The Ergosphere
Thursday, September 08, 2005




Question #1:  Can ethanol from corn or other grain replace gasoline?

Answer:  Almost certainly not, for several reasons.
  1. There isn't enough grain.  The best process we have makes about 2.66 gallons of ethanol from a bushel of corn (maize).  The 2004 maize harvest was about 11.8 billion bushels; if all of it was used for ethanol, it could make a maximum of 31.4 billion gallons of ethanol (with energy equivalent to about 22 billion gallons of gasoline).  US gasoline consumption in 2003 was roughly 134 billion gallons, or more than 6 times the amount which can be replaced by ethanol production from corn.  Total US motor fuel consumption (gasoline and diesel fuel) is approximately 200 billion gallons per year.
  2. Ethanol requires too much other fuel to produce it.  A gallon of ethanol (84,200 BTU) consumes about 33,000 BTU of heat in the distillation process alone.  Some of this heat comes from coal or cogenerators, but most distillers burn natural gas or LPG.  LPG is a petroleum byproduct, and natural gas supplies are tight and getting tighter.  Ethanol producers are competing with people who need to heat their homes.  The energy losses of the ethanol process make it more efficient to burn the grain for heat, and use the LPG or natural gas as motor fuel (source).

(added 2005-Sep-08)

Question #2:  Someone sent me an e-mail about bio-butanol as a replacement for gasoline.  Could we get rid of oil this way?

Answer:  No.  Environmental Energy, Inc ( claims a process which yields 2.5 gallons of butanol per bushel of corn (maize).  They further claim 105,000 BTU/gallon of butanol vs. 84,200 BTU/gallon of ethanol (~25% more energy) which makes it a superior fuel.  This is true so far as it goes, but this also runs into limits of raw materials; 11.8 billion bushels of corn would make 29.5 billion gallons of butanol.  This would displace less than 1/5 of US gasoline consumption, with nothing extra to replace diesel fuel.  The major advantage of butanol over ethanol is that it would require far less energy to separate it from water; it would be worthwhile to promote butanol rather than ethanol for energy-security reasons.
Source:  Environmental Energy, Inc (
(added 2005-Sep-08)

Question #3:  Could ethanol from crop wastes replace gasoline?

Answer:  Probably not; there almost certainly isn't enough biomass available.  The surplus biomass of corn stalks and such (corn stover) is the largest single biomass source in the US; it yields about 2.5 tons/acre (source) at the average yield of 146 bu/ac.  The surplus biomass over the entire 80.7 million acres planted to corn is roughly 200 million dry tons per year.  Even if the entire dry mass was converted to ethanol with the same efficiency as grain (2.66 gallons per 56-lb bushel, or 31.3% by weight), it would only produce 62.6 million tons (19.0 billion gallons) of ethanol, equivalent to about 13.3 billion gallons of gasoline.  In practice only 30% to 60% of this biomass could be made available for fuel production, and the energy requirements for distillation come on top of this.
Source: (corn stover yield)
Source: (2004 corn harvest)
(added 2005-Sep-08)


Question #1:  How efficient are batteries?

Answer:  It depends on the type of battery.  Lead-acid requires equalizing charges which make it relatively inefficient overall, while modern Li-ion has over 95% efficiency.
(added 2005-Nov-04)


Question #1:  Can cogeneration be made quiet and friendly enough to use in a dwelling?

Answer:  Many generators are already quiet enough to use near a home, and the backers of Climate Energy LLC are betting money that they can sell cogeneration systems for people to put in their homes.
(added 2005-Dec-21)


Question #1:  Is there any truth to the claim that oil is abiotic in origin, and we'll never run out?

Answer:  Almost certainly not; there may be trivial amounts of abiotic hydrocarbons coming out of the earth, but
  1. All chemical and geological evidence (on-line source) indicates that the source is from ancient organisms, and
  2. Even the most cursory arithmetic shows that the rate of production cannot be remotely close to our rate of use.

Source:  No Free Lunch, part 3 of 3
The Oil Drum
(added 2005-Nov-04)


Question #1:  Do solar panels ever pay back the energy needed to make them?

Answer:  Yes.  As of the late 1990's, systems based on crystalline silicon PV panels returned their energy of manufacture in less than 4 years (about 3 years for the module and frame), and systems based on thin-film panels in a bit over two years (2 years for the module and frame); advances were expected to reduce the system figures to about 2 years and 1 year, respectively.
Source:  NREL
(added 2005-Sep-08)



Question #1:  What's the skinny on vehicle-to-grid?

Answer::  See the Vehicle-to-grid page at the University of Delaware.
(added 2006-Sep-30)


Question #1:  Do wind turbines ever pay back the energy needed to build them?

Answer:  Yes, and very quickly too.  One analysis found that a land-based wind farm would return its invested energy in a mere 0.26 years (3 months 4 days), and a sea-based wind farm would pay back in 0.39 years (less than 5 months).  This analysis was for 1.5 MW turbines, which are already small compared to the 5 MW turbines which are soon to be current and will be dwarfed by the 10 MW turbines considered to be most economical.
Vestas is slightly less optimistic about their latest, claiming a payback in 6.8 months.
A more recent summary of analyses is not so optimistic on average, but strongly positive nevertheless.
      The Oil Drum | Energy from Wind: A Discussion of the EROEI Research
(updated 2006-Oct-19)

Question #2:  How much wind power is available, world-wide?

Answer:  The latest estimate is 72 terawatts from areas of class 3 (6.9 m/sec wind speed) or greater.

Further information:  Mark Z. Jacobson's wind page
(added 2005-Oct-30)
(updated 2005-Dec-02)


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