in their cars.  In addition, if the distribution networks need to be upgraded, then you can be sure that the transmission network needs to be upgraded as well.  One single transmission line from Fort MacMurray to the US border costs a few billion dollars, and I shudder to think of how much money we would need for many such construction projects if we wish to replace the distribution of energy in the form of fossil fuel with a system of distribution in the form of anything else.  Anything other than fossil fuel requires electric energy in massive quantities.  It even requires the construction of many new power plants at the cost of about $1.6 billion each.

I am certain that some comparable concerns apply to compressed-air-powered cars.  Somehow, the enormous amount of energy required by all of our cars needs to be transported to all those service stations we need to equip and provide for that.  It is all in place now.  I doubt is very much that we can afford to replace it.  Until we can, both, compressed-air- or battery-powered cars will be a curiosity that is impractical and too expensive to have for all.

By the way, we did not wish you a Merry Christmas.  To make up for that, I offer you a story of a modern Christmas that I am sure you will enjoy.  The story will drive home the point of how much things have changed over the last 2000 years and that, no matter how hard we all tried to have Paradise on Earth, the harder we tried, the farther away from it we got, even though we now live on average a lot longer than people did then.

Our best wishes for the new year to you and yours,

Walter (and Ruth)

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