Compressed air for mobile energy storage

Oriel College chapel

All of a sudden, the air car concept is popping up everywhere. I hadn’t head of it before someone left a comment yesterday. Now, it is on Metafilter, Slashdot, and YouTube.

I must admit that the prospect of a $7,500 car that can run for 200-300km on $3 worth of compressed air sounds pretty amazing. Of course, the compressed air would just be a storage mechanism for energy generated in other ways. The advantage over hydrogen and fuel cell systems of biodiesel could lie in lower infrastructure costs. Installing compressors in homes and service stations already connected to the electrical grid is a lot cheaper than developing a whole new hydrogen infrastructure, leaving more money to direct towards genuinely renewable sources of energy. The compressors could also be powered directly by wind or water turbines, as well as solar power systems. As for biodiesel, once you factor in the energy required to grow the crops and process them, as well as the inefficiency of internal combustion engines and the continued reality of toxic emissions, it doesn’t seem like a hugely alluring prospect to anyone but corn farmers.

While it is unlikely that one technology will allow us to overcome fossil fuel dependence, it does seem sensible to think that something like this could be part of the mix. Especially if the energy being used to compress the air is coming from a renewable, non-greenhouse-gas-emitting source, these cars could make a big difference in the developing world. They could also help tackle urban air pollution, such as the kind plaguing Beijing.

PS. I got today’s photo of the day in Oriel College, as part of my initiative to photograph each college at least once. While there, I discovered a sizable conference on climate change ongoing, about which I had heard nothing. This goes to show just how many people are working on the issue, both here at Oxford and more generally.

Author: Milan

In the spring of 2005, I graduated from the University of British Columbia with a degree in International Relations and a general focus in the area of environmental politics. In the fall of 2005, I began reading for an M.Phil in IR at Wadham College, Oxford. Outside school, I am very interested in photography, writing, and the outdoors. I am writing this blog to keep in touch with friends and family around the world, provide a more personal view of graduate student life in Oxford, and pass on some lessons I've learned here.

14 thoughts on “Compressed air for mobile energy storage”

  1. I want a compressed-air booster for my bike.

    The exercise is good for you. While climate change is a big deal for society, for individuals in western countries heart disease is a more immediate and personal danger.

  2. At 6:20 in the YouTube clip, it shows what my friend Matthew is a Wankel rotary engine. Apparently, the Mazda RX-8 uses one (that burns gasoline).


    “They have a problem, which is large flat faces (the faces being in the same plane as the screen). The flat faces are a relatively large area through which heat loss occurs and thus inefficiencies arise. The traditional piston in cylinder design has smaller flat faces (the face of the piston itself being one) because the circular cross-section of the cylinder maximizes volume and minimizes surface area.”

  3. I don’t know, the air pressure in these cars is obscene. Also, these milage figures need to be compared to gasoline cars of equivalent weight, which are themselves over 100mpg (see the audi A2 for an example).

    Also, the air pressure in these tanks is obscene. Even if the tank only “splits” in a crash, it could still easily kill you. 100 times what you put in your tires? That’s like 3000 psi. Compare that to a shop compressor, 120-150 psi. And that amount of air pressure can easily kill you if it gets under your skin.

  4. The Ford Global Challenge – A Green Car That Runs On Air?

    By Phil Hart on compressed air

    Forget petrol, forget electric… how about air?: Hanafin and de Souza believe their model, which has an engine powered by the release of compressed air, fits the bill.

    “Fitting the compressed air technologies into cars of today which are quite heavy and large is infeasible,” de Souza told 2GB’s Jason Morrison. “Whereas the concept we’ve come up with is a really small, lightweight vehicle that can make use of this type of technology.”

    Although the idea of a compressed air engine suggests it wouldn’t last long without needing a ‘re-fill’, de Souza insists his model would have real staying power.

    “One of the conditions [of the competition] is that it had to have a 200 kilometre range. So we’ve engineered it to make sure we have that range,” he said. “It’s a slightly tweaked system where we re-heat the air… which gives it a bit of a boost. If you just used plain compressed air you’d probably get 60 to 70 kilometres.”

  5. Giving serious consideration to compressed-air energy storage

    My Clean Break column today is actually more of a feature looking at compressed-air energy storage (CAES) and how Ontario, geologically, would be an excellent location to give it a try. About 50,000 natural gas and oil wells have been drilled in southwestern Ontario over the past 150 years and most of them are depleted. Turns out that depleted gas fields are one of several types of underground reservoir that can be used to store compressed air. Salt caverns are another option, and we have plenty of those as well. In fact, 60 per cent of Canada’s natural gas storage is in the region. Compressing and storing air wouldn’t be that different technically.

  6. Monitor
    Running on air

    Jun 4th 2009
    From The Economist print edition
    Transport: Powering hybrid cars with compressed air rather than electric motors could be a cheaper way to increase fuel efficiency

    BEING green can be expensive, as any driver of a Toyota Prius can tell you. The car is a hybrid, combining a petrol engine with an electric motor that powers it at low speeds in the city and provides bursts of acceleration when needed. It is the most fuel-efficient car sold in America, but it costs upwards of $22,000, a price that can wipe out the savings on fuel. One reason for the high price is that the car contains expensive batteries. Another is that the transmission system had to be completely redesigned. But there may be a cheaper and simpler way to make a hybrid, using air power instead of electricity.

    Using compressed air to power a car has one obvious disadvantage: compressed air has a low energy-density, so not very much energy can be stored. However, in urban driving this may not matter. One of the most important roles of the batteries in a hybrid is to store energy recovered when the car brakes. The idea with a pneumatic hybrid is to store this energy as compressed air. Such a vehicle would run on petrol but would use its reservoir of compressed air to boost the engine’s power when needed. This would not demand a serious redesign because every car already has a makeshift air compressor in the form of the engine itself. Building a pneumatic-hybrid car would thus be relatively cheap.

  7. Berkeley Engineers Have Some Bad News About Air Cars

    “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.”

  8. Not Just Blowing in the Wind: Compressing Air for Renewable Energy Storage

    May 20, 2013 — Enough Northwest wind energy to power about 85,000 homes each month could be stored in porous rocks deep underground for later use, according to a new, comprehensive study. Researchers at the Department of Energy’s Pacific Northwest National Laboratory and Bonneville Power Administration identified two unique methods for this energy storage approach and two eastern Washington locations to put them into practice.

Leave a Reply

Your email address will not be published. Required fields are marked *