What’s the greenest car? An extremely short guide to vehicle emissions

Vehicle emissionsA few months back I did a post called The World’s 7 Greenest Vehicles.  It only included one car.  Since then a few readers have emailed to ask if I could do a similar comparison, but for cars only.  So here’s a very brief guide to vehicle emissions.

In the graph above I’ve compared the full vehicle emissions of four petrol cars (20, 30, 40 and 50 MPG) to that of an electric vehicle using four different types of electricity (coal, oil, gas and solar).  In each case I include the emissions from vehicle manufacturing plus the full scope of petrol and electricity emissions. What a wonk might call well-to-wheels plus manufacturing.

The results are pretty clear.  The better the fuel economy of a petrol car the lower its emissions.  For the electric car the major difference is the source of electricity.  The lowest emissions by a distance is the electric car using solar electricity. I’ve chosen solar (45 g CO2e/kWh) because there is high co-ownership of solar and EVs, but the emissions would be just as low using hydro, nuclear, wind or any other low carbon electricity.

That’s it, very brief as promised.  Diesel is slightly better than petrol but has a particulate problem. Do you think electric cars are going to be the low carbon vehicles of the future?  How about next-gen biofuels or hydrogen fuel cells?  For more on vehicle emissions check our posts on electric vehicle emissionsyour driving emissions and the world’s 7 greenest vehicles.  

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  • http://www.EcoReality.org/wiki/User:Jan_Steinman Jan Steinman

    It would be interesting to do “well to wheels plus manufacturing” for the different electricity sources mentioned, or accounting for what HT Odum called “emergy.”

    I notice your methodology would lump solar together with hydro, nuclear, and wind. I’m guessing those three have very different emergy profiles!

    Solar has very high embedded energy, and is not truly renewable in that regard — there is not a single solar-powered solar cell factory that I know of.

    Big hydro uses lots of cement, which has a fair bit of embedded energy, but at least it’s fairly low maintenance, once established.

    Nuclear… proponents are fond of ignoring the “externalities,” citing only the operating cost and radiological hazards of an operating plant. But boy is there ever a “long tail” with nuclear!

    Gail Tverberg says that wind power is fueled by a continuous stream of spare parts! Plus it uses exotic rare-earth materials that we may be hitting resource limits on.

    I don’t have numbers on any of these, but living in an area served by abundant hydropower, I think I can be a bit smug about an electric vehicle.

    • Lindsay Wilson

      All the low carbon forms of energy fall between 72-79 g for this purpose. This includes solar, who’s embodied energy is only a little higher than things like nuclear or wind. I covered this all in last weeks post. The data is very solid and comes from the IPCC meta study. As for hydro . . it depends what the effect of the build is. If they drain a peat bog its a nightmare


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