Farrell article

1. Farrell article

2. Summary • Evaluated potential effects of increased ethanol use • Reviewed a number of previously published articles on corn ethanol • Ethanol results in less petroleum usage, but minor differences in GHGE • Need for additional research in environmental metrics

3. Summary • Adjusted the studies to have equivalent bounds • Corrected some of the data sources in the other articles • Large scale use of ethanol would require cellulosic technology

4. Methods • Checked data sources of 6 current reviews on corn based ethanol • Looked at net energy, but highly dependent on system boundaries • Finding intuitive and meaningful units besides net energy is needed

5. Methods • Add coproduct credit • Apply consistent system boundary (include effluent processing energy and neglecting laborer food requirements) • Account for different energy types • Calculate policy metrics (not sure what this is)

6. Sensitivity Analysis • Most sensitive to coproduct allocation • Corn ethanol produces valuable coproducts • Studies that showed a negative energy balance for corn ethanol assumed no coproducts

7. Results • Ethanol significantly reduces petroleum usage • Only 5 to 26% of the energy is renewable though • GHG reduction was between a 20% increase and a 32% decrease • Their results • Reduce petroleum by 95% on energetic basis • Reduce GHGE by 13%

8. Uncertainty Results • Uncertainty analysis suggests results are good • Variation in performance by location • Given appropriate policy incentives, corn ethanol could be improved • Only cellulosic ethanol appears to save GHGE

9. Supplemental Data • Well laid out spreadsheet (go over briefly) • LHV versus HHV • LHV energy – water is evaporated from the fuel during combustion • HHV energy – recovers energy in water vapor

10. Net Energy Value • Different definitions in each study • Don’t define nuclear or renewable electricity • Ignore differences in energy quality • Very sensitive to coproducts • Are coproducts subtracted from energy inputs • Are coproducts added to energy outputs • Results in a different ratio • Makes net energy ratio difficult to use

11. Metrics • GHGE / MJ fuel • Petroleum inputs / MJ fuel • Coal inputs / MJ fuel • Natural gas inputs / MJ fuel • Other energy inputs / MJ fuel • X – is the variable of interest • A – MJ energy per l of ethanol • Calculations in terms of x/a

12. Agricultural Inputs • Problems with lime application • Inputs to farm machinery • Used an economic input output model from Carnegie Mellon University

13. Coproducts • Anything that adds value should be counted as a positive impact • Looked at process, market-based, and displacement • Process method • Use a tool like ASPEN to model mass and energy in process • Allocate according to the process simulation

14. Coproduct • Market Based • Allocates total energy according to the relative value • Displacement method (system expansion) • Preferred method – according to some other studies • Most comprehensive would be market based with the displacement

15. GHGE • Use IPCC on global warming potential • GHGE for nitrogen fertilizers shown in S-8 to S-10 • Assume small changes on unfarmed land into cultivation • Some crop shifting • Importing ethanol would cause some land use changes

16. Sensitivity Analysis • Determined by 1% change in input parameter • Major factors • Refinery energy • Farm yield • Refinery yield • Coproduct credit • Nitrogen energy • Nitrogen application rate

17. Sensitivity Analysis • N2O big factor • Two key implications • Any feedstock that relies heavily on nitrogen will not provide significant GHGE relative to gasoline • Relatively little petroleum is used for corn or cellulosic ethanol, so large reductions in petroleum consumption are likely