Energy Use
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Conceptually, biofuels sounds like a really good idea. Plants grow by photosynthesis, a process in which the sun’s energy is used to split water molecules into oxygen, protons and electrons. This allows carbon fixation in which inorganic carbon, carbon dioxide, is converted into free oxygen and organic carbon compounds – biomass which has stored chemical energy which is released when we burn wood in fireplaces. So plants take the carbon dioxide out of our air while they grow, and then burning the plants releases stored chemical energy in the organic carbon, with carbon dioxide as a combustion product. Theoretically, it’s a free lunch in terms of net carbon dioxide in the atmosphere.
One complexity is that modern transportation – cars, planes, ships – depends on liquid fuels to make things go. Nature, using millions of years, gravity and heat, has done the work of converting the organic carbon in dead plants and animals into the fossil hydrocarbons available at your gas pump. It turns out that one of humanity’s very old technologies, fermenting plant carbohydrates into drinking alcohol, is one answer to the question of how to replace nature’s time and pressure. Corn starch yields ethanol in fermentation, and the same alcohol that goes into your draft beer can fuel your car.
The federal government launched a massive program in 2005 to encourage biofuels, and the Renewable Fuel Standard Act requires production of 13.2 billion gallons of biofuel from corn in 2012, which may consume 40% of the nation’s corn crop. But the question of “ethanol’s fuel energy balance,” of whether replacing the ancient processes which give us liquid hydrocarbons with fermenting corn starch takes as much energy as its gas-pump yield, has dogged the program from the beginning. It takes energy to grow the corn and harvest and process it into ethanol, and that energy comes largely from burning the same fossil fuel hydrocarbons the ethanol is supposed to replace. There have been many studies, and one plausible answer is that the corn biofuel process yields about about 1.3 units of energy for every unit of energy input. On a different issue, Nobel prize winner Paul Crutzen concludes that ethanol produced from corn had a “net climate warming” effect when compared to oil when the full life cycle assessment properly considers the nitrous oxide (N20) emissions that occur during corn ethanol production.
One complication is that growing corn needs lots of water, and the Midwest is experiencing severe drought and lower corn harvests, which means more competition between corn as fuel and corn as food. One headline on an Associated Press story today captured the situation – “A withering outlook for corn: With no drought relief in sight, government cuts yield forecast 17%” – and outlined livestock producers’ efforts to limit ethanol producers’ corn allotments. So there’s really no free lunch, and we’re back to our basic problem: We consume too much.
Image by Khairuzzaman (Own work) [GFDL (http://www.gnu.org/copyleft/fdl.html) or CC-BY-SA-3.0 (http://creativecommons.org/licenses/by-sa/3.0/)], via Wikimedia Commons