I see no facts criticised with no facts. Save the atta-boys for something worth reading not put-downs.

http://www.quaker.org/tqe/2006/TQE145-EN-Hybrid-Details.html

OK, it's one source and who knows how close it is, but let's see what happens...

Assume 4 sun hours per day (4 hrs at 1000 watts/sq.m), a 12% efficient panel will produce 1000x0.12x4x365=175,200 Whr per year.  Take 4000 TW (4E15 Watts) divided by 175,200 = 22.8E9 square meters, = 22831 sq. km = 8800 sq. mi.  for a square area that equates to 93 miles x 93 miles.  To cover the electrical use for the entire country.

So unless the 4000TW number is off by orders of magnitude, we are nowhere near having to cover the US with solar panels to provide our current consumption (which BTW could be easily reduced substantially, but that's another topic).  Does the rest of the world consume orders of magnitude more electricity per surface area than the US?  I'd bet dinner not, and I only bet dinner when I know I'm going to win.

Ah, but the trucking fleet runs mainly on diesel, which is not included in the gasoline number. Diesel has an even higher energy content than gasoline, and diesel engines are far more efficient. So, to replace the 50 billion or so gallons of diesel we use each year would take around 100 billion more gallons of ethanol.

Regarding the energy content of gasoline versus ethanol, ethanol has about 65% of the BTUs of gasoline.

However, using your numbers, it does seem that it could make a difference. I have argued before that 10% of consumption on a BTU basis would make ethanol a huge contributer to replacing declining oil reserves. Even 10% of gasoline use would mean a lot, both in terms of its contribution as a fuel and as a replacement for the lightest refinery products - freeing up much needed capacity.

So, 10% of 150 billion gallons times 1.3 (to convert from volume to BTU) equals about 20 billion gallons. This is about 10.5% of the 190 billion gallons figure you cite for all US agricultural land.

Now, I also acknowledge that taking a mid-range EROEI figure of of 1.25, the net contribution to energy is only about 2% of gasoline use with the remainder being converted from other fuel sources.

My point is not that it is a good thing to do. It may not be. However, this analysis reveals a lot more about the actual tradeoffs than dismissing it because it can't solve all of our energy problems single handedly.

The average yields cited per acre are in places that have 8-10 feet of rich soil and sufficient water.

"Ethanol, butanol and any liquid fuel that has a shot at replacing our gasoline needs has to scale up to 2,000-3,000 gallons per acre."

Using your own calculations if cellulose ethanol is scalable to 2,000 bushels per acre as Mr. Khosla seems to believe, then it would require less then 10% of the U.S. arable land to completely replace our gasoline consumption with cellulose based ethanol.  10% seems like a much more reasonable number and something that may be achievable.

However this changes the main question to, "What is the evidence that Cellulose Ethanol can be scaled to 2,000 bushels per acre, given current methods."  I think this question deserves much consideration, because it is at the heart of the debate.

- Jack