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"Bob Eldred" <nsmontassoc@xxxxxxxxx> wrote in message
news:_jZCe.850$Fk4.520@xxxxxxxxxxxxxxxxxxxxxxxxxxxxx
>
> "The Phantom" <phantom@xxxxxxx> wrote in message
> news:ercod1do64rqeedsrhn0ejq6797osj7jh5@xxxxxxxxxx
> >
>
http://seattletimes.nwsource.com/html/nationworld/2002387520_ethanol18.html
>
>
> In the case of ethanol they claim that it takes 29% more fossil energy to
> make ethanol than one gets out of it. I take that to mean that it takes
129
> BTU's input to get 100 BTU's of ethanol output. I don't know
> if that is an accurate number or not, but taking it at face value, what if
> the 129 BTU's came from ethanol or other bio-fuels to net 100 BTU's of
> ethanol product. Would not the yield be 100/129 X 100% = 77.5%. In
> otherwords, using their numbers and using green fuels to power the
process,
> the yield of ethanol is 77.5%. That sounds pretty damn good to me. I'll
bet
> it is as good or better than gasoline from petroleum using the same
> rational.
You misunderstood the gist of the argument. Making 100 Btu's of ethanol
fuel value requires an input of 129 Btu. This means that for every 100
Btu's of ethanol you get, you've already used 129 Btu's of something else.
If you assume you use ethanol as the fuel for the process, then you keep
losing ethanol.
The efficiency isn't 77.5% because you've done the math wrong.
Eff = (output - input)/input = (100-129)/129 = -22.5%
Negative efficiency means you are putting more in that you are getting out.
The 100 Btu's they talk about in the article are NOT net. They are GROSS.
Therefore you are LOSING 29 Btu's for every 100 Btu's of fuel you made. Not
a very good business model - unless you have a subsidy.
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