A probabilistic analysis of the switchgrass ethanol cycle

The switchgrass-driven process for producing ethanol has received much popularattention. However, a realistic analysis of this process indicates three serious limitations: (a)If switchgrass planted on 140 million hectares (the entire area of active U.S. cropland) wereused as feedstock and energy source for ethanol production, the net ethanol yield wouldreplace on average about 20% of today's gasoline consumption in the U.S. (b) Becausenonrenewable resources are required to produce ethanol from switchgrass, the incrementalgas emissions would be on average 55 million tons of equivalent carbon dioxide per yearto replace just 10% of U.S. automotive gasoline. (c) In terms of delivering electrical ormechanical power, ethanol from 1 hectare (10,000 m²) of switchgrass is equivalent, onaverage, to 30 m² of low-efficiency photovoltaic cells. This analysis suggests that investingtoward more efficient and durable solar cells, and batteries, may be more promising thaninvesting in a process to convert switchgrass to ethanol.