Well-To-Wheels Energy Use and Greenhouse Gas Emissions of Plug-in Hybrid Electric Vehicles

The Greenhouse gases, Regulated Emissions, and Energy use in Transportation (GREET) model incorporated fuel economy and electricity use of alternative fuel/vehicle systems simulated by the Powertrain System Analysis Toolkit (PSAT) to conduct a well-to-wheels (WTW) analysis of energy use and greenhouse gas (GHG) emissions of plug-in hybrid electric vehicles (PHEVs). Based on PSAT simulations of the blended charge depleting (CD) operation, grid electricity accounted for a share of the vehicle's total energy use ranging from 6% for PHEV 10 to 24% for PHEV 40 based on CD vehicle mile traveled (VMT) shares of 23% and 63%, respectively. Besides fuel economy of PHEVs and type of on-board fuel, the type of electricity generation mix impacted the WTW results of PHEVs, especially GHG emissions. For an all- electric range (AER) between 10 to 40 miles, PHEVs employing petroleum fuels (gasoline and diesel), a blend of 85% ethanol and 15% gasoline (E85), and hydrogen were shown to offer 40-60%, 70-90%, and over 90% reduction in petroleum energy use, and 30-60%, 40-80%,and 10-100% reduction in GHG emissions, respectively, relative to an internal combustion engine vehicle (ICEV) using gasoline. In addition, PHEVs offered reductions in petroleum energy use as compared to regular hybrid electric vehicles (HEVs). More petroleum energy savings were realized as the AER increased, except when the marginal grid mix was dominated by oil-fired power generation. Similarly, more GHG emissions reductions were realized at higher AER, except when the marginal grid mix was dominated by oil or coal. Electricity from renewable sources realized the largest reductions in petroleum energy use and GHG emissions for all PHEVs as AER increased. GHG emissions benefits may not be realized for PHEVs employing biomass-based fuels, e.g., biomass-E85 and -hydrogen, over regular HEVs if the marginal mix is dominated by fossil sources.