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    Biofuels, Diet & Exercise
    By Jack Vermillion | November 13th 2009 12:35 PM | 3 comments | Print | E-mail | Track Comments

    Now we get to corn.  It seems that everything having to do with generating chemical energy, like methane and alcohol, making plastics is lumped under the moniker “biomass.” 

    The fun with biomass is to follow the money.  Take biodiesel.  We just grow soybeans, rapeseed, sunflowers – whatever you want to make oil out of, press them and run diesel engines with it. Diesel engines are great machines and happy burning just about any fuel –  hydrogen included.


    First start with natural gas to make hydrogen to make ammonia to make fertilizer.   Then plant soybeans, irrigate them, use the carbon fertilizer on them, use oil based insecticides and herbicides.  Run the pumps and tractors with oil.  Use oil to harvest and separate them.  Use electricity to squish and process them.  If you want the nitty-gritty  go to the U.S. Department of Agriculture and the U.S. Department of Energy report titled: Life Cycle Inventory of Biodiesel and Petroleum Diesel for Use in an Urban Bus. (NREL/SR-5R-24089, UC Category 1503, May 1998.)


    The NREL report includes a very good analytical model of the entire soybean lifecycle from seeds to biodiesel.  It accounts for everything from the potash used as fertilizer, to the steam used in the oil presses, to the energy cost of the growing of the seed to plant.  It also adds in the various emissions and waste issues.  This analyses predict a 3-to-1 ratio for energy in the biodiesel  to the oil energy needed to make it.  A 66% efficiency, in other words.  That is for every 3-units of biodiesel energy you make you only have to spend 1-unit of carbon energy.  You can replace the carbon energy with biodiesel energy at some point, but the efficiency will always be 66% +/-.  You cannot not spend more energy to grow and process the soybeans than you get out – otherwise you would have a perpetual motion machine of the first kind.  Can’t have one of those - no matter how much money you send to the website in New Jersey.


    66% efficiency is great! But, the soybeans do not grow in isolation.  They exist in a system that includes land use and economics.  Aargh, reality is so messy.  The easy part is getting the land use numbers, which in the US is 75,208,000 acres planted in soybeans in 2004 according to USDA National Agricultural Statistics Service.  The same source lists total US cropland at 434,164,946 acres.


    The hard part is to find any good numbers for how many gallons of biodiesel you get for your acre of soybeans.  (The NREL report is just numbers thrown together, not the real world.)  Some excited environmental web sites give ranges of 100-150 gallons per acre and Wikipedia gives a range of 40-50 gallons per acre.  There is press and public relations talk about algae, palm oil, and imaginus plantus being way better than soybeans.  None of them present measured data and analysis, of course.


    Take the highest number anywhere – 150 gallons per acre.  Then soybeans yield net .66 X 150 or 99 gallons per acre.  If we take every single soybean grown in the US and make biodiesel out of them we would get about 7.4 billion gallons of diesel per year. 


    The Green Car Congress published a 2003 Energy Information Administration (EIA) estimate for total US diesel consumption of 37.1 billion gallons.  So, if every acre of soybeans in the US were turned into biodiesel it would provide 20% of the 2003 demand for transportation diesel.  Using 100% of the agricultural land in America, 434 million acres, for soybeans, you could make 43 billion gallons of biodiesel, or 116% of the 2003 US diesel demand.  That leaves a few acres left over for food! (60 million acres)  Yea!  We can eat too!  And, be on a real strict diet and loose lots of weight!  Yes!


    There is another way to look at biodiesel too.  That is to compare it to other uses for the land – besides eating!  Put solar collectors in Iowa.  A gallon of biodiesel is about 130,000Btu of energy.  (That is a little less than regular diesel which has 140,000Btu – another efficiency factor to throw in.)  So our acre of farm land in Iowa makes about 150gal/acre x .66 x 130,000Btus or 85,800Btu/year of energy.  ( 25.1Kwh in SI units.)


    Go to the National Renewable Energy Laboratory (NREL) solar tables and look up Sioux City Iowa for June:  6.0Kwh/m2/day solar incident for flat plate solar collectors facing south and tilted at the latitude of Sioux City.  You know where this is going now, don’t you?  Soooo – one acre of currently available solar cells at 18% efficiency, a very good collector you can buy now,  generates about 4370kwh in one average day in an average June.  That is 181 times the amount of energy as that fields could produce in one year in biodiesel.  For 4.8kwh/m2/day/year (NREL data), the solar acre collects 1,276,230kwh/year. 


    The total energy efficiency of a field of soybeans for biodiesel energy compared to 18% efficient solar collectors on the same field, from the above, is 0.002%.  Compared to 100% solar incident, soybeans are 0.00036% efficient in converting solar energy to biodiesel from the seed to the gas tank.  Or, or, to put too sharp a point on it, just use one of those solar panels.  That panel would produce 355kwh for the year – three times the net biodiesel energy output of the whole acre of soybeans.


    Oh yes, corn.  The bad guy of US agriculture, food production, obesity, and now energy!  It seems some people have calculated that to make ethanol out of corn it takes more energy from fossil fuel than you get from the alcohol.  Others are saying: “Nah, nah, nah! my calculations show a factor of one-point-a little bit.  You are wrong, you nasty people who say it is a bad idea!”  Well, not exactly that way, literary license.  Who really cares?  It is a lot worse way to make stored chemical energy than soybeans.  That does not even count water use, alternative land use, chemical buildup in the soil, and the rest.    


    Oh, wait, I missed the point.  Silly me.  I thought those people were arguing about technology, economics, energy, and the environment.  They were really talking about who gets a corn subsidy from the taxpayer.  Wikipedia once gave a nice little breakdown for ethanol subsidies awhile back (may be a little different every year).  The breakdown was: $0.214/gallon for the alcohol, $0.61/gallon to the corn farmers, and another $0.54/gallon if the ethanol is sold as fuel in the end.  (Government simplicity strikes again!)  That is $1.364/gallon for corn ethanol that is mixed with gasoline here in California to keep our air clean.  And, you thought that the government did not support alternative energy and pollution controls!


    Then there are the palm oil plans and the algae proponents that will solve the problem because those are way better solar chemical energy collectors.  So, cool, go do it.  What is stopping you?  Make money and get rich.  Become the Microsoft of bioenergy.  Oh wait - you want a subsidy too?  There I am being silly again.


    Comments

    I have a chemistry problem concerning synthetic gasoline.
    In Chemtech Magazine November 1990, there is an article about producing methanol with carbon dioxide and hydrogen gas over a copper catalyst. In the mid 1970's the Mobil process was developed to convert methanol through a zeolite catalyst into gasoline. If the electricity from your solar panels were used to produce the hydrogen for methanol production, how much gasoline could an acre of land of solar panel produce in a year?

    rholley
    A very good question, but not one which I can answer at the drop of a hat.

    Nevertheless, I just saw this:

    Bacteria turn carbon dioxide into fuel


    from which I quote
    The modified bacteria are highly efficient and powered by sunlight, so a future goal is to set up colonies near to industrial plants. This would allow greenhouse gases to be recycled into useful chemical feedstock - supplying several hydrocarbons that are typically obtained from petroleum.
    Promising? 
    Robert H. Olley / Quondam Physics Department / University of Reading / England
    I think it would be interesting to have an economic battle between coal power company produced gasoline (by bacteria or chemical) versus oil company produced gasoline. You have to wonder at what point does gasoline become more profitable than producing electricity.