Energy that does not degrade the environment will have to be harvested by dipping into the large stream of it that the sun sends our way, rather than by extracting it from geologic strata.
Plants are fairly adept at fixing solar energy; the whole plant can be viewed as fixed sunlight. Most people imagine that the usable portion is in the plant's seeds, and many schemes are in development to use those seeds as energy currency. Grains are brewed in gigantic fermentation installations, into what amounts to wine, and the alcohol in it is distilled to furnish motor fuel; oil seeds are harvested and transesterified with methanol to furnish biodiesel.
Much less attention goes into using whole plants for energy other than to simply burn them with, at best, the creation of steam in stationary installations. There are attempts to develop enzyme systems that might turn cellulose (paper pulp) into sugars that could be fermented and furnish alcohol; however, cellulose's claim to fame as a material of construction in trees is that it is very resistant to degradation into sugars.
I hear that a demonstrated technology is commercially offered for fast pyrolysis of biomass into liquid fuel. The installations required are very small compared with those necessary for the alcohol-from-grain scheme. I am told that a commercial demonstration plant already exists in Malaysia, in addition to a pilot plant in the Netherlands.
Leonard Greiner's comments merit serious attention from all concerned readers (C&EN, Jan. 30, page 4). He correctly suggests that rapid-growth plants require no special nutrients. Regrettably, he doesn't go quite far enough. Use the weeds to make power alcohol instead of burning petroleum to spray them with petrochemical pesticides. Extract phytoestrogens from kudzu instead of spraying it with xenoestrogenic pesticides. C&EN readers more than anyone else should see the beauty of mining weeds for their phytochemicals, which are increasingly expensive to synthesize as the cost of petrofuels increases. Each weed contains thousands of phytochemicals, some of them high priced and useful, though at low parts-per-trillion or parts-per-million levels. Take out those valuables, and leave all that residual biomass to be converted by C&EN chemists into alcohol to dilute and ultimately replace our ever more expensive petroleum imports.
James A. Duke