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I'm curious about the efficiency of using Oxyhydrogen as a home heating method. Oxyhydrogen can be generated from water.

I understand the fact that it takes more energy to generate the oxyhydrogen, but perhaps if I use a combination of wind/solar power it might make more sense to use this in a furnace similar to a propane furnace.

How can I compare the energy required to power say, a baseboard heater, to the energy required to produce similar heat from oxyhydrogen? There are propane versus electricity comparisons, so maybe just comparing the cost of generating similar amounts of oxyhydrogen/propane would be sufficient?

EDIT: I would never propose to store this gas for later use. It should always be used as it is made.

For further clarification, what I'm trying to analyze is this: An electric space heater is only so efficient. How much more or less efficient would the process of creating and burning oxyhydrogen be? It is easy to say "oh, it's much less efficient", but I'm trying to figure out how much less efficient. Does it burn hot enough to heat a larger area for the same electricity? Probably not, but the equations/math to determine that is beyond me. I didn't do well in physics class I guess. Maybe this is a question for a physics community!

  • Using something described as bang-gas sounds somewhat unsafe! – andy256 Mar 27 '15 at 2:57
  • @andy256 I've used it before in an older model car to increase gas mileage (which it only did by very little) but it's actually quite safe when used as it is produced. It's no more unsafe than say, propane. – Andrew Grothe Mar 27 '15 at 13:35
  • We need some more information on just how you propose to do this. Are you planning on generating it (with PV, wind, etc) during the summer & storing it for use in the winter? In that case, you'll have to separate & compress the hydrogen, or you'll have effectively created a rather large bomb. You'll also get back less heat than went into the separation, whereas if you run a ground-source heat pump off PV/wind, you can get maybe 4-5 times as much heat. – jamesqf Mar 27 '15 at 18:57
  • @jamesqf your statement "maybe 4-5 time as much" is exactly what I'm trying to define. I'm at a loss on how to properly calculate this though. My initial though was, does the oxyhydrogen burn hot enough to make it worth while, but how much energy is actually lost producing the gas versus energy lost using an electric space heater, say? – Andrew Grothe Mar 28 '15 at 13:48
  • @agrothe: I think you have a lot of misconceptions. For instance, what matters is not how hot the hydrogen/oxygen mixture burns, but the amount of heat produced. For instance, an actylene cutting torch burns very hot, but doesn't produce nearly as much heat as the cooler flame of a furnace. For heating from PV electricity, anything but a heat pump is a major loss. See e.g. en.wikipedia.org/wiki/Geothermal_heat_pump – jamesqf Mar 28 '15 at 21:54
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You will always put more energy into generating this gas mixture than you will get back by burning it. The second law of thermodynamics (which for this context can simply be thought of as saying that nothing can be 100% efficient) guarantees that. So rather than using energy to split water to produce gas for burning, you would be better off using that same energy to heat your home directly.

(also, a h2/o2 mixture is not known for burning in a controlled way.... ;-))

  • These are the same thoughts I had, but I have yet to see a quantitative comparison regarding oxyhyrodgen. That in itself might answer the question, but there is nothing quite like hard numbers to definitively answer a question. – Andrew Grothe Mar 27 '15 at 13:34
  • @agrothe you don't need a quantitative comparison. If you could go from electricity to O2+H2 to heat and end up with more energy than you started with, you would be breaking some fairly fundamental rules of physics. You will always be better off (or at least no worse off) just using the electricity for heat directly. – Flyto Mar 27 '15 at 14:11
  • But is a baseboard heater more efficient then a furnace burning O2+H2? How much more efficient? – Andrew Grothe Mar 27 '15 at 16:48
  • @agrothe I don't know what a baseboard heater is. But, it's unlikely to matter. – Flyto Mar 27 '15 at 17:54
  • @SimonW I think the real question is whether oxyhydrogen is an efficient way of storing energy that is produced during the day (or summer) and used during the night (or winter). He doesn't just want to use "the energy" which may come from solar power at noon to heat his house at noon. Grid-wise, generating power sustainably during peak time is always good, but for a single household during winter, peak time may be between 5 and 9 at night, where there is no solar power. – Earthliŋ Mar 28 '15 at 2:55
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It is appealing to use wind or PV whenever they are available, and to have heating when it is required - and something is required to help those align in time.

Using the energy to synthesise storable fuels is one way to do it.

However, you need special burners to make the most of burning a mix of hydrogen and oxygen. You need special equipment to store the hydrogen and oxygen. And you may find your municipal authority taking a close interest in what you're storing, and how you're storing it.

So, expense and complications.

The alternative that is easier and cheaper in most circumstances, is to store heat itself. Heat's pretty cheap and easy to store: but it does need space, and a bit of planning. A large underground thermal (hot-water) tank is one way to do it. Some people have looked at using the ground itself as thermal store, and combining a solar thermal system with a ground-source heat-pump, to store more heat in the ground in summer, and take it out in winter. The key here is volume: seasonal stores need to be huge; one-day stores can be a few hundred liters. The bigger the store, the more smoothing over time it gives you.

But if you're not interested in time-shifting - if you want to use the electricity when it's generated - then there's no sense in electrolysing water. Electricity is pretty much as exergy-intensive as it's possible to get: if you want to get things done, electricity will in general do it far better than any other energy vector can. For heating, either use a resistance heater, which is very cheap to buy, and better efficiency than any chemical route; or if it will be running for a large proportion of the time, consider investing in a heat pump, which will allow you to harvest more joules in heat than the joules of electricity you put into it.

  • "A large underground thermal tank is one way to do it." Would that be storing heated water? – Earthliŋ Mar 28 '15 at 2:49
  • Perhaps worth mentioning that since there's plenty of oxygen around anyway, he could just store the Hydrogen - which reduces the explosive potential and is a relatively mainstream solution, with off-the-shelf hardware. – Flyto Mar 28 '15 at 7:34
  • I should update the question i guess, but this stuff should never be stored, always used on demand. – Andrew Grothe Mar 28 '15 at 13:49
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Mixed Oxygen + Hydrogen can be both stored and burned safely (with due attention to details) despite this seeming unlikely. The Wikipedia page you cite covers this in more detail. There is much hype associated with this area with terms like "HHO" and "Brown's gas" usually indicating that some 'non main-stream physics' is about to be encountered. Despite this the basic science involved is sound.

Efficiency of production versus recoverable energy depends on how close you can get the potential of an electrolysis cell to the minimum required potential. This Wikipedia page Electrolysis of water provides a hgood overview. Cheaper electrolysers using Alklaine electrolytes (as a boy I used washing soda) achieve in the 60-75% efficiency range and the best PEM units may manage 90%. Higher efficiencies are possible with very special magic - such as advanced (and usually secret and expensive) catalysts, but are unlikely to be available to we mere mortals.

It almost certainly makes no sense to generate and then immediately use the gas as there will be a loss of energy with no gain. Storage and later use makes sense if the energy cost varies by a factor of say 2:1 or more or if load shifting can be achieved. eg If you can store it for a while there may be gains in storing eg solar energy by day and using it at night or low cost power from early AM grid power for daytime use. If desired Hydrogen and Oxygen could be stored separately and recombined at the point of combustion. A gasometer system using eg inverted 40 gallon / 200 litres drums over water may be viable.

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