How does the grid’s emissions profile impact the lifetime emissions of PHEVs and HEVs

    The grid's emissions profile significantly influences the lifetime emissions of Plug-in Hybrid Electric Vehicles (PHEVs) and Hybrid Electric Vehicles (HEVs) because these vehicles partially or fully rely on electricity from the grid, whose environmental impact varies depending on the generation mix and timing of charging.


<h2>Impact on Lifetime Emissions of PHEVs and HEVs</h2>

<strong>1. Grid Carbon Intensity Determines Charging Emissions</strong>
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        The emissions associated with PHEV charging depend on the carbon intensity of the electricity grid where charging occurs. Grids dominated by fossil fuels such as coal or natural gas tend to have higher carbon dioxide (CO2) and sulfur dioxide (SO2) emissions per megawatt-hour (MWh) generated compared to grids with a larger share of renewables or nuclear power.
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        Studies have shown marginal CO2 emissions rates for PHEV charging ranging from about 582 to 935 kg CO2 per MWh, with SO2 emissions between 0.9 and 1.2 kg per MWh on fossil-heavy grids.
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<strong>2. PHEVs Can Yield Lower Emissions than Battery Electric Vehicles (BEVs) in Certain Grid Conditions</strong>
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        Because PHEVs can switch between electric mode and gasoline mode, their total emissions depend on the split between electric miles driven and gasoline miles. In grids with high emissions, PHEVs may produce lower total emissions than BEVs that rely entirely on the grid for propulsion, especially if the gasoline engine is relatively efficient.
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        Conversely, on low-carbon grids, BEVs generally outperform PHEVs in life cycle emissions.
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<strong>3. Timing and Flexibility of Charging Affect Emissions</strong>
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        Flexibility in when PHEVs are charged can improve the emissions profile by shifting charging to periods when cleaner or more efficient generation units operate. For example, charging during off-peak hours or when renewable generation is high can reduce emissions.
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        Integrating Vehicle-to-Grid (V2G) services, where PHEVs provide grid support such as spinning reserves or energy storage, can further reduce emissions of CO2, SO2, and nitrogen oxides (NOx) by optimizing generator dispatch and improving overall grid efficiency.
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<strong>4. HEVs Have Limited Grid Dependency but Still Benefit from Cleaner Grids</strong>
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        HEVs do not plug into the grid and rely mainly on gasoline engines with electric assist. Their lifetime emissions are primarily from fuel combustion. However, in scenarios where HEVs are used in combination with PHEVs or BEVs, the grid’s emissions profile affects the net environmental impact of the overall vehicle fleet.
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<h2>Summary</h2>


    The lifetime emissions of PHEVs and HEVs are heavily influenced by the emissions profile of the electricity grid powering PHEV charging. Grids with high fossil fuel dependence lead to higher emissions per electric mile, reducing the environmental benefits of PHEVs, while cleaner grids enhance these benefits. Proper management of charging times and incorporating grid services like V2G can optimize emissions savings. HEVs are less directly affected by grid emissions but their broader impact is tied to the energy and emissions landscape shaped by electrified vehicles.



    Thus, improving grid cleanliness and leveraging smart charging are key to maximizing the emissions benefits of PHEVs and HEVs over their lifetime.