Charging electric cars at night reduces pollutants

Researchers in America have shown that ozone - a known pollutant at low levels in the earth's atmosphere, causing harmful effects on the respiratory system and sensitive plants - can be reduced, on average, when electric vehicle charging is done at night time.

Ozone forms as hydrocarbons and nitrogen oxides, emitted into the air, react with sunlight. Two of the largest emitters of these pollutants are vehicles and electricity generating units (EGUs) with some of the most densely populated regions in the US still failing to meet the National Ambient Air Quality Standards after 30 years of regulation.
Plug-in Hybrid Electric Vehicles (PHEVs) have risen in popularity over the past decade as a result of cheaper fuel costs (versus gasoline), increased efficiency, and positive impact on the environment due to lack of exhaust fumes.

Charging PHEVs at night time is known to be more cost-effective and reliable; however, researchers publishing their work today, Tuesday 19 April, 2011 in IOP Publishing's journal Environmental Research Letters, have now found that charging at this time also leads to lower levels of pollution on average across four cities and over four representative modelling days.

PHEVs have the capability to run off battery power and gasoline. When PHEVs run off battery power they emit no pollutants from their exhaust, however, the EGU's -  which provide electricity to charge batteries - do give off pollutants.

As such, researchers at the Massachusetts Institute of Technology (MIT) and the University of Texas modelled the effect of replacing 20 per cent vehicle miles travelled (VMT) by gasoline-run cars with PHEVs, using three different electric car charging scenarios to study the emission of pollutants, specifically ozone, in the state of Texas.

There has been much debate regarding the best way to charge electric cars. The first scenario in this study was based on charging the car at off-peak times in the night. The second scenario involved charging to maximise battery life (charging just before use and only the amount of charge needed to complete the trip) and the third scenario involved charging the battery when it was a convenient time for the driver (typically just after vehicle use).