It takes a lot of energy to get a kg of ethanol from natural sugars (corn in the US, sugarcane in Brazil, wheat in Europe, according to Schmidt, 2004). The energy value return per unit input ranges from about 1.3 to 0.58 according to Richter (2004). If the return in less than 1.0, it means that it take more energy to make the ethanol than can be recovered by burning it. Producing ethanol with a return of less than 1.0 is not economically feasible and must be justified on other grounds.
References
Richter, B., 2004: Letter to Science. Science 305, 340.
Schmidt, L. D., 2004: Letter to Science. Science, 305, 340.