Plug-in hybrid vehicles will reduce CO2 and nitrogen oxide emissions levels – but they are also expected to push up sulphur oxide emissions, according to a new study by the Carnegie Mellon University.
A team at Carnegie Mellon University has modeled the net emissions in two regional transmission operators (PJM and NYISO) from PHEVs under different scenarios for future power generation; different size battery packs; charging strategies (home, work and smart); and PHEV fleet percentages between 0.4 and 50%. Scott Peterson, J. F. Whitacre and Jay Apt found that compared to 2005 gasoline fleet efficiency levels, all charging strategies and CD mode efficiencies yield reduction of CO2 emissions.
The study suggests that if a 2020 conventional vehicle fleet efficiency target of 35mpg (6.7 L/100km) is compared to the 2020 charge depleting efficiency then net CO2 emissions will drop by switching from gasoline to electricity but less in PJM because of differences in generation, unless power generation with carbon capture and storage (CCS) is used.
In a paper published in the ACS journal Environmental Science & Technology, they present their results for a 10% PHEV market share. They estimate that plug-in hybrid electric vehicles will have lower net CO2 and NOx emissions than a conventional vehicle fleet but SO2 will increase unless a cap binds.
Other PHEV market shares are included in the paper’s Supporting Information, but the results are similar except for the lowest 0.45% level (with fewer PHEVs charging, emissions are more sensitive to the specific plant used to charge them).
Among the results of the study are that the differences in timing will result in changes in the generator mix and emissions. Battery size has few qualitative changes while home charging does not decrease CO2 emissions as much as smart or work charging.
They conclude that there are strong arguments for electrification and if plug-in hybrid electric vehicle cars replace light trucks and SUVs, as well as vans from the fleet, emissions will be further reduced.
