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Why not use electricity directly instead of hydrogen

  1. Aug 17, 2016 #1
    Hi PhysicsForums,

    I'm asking this as part of a small research project of mine in exploring hydrogen as an alternative energy source to fossil fuels.

    Based on my limited understanding, hydrogen is a good alternative to fossil fuels (especially in cars) because the only waste product is water. However, the main problem is that obtaining hydrogen presently involves extraction from natural gas (a form of fossil fuel so it kind of defeats the purpose). I was looking at the possibility of obtaining hydrogen from electrolysis, which uses electricity that again comes from fossil fuel power plants. Some sources I've come across suggest that we can carry out the electrolysis of water using renewable energy sources like wind/nuclear/hydro.

    Here is my question: since electricity is needed to break water down into H2 and O2, is it not wiser to just use that electricity obtained from wind/nuclear/hydro to directly power an electric car and bypass the electrolysis/hydrogen fuel cell completely? The reasons I can think of are: 1. recharging an electric car takes time while refueling hydrogen is quick, akin to traditional refueling 2. its more difficult to store and transport electricity (needs a battery I presume) than it is for hydrogen gas.

    Do note that this is only a hypothetical research writeup for a module of mine (I don't actually have to carry out the research, and the idea need not actually really be feasible. This module focuses more on the process of idea generation and report writing etc), so I'm just assuming theoretically if obtaining hydrogen from electrolysis of water using renewable energy sources is feasible, which sounds great since water is abundant and renewable energy is well, renewable.

    Thank you for your time!
     
  2. jcsd
  3. Aug 17, 2016 #2

    DrClaude

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    As far as I know, that's basically it. You lose in efficiency by using hydrogen as an intermediary, but the idea would be that it would be as easy to use as gasoline. The main problem is that is way more dangerous than gasoline.
     
  4. Aug 17, 2016 #3

    russ_watters

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    10 years ago we had a lot more threads on the potential for hydrogen replacing gasoline than we have today. I think the improving viability of hybrids and pure electrics, fracking unlocking vast new sources of oil and a lack of progress in hydrogen technologies explain why.
     
  5. Aug 17, 2016 #4
    What keeps H2 alive as a fuel is that 10 pounds can propel a fuel cell car 300 miles.
     
  6. Aug 17, 2016 #5

    Bystander

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    ... of course, "scrubbing" it clean enough to use is far more expensive than it's worth ... or, will ever be worth.
     
  7. Aug 17, 2016 #6

    Vanadium 50

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    Why is this a big thing? One kilo of hydrogen has the same energy as a gallon of gas. So one pound of hydrogen is the same as three pounds of gas. That lets your car be maybe 50 pounds lighter. Why is this a big thing?
     
  8. Aug 17, 2016 #7
    No "range anxiety."
     
  9. Aug 17, 2016 #8

    jack action

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    Yes but compared to the 1600 pounds for the batteries of a Tesla III that has a 200 miles range, that is a big thing.
     
  10. Aug 17, 2016 #9

    Vanadium 50

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    I have a PHEV, and I don't have any range anxiety. Once every two weeks I use the gas engine. I use 92% less fuel than my previous car, and that means that in terms of reducing emissions, I already have 92% of the maximum possible gain. I don't see the need for heroics to get 8% more.
     
  11. Aug 17, 2016 #10
    I drive a Honda Insight and average 50 mpg...what's your point?
     
  12. Aug 18, 2016 #11

    Vanadium 50

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    My point is that there are existing technical solutions for range anxiety. It's a solved problem.
     
  13. Aug 18, 2016 #12
  14. Aug 18, 2016 #13

    jack action

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    Not an expert on hydrogen tanks, but I'm guessing less than 700 kg (1543 lb), a lot less.

    But for gas, I know that 70 L of gas weights 50 kgf and you can add about 20 kgf for the tank, fuel pump and other fuel delivery accessories. Still way below the 725 kgf (1600 lb) of a battery pack.
     
  15. Aug 18, 2016 #14

    russ_watters

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    Apparently there are people who don't like the solution. I think for some it is because 92% isn't good enough.
     
  16. Aug 18, 2016 #15

    CWatters

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    The best way to approach this subject is to realise that what cars need is an energy storage mechanism, be it a gas tank, a hydrogen tank, a battery, a fly wheel or a twisted rubber band. They are all energy storage mechanisms with different energy densities. Both the mass and volumetric energy density matters..

    Wikipedia has a good page on energy density that includes info on just about every type of energy storage system, everything from Uranium to a Ham and cheese sandwich...

    https://en.wikipedia.org/wiki/Energy_density

    Some of the data includes any "containment" required (such as the tank) but some doesn't.
     
  17. Aug 18, 2016 #16
    Just to answer this. It's already being done large scale on Iceland.

    http://www.sciencedirect.com/science/article/pii/S0360319909001992

    (sorry for barely related article, tablet and not on University network)
     
  18. Aug 18, 2016 #17
    Sorry, I'm not trying to be argumentative here, but... That 10 pounds of H2 you say can carry you 300 miles: at atmospheric pressure, it occupies over 1900 ft3. To put it into your car, you need to compress it. If you compressed it to fit in the same space as you current gasoline tank (say, 25 gallons), the tank pressure would be over 8400 psi. For the metric guys, that's 58 MPa or 580 bar... A tank at that pressure will have walls several inches thick and weigh probably over 1500 pounds. Of course, you could use a bigger tank at lower pressure, with thinner walls, so there's probably some optimum size for the tank. But any reasonably sized tank (that fits into your car) is going to be a hefty piece. Liquefying the H2 (like they do with propane) isn't an option, as far as I know.
     
  19. Aug 18, 2016 #18
    The reason you would use electrical energy to create hydrogen to use in a car comes down to how far you can go on one "fill".
    With hydrogen you can go much farther because batteries simply can't - and likely won't - contain anywhere near the energy.
    Hydrogen is tricky to work with and store. Because the molecule is so small, you must use very thick tanks with an inner rubber coating, or you lose gas through the sides of the tank! So storage of large amounts is difficult and expensive. Once we perfect the technology, I wouldn't be surprised to see hydrogen fuel cell cars being used.
    Right now, fossil fuels are the most affordable and we are set up to handle it, so I can't see it going away anytime soon - it'll just be used more efficiently
     
  20. Aug 18, 2016 #19

    jack action

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    Please do, I know nothing about hydrogen and I love to learn.

    See, I never thought about that and turns you are right. Will go to bed a little bit more knowledgeable tonight.

    After a simple search, apparently they can go well below the 1500 lb mark rather easily. From 45 kg (@145 L) to 215 kg (@55 L) for 3 kg of H2 (130 mi range) and from 90 kg (@320 L) to 222 kg (@200 L) for 7 kg of H2 (435 mi range). The source is from 2002 and there seems to be room for improvement.

    Yeah, they don't say how much they cost ...
     
  21. Aug 19, 2016 #20
    As things stand the most easy to use and longest range power supply for a vehicle is still hydrocarbons, directly or indirectly
    If there was a way to dump the carbon, even producing useful carbon products as a result that would be wonderful.
    So far though, we are still stuck with burning the carbon into CO2 to get energy out, which is a problem.
     
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