In the Daily Browse story, The Electric Underground, we reported on a modified Toyota Prius that could get as much as 180 miles per gallon, according to its developer. With petroleum prices rising sharply, such vehicles could forestall a potential oil crisis. The catch was that the car was a plug-in electric hybrid (PHEV) that drew some of its power from ordinary household electricity. That meant that while the car could use gasoline sparingly, it still required the same amount of energy to cover the same distance, perhaps more. Given that over half of the United States’ electricity is generated by coal-fired power plants, perhaps PHEVs are really guzzlers that belch their pollution in someone else’s neighborhood. Initial results of a new study may provide some clues.

 

Several years ago, the Electric Power Research Institute (EPRI) gathered a working group of interested parties to learn more about the efficiency and emissions of hybrid electric vehicles. As its name suggests, the EPRI represents the interests of electrical utilities. Its own company history explains, "In 1971, threatened by Senate proposals to create a federal agency to conduct electricity-related R&D, America's public and private utilities banded together to develop an industry-organized alternative…" If Americans embrace PHEVs, the EPRI members stand to profit from increased demand for electricity. Nonetheless, participants in the working group included the California Air Resources Board, the South Coast Air Quality Management District, and Argonne National Laboratories.

At each stage of electricity production and consumption, there is a loss of energy.  When electricity is produced by burning diesel oil, for instance, much of the oil’s energy is lost as waste heat, resulting in a maximum efficiency of approximately 50%.  Transmission from the power plant to homes results in more losses.  In the case of a plug-in hybrid electric vehicle, even more energy is lost as the electric power is stored and then summoned from the vehicle’s batteries.  Converting the electric power back into torque via the car’s electric motor introduces further loss.  With all of these losses, it is hard to imagine the energy efficiency of a plug-in hybrid matching or exceeding that of a conventional car, which turns its fuel directly into torque with a thermal efficiency of roughly 25%.  The gasoline engine of a Prius is even more competitive, with a maximum efficiency of 34%.

EPRI takes these considerations into account in its study and has produced what it calls a well-to-wheels measure of efficiency.  According to the study, plug-in hybrid electric vehicles consume less energy overall than both conventional internal-combustion-engine vehicles and hybrid electric vehicles.  The study also concludes that the greater the distance the plug-in hybrid can drive solely on electricity, the more efficient it is overall.

More good news comes from the study regarding air pollution.  Measures of nitrous oxides and reactive organic gasses are lower for hybrid electric vehicles and lower still for PHEVs.  As was the case for fuel efficiency, the PHEVs with greater all-electric range also excel in reducing emissions.

Daily Browse has requested the full study report from EPRI, whose web site shows results available only to its member utilities.