Field of Science

The end of biofuels?

Hartmut Michel from the Max Planck Institute of Biophysics has an editorial (open access!) in Angewandte Chemie with a title that makes his views clear: "The Nonsense of Biofuels". He essentially comes down hard on biofuel proponents of all stripes and not just the much hyped ethanol-from-corn lobby. Michel won the Nobel Prize for cracking open the structure of one of earth's most important proteins - the photosynthetic reaction center - so he certainly knows his photosynthesis.

He starts by looking at the energy efficiency of the process. It's not always appreciated that for all its rightly deserved glory, photosynthesis is not as efficient as we think, which would indeed be the case for something that's been tuned by evolutionary fits and starts and historical contingency. For one thing, UV, IR and green light cannot be utilized by plants so that leaves out a pretty high-energy part of the spectrum. Then there's all the wonderful machinery of electron transfer and light-harvesting proteins involved in the dark and light processes. The light step essentially captures photon energy and generates NADPH and ATP, and the dark step uses this energy source and reducing potential to synthesize carbohydrates from CO2. Considering the inefficiencies inherent in using the energy of massless, transient photons, only about 12% of energy from sunlight is stored as NADPH.

Then there's the question of light intensity which seems to invoke a classic catch-22 situation. At low intensities where the process is most efficient you don't have a lot of photons by definition. But try to improve the efficiency by bumping up the intensity and you get photodamage which, in Michel's words, 3.5 billion years of evolution hasn't been able to circumvent. To avoid this photodamage, plants have to recycle one of the key proteins in photosystem II about thrice every hour which inherently limits the efficiency. Finally, the key protein in the second step, RuBisCO, has a hard time distinguishing between CO2 and O2. A significant amount of energy has to be spent in getting rid of the product formed from O2 insertion.

All these hurdles lead to a rather drastic lowering of photosynthetic efficiency which gets watered down to a rather measly (but still staggeringly efficient by human standards) 4% or so.

It's pretty clear from this description that any kind of efforts to get better efficiency from biofuels will have to overcome enormous protein engineering hurdles. This does not bode well for current studies aimed at such goals. While these are very exciting from an academic standpoint, they will have to lead to a very drastic retooling of the basic photosynthetic apparatus, involving re-engineering numerous genetic pathways and their products, to be of large-scale commercial value. It's all too easy to underestimate the sheer amount of energy that we want to generate from these technologies. I feel the same about the synthetic biology efforts that seek to produce all kinds of valuable industrial chemicals and drugs from engineering bacteria. These efforts are undoubtedly promising, but getting bacteria to do something which they have not evolved to and that too on a scale rivaling the fossil fuel industry is a very long shot indeed. Michel doesn't even seem optimistic about the recent excitement regarding biofuel production from red algae, and reading his prognosis one wonders how much collaborations such as the one between Exxon and Craig Venter are actually going to yield. And finally, there's all the alternatives which that land for biofuels and the biofuel feedstock itself can be put to, which is a question still being pondered.

Michel is much more optimistic about photovoltaics which already promise energy conversion efficiencies of more than 15%. When the end product is used in a car, photovoltaic batteries also funnel about 80% of their energy into propelling the vehicle. In addition, Michel sees promise in recent advances in battery technology leading to much higher energy density.

Personally I am a proponent of context-specific energy use. I think that considering the vast variation of resource distribution, geography, energy requirements, paying capacity and economics, it doesn't make much sense to search for any one-size-fits-all solution. But that seems to usually be the case every time someone touts a single, seemingly miraculous solution as being universally applicable around the world. I have similar thoughts about solar energy. The solutions currently available don't seem to solve the problem of transmission and availability in regions where the sun doesn't shine that much. Part of Michel's "vision" is the widespread deployment of superconducting cables which even now (more than 25 years after the discovery of "high-temperature" superconductors) seems like a minor fantasy. Notwithstanding these issues though, solar power certainly seems to have a much larger role to play in our economy than it currently does, especially in regions which get plenty of sunlight.

But biofuels? The problems there seem much more grounded in fundamental biological constraints rather than technological ones. And it's hard to overturn 3.5 billion years of evolution so I am not sure I should hold my breath. Time will tell.


  1. Personally I am a proponent of context-specific energy use. I think that considering the vast variation of resource distribution, geography, energy requirements, paying capacity and economics, it doesn't make much sense to search for any one-size-fits-all solution.

    Thoroughly agreed - I'm always a bit perplexed when someone suggests that such-and-such method won't work in his or her part of the world. Well, OK, fine - but why try and prevent those for whom it could be an effective source of energy from implementing it?

    Insofar as the tie-in to photosynthesis...I was always under the impression that much of the interest was driven by the "splitting water under ambient temperature & pressure" aspect and the remarkable quantum efficiency in the reaction centers, and less on the lossy aspects of light harvesting and downstream biochemistry.

    Of course, as I always remind people with a smile, solar power provides an upper limit on people's tolerance for nuclear power - no one seems to strenuously object to a fusion reaction 93 million miles away.

    1. Quite so. Even if you don't like geothermal, I don't see why you should stop the people of Iceland from using it. I think part of the problem is that many of us are looking for the one magic solution when ironically even now our energy comes from a mix of technologies (even if it's dominated by fossil fuels).

      I like your quip about nuclear power; it's interesting that nobody seems to be concerned if a part of the electricity that's currently powering their home appliances is coming from nuclear, as it does for most people living in this country. So most people seem to be at least implicitly ok with nuclear as long as it's not in their backyard. But they won't say that aloud.

    2. Splitting water is 85% efficient in commercially available electrolysis units.

  2. With all due respect to Hartmut Michel, I think his editorial is both grossly oversimplified and misleading. There are numerous points in his article that are of dubious validity, among them the following:

    --He discusses photorespiration, i.e. O2 insertion catalyzed by RuBisCO, but completely fails to mention C4 and CAM photosynthesis, both of which reduce loses to photorespiration. (If you look, you'll notice his article refers specifically to C3 photosynthesis.) This omission is bizarre, because many of the plants most often cited as possible biofuels crops are C4 (e.g. switchgrass).

    --He claims that more than 50% of the energy stored in biofuel must be invested during production and that "some scientists doubt there is a net gain of energy", but these figures and this claim clearly refer to corn ethanol (and indeed this is even specified in the article). But corn ethanol IS NOT THE ONLY OPTION -- there are many others -- and this claim is an absurd generalization. His claim that bioethanol from sugarcane in Brazil is "an extremely inefficient use" is presented without any justification, even though bioethanol from sugarcane DOES have a net positive energy balance (unlike corn ethanol) in part because bagasse is burned for fuel.

    --He claims that growing crops for biofuel will displace food production. This is true ONLY IF you are talking about first generation biofuels (e.g. corn ethanol, soy biodiesel etc.) If you are talking about cellulosic ethanol from agricultural waste, you are not displacing food production in any way; and the same is true for algae biofuel production.

    I could go on, but I don't want to belabor the point. This editorial strikes me as a flimsy and dismissive attempt to take valid criticisms of first-generation biofuels (corn ethanol and soy biodiesel) and use them to mischaracterize second- and third-generation biofuels (algae & cellulosic), both of which are very different from first-generation. While he portrays biofuels as being much worse and more inefficient than they are in reality, he at the same time tries to portray other technologies which he favors (electric cars etc) as being an ideal solution, completely ignoring the challenges these other technologies face.

    Ultimately I don't think there is any "one-size fits all" universal globally-applicable solution to the energy challenge -- Michel to the contrary.

    1. Thanks for your comments. I too was wondering about C4 plants and cellulosic ethanol. Do you have some figures for how the percentage efficiency of C3s which Michel points out compares with C4s? Personally I found the article most interesting for the problems with protein engineering that it points out. I have a little bit of experience in protein design and any kind of fundamental engineering of photosynthetic proteins is indeed going to be tremendously challenging and I really can't see how it can be deployed on a global scale in the near future. I see Michel's article mostly as a valid criticism of genetic engineering efforts to produce biofuels. I do agree with your points about photovoltaics and existing biofuel efforts.

    2. Cellulosic ethanol runs into the problem that you need energy to remove the water. Also, you have to move the trees to the factory first. You carry a lot of water around. Another energetic loss. Therefore no large scale cellulosic ethanol production exists by now. Nowhere on the planet.

  3. CW,

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  4. No one expects to replace all petro-fuels with bio-fuels. That is a straw man argument. It is also wrong to judge every approach to bio-fuels by the limitations on first generation fuels such as maize ethanol or rape biodiesel.

    One well financed startup is claiming the production of 4,000 gallons of bio-gasoline per acre of the cellulose crop giant miscanthus. The company is backed by Google, GE, Conoco-Phillips, BP, and a few other giant industrial powers.

    More information at Al Fin Energy,

  5. Only when Bio-fuels can compete on the open market without Government subsidies will they be any more than a Eco-fanatic wet dream.

    Probably never more than a niche market, constrained in area by supply and distribution.

  6. Too bad the latest scheme from the Obama Administration, fuel from algae, will likely be used to launder US Taxpayer money into campaign contributions as was done with Solyndra and other "Alternative Energy" proposals.

  7. Actually, I am a big proponemt of the original bio-fuels that have been used for millenia, and are still in use today, Oil, Natural Gas, and Coal.
    And wood fires for a wood-stove or fireplace, and for smoking delicious meats too.

  8. Anon 2/24/12 15:26 Sure, but they took millions of years to make - burning them in millenia isn't going to work out well for humanity. I kind like the option of seeing New York City in something other than glass-bottomed boats, or not turning North Dakota into Arkansas, or not rehashing "Fifty-Four Forty or Fight" as a slogan for 22nd century ambitions.

    Of course, Michel seems to have elided one of the bigger problems with solar - where do you store the energy? For individual transit, you've got to carry your energy with you. The current and next generation batteries don't really help you there. If you want individual transit, you probably need liquid fuels, which biofuels (as well as oil and coal) can provide. For other uses (homes, businesses), solar works sometimes, but not always (and where it works is far from where the energy is needed, and moving it is lossy).

    In addition, citing efficiency is helpful when you look at human input - it doesn't matter if only 4% of the solar energy is converted to fuel, because you didn't have to do anything to get it, unless you're already using it all (when efficiency becomes the bottleneck). In addition, lots of space and volume that solar can't use is used or can be used for biofuels. 15% efficiency on 20% of the world loses to 4% efficiency on 90% of the world. (with the bonus that much may not be lost to other use, though that can be true with solar, too).

    A negative for biofuels is pulling biomass out of the system - if you use it for fuel, you can't fertilize the ground with it. Eventually those nutrients will need to be replaced, and since ammonia production is a big energy sink, you're going to have to pay for it.


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