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Re: [Phys-l] Biofuel Generator



This is interesting news but I'd be very skeptical of biofuel as a total solution for US transportation needs.

Overall plant efficiencies are typically under 1% for converting sunlight to biomass (and this is after millions of years of evolution at work looking for more efficient ways to use the sun). The following paper (below) claims that maximum possible plant efficiencies are probably less than 8%. Using current soybean/biodiesel efficiencies per square meter and planting the total arable land in the US for soybeans (no food, no national parks, no lawns, all soybean) we could possibly produce about 24-25 EJ of energy per year using current technology. Our current annual transportation fuel consumption (primary energy) is around 27 EJ. Sugarcane (which doesn't grow here) would produce a more than we currently use but not by a whole lot. So biofuels might be a partial solution for transportation (particularly if we engineer plants to make fuel directly) but isn't going to be a one stop solution. Commercial PV solar cells are around 20% efficient however .... (around 40 times more energy per square meter than surgar cane and a 6-8 month energy payback time).

Electric cars might also be a solution but a quick back of the envelope calculation (see my book 'Fundamentals of Environmental Physics' Forinash) reveals that, for 50% efficient car and distribution technology we would need about 450 more power plants (1000MW each of whatever type; coal, gas, nuclear) which is half again as many as we currently have (equivalent to around 950 1000MW plants). Doable but not trivial. For 2MW windmills we need around 450,000 new windmills to convert all cars to electric.

'What is the maximum efficiency with which photosynthesis can convert solar energy into biomass?' X. Zhu, S. Long, D. Ort; US Department of Agriculture, Agricultural Research Services.

I can send copies of this paper if anyone is interested.

kyle
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Message: 9
Date: Wed, 26 Jan 2011 18:14:31 -0500
From: chuck britton<cvbritton@mac.com>
Subject: Re: [Phys-l] Biofuel Generator
To: betwys1@sbcglobal.net, Forum for Physics Educators
<phys-l@carnot.physics.buffalo.edu>
Message-ID:<a0624080ec9665ac75df5@[192.168.1.108]>
Content-Type: text/plain; CHARSET=US-ASCII; format=flowed

Dang!! All those moonshiners back home will be out of work if they
don't upgrade to this newfangled technology!!!!

;-)


At 5:05 PM -0600 1/26/11, brian whatcott wrote:
Fingers crossed!

Monday, January 24, 2011

Biotechnology firm Joule Unlimited may have come up with a game changer
in the quest for economically viable biofuels.

"---Our technology has already been proven with the direct
conversion of CO2 to --- ethanol, ----."

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--
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'Before you open your mouth, just remember,
the empty wagon rattles the loudest.'
-- my dad

kyle forinash 812-941-2039
kforinas@ius.edu
http://Physics.ius.edu/
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