Energy Efficiency of Biofuel Production Most of the plant material currently used for biofuel production consists of food crops—mainly corn, soybeans, and sugarcane. In 2006, David Tilman and his colleagues published the results of a 10-year study comparing the net energy output of various biofuels. The researchers grew a mixture of native perennial grasses without irrigation, fertilizer, pesticides, or herbicides, in sandy soil that was so depleted by intensive agriculture that it had been abandoned. They measured the usable energy in biofuels made from the grasses, and also from com and soy, then measured the energy it look to grow and produce biofuel from each kind of crop (Figure 6.1).
FIGURE 6.1 Energy input and output of biofuels made from three different crops. One hectare is about 2.5 acres.
About how much energy did ethanol produced from one hectare of corn yield? How much energy did it take to grow the corn to make that ethanol?
To determine: How much energy did the ethanol produced from one hectare of corn yield and how much energy did it took to grow the corn.
Concept introduction: The plants and other organic material other than fossils can also be used as a source of energy. The oils, gases, and alcohols made from these materials are called biofuels. Corn and other food crops are rich in oils, starches, and sugars that can be easily converted into biofuels.
The researcher D and his colleagues studied for 10 years and compared the net energy output of various biofuels. The researcher grew a mixture of native perennial grasses, corn, and soy. The grasses grew without irrigation, fertilizer, and pesticides in sandy soil. The usable energy in biofuel (grasses, corn, and soy) is measured along with the energy it took to grow.
Refer to Fig. 6.1 “Energy inputs and outputs of biofuels made from three different crops” in the question. The graph plot shows the energy per hectare versus the ratio of energy output to input of the three different biofuels.
The graph shows the ethanol obtained from one hectare of corn produced of energy and it required growing the corn.
The ethanol from one hectare of corn produced approximately 23 × 106 kcal. It took approximately 18 × 106 kcal energy to grow the corn that was used to make the ethanol.
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