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Just the Facts: According to the pro-ethanol USDA, making 4 gallons of ethanol uses up the energy in 3 gallons of ethanol. So you must make 4 to save 1 But you must save 15 gallons of ethanol to save the energy in 1 gallon of gas. Bottom line: you must make 6 gallons of ethanol to save the energy in 1 gallon of gasoline.
Another view: If we made ethanol by using ethanol itself instead of fossil fuel, we would have to make 585 gallons of ethanol to have 148 left over, which is enough to replace one gallon of gas. Documentation (popNotes): The Basic Idea Step 1 In round numbers, the USDA tells us that making 4 gallons of ethanol requires as much energy as is in 3 gallons of ethanol. So to save the energy in a gallon of gas, we must scale up step 1 by 50%. So here's step 1 again, scaled up: Step 3 To save 15 gallons of ethanol (or 1 gallon of gas) we must make 6 So it requires (in round numbers) the production of 6 gallons of ethanol to save the fossil energy in 1 gallon of gas. The USDA ratio of 4 to 3 includes credits for byproducts. Energy Content and Balance of Ethanol Only two facts are used in this diagram.
Fact 1 tells us: Step 1 1 GG energy input ==> ethanol with 134 GGs. Multiply by 294: Step 2 294 GG energy ==> 394 GG ethanol. Combine steps 2 & 3 to get: Step 4 294 GG fossil energy make 585 gallons of ethanol. Divide 585 by 1483 to get: Step 5 585 gallons of ethanol replaces 394 gallons of gas. of Energys Annual Energy Review, Appendix A tells us that the heat content of Conventional Gasoline = 5253 MBtu/Barrel Fuel Ethanol = 3539 MBtu/Barrel Dividing gives: gasoline has 1483 times more energy per gallon. So 1483 gallons of ethanol has the energy of 1 gallon of gas.
Over the last 10 years, Table 6 in DOEs Petroleum Marketing Monthly shows the Rack price of regular averaged 15-c- less than the price of sales through retail outlets, for regular gasoline (the price difference is more stable than the % difference).
Issue Brief for Congress, IB10041, Energy Tax Policy, June 17, 2005, page 14. To be conservative, I have ignored the small producer credit. I have used the price of premium gasoline because that makes ethanol look more attractive. The extra cost of the ethanol approach substracts out the cost 394 gallons of gasoline. So every penny increase in the cost of gas reduces the extra cost of ethanol by 394-c-. But the total cost adds back in the cost of 1 gallon of gasoline, so the net effect on total cost of a one penny increase in our estimate of price of gasoline is to decrease the total cost by 294-c-. The higher the price of gas used in the calculation, the lower the estimates of the extra and total costs of the ethanol approach.
For example, if ethanol had half the energy per gallon of gasoline, but was more than twice as cheap per gallon, you would have to pay twice as much tax to drive the same distance with ethanol as with gas. Some states, like Hawaii, give ethanol the appropriate tax break, and some, like South Dakota, over do it.
Total US corn production 1995--2003 = 83,696,000,000 bushels. The USDA tells us the conversion rate of corn to ethanol is 25 gallon per bushel. I use the (pro-ethanol) USDA's value for the energy needed to produce ethanol. I do not use the values suggested by any of ethanol's critics. I ignore the tax break some states give to ethanol at the pump. I assume ethanol should be taxed at a 1/3 lower rate because it has 1/3 less energy. I compare ethanol's price with the price of premium gasoline, when estimating the extra cost of ethanol. A GG is a Gas-Gallon of energy, the energy in 1 gallon of "conventional gasoline."
DOE, AER, Appendix A says conventional gasoline has 5253 million Btu / barrel, so A GG = 125,071 Btu of energy That's why this unit is convenient. It's easier to figure that 394 gallons of gasoline has 394 GGs than to figure is has 394 x 124,071 = 492,780 Btu.
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