MIT: Charge PHEVs at Night to Reduce Overall Pollution


Plugging in your electric school bus at night might just reduce ozone and further decrease the carbon footprint. That’s what researchers at MIT suggest in a new study published this week.

As the Institute of Physics reported, the scientists tested three charging scenarios of PHEVs at four locations across Texas, granted to gauge the air quality impacts of replacing approximately 20 percent of the gasoline-powered light duty vehicle miles traveled (VMT) with electric VMT by the year 2018 and not a diesel-electric power train. And the new 2010 diesel engines are already very clean.

But re-charging PHEVs at non-peak hours is widely recognized as being more cost-effective and reliable. The practice apparently can also lower pollution.

Researchers first charged vehicles at off-peak times in the night. Then, they charged to maximize battery life, or just before use and only enough to complete a trip. The third scenario involved charging the battery when it was a convenient time for the driver, such as right after using the vehicle. They found that charging at night resulted in higher levels nitrogen oxides, but there is less sunlight at night for the emissions to react with. As a result, the overall levels of pollution were lower than those associated with 20 percent of gasoline VMT.

STN contributing editor Robert Pudlewski recommended that operators of PHEV school buses utilize timers when charging to measure the amount of electricity being consumed and to ensure charging is limited to off-peak hours.