Ethanol, Ethanol Everywhere, Time to Stop and Think

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Ethanol (a.k.a. alcohol) will certainly grow as a business and serve as a partial solution to our energy problem, particularly given that it is now taking the place of the gasoline additive MTBE. However, even if large-scale cellulosic ethanol technology is perfected, I don't believe it can become the primary solution to the world's energy needs.

The often-used example of Brazil does not apply to most parts of the world and may not even apply to Brazil if they see high economic growth with its attendant energy demands. Brazil is in the tropics with an all year round growing season and an enormous amount of arable land relative to its population food requirements and the number of cars on the road.

In contrast, domestic ethanol as the primary solution will definitely not work for the world's most populous countries, such as Japan, China, India, Pakistan, Indonesia, etc. Those countries are either breaking even on domestic food production or are net importers. If you argue that ethanol is to be grown elsewhere and shipped, where are the vast tracts of unused arable land? And, bear in mind, the calories burned by two ton cars are much greater than those burned by 170 pound humans.

Let's consider the specific example of the United States vs. Brazil (production is taken from the Oil & Gas Journal and consumption from the BP Statistical Review, 2002 data). Oil consumption in the US is 27 barrels per person per year (BPY) vs. 4.2 BPY in Brazil, but the US also produces more oil at 11 BPY vs. Brazil at 3.35 BPY. Therefore, Brazil has to close a gap of 0.85 BPY, whereas the US has to close a gap of 16 BPY, resulting in a per person supply/demand imbalance 19 times greater than that of Brazil! Moreover, the US has a population 50% greater than Brazil, but has less arable land and a shorter growing cycle. If the US had the same per person oil usage as Brazil, it would be a major oil exporter. This is why the "Brazilian Miracle" is still limited to Brazil.

Photosynthesis vs. Photovoltaics

Another way to think about the problem is that plants are essentially just a very inefficient way to convert sunlight into stored chemical energy. Crops typically have a net efficiency of about 1/2% or so, compared with commercially available photovoltaics at 20%. That means you need about 40 times more land area for crops than you do for photovoltaics to capture the same energy. Complicating the issue is that crops require arable land, which will apply great pressure to what little remains of unfarmed wilderness areas around the world. In contrast, photovoltaics can usually be installed on your home or business rooftop, efficiently delivering energy right where it is consumed and taking up no extra land at all.

If you want to use plants most effectively as an energy source for transportation, the best way is to burn them whole (no processing needed!) in a combined cycle biomass electric generator at 60% efficiency and use the output to charge electric vehicles. That requires no technology breakthroughs, uses the full energy content of the plant, and is far more efficient than refining a small part of the plant or even most of the plant, using cellulosic technology, into ethanol to power the 20% efficient internal combustion engines of cars.

Photovoltaics and Ethanol Efficiency
Photovoltaics and Ethanol Efficiency

The map shows the relative areas required to offset 50% of the miles driven in the US for photovoltaics, cellulosic ethanol and corn ethanol. Compared to photovoltaics, cellulosic ethanol, which is still unproven at large scale, requires a huge land area, even when using the assumptions of its most optimistic proponents. That is why Tesla Motors will be co-marketing solar panel solutions from partners like SolarCity. With just a small 10 ft by 15 ft solar panel tucked away on the roof of your garage, you will generate enough electricity to travel about 400 miles per week in the Tesla Roadster. If you travel less than that, you will be energy positive with respect to transportation and the excess electricity will offset your home's power usage.

---- UPDATED SEPTEMBER 8, 2006 ----

Crop Efficiency

[From a discussion I had with Prof. Nate Lewis at CalTech]
The fastest growing crop, switchgrass, stores energy at a yearly averaged rate of 1 W/m2, for a peak solar efficiency of less than 0.5% (220 W/m2 mean latitude yearly averaged insolation). However, you would be lucky to get 0.2% after considering energy inputs and outputs. Wang and the Argonne GREET model are somewhat more optimistic, achieving about 0.3% net for taking the fastest growing crops and just burning them. Making ethanol is another story altogether, and if not negative, is less than 0.1% at best and more like 0.01% from current corn technology and maybe 0.1% from cellulosic if cellulosic is ever actually developed to work at commercial scale. There is an excellent paper by Pimentel, a professor at Cornell, and Patzek, a prof at Berkeley, in Natural Resources Research (Vol. 14:1, 65-76) on the energy yields of a variety of crops, including corn, switch grass, wood, soybeans and sunflowers.

The Future of Electric Energy Storage

Lithium-Ion batteries are the most efficient way to store electricity today, but I suspect we will find that there are even better technologies down the road. In fact, my original reason for moving to Silicon Valley about a dozen years ago, before I got distracted by the Internet, was to do a Ph.D. at Stanford in the physics and materials science of high-energy density capacitors, specifically for electric vehicle applications. Prior to that, I had worked for two summers at a small company called Pinnacle Research, which focused on ultra-capacitors. Capacitors have the advantages of a quasi-infinite cycle and calendar life, extremely low charge/discharge losses, and charge times measured in minutes (if you have high voltage and thick wire) for a car-size pack. If the capacitor energy density problem is solved, the gasoline vs. electric car contest goes from being a contestable fight to gasoline getting the Wrestling Smackdown.

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Comments

dollarswest@gma...

how good can ethanol for fuel. best desktop computers

MargaridaR

Although I have noticed I am a bit (about 6 years) late on the blog commentary, I wanted to say that I totally agree with you on the ethanol matter. And by reading your posts I actually learnt a few things that I personally did not know and it is fascinating to see how your way of thinking is so down to earth, logic and rational. So for that... thanks.
First, I have to congratulate you on the amazing projects you are embarking. It gives me great pleasure to see that major issues of our civilization are finally being efficiently tackled, and for me, you a true inspiration of the 21st century and one of the few living people which I have high regards towards. I did try to see if I could work in any of your companies but as I am starting my career in molecular biology.... that does not fit in your company plans. But if anything you have inspired me to revolutionize my area of work and I have already a few ideas of my own!
Now, my personal view on the extensive farming for the production of ethanol: I think it is very silly to farm and process plants for the single propose of obtaining a bi-product to attend the energy needs of a population. This is because not only as you mentioned, it demands large areas of land (which I must say that most of the time is achieved by deforestation, Brazil being one of the sad examples) but it also leads to de-nutrition of the soil, increased use of pesticides and high demands of water. In fact, roughly only 1% of the water in the world is available for human consumption and of that a staggering 70% is used for farming! Not to mention that lack of potable water is still a major issue in various countries. Furthermore, increased and constant use of pesticides creates three big issues; it kills a wide range of animals (from small vertebrates to invertebrates) as they are designed to interfere with essential life processes, it contaminates the soil and its extensive use against crop pests increases the chances of the development of mutations in a pest population rendering them resistant driving further costs to the development of new control strategies.
It is well known that the earth ecosystem is very complex with lots and lots of interactions which we are still being unveiled, and it is just plain silly to start tempering with it at large scales without even knowing the full effects it could have. I personally believe that plants should be protected, let to grow freely and focus on its optimization for the feeding demands of our world by modulating plants to optimize their resistance to pests, yield higher nutrition values and consume less water. And of course, now with Space X, it would be interesting to continue plant research for its use in other planets with projects such as the biosphere and maybe start studying and introducing specially picked and genetically constructed plants for the use in outer space.
Once again, thank you for the amazing work you are doing, you are a true inspiration to me and as I am finishing my PhD at 25 I hope to be able to act a little bit more like you and not be scared of a challenge as long as it is well thought through, relevant and helpful to the future.
On a lighter note, I love the Tesla (best name you could have picked, and thank god you didn’t go for Eddison which was really mean to Tesla and electrocuted an elephant!) and I am looking forward for the roadster experience at the Olympic Park in London so I can finally see one in action, maybe I will even be able to test drive it.
Hope to see your blogs more often, they are really good. And wish you all the best and keep up with the good work!

Solar Powered B...

I agree that Ethanol is only an intermediate solution (actually, I think that Biodiesel is better than Ethanol). Eventually it will be a combination of renewable energy sources and the most used source will be solar appliances.