On Mar 9, 2006, at 12:19 PM, Jed Rothwell wrote:
See:
http://rael.berkeley.edu/EBAMM/ERG-NPR-letter-1-30-06.pdf
Farrell agrees with Pimentel that ethanol takes a lot of input
energy -- although he does not specify how much in this letter. He
says that Pimentel was wrong and that the Berkeley study did take
into account the energy used by farm machinery.
His main point is that much of the input energy for ethanol
production comes from fuels other than oil, so it produces a net
increase in transportation fuel. Maybe so, but I doubt it is
economically viable, I doubt it does anything to reduce CO2
emissions, and I expect that if the subsidies were withdrawn no one
would buy the stuff.
- Jed
Looking at Farrel's original article, I don't see any mention of the
energy required for soil restoration. Nitrogen fixation alone is
extremely energy intensive. A typical source of hydrogen for this
purpose is natural gas - which could more efficiently be used as a
vehicle fuel directly.
In regard to nitrogen, the detailed spreadsheet model only mentions:
"Nitrogen fertilizer production (MJ/ha)": 66. The total given for
nitrogen, phosphorus and potassium fertilizers is 66 + 67 + 117 Mj =
250 MJ/acre. This seems way low. Also, I don't see natural gas
mentioned in this regard.
http://www.yara.com/en/products/fertilizer/about_fertilizer/
fertilizer_use_inter.html
shows about 170 kg/hectare nitrogen fertilizer use, or about 8 GJ/
hectare. This is 32 times the energy input used in Farrel's model.
Other sites show 100-200 kg/hectare fertilization rates for various
crops. I would expect soil restoration to be extremely energy
intensive if every part of the crop is taken for cellulose
digestion. Also, heavy fertilization itself can produce air and
water pollution.
Horace Heffner
