A Probabilistic Analysis of the Switchgrass Ethanol Cycle

Abstract: The switchgrass-driven process for producing ethanol has received much popular attention. 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) were used as feedstock and energy source for ethanol production, the net ethanol yield would replace on average about 20% of today’s gasoline consumption in the U.S. (b) Because nonrenewable resources are required to produce ethanol from switchgrass, the incremental gas emissions would be on average 55 million tons of equivalent carbon dioxide per year to replace just 10% of U.S. automotive gasoline. (c) In terms of delivering electrical or mechanical power, ethanol from 1 hectare (10,000 m2) of switchgrass is equivalent, on average, to 30 m2 of low-efficiency photovoltaic cells. This analysis suggests that investing toward more efficient and durable solar cells, and batteries, may be more promising than investing in a process to convert switchgrass to ethanol.