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  • From: Toby Hemenway <hemenway@jeffnet.org>
  • To: permaculture <permaculture@lists.ibiblio.org>
  • Subject: Re: [permaculture] Hydrogen
  • Date: Tue, 17 Jun 2003 12:35:31 -0700


robert waldrop wrote:
Because hydrogen must be manufactured, it will always take more
energy to make the hydrogen than the hydrogen will yield as useful work.

Right as rain. All fuels, whether hydrogen or petroleum, are simply ways of storing energy (fossil fuels are stored sunlight, right?). Hydrogen is attractive because it has about 3x the energy stored in it per pound than gasoline, and it burns clean. But it's got serious drawbacks: hydrogen, even at high pressure, takes up about 5x more space than an equivalent weight of gasoline, so it's bulky to store; and fossil fuel, as Robert said, is by far the easiest-to-convert source of hydrogen. Here are some figures (from the PDF linked below)

"Production of hydrogen currently costs from 3 to 15 times more than natural gas, and from 1.5 to 9 times more than gasoline, depending on the method used."

Mike wrote:
Please offer any information you've seen about the efficiency of converting water to free H and O. I think it's a little better than that.

"the cost of burning fossil fuels to generate electricity for electrolysis [H2 from water] is three to five times that of reforming [producing] the hydrogen directly from the fossil fuel." (from http://www.ott.doe.gov/otu/field_ops/pdfs/fcm02r0.pdf

Hydrocarbons release energy when they give up their hydrogen; but water requires an input of energy to release its hydrogen. So getting H2 from water will take a lot more energy than from fuels; it's basic physical chemistry (the link above talks about that).

Also, when you generate H2 from oil, all you're doing is pushing the pollution "upstream." The hydrogen vehicle burns clean, but the H2-producing plant burns dirty. Ideally we'd be using PV panels to use sunlight to crack water into hydrogen and oxygen, but even that still is far less efficient than just using the PV panels to produce electricity directly (3 steps versus 2 steps; more losses). So hydrogen may be a part of some future energy mix, but once the oil runs out, we're tied to a solar budget (with a little help from hydro and nukes).

I read that each day humans consume 7 years worth of stored solar energy in the form of fossil fuels. So we are over-consuming the solar budget by something like 7 x 365 = 2555-fold. That's an ugly statistic that suggests a big die-off to break the addiction.

For somelinks on hydrogen, there are some good, college-level PDF files at
http://www.ott.doe.gov/otu/field_ops/hydrogen_class.html

and H2 info for different age and education levels at
http://www.eere.energy.gov/hydrogenandfuelcells/education.html

Toby





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