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Why not Solar -> Electrolysis -> Burn to make steam energy?

  1. Feb 13, 2014 #1
    Why not Solar --> Electrolysis --> Burn to make steam energy?

    Solar heat and light are both available in abundance, especially in the tropics. That being so, why is that no attempts have been made to use Solar-Electricity to split water in large amounts, into H2 and O2 to boil water to produce steam to run power plants? By burning the H2 and using the O2 to increase the heat very large quantities of steam could be produced. So, why is this not being done on a large scale?
     
  2. jcsd
  3. Feb 13, 2014 #2
    The keyword here is "economy".
     
  4. Feb 13, 2014 #3
    Once you have electricity from your solar panel, you might as well just use the electricity, rather than going through the Rube Goldberg-like process of electrolyzing water and then burning the resulting hydrogen to produce electricity again. Even if you managed to make the entire process 100% efficient -- the maximum theoretically possible -- you would only recover the same amount of electrical energy that you got out of the solar panels. In practice even that is unachievable, and you would end up with efficiencies in the 30% range, meaning that using hydrogen as an intermediate step results in throwing away 70% of the energy.
     
  5. Feb 13, 2014 #4

    Integral

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    Photo voltaic cells are not all that efficient either. Just use parabolic reflectors to directly heat water to drive the turbines.
     
  6. Feb 13, 2014 #5

    Borek

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    Either split water or boil it to produce steam, not both. These are completely different things.
     
  7. Feb 13, 2014 #6

    Dale

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    In addition to the other points made above, H2 is a suboptimal way to store energy. Its energy density is very low. It is quite unstable. It damages metal. It ignites at very low compression and temperature. And it generally is just not very convenient.
     
  8. Feb 13, 2014 #7

    SteamKing

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    The problem with electrolysis, which has been ventilated at PF before, is that it only works well when you use relatively pure water. If you use electrolysis to desalinate seawater, for instance, you generate chlorine gas along with hydrogen and oxygen, as well as elemental sodium, among other byproducts. Some byproducts might be economically useful, others, like, chlorine gas, are definite hazards.

    There's plenty of sand and sun in the desert, but not much else. Building and operating any kind of generating plant in the middle of nowhere is costly, and getting someone to work there would also be problematic.
     
  9. Feb 14, 2014 #8
    Here is a recent article: http://phys.org/news/2014-02-huge-thermal-solar-industry.html A 400 MW heliothermal power plant officially went online on Feb 13. Yet: "According to U.S. Energy Information Administration data, the cost of building and operating a new solar thermal power plant over its lifetime is greater than generating natural gas, coal or nuclear power. It costs a conventional coal plant $100, on average, to produce a megawatt-hour of power, but that figure is $261 for solar thermal power, according to 2011 estimates."

    And that is just at generating electricity. Adding electrolysis, storage and transport of hydrogen, then burning it and generating electricity again will make the price tag much, much higher.
     
  10. Feb 14, 2014 #9

    Integral

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    I believe that this is what voko is referring to
     
  11. Feb 14, 2014 #10
    Solar heat and light are abundantly available and so there should be no talk of wasting any electricity produced by both. With abundant electricity, let's say in the deserts of Saudi Arabia, thru' solar, there should be no problem splitting water into H2 and O2.

    Now H2 being a fuel and O2 being able to work as a "booster" there should be an abundant production of steam to run turbines which run e-generators.

    My point is this: Why not use the H2 in sea water as an efficient fuel boosted by the O2 supply in the same sea water?

    If we were to use fossil fuel to heat water to make steam that would be prohibitive. But using free solar energy, I don't see a problem. Who cares if we get only 10% efficency output since the fuel is free.

    Is it not what we get out of Hydro power plants? Maybe 30%! Huge initial expenditure but very little running costs. With solar only land that is not used at all for food production can be used in the deserts. Btw, there is clean drinking/farming water coming out as a free by-product with H2 burning with O2.
     
  12. Feb 14, 2014 #11
    You are obviously not listening. Nothing is free and everything has a cost. Your scheme is not economically viable at this time.
     
  13. Feb 15, 2014 #12
    Is not the air I take into my lungs and all other human beings and all animals take into their lungs not free? How about sea water in all the oceans free for anybody to swim in if they want to? How about the rain that comes down from the clouds?

    So the adage that nothing is free is not true. There are many things in life that are free. How about sunlight and moonlight and starlight and the wind that cools my apartment?

    When we start with a false statement we end up with false theories.

    I live by the Indian ocean. If I want to make my own free salt, no problem. I put a few gallons of sea water into a flat pan and keep it out to evaporate. In a few days I have FREE salt.

    I still believe that Sunlight and sun-heat can be used to produce the fuel H2, and O2 in abundance unlike fossil fuels which deplete, to produce electricity at of course a very high cost initially, but low cost down the road.
     
  14. Feb 15, 2014 #13

    Dale

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    Your OP has been clearly answered. Since you just as clearly have no intention of learning anything from the answers, this thread is closed.

    Regarding nothing being free, the point is to get you to consider hidden costs. You certainly need considerable work on that. For instance, here:
    You failed to identify a number of fairly obvious direct costs and therefore incorrectly identified the salt as free. The total economic cost of something involves all of the costs, both obvious and hidden, including opportunity costs.

    As another example where you fail to correctly understand costs:
    Taking air into your lungs is certainly not free. First, air has a very high supply, so the price of air is extremely low, but low price is not the same as free. For example, any circumstance which would restrict the supply of air would increase its price, per normal market forces. Consider the price of air on the ISS, where supply is considerably reduced.

    Furthermore, even with abundant supply you have to consider opportunity costs, or the amount of money that you forego by not using a resource for its next most profitable activity. For air, breathing air requires lungs, which have an estimated market value of greater than $300k each. So drawing that breath requires you to pay the >$600k opportunity cost of not selling your lungs to someone else. So breathing air is actually far from free, it involves very low (but non-zero) direct costs under normal circumstances and very high opportunity costs under all circumstances.

    Until you learn to identify hidden costs and opportunity costs, you will not understand why the answers to your OP were correct.
     
    Last edited: Feb 15, 2014
  15. Feb 15, 2014 #14

    russ_watters

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    I know the thread was closed, but I don't think this was adequately/correctly answered:
    The problem isn't that water isn't free, the problem is that it isn't fuel. Water is the waste product of combustion, so trying to use it as a fuel is like trying to use the smoke coming out of a chimney as fuel. There's no energy left to harness.

    Now, you can "unburn" a fuel and then burn it again, but since the chemical reaction is the same - just run backwards - (H2 + O <=> H2O + E)you use exactly as much energy to "unburn" it as you get when you burn it. So there isn't a 10% efficiency gain; the maximum possible efficiency gain is exactly 0%.
     
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