A biorefinery for mobility?

Biofuels are considered as a carbon neutral alternative to hydrocarbons in the transport sector and this approach has triggered concerns about the impact the production of biofuels might have on land usage. Another option that might also lead to reduced emissions in the transport sector is electricity based on renewable energy sources such as biomass. Below, we assess the benefits and drawbacks of the joint production of ethanol and electricity in a sugar cane based refinery, and the use of both energy forms in privately owned automobiles. In this analysis, we have considered technology for energy production that is currently available and cost competitive. The results show that the amount of land that is required to power our current automobile use needs is less than what is typically stated. According to our results that are based on 2010 values, 2 million ha of land are sufficient to power the Brazilian automobile fleet, 25 million ha are enough to satisfy the needs of the U.S. fleet, and 67 million ha are sufficient to cover the global autofuel requirements. When minor efficiency gains are considered, 19 million ha will be enough to satisfy the fuel needs of the U.S. fleet in 2030, whereas land required to supply the Brazilian and global fleet remain basically unchanged. Our analysis shows that the harvested energy density of sugar cane is 306 GJ/ha/yr, which is 1.7 times the value usually reported in the literature for biofuels. As a result, taking advantage of the primary energy potential of sugar cane, only 4% of the world's available cropland area would be sufficient to produce fuels that would power the global car fleet.