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Posted by David Sherman on Wednesday, May 14, 2008 at 20:56:12 :
In Reply to: Re: OT - Biofuels, not so green posted by M Fanoni on Wednesday, May 14, 2008 at 19:59:20 :
If energy "comes from the CO2", we wouldn't need the algae, would we? We could just use the CO2 directly. The reason algae or any other plants work as a fuel source is that they use sunlight to separate the "C" from the "O2", putting the O2 into the air and the C into some sort of fuel, be it wood, oil, or alcohol. It takes a lot of energy to separate the carbon from the oxygen, which is why we get a lot of energy out when we burn things. To say that CO2 is an energy source makes no sense at all. One might as well burn rocks or water.
It's not about whether or not one has "faith". It's about the laws of chemistry and physics. Unfortunately the vast majority of alternative energy schemes I read about are backed by vast amounts of faith and no chemistry or physics. Using algae to convert solar energy to chemical energy may well work out to be economical if oil stays expensive. Saying that the light needed to grow the algae can be provided artificially, however, does indeed ruin the whole equation.
I'm an engineer. When I design something, it has to work because it complies with the laws of nature. It's not like politics or religion where if I can convince somebody to have faith in me, then I'm done. If you and I are arguing about whether or not something is technically feasible, the only real way to settle it is to build the thing. I've lost count of all the guys who've told me with great enthusiasm about some alternative energy scheme that they either dreamed up or read about that they think would work great. They have great faith. Half the time they even believe that somebody else once built it but it was "suppressed". The funny thing is, they never actually go ahead and build it themselves. In this case, if you think that algae can use CO2 as an energy "source", with only a tiny bit of artificial lighting, and produce more fuel than it took to run the lights, the way to settle the question is to build the thing. Measure how much energy it took to run the lights. Measure how much energy you get when you burn the resulting biomass. See if the first number is bigger or smaller than the second number. Now, if you're using waste as an input, that adds another term to the equation in that you need to account for the energy value of the waste before it was worked over by the algae.
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