Analysis of lifecycle water requirements of alternative energy pathways: Case study of ethanol from corn grain and crop residue, and electricity from geothermal resources

This document describes the methodology and results of analysis of lifecycle water requirements of three renewable fuel pathways – ethanol from corn grain and crop residue (Section I); and electricity from geothermal resources (Section II).;The model for ethanol from corn grain and corn cob is based on default or user inputs of crop evapotranspiration, pre-irrigation requirements for salt leaching, irrigation methods and their efficiencies, conversion technologies, and projected crop yields. Water requirements also depend upon allocation procedures selected at various stages of the lifecycle. The model characterizes water requirements in terms of withdrawal and consumption; and source – ground water, surface water, precipitation, and soil moisture.;The geothermal model estimates water requirements of electricity from various forms of geothermal resources. It considers two types of hydrothermal resources – wet steam and hot water; as well as enhanced geothermal systems (EGS). Electricity can be generated using flash or binary (organic Rankine cycle) depending upon the temperature and pressure of geothermal fluid. Power plants can use four different types of cooling technologies – wet re-circulating, dry systems and finally hybrid cooling systems. Requirements are calculated separately for freshwater, degraded water and geothermal fluid.;The study’s conclusion is that corn ethanol and geothermal electricity have higher water requirements than conventional fuels they are replacing. In case of ethanol, requirements are many orders of magnitude higher than that of gasoline. In case of geothermal electricity; freshwater requirements are around 2-5 times higher than water requirements of conventional thermoelectricity. Geothermal electricity generation also requires large volumes of degraded water.;As part of the project, two spreadsheet based models were developed which are available at http://steps.ucdavis.edu/research/Thread_6/lcfs/water. These models were used to calculate water requirements for the two fuel pathways based on various scenario assumptions.