Chris Wood
Wednesday October 12th, 2011

Solar Diesel

I read an article that suggested that cars in future will be fuelled with hydrogen. So I have written up my doubts about this. I am no expert, but some of my arguments may be useful for other non-experts.

My younger daughter recently bought a (used) car driven by natural gas, proud to be doing something for the climate. She was surprised when I told her this fuel is little better than diesel, if at all. Hydrocarbons have similar calorific value per gram, and the weight is largely carbon. And diesel motors are rather efficient.

I see little sense in fuelling cars with hydrogen. The energy from burning hydrogen is about 2½ times as much as from the same weight of hydrocarbons. But this advantage is wiped out by the difficulty of light compact storage. For instance one car manufacturer (according to Wikipedia) is investigating use of NaBH4. But the hydrogen in this comprises about 10% by weight. So hydrocarbon fuel effectively weighs a quarter as much.
Surely it makes more sense to produce hydrocarbons, and continue to use them. This continues to use highly developed motors and the current infrastructure. Using a suitable power source, (the sun, or perhaps eventually thermonuclear power), it is possible to have a cycle producing diesel (and oxygen) from water and carbon dioxide, which are recycled via the atmosphere when the diesel is burnt. Of course such diesel fuel is much more expensive than when the hydrocarbons come almost for free from underground.

There is already research using algae to produce hydrocarbons. One problem is that green plants store only about 3% of the solar energy. Other ways of producing transportable fuel from solar energy, (including use of batteries), are hardly better. Of course diesel is already produced “commercially” from solar energy using maize or sugar-cane. But this wastes fertile land that is needed for food production, (assuming we want to continue to overpopulate the world). We need to produce diesel rather more efficiently on the oceans or deserts.
Some energy is lost when CO2 is concentrated out of the atmosphere. How significant is this?
Perhaps I am missing some other point. Is less energy needed to get a hydrogen atom from NaBH4 than from H2?

But I suspect that the neglect of diesel production has other reasons. It is in too direct competition with current diesel. It is competitive only paying full attention to climate change and limited resources. The oil companies would be best positioned to get involved in this, but can hardly get enthusiastic about it.
Electric power and hydrogen seem an attractive alternative to diesel, as long as one ignores where they come from, mainly cheap oil, gas, coal, and nuclear power. They give the car firms a chance to sell new products, if only in small numbers, and to seem to be doing something about oil shortage and climate.

6 Kommentare zu “Solar Diesel”

  1. KH (Wednesday October 12th, 2011)

    Ich möchte gern den Deutschen TÜV kennen lernen, der jemals genehmigen wird, dass ein mit Wasserstoff betanktes Auto in einer deutschen Garage steht in der man elektrisches Licht anknipsen kann. Jedes Dorf wär mit unzähligen Sprengfallen übersät, und es sage mir keiner aus solchen Autos würde niemals das Gas entweichen…

  2. JUS (Friday October 14th, 2011)

    Zum Kommentar von KH: Der TÜV hat da gar kein Problem, die Feuerwehr, wenn ein Gasbetriebenes Auto (egal ob LPG oder CNG oder H2) brennen sollte, auch nicht. Es ist mitnichten weder Feuer- noch Sprengfalle, aber hat schonmal jemand eine Lache von mehreren Litern Benzin brennen gesehen?

    Die ganze Klimadiskussion, die hier zum Steckenpferd einiger Autoren gehört, ist sowas von langweilig! Ob die Erde nun ein paar Jahrhunderte früher oder später durch Klimaveränderungen (die übrigens für die gute alte Erde völlig normal sind) vom Homo Sapiens befreit wird ist echt völlig egal. Und wenn es soweit ist dauert es nicht lange, und die Natur hat sich alles wiederbschafft, was ihr vom Mensch abgerungen wurde. Wir sind nunmal nur eine winzige Episode in der Erdgeschichte und erst recht in der kosmischer Sichweise, nur leidet der menschliche Duchschnittsbewohner dieses Planeten unter einer ziemlichen Großmannsucht, das allesbeherrschende Lebewesen zu sein. Etwas mehr weitblick bitte. JUS

  3. six (Friday October 14th, 2011)

    Ja, er hat schon recht, der JUS. Aber zur Hybris der Menschen auf dieser Erde gehört auch, dass sie den Abstand zum Tier ständig durch die göttergleiche Gabe der ausgefuchsten Planung beweisen wollen – auch wenn dieselbige genau so ständig schief geht. Wir fühlen uns einfach zu Höherem berufen. Mein Motto dazu: Wenn Du nach den Sternen greifst, wirst Du sie vielleicht nicht erreichen, aber Du kommst wenigsten nicht mit einer Hand voll Scheisse zurück.

  4. Chris Wood (Friday October 14th, 2011)

    I cannot understand how anyone can regard the question of the survival of civilisation on Earth as boring. (Although a good game of cricket may be briefly more exciting).

    If your English is good enough, listen to

    Here, Sir Martin Rees, perhaps the greatest living scientist, gives his view that we are living in an extraordinary century. Civilisation has the chance to destroy itself or to continue to advance, and to do so ever faster.
    Our failure to find other advanced life in the Universe suggests that civilisations at our level tend to destroy themselves. Yet I still think we have a small chance of getting it “right”. Along with my next meal and the fates of my daughters, this is something that matters to me.
    If we destroy civilisation, it will take many millions of years to happen here again, if at all.

  5. JUS (Monday October 24th, 2011)

    No, not the survival of civilisation is boring, the way people discuss it here is.
    I mean that some people think they can save the world by riding by bicycle to work and other people using cars will destroy it. Have you ever travelled to other countries except europe?

    My english is quite good and I listened to Mr Rees. Quite nice but nothing any professor in physics of an german university could do, because the search for the big unifiyng theory ist already quite old, by the way Maxwell found on his search his well known equatations.

    Science is so full of holes (for example before we discover the universe – how about to discover the oceans on our nice spaceship called earth). Scientists just do guesses and instead of trying to explain EVERYTHING, why not trying to understand, how life works? (And there was NO God who did it in 7 days!!). It’s very complex chemistry, a human brain has more synapses than stars in the universe. JUS

  6. Chris Wood (Tuesday February 28th, 2012)

    Dear JUS, I see that I failed to answer your question. Yes, I have been outside Europe. I was once in Tunisia, and a few times in USA and Canada. But what is the relevance of that? My most eye-opening travel experiences were in (European) communist countries, for instance playing table tennis with Mongolian students, or talking to a Russian half-dissident.

    I too do not believe that a German professor could talk as well as Mr. Rees. On TV, Prof Lesch is not bad, but too populist for my taste. I prefer Prof Spitzer, but his presentation is a bit too sober. I do not understand why you make this comment. Perhaps a “not” has been lost from the sentence?

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