Last updated on 2012.08.22
- We still lack viable technology for large-scale cellulosic ethanol production.
- Scaling up cellulosic ethanol production may be so expensive that even government subsidies won't overcome investor hesitance.
- Meeting our biofuel mandates will probably require converting cropland or currently uncultivated land to dedicated annual energy crops. The greenhouse gases emitted in that one-time conversion may offset any greenhouse gas savings gained in the long-term from replacing fossil fuels with ethanol.
- Additional cropland dedicated to ethanol will further drive up land prices.
- Even giving cellulosic ethanol the best cost estimates, it doesn't deliver energy more economically than oil at $111 a barrel.
Increased biofuel usage will also impact water availability. Among the crops available for ethanol production, sugar cane uses the least amount of water to produce each unit of energy (see p. 244, Table 5-10). However, replacing just 25% of each American's fossil fuel energy usage (based on 2010 consumption) would require just over 400,000 gallons of water per energy user. That's 10 times the amount of water my household drinks and washes in each year. Using a combination of corn and stover to produce that amount of ethanol energy would use about 750,000 gallons of water per person. Using switchgrass to produce the same amount of energy would require over 1.4 million gallons of water. The big hog among biofuel crops would be soybean biodiesel: replacing a quarter of your fossil fuel energy usage with soy diesel would use 4.9 million gallons of water. (Update: Water usage in the production of oil, even heavy oil, appears to be significantly less per energy unit produced.)
You can download the full 650-page pre-publication edition of the report here.