Ethanol can be produced via an intracellular photosynthetic process in algae, excreted through the cell walls, collected from closed photobioreactors as a dilute ethanol-in-water solution, and purified to fuel-grade ethanol. This sequence forms the basis for a biofuel production process that is currently being examined for its commercial potential. We calculate the lifecycle energy use and carbon footprint for three different system scenarios for this algae-to-ethanol process, using process simulations and thermodynamic calculations. The energy required for separation increases rapidly for low initial concentrations of ethanol, and, unlike other biofuel systems, there is little waste biomass available to provide process heat and electricity to offset those energy requirements. With a scenario based on a natural-gas-fueled combined heat and power system to provide process electricity and extra heat, and for heat exchange efficiencies of 80% or 90%, the net lifecycle energy consumption ranges from 0.61 MJ/MJEtOH down to 0.25 MJ/MJEtOH, and the net lifecycle greenhouse gas emissions range from 27 g CO2e/MJEtOH down to 11 g CO2e/MJEtOH for initial ethanol concentrations from 0.5 wt% to 5 wt%. These values are 29% and 12%, respectively, of the carbon footprint of gasoline, 93 g CO2e/ MJEtOH. Greenhouse gas emissions can be further reduced with use of solar thermal for some of the process heat, potentially reducing lifecycle greenhouse gas emissions to the range of 21 g CO2e/MJEtOH to 10 g CO2e/MJEtOH for the same range of initial ethanol concentrations.