Farming the World's Energy by Christian Wüst, a Der Spiegel special report, is an excellent crash course in the practicalities of growing crops to directly convert solar energy to produce energy useful liquids - rapeseed, corn etc. and the use of raw biomass as an energy feedstock, straw, woodchip etc., in Europe.
A recommended read.
The conversion of organic waste (e.g., turkey guts and feathers), into biofuel may become an economically important process, but growing crops as an energy source is unlikely to play a significant role in the world's energy future. (Unless biofuels are adopted as a form of birth control -- use much of the world's crop land for biofuel production to keep oversized, fuel wasting SUV's on American roads and you could starve a fair few people in Africa and elsewhere. But if you want to use the sun, do it directly. Crops will never capture more than 2-5% of the sun's energy, whereas solar cells currently have efficiencies of up to 37% and could, theoretically, achieve efficiencies of up to 70% (http://www.lbl.gov/Science-Articles/Archive/MSD-full-spectrum-solar-cell.html). And electricity can be used much more efficiently than biodiesel (see: http://www.teslamotors.com/display_data.php?data_name=21stCentElectricCar).
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