Is a Prius Really Cleaner Than an Electric Car?

By Bill Moore

Posted: 12 Nov 2009

Let me make this very clear right up front. The world is going to need more than just electric-drive vehicles to solve its problems. Even the greenest Renault Fluence, Mitsubishi i-MiEV, Think city or Prius Plug-In won't reduce road congestion in central London. Fewer cars and smaller ones can help, but modestly so. Public transit, bicycles, electric scooters and a good pair of leather will do much more.

Still, there will always be a need for automobiles and the greener the better. But what's it mean to be "greener"? Certainly a vehicle that produces few if any tailpipe emissions is a good starting point; and electric cars clearly meet that criteria IF you ignore the source of the electric power. In many parts of the world, including Britain, a significant percentage of that electricity comes from the conventional thermal power plants consuming natural gas, coal and even oil; and in the process generate millions of tons of carbon dioxide and other harmful emissions from mercury to sulfur dioxide.

So, it would be natural for critics to complain about the "long tailpipe" of electric cars that ends at a coal plant's smoke stack. The most recent body to make this claim is, of all people, Britain's Environmental Transport Association, which recently warned that increased reliance on electric cars will mean the release of more harmful emissions than those produced by gasoline/petrol-electric hybrids like the Prius.

Reports the Daily Mail...

The report warned that European officials have assumed that electric cars are 'zero-emission', and failed to take into account the electricity they use.

But it said that once the effect of burning fossil fuels is taken into account, they actually emit more CO2 than a hybrid car.

It calculates that an electric car has emissions of 106 grams of CO2 for each kilometre used, compared with 172 grams for an average petrol car. By comparison the latest Toyota Prius hybrid car has official emissions of 89g/km.

While the Prius is a wonderfully efficient car -- after all, my wife and I own one -- to conclude that it's cleaner than an all-electric car struck me as odd, so I decided to do my own calculations.

The first thing I did was find out how much of Britain's electric power comes from coal versus other, cleaner fuels. According to the U.S. Energy Information Agency, 73% comes from thermal power generation, while 23% comes from nuclear. The rest is produced by hydropower (1%) and renewables (2%). That 73% comes from burning natural gas (53%), coal (44%) and oil (2%).

Having established the percentages of each fossil fuel, I then found how much carbon dioxide each produces on a per kilowatt hour basis. Natural gas creates 190 gm per kWh. Burning coal results in the release of 320 gm/kWh. I didn't bother with oil given its 2% contribution.

Next, I asked how many miles does the average British motorist drive a year? According to a couple different sources, it ranges from a low of 5,433 to 6,815 miles yearly. The average length per trip is a surprisingly short 5.9 miles.

With these figures in hand, I started doing the math, beginning with the amount of electric power an EV might consume on a watts per mile/kilometer basis. Using our own plug-in Prius as a reference, I assumed the electric car would use about 250 watt hours per mile or 155 watts hours per km.

That 6 mile/10 km trip would then require 1550 watt hours (1.55kWh) of energy. Of that, 821 watts hours would come from natural gas and 682 from coal. To generate this mix of natural gas and coal would, by my calculations, produce 373 gm of CO2 (excluding the 2% oil) for that 10 km commute; or a mere 37.3 grams per kilometer, less than half that created by the super-clean, but still gasoline powered Prius.

Of course, the 37.3 grams can be pushed even lower if those cars were being charged from solar during the day and wind power overnight. The same can never be said for the gasoline or diesel-hybrid.

Finally, my 250 watt hours per mile is on the upper end of the scale. Small electric cars like the Think city, MegaCity or newly announced T.27 from Gordon Murray, will more likely be in the sub-200 watt hours per mile; and electric bicycles and scooters will be below the 100 watt hours per mile.

Yes, EV's might now have a "long tailpipe," but it doesn't stretch halfway around the world to oil fields and tar sands in distant lands, and it can get cleaner if we put in place the right policies and incentives.

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