Well-Thought Out Argument Against BiofuelsDr. Hartmut Michel won the Nobel Prize in Chemistry in 1988 for his work on photosynthesis, and he's currently the director of the Molecular Membrane Biology department at the Max Planck Institute for Biophysics. It's fair to say that he's not only one of the smartest people in the world, but also one of the top experts on how plants turn sunlight into energy. To say that he's qualified to comment on biofuels - which is basically all about turning sunlight into chemical energy via plants - is an understatement. His views on this topic should carry a lot of weight.
So what are Hartmut Michel's views on biofuels?
The Math Doesn't Add UpBeing a top scientist, Dr. Michel reasons from first principle. What are the physical limits to each step of the process, and when you then put it all back together, what have you really got? Here are choice excerpts from a recent editorial that highlight his reasoning:
1. How efficient is photosynthesis?
The photosynthetic pigments of plants can only absorb and use 47% (related to energy) of the light of the sun. Green light, UV, and IR irradiation are not used. [...] Photosynthesis is most efficient at low light intensities. It is already saturated at 20% of full sunlight and 80% of the light is not used [...] As a result of the limitations described above, 4.5% is considered as the upper limit of the photosynthetic efficiency of C3 plants. However, in reality, values of only around 1% are observed, even for rapidly growing trees like poplars.
So right from the start, plants are only converting about 1% of the sun's energy into chemical energy. Leaving 99% of the energy on the table isn't a very good start... And this compares very badly with commercially available solar panels which can convert around 20% of sunlight into electricity, two orders of magnitude more (and better efficiencies are possible).
2. How efficiently can we turn biomass into biofuels?
When the yields of biofuels per hectare are known, one can easily calculate how much of the energy of the sunlight is stored in the biofuels. For German “biodiesel” which is based on rapeseed, it is less than 0.1%, for bioethanol less than 0.2%, and for biogas around 0.3%. However, these values even do not take into account that more than 50% of the energy stored in the biofuel had to be invested in order to obtain the biomass (for producing fertilizers and pesticides, for ploughing the fields, for transport) and the chemical conversion into the respective biofuel. This energy normally is derived from fossil fuels.
So a minuscule fraction of the sun's energy ends up in biofuels, but a large fraction of even that end product had to come from fossil fuels. This means that carbon emission reductions are minimal, and sometimes there might not even be any. And to do that we have to use large quantities of arable land and food, thus degrading precious soil and putting pressure on food prices, hitting the poor especially hard.
3. Can we improve the process?
Dr. Michel then looks at what could possibly done to improve the efficiency of photosynthesis. Many things would be possible (plants that absorb more of the light spectrum, for example), but nothing that would totally transform the math and make biofuels superior to the alternatives. He concludes:
Improving photosynthesis, although a highly important goal towards securing food security, cannot change the superiority of the combination photovoltaic cells/electric battery/electric engine. [...] Because of the low photosynthetic efficiency and the competition of energy plants with food plants for agricultural land, we should not grow plants for biofuel production. The growth of such energy plants will undoubtedly lead to an increase in food prices, which will predominantly hit poorer people.
He concludes with this sentence: "The future of our individual transport has to be electric!"
4. Using biofuels: How efficient are internal combustion engines?
Indeed, electric vehicles look even better if you add another step to Dr. Michel's reasoning and look at the efficiency of internal combustion engines vs. electric motors. The efficiency of the average gasoline car hovers between 20-30% while for diesels it can be between 30-40%. This doesn't compare well with the 88% drive efficiency of the Tesla Roadster (and a few more percentage points will no doubt be squeezed out of EVs as the technology matures).
Interestingly, these conclusions are very similar to Elon Musk's when asked about biofuels in a recent Q&A. Great minds...
Some Uses for Biofuels?Personally, I've been against corn ethanol ever since I saw the studies that show just how little net energy is produced, if any at all, and even then, using arable land and food to make fuel will never be sustainable. Biodiesel made from waste is a lot greener, but sadly it doesn't quite scale up and recent diesel vehicles have sophisticated emission controls that don't always play nice with biodiesel. Then there's second and third generation biofuels made from non-food sources like switchgrass and algae. Those have the potential to be a lot greener, but you still run into the inefficiencies explained by Dr. Michel and others.
The only benefit is that you get an energy-dense a liquid fuel, so maybe those types of biofuels can be used in aviation where electrification isn't on the horizon for the foreseeable future. But for other types of transportation, it still would be orders of magnitude more efficient to collect solar energy with solar panels or solar thermal than via plants.