Are there specific regions where PHEVs or HEVs are more beneficial for reducing emissions

The benefits of plug-in hybrid electric vehicles (PHEVs) and hybrid electric vehicles (HEVs) for reducing emissions are indeed region-specific, largely due to differences in the electricity generation mix across regions.

Regional Impact of PHEVs and HEVs on Emissions

1. Influence of Regional Electricity Generation Mix

• In regions where the power grid relies heavily on coal or other fossil fuels, such as the U.S. Midwest, PHEVs can reduce carbon dioxide (CO2) emissions intensity. This is because charging PHEVs in these coal-dominated areas may actually lower the overall CO2 emissions per megawatt-hour (MWh) relative to emissions from internal combustion engine vehicles (ICEVs). This occurs when PHEV charging helps optimize power generation and can reduce the need for higher-emitting peak power plants.
• Conversely, in regions with significant clean energy sources like hydroelectric or renewables, charging PHEVs can sometimes increase CO2 emissions intensity. This happens because the additional electricity demand from charging might cause fossil fuel generators on the margin to operate more, offsetting the benefits of clean electricity generation and potentially raising emissions.

2. Local Pollutant Emissions and Exposure

• PHEVs reduce local tailpipe emissions of pollutants such as nitrogen oxides (NOx) and sulfur dioxide (SO2) by shifting emissions from vehicles to power plants, which are often located outside of densely populated areas. This spatial shift generally lowers human exposure to harmful pollutants due to dilution and chemical transformation in the atmosphere, even if total emissions may not decline as much.

3. Comparison Between PHEVs and HEVs

• PHEVs tend to outperform HEVs in reducing lifetime greenhouse gas (GHG) emissions, especially when the electric utility factor (the share of driving done on electricity rather than gasoline) is high. The smaller battery and hybrid system of PHEVs provide a balance that reduces emissions more effectively across various grid emission intensities.
• In regions with high grid emissions (such as those with coal-dependent electricity), PHEVs and HEVs can have roughly equivalent emissions benefits, but overall PHEVs still tend to have slightly better climate performance than HEVs across the grid emissions spectrum due to their greater use of electric power in driving.

4. Role of Grid Decarbonization

• The benefits of PHEVs and HEVs improve significantly as grids decarbonize. Projections suggest that by 2035, with the anticipated reduction in electricity emission intensity globally, lifetime emissions from PHEVs can be reduced by up to 35% compared to conventional vehicles, and even greater improvements occur with increased electric driving share.

Summary

• PHEVs and HEVs are more beneficial for emissions reductions in regions with carbon-intensive electricity grids (e.g., coal-heavy regions), where shifting from gasoline to electricity reduces overall CO2 emissions intensity.
• In regions with clean electricity grids, the relative emissions benefit of PHEVs and HEVs may be less or even negative for PHEVs if electricity demand displaces renewable generation.
• PHEVs generally offer greater emissions reductions than HEVs, especially when the grid is moderately clean and the electric driving share is high.
• Grid decarbonization amplifies the emissions benefits of both PHEVs and HEVs over time.

Thus, the regional electricity generation mix and the timing and profile of vehicle charging are key factors determining where and when PHEVs and HEVs are most effective at reducing emissions.