Night charging better for electric cars

2011-04-19 19:03

Paris - Charging electric cars at night eases a smog problem caused by fossil-fuel plants which provide the power for these vehicles, researchers reported on Tuesday.

Plug-in cars are viewed as a key tool in the fight for a cleaner planet as they do not emit tailpipe pollution when they run on electricity.

But they contribute indirectly to pollution, as well as global warming, if their electricity comes from a power station that runs on coal, oil or gas.

In a study published in a British journal, scientists in the US simulated the local impact from "plug-in hybrid electric vehicles", or PHEVs, which are cars that can switch from battery power to petrol.

Their computer model was based on predictions for 2018 of emissions of nitrogen oxides, the basic ingredient for ground-level ozone, in four major cities in Texas: Dallas/Fort Worth, Houston, Austin and San Antonio.

Extra demand

Power generation for this grid in 2009 was provided by gas (46%), coal (35%), nuclear (13%) and wind (4.5%).

The study compared likely pollution levels when 20% of mileage in the region was carried out either by PHEVs or by vehicles that were only petrol-powered.

Regardless of the scenario, ozone pollution improved when PHVs were used, because they did not emit nitrogen oxides. As for when PHEVs should be recharged, the paper found it was smarter to plug in the vehicle at night.

Extra demand from fossil-fuel power stations at night did cause levels of nitrogen oxides to rise compared to the typically shorter recharging periods in daytime.

But much of the gas emitted at night time had dissipated by daybreak. This eased the smog problem by a small but detectable margin.

Ozone, a triple molecule of oxygen, is protective when it is in the stratosphere, because it filters ultraviolet rays that can cause skin cancer and DNA mutations in plants.

But at ground level, where it forms from a reaction between sunlight and nitrogen oxides from fossil fuels, ozone irritates the body's airways, becoming a hazard for people with cardiac or respiratory problems.


The finding will guide policies on how to encourage cleaner cars, the authors said.

"This further supports efforts to develop regulation to encourage night-time charging - an example would be variable electricity pricing," said Tammy Thompson of the Massachusetts Institute of Technology (MIT).

"As more of the fleet switches over to PHEVs and larger demand is placed on the electricity grid, it will become more important that we design and implement policy that will encourage charging behaviours that are positive both for air quality and grid reliability."

The paper appears in the journal Environmental Research Letters.

  • noitall - 2011-04-20 06:29

    Every electric car should come with a solar charger, during the day the sun stores energy in batteries and when you get home in the evening the car gets charged from stored solar power, mains can back up the short fall, but the really cool thing about solar is that you can add panels and batteries at any time to increase your capacity until you get enough from the sun alone to completely charge your car. Then your car actually runs for free. No cost, no pollution.

      Albertus Bredekamp - 2011-04-20 08:03

      or you could use the solar electricity directly in your home during the day and charge the car from the grid at night. It would have the same overall effect and you dont have the conversion losses of multiple DC-AC-DC and battery storage conversions.If ESKOM can sort themselves out one can even "store" the solar power on the grid, elliminating the storage batteries

      Zulumoose - 2011-04-20 08:57

      Noitall you have no idea, solar to electricity produces very little power, it would take 1000 panels running all day without loss to power a car just enough for a daily commute. Solar is good for water heating and powering very low power devices or charging very small batteries, but useless for anything more than a few hundred watts, typical panel produces 10-40W, typical car engine 40-80 KILOwatts.

  • Ander Stander - 2011-04-20 08:29

    I might not know much , but as a motoring enthusiast I think that these electric powered vehicles do not represent the future of the automobile, instead I think that the energy-optimized vehicles, such as the VW Polo Bluemotion, are much more effecient and less damaging to the environment. The Polo Bluemotion is just about the most economical car in SA at a claimed 3.4l/100km (Volkswagen) and a more realistic 4.something l/100km (as tested by Car Magazine). What's more is the fact that these energy-optimized vehicles are MUCH cheaper than hybrids/battery powered electric cars and do not pose such a great environmental impact when they are being disposed of. So once the mass market can afford economical cars it will have a far greater (and more positive) impact than the select few that can actually afford hybrids/battery powered vehicles.

      Zulumoose - 2011-04-20 09:10

      Ander I agree up to a point, extremely efficient cars are the immediate future, but that won't help in the long run. Oil use as fuel took off only when the internal combustion engine became common and we are about halfway through oil reserves at the moment, with more efficient use being negated by more widespread use. Twice as many cars using half the fuel but being stuck in traffic for longer is actually worse overall. There will be mucking about with hybrids etc, but what is really needed is new battery technology reducing weight and cost, then any source of power can be put to use anywhere, by being transmitted through the grid to charge vehicles. I cannot see anything short of that solving the inevitable oil shortages of the future. Once electricity is the norm for vehicles, there will be huge focus on efficient power generation, with fewer emmisions and more alternative sources being brought online. The ultimate answer though, is to reverse population explosion. Humanity simply needs to do an about turn on the mind-set that growth is good. It stopped being good a long time ago. How many people is enough?

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