When cleaner charging does not cut total emissions

The tempting story is simple: charge when the grid is cleaner, and emissions fall. In a mixed fleet, there is another decision hiding inside that sentence: which vehicles the company chooses to send.

Under the paper's baseline Beijing tariff and carbon price, the carbon-guided plan produced 191.17 kg of total emissions, compared with 189.81 kg under unordered charging. The charging decision improved one part of the system, while the resulting fleet mix changed another.

The paper then changes the setting: an additional midday valley-price period and a higher carbon price. In that comparison, carbon-guided charging reports 97.71 kg of total emissions versus 169.74 kg under unordered charging. This is a different policy setting, so it should not be read as proof that any single price change caused the whole difference.

The useful question is bigger than the plug

Charging time, electricity price, grid carbon intensity, and vehicle assignment interact. A charging rule should be judged by the whole delivery system: electricity emissions and fuel emissions together, under the same task and operating assumptions.