The negative energy theory may have been true years ago but not now. Believe me, there's a million things that aren't being factored in in just the production stage. Ethanol and Biodiesel are tied together tightly in the production area.
They can make gas out of turkey and have been able to do that for years now but its not feasible enough to do widespread. Geuss what? there's still improving it! Should they stop bc its not penciling out?
Ok let's do some math.
Let's assume:
1. Corn is as efficient as sugar cane in producing ethanol. The reading that I have done is that it is still much less productive at converting mass into fuel, but let's roll with this for simplicity's sake.
2. Ethanol has as much energy in it per volume as gasoline. I seem to remember it is a bit less, but again, simplicity.
From the wikipedia article on ethanol in brazil, we can pull out the following information:
Amount of sugar crop acreage allocated to Ethanol in 2003-2004:
8789 square miles.
45,000 km2, of which half is used for ethanol, and converted into square miles)
This square area produces:
88 Million barrels of ethanol per year
(cubic meters converted to liters at 1000 liters per cubic meter, converted to gallons at .256 liters per gallon, converted to barrels at 42 gallons per barrel of petroleum)
Directly converting this to gasoline would yield 88 million barrels of gasoline per year using our simplified assumptions.
The US uses 3,321,500,000 barrels of gasoline per year per ( http://www.eia.doe.gov/emeu/aer/ep/ep_frame.html )
3.3Bn divided by 88M= 37.75 (the number of times larger that US gasoline consumption is than Brazil's consumption)
37.75 times 8789 square miles is 331,521 square miles.
Assume we can find 50% of that figure in unused crop land, that leaves us with 160,500 square miles of NEW crop land that would be need to completely replace gasoline with ethanol at current usage rates.
Factor in the fact that Ethanol has less energy per unit of mass, and that square mileage will go up. Subs ute a less efficient crop of corn, and that square mileage will go up.
According to the CIA factbook the united states has only 87,000 square miles of irrigated land now.
Where would we get the water to irrigate the HUNDREDS OF THOUSANDS OF SQUARE MILES of crop land that fully replacing gasoline with ethanol will take, ASSUMING we can find the arable land?
Saying "let's just replace our gasoline powered cars with ethanol" doesn't make it viable as a realistic solution.
Rolling forward a bit:
Yes, we will have to start driving less and buying more efficient vehicles. This will reduce the square mileage needed.
Our population is also growing, as is the economy. This will increase demand for fuel. This will offset gains from efficiency somewhat, if not a lot.
Yes, agricultural production will become more efficient, again reducing the square mileage issue. But not by enough of a conceivable factor to replace gasoline as it stands.
Biodiesel will face the same problems of water and arable land. Keep in mind that the figure given was just for gasoline, and not for diesel. Replacing oil-diesel with biodeisel will require a similar ramp up in devoted area to crops.
One good factor that the wikipedia article pointed out is that a good chunk of the waste mass from producing ethanol can be used to produce electricity beyond what the refining process uses.
I am not saying that ethanol is stupid.
Ethanol is certainly part of what I consider part of an energy solution that takes a longer term view. I am all for ramping up usage of this renewable source of energy.
I simply wanted to point out the scale of the problem we are trying to address.
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