Compressed air cars - good or bad for cyclists?

Lawrie9 · Post by **Lawrie9** » 18 Feb 2008, 5:39pm

I heard on the radio that a French chap has invented a car powered by compressed air. I thought this is great for cyclists - no more fumes from petrol and diesel engines but then realised, how are the government going to tax air. The loss of tax revenue would be huge so the roads would be in an even poorer state than they are now. And the number of vehicles on the road would rocket so it would very much be a double edged sword.
Hope you all had a good weekend on yer bikes. I cycled for 3 hours on Saturday afternoon and the only form of life I encountered was a fox and some buzzards. No humanity whatsoever..Ah what bliss. Also saw 2 foot long icicles - is this a record?

Ben Lovejoy · Post by **Ben Lovejoy** » 18 Feb 2008, 5:49pm

The govt will find a way to tax air - count on it ...

Deckie · Post by **Deckie** » 18 Feb 2008, 6:55pm

They already do - for this anyway. The air has to be compressed first, this requires electricity to power the compressor (or fossil fuel if not electric, but it all boils down to the same thing as the electricity has to be produced somehow...).

So for the compressed air car the air in its compressed state acts as the store of energy, or battery if you like. Only a chemical battery (lead acid, MiNm, Li) is far more efficient at storing and releasing energy than compressed air. Electric storage and drive can be 50%+ efficient, compressed air may struggle to be 20 - 30% efficient.

jocks · Post by **jocks** » 19 Feb 2008, 3:42pm

Deckie wrote:They already do - for this anyway. The air has to be compressed first, this requires electricity to power the compressor (or fossil fuel if not electric, but it all boils down to the same thing as the electricity has to be produced somehow...).

So for the compressed air car the air in its compressed state acts as the store of energy, or battery if you like. Only a chemical battery (lead acid, MiNm, Li) is far more efficient at storing and releasing energy than compressed air. Electric storage and drive can be 50%+ efficient, compressed air may struggle to be 20 - 30% efficient.

Actually the overall efficiency of the electrical charge/discharge system is a maxuimum of 40% according to the laws of thermodynamics. A further problem with this is the batteries are an ecological disaster in themselves e.g. lead, rare metals, acids etc. All that electrical vehicles do is shift the problem somewhere else. The compressed air car is slightly better than electrical because it can be refilled quicker and does not necessitate cables running across pavements.

The simple solution is to not use your car, but we are all cyclists and we know this already!

hamster · Post by **hamster** » 19 Feb 2008, 4:10pm

I'm intrigued at the 40% figure - why?

Deckie · Post by **Deckie** » 19 Feb 2008, 5:35pm

The car may be faster to fill from a compressed air reservoir held somewhere, for example on a garage forecourt, but the compressor pump would have to run 24 hours a day to keep the reservoire full at a higher pressure than the car reservoir requires. That would burn an awful lot of fuel / electricity.

Air compressor reservoirs (air receivers) have to be serviced annually for H & S and so are generally well looked after, even so they cannot hold pressure overnight. The same would be true of the proposed filling points and the cars. You would have to fill up at the start of every journey.

fullupandslowingdown · Post by **fullupandslowingdown** » 19 Feb 2008, 6:07pm

charging a battery is only between 70 and 80% efficent
discharging it is only between 50 and 70% efficent, this been because the 'last few drops' aren't of use. the weight of batterys is signifcant so the are using some 20 to 30% of their power just to propel themselves. So by the time you have done you are lucky to get an overal 40% figure from mains to road.

Ben Lovejoy · Post by **Ben Lovejoy** » 19 Feb 2008, 6:20pm

As a matter of idle curiosity, how does the efficiency of a cyclist compare?

If we take into account all the energy required to grow food, transport it, cook it and consume it. what's the overall efficiency?

Ben

reohn2 · Post by **reohn2** » 19 Feb 2008, 6:25pm

Compressed air cars,my mind is running amok

monster · Post by **monster** » 19 Feb 2008, 6:59pm

"there is potential to double the primary energy efficiency using electric drivetrains in vehicles, such as BEVs, HEVs or FCEVs, compared with present ICEVs. All vehicles with an alternative powertrain have the potential for higher primary energy efficiency than vehicles with an improved conventional powertrain."

Primary energy efficiency of alternative powertrains in vehicles
Energy, Volume 26, Issue 11, November 2001, Pages 973-989
Max Åhman

i.e. electric cars are twice as efficient as petrol cars.
-also they can be run from renewables so they can be 100% carbon neutral.

andrew_s · Post by **andrew_s** » 19 Feb 2008, 6:59pm

Ben Lovejoy wrote:As a matter of idle curiosity, how does the efficiency of a cyclist compare?

If we take into account all the energy required to grow food, transport it, cook it and consume it. what's the overall efficiency?

Ben

But do you actually eat any more that you would if you weren't cycling?
Or do you just expend less energy hauling excess lard around?

Ben Lovejoy · Post by **Ben Lovejoy** » 19 Feb 2008, 7:07pm

andrew_s wrote:
Ben Lovejoy wrote:As a matter of idle curiosity, how does the efficiency of a cyclist compare?

If we take into account all the energy required to grow food, transport it, cook it and consume it. what's the overall efficiency?

But do you actually eat any more that you would if you weren't cycling?

Yes. TANSTAAFL - the energy has to come from somewhere.

Ben

monster · Post by **monster** » 19 Feb 2008, 7:10pm

cyclists will be very energy efficient because we are light weight and don't go very fast. also because we have to do the work our selves we actively conserve our energy during the ride.

however our muscles make inefficient motors and our food is a very inefficient fuel. the best option is electric bikes.

professorlandslide · Post by **professorlandslide** » 19 Feb 2008, 7:46pm

Ben Lovejoy wrote:The govt will find a way to tax air - count on it ...

read your water bill small print... They charge you to take away the rainwater that falls on your house and then sell it back to you. Its only a small step..

Technically i suppose, vehicle tax is an air tax - its a tax on how much rubbish you pump into the air from your engine...!

Tom Richardson · Post by **Tom Richardson** » 19 Feb 2008, 7:46pm

Ben Lovejoy wrote:
andrew_s wrote:
Ben Lovejoy wrote:As a matter of idle curiosity, how does the efficiency of a cyclist compare?

If we take into account all the energy required to grow food, transport it, cook it and consume it. what's the overall efficiency?

But do you actually eat any more that you would if you weren't cycling?

Yes. TANSTAAFL - the energy has to come from somewhere.

Ben

not so much where the energy comes from but where it goes to. I agree with Andrew - I eat the same whatever but if I don't cycle I get fat.
It seems to be a common outcome