The “new study” by Pimentel and Patzek in Natural Resources Research, Vol 14, (March, 2005) showing negative energy value in all biofuels is even more biased and less scientific than most of what we’ve seen from Pimentel for the past 25 years.
Perhaps the biggest technical problem in Patzek’s works is the value used for the fossil energy input in production of fertilizer. This energy requirement has been steadily decreasing over the past 35 years. The theoretical minimum for NH3 is around 25 GJ (HHV) per ton of NH3. The mean for plants built in the 1960s was 75 GJ/t, and for new plants constructed in 1997 it was around 33 GJ/t. The average for all U.S. plants in 1995 was 40 GJ/t, or 11.1 MWh/t, or 17,600 BTU/lb. Patzek (in a 2003 paper) mentions this 1995 U.S. average number, then inflates it (unnecessarily) 10% for transportation and handling. He then jumps to an energy value for urea (which is more energy intensive than ammonia and accounts for about 50% of nitrogen application) from the 1980’s (28,800 BTU/lb), inflates it by 10% for transportation and handling, and applies this number to all fertilizers.
A more realistic number for mean fossil energy per pound of fertilizer just 5 years from now is about half of what Patzek assumes. And of course, 20 years from now, it could easily be just 20% of what Patzek assumes if there is aggressive support of production of renewable fertilizers on wind farms.
Then there is the question of how much fertilizer is used. Are the reported numbers in pounds of NH3 or pounds of nitrogen? Patzek assumes agricultural reports are always quoting nitrogen fertilizer amounts in nitrogen content, whereas in some cases they were reporting ammonia amounts and nitrogen would be 14/17 as large. He then consistently uses the highest reported fertilization rates from various studies. His phosphorus application rates, for example, are at least 30% above more commonly reported mean rates, which are steadily decreasing.
There are similar problems in his analysis of energy required for processing the corn into ethanol, where he relies heavily on data from the 80’s, which he then inflates by 20% to account for the energy required to make the concrete and steel in the ethanol plant (even though the plants may have a 40 year design life). His credits for the value of co-products are unrealistically low by even greater proportions. His analysis of ethanol from cellulose and hemicellulose, based on processes from the 70s and 80s, is not even worthy of comment.
Finally, for special effects, Pimentel and Patzek like to report the total energy input, including the solar energy, just after he’s been summing fossil energy input and net energy output in an attempt to mislead the unwary reader into thinking the total ethanol energy output is 35% of the fossil energy input – though he is careful not to actually state that.
Pimentel’s support of solar and wind is commendable, but that is no excuse to distort the case for biofuels. It is certainly quite possible that analyses by biofuel supporters are rather optimistic for current standard practice; but this is excusable, as there has been a significant trend toward improving efficiencies over the past 15 years, even though fossil energy costs have been very low during most of that period. With fossil energy costs now rising rapidly, we can expect rapid strides in all efficiencies involved in biofuel production over the next five years.
See Shapouri,
http://www.ethanolrfa.org/net_energy_balance_2004.pdf , for a balanced analysis of corn-ethanol.
See U.N. report #26,
http://www.fertilizer.org/ifa/publicat/pdf/part1.pdf , for all you ever wanted to know about the fertilizer industry.
See Greene, “Growing Energy”, NRDC,
http://www.bio.org/ind/GrowingEnergy.pdf for serious analysis on cellulosic ethanol.
See Doty,
http://www.dotynmr.com/PDF/Doty_FutureFuels.pdf , for a sound look at Future Fuels.
See Patzek,
http://petroleum.berkeley.edu/papers...Patzek-Web.pdf , for some extremely biased analysis based on obsolete data.
F. David Doty, PhD, physics
