Berkeley Engineers Have Some Bad News About Air Cars

cheeks5965 writes "We've argued before over compressed air vehicles, a.k.a. air cars. Air cars are an enchanting idea, providing mobility with zero fuel consumption or environmental impacts. The NYTimes' Green Inc. blog reports that the reality is less rosy. New research from UC Berkeley and ICF International puts a period at the end of the discussion, showing that compressed air is a very poor fuel, storing less than 1% of the energy in gasoline; air cars won't get you far, with a range of just 29 miles in typical city driving; and despite appearing green the vehicles are worse for the environment, with twice the carbon footprint as gasoline vehicles, from producing the electricity used to compress the air. Given these barriers, manufacturer claims should definitely be taken with a grain of salt."

Comments

At least they don't pollute the city directly

[jandrese]

There appear to be two primary advanages of these cars: They're cheap to make and they don't directly pollute the city air. If the power plant is downwind they could actually improve the air quality in the city. You also get "free" AC, although heating the car is an issue. Since these are primarily targeted at cities like Mumbai the cooling is more important anyway.

Re:At least they don't pollute the city directly

[wizardforce]

What benefits do these air powered cars have that aren't significantly exceeded by electric vehicles?
The range of these cars is 1/5 of electric cars *and* is less efficient.

Re:At least they don't pollute the city directly

[Sique]

They were first developed to be used in environments, where sparks could lead to an explosion (e.g. chemical plants or refineries). There you can't use electric cars.

Re:At least they don't pollute the city directly

[Sique]

To actually get an asynchronous motor in a car working and to control the speed you need some sophisticated electronics which weren't available when the gas pressure cars were initially developed.

You should use two measures of electric vehicles

[presidenteloco]

The significant fact about electric (or hydrogen fuel cell), or electrically compressed air vehicles
is that electricity (and hence hydrogen via electrolysis, or compressed air tanks) can be generated
in all manner of relatively or completely "green" ways, whereas fossil-fuel transportation is
at least presently restricted to getting its fuel by digging up stored carbon from the Earth at
unsustainable rates.

So electric vehicles (or hydrogen fuel cell, or even relatively inefficient compressed air) vehicles,
are stepping stones on the path to a non-GHG producing future energy system.

So the "green-ness" or carbon footprint of these electrically based technologies should be
measured with two separate baselines:

1. What would their carbon footprint be if all electricity was generated with carbon-neutral generation
methods such as wind/solar/geothermal/hydro/wave/nuclear.

2. What is the carbon footprint assuming the US continues to maintain arguably the most carbon-dirty
electrical generating mix in the world.

Measured in this light, it can be seen that the complete issue is changing the electrical power source for the
US, in parallel with adopting one or multiple forms of transportation technology that is electrically based.
Either change without the other does not work. Both are necessary for effective improvement in emissions
reduction of transportation.

I guess congratulations are in order

[MoellerPlesset2]

Not on debunking this, because it's a completely ridiculous idea that anyone who's taken even introductory engineering thermodynamics should be able to debunk. Rather, they should get credit for going the extra mile and actually getting a paper out of the thing (and media attention!).

I mean really. There's perfectly good reasons why we're not using compressed air as a 'fuel', and it's not that we hadn't thought of it. The idea (and applications) have been around since the 19th century.

Re:I guess congratulations are in order

[bmajik]

The problem of humanity is one of the capture, storage, and application of energy.

Gasoline is a fantastic medium for energy storage: it's a better battery than any battery we know how to cheaply produce and service, and that's why we use it. But the energy capture function for gasoline [getting the energy into the gasoline] sucks. And the energy dispersal/application of gasoline has some environmentalists pretty upset.

Nature gives us many ways to store energy now and release it later. The chemical combustion of gasoline is one such mechanism. The desire of a compressed gas to push forcefully against its container is another such mechanism. The strong nuclear bindig energy is a particulary potent and pervasive mechanism. The specific heat of water is yet another.

The fundamental mechanisms of energy storage have been known about for a long time. Taken as a complete system to let humanity accomplish some goal, we are concerned with how we capture the energy, how much of it we can store [and at what cost], and how easy it is to get it back out in a form condusive to the sort of work we want to do with it.

As technology changes we must continually re-evaluate the end-to-end story for a particular aqcuisition/storage/application energy cycle. We may find that we are willing to tolerate a 100 fold decrease in energy storage performance for a 200 fold increase in acquisition efficiency and a qualitative improvement in application performance.

For instance, if i live in arizona and i have a sterling-engine powered air compressor that pumps my 50G tank to 100psi after 12 hours of sunlight, and this lets me go about 10 miles with no consumption of anything other than sunlight... I'm interested. If i commute 5 miles each way, I can get to work and back using nothing but solar energy. And unlike with PV panels and electrical batteries, a guy with a pipe threading die and a welder could build refueling system in his garage, out of stuff that has zero environmental impact whatsoever.

I think that's cool. I'm obviously playing fast and loose with the numbers. Since the kJ/m^2 of solar radiation is known at gridsquares all over north america, you could actually make some ballpark efficiency guesses about peices of the process and plug in real numbers to my hypothetical example. Even if reality is 1 mile @ 30mph after 8 hrs of sunlight.. that fits _some_ usage profile.

It used to be that every farm in North Dakota [where I live] had a windmill powering the farm. Then they disappeared and became an anachronism paying homage to a bygone era. Now windmills are dotting the countryside again. It didn't get windier here.

What changed?

The physics of energy capture, storage, and dispersion have always been the same; our efficiency and the context of the problem space continue to change. As such we must constantly re-evaluate what we did in the past against the realities of today.

Re:Zero Emissions are worse??

[Gerafix]

Bullshit. There's no such thing as zero emissions unless you're knee deep in shit in the middle of the wilderness, burning wood for heat. Killing wild animals with your bare hands or tools you hobbled together yourself. Living in a hut made of shrubs down by the river.

Those solar panels, wind turbines, penis pumps etc had to be manufactured somehow and that manufacturing process creates emissions. "Carbon offsets" is a joke, wake up people! Any emission is an emission.

Re:Zero Emissions are worse??

[commodore64_love]

>>>all those Prius owners don't really seem to care about Lithum strip mines

Prius cars don't use lithium. They use nickle and hydride, and when disposed are no more harmful than throwing-away coins and water. (Although recycling the metal would be better.)

Cold Steam Engine?

[Banichi]

It occurs to me that a compressed air vehicle could be compared to a "cold" steam engine.

Have there been any scientific advances that could make steam engines in general viable for car sized engines?

Re:Zero Emissions are worse??

[AmigaHeretic]

"Carbon offsets" is a joke, wake up people! Any emission is an emission.

I hold all my farts in sir!

compressed air uses

[stimpleton]

I did an apprenticeship in Motor Mechanics for 4 years when I left school 25 years ago. I recall a question to the tutor back then about compressed air to drive a car. Here was his answer: Compressed air is not good as a primary driving medium, it is only good as a buffer(the storage tank) or where electricity might add risk. Examples being driving air tools in a pit below ground. By its nature, compressed air must pass thru constricted orifices. There is tremendous loss of pressure over distance. I recall our workshop compressor...very different from what you buy at a hardware store. Huge tank, dual motors, each on three phase power. The newbies job was to empty the water and oil traps from the Air Intake system. About 20 litres per day and about 200 mls of oil like fluid(The atmosphere in the workshop back then was a haze of car fumes and dust). We had 4 electric hoists and one compressed air hoist too. The air hoist could lift many times the wieght of the electric.

I think compressed air cars will serve a specialist role, operating in specific roles. Whether there is commercial visbility, I do not know. Aside from the modern buzzword of "Footprint", the technology to compress air is as old as stem and pistons. That wont change. Even on high tech air craft carriers, the landing restraints have huge hoary old compressed air pistons dampenening the jets planes. The tech below deck, keeps the ram clean and applies some lubricant periodically....just as would happen in steam train days.

Time for a new tagline

[heffrey]

Slashdot - news for idiots, stuff that's obvious

No kidding?

[Brett Buck]

This is a surprise to someone? Who ever though this *could* work? Certainly not anyone with any knowledge of thermodynamics. The only compressed -gas systems that even have a chance of working are those that store the working fluid as a liquid, meaning it has to be able to be liquified at room temperature at a reasonable pressure (few hundred PSI at most). Otherwise the tanks are huge and heavy (meaning it will barely move under power) or they are small and heavy (meaning it has no range). Two excellent working fluid for this purpose are - wait for it - CO2 and Freon! Oops.

          Brett

There are other ways to compress the air.

[jcr]

Compressing air can be done with any source of mechanical energy. Put a windmill on your roof, gear it down, and have it drive the compressor directly.

Come to think of it, having a sizable amount of compressed air storage in one's house would be handy. Great for dusting.

-jcr

Re:There are other ways to compress the air.

[Cyberllama]

But you could just as easily have that windmill power a turbine to generate electricity to charge the battery in your electric car and get a far higher energy density leading to more mileage per charge and per each day's wind. I think that's the point that's being made. There's lots of clean ways that can generate energy -- any of which can be used to compress air, but why add that extra unnecessary step in the middle when it's just an added inefficiency?

Re:"zero fuel"?

[oldhack]

Does it involve an electric middle stage? If so, electric energy storage would be more efficient, I'm guesssing?

Re:Burning wood is not zero emission

[slim-t]

It releases the carbon that the tree had already taken out of the atmosphere, and the tree that grows in its place will recapture. So the net is zero emission.

As said in great grandparent post, compressed air and hydrogen are energy storage mediums. Wood is the same thing. Trees use solar energy to convert CO2 into carbon. When you burn the wood, you put the CO2 back into the air and get the energy back as heat.

It doesn't matter if we burn the wood for something useful, the trees dies and rots, or the tree is burned in a forest fire: at some point the carbon is coming back out of that tree.

Re:Zero Emissions are worse??

[mweather]

Easy. Use solar panels to power the factory.

I was greatly disappointed by the lack of hovering

[Cormophyte]

"...Air Cars" is an amazingly deceptive headline :(

Oh thank [insert deity here],

[kothmac]

I thought this was going to be a story crushing my hopes of owning a flying car.

Re:Zero Emissions are worse??

[MeatBag PussRocket]

i'm curious as to how much thought you're really given to this, above and beyond the 'mythbusters' level. firstly, you're right, Priora are not built with lithium batteries, though you should wish that they were. Lithium is NOT stripmined, Lithium salts are extracted from the water of mineral springs, brine pools and brine deposits. The metal is produced electrolytically from a mixture of fused lithium and potassium chloride. Nickel on the other hand IS strip-mined and while their disposal may not be all that bad, the production of nickel batteries is extremely harmful to the environment. IIRC there is a mine in Canada used for the production of Prius batteries, if thats the one i'm thinking it is, there is a 60 mile dead zone around it which contains about as much life as the surface of the moon.

there are of course problems with most forms of energy storage, the trick is finding ways to manage those problems.

Technology transfers poorly from guitars

[Lemming Mark]

I own an air guitar and it's actually pretty sweet - I can make like I'm rocking out wherever I am. Whereas an air car ... I don't see the market. You're at a party and the music's pumping and you just decide to "air drive" to the shops? Not cool.

Re:Zero Emissions are worse??

[SlashSim]

The nickel mine you are thinking about is probably Inco's mine in Sudbury Ontario. There is indeed a dead zone, but it is not a strip mine, the mine is underground. The dead zone is the result of acid fallout from the smelter. After killing off the area, and facing criticism, Inco built what was then the world's largest smokestack in the early seventies. The smelter still belches sulfur compounds, but now they are dispersed over a much larger area.

Much of the area still looks like a moonscape.

http://en.wikipedia.org/wiki/Inco_Superstack