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Northern California MPGe?

Discussion in 'California' started by Pmacafee, Jun 2, 2013.

  1. Pmacafee

    Pmacafee Member

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    Nov 27, 2012
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    Location:
    San Francisco
    I live in Northern California and our power is provided by Pacific Gas & Electric. Currently about 62% of our power comes from non-carbon emitting sources, (reand the remainder comes from natural gas fed power plants. I am wondering what our local MPGe would be because I think we are a bit cleaner than the average state/area.

    Philip Macafee
     
  2. stopcrazypp

    stopcrazypp Well-Known Member

    Joined:
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    Plug-to-wheel MPGe (the number on the EPA sticker) will be the same no matter where you get your electricity because all it does is measure energy usage from the plug (upstream from powerplant is ignored):
    95MPGe for 60kWh and 89MPGe for 85kWh.
    http://www.fueleconomy.gov/feg/Find.do?action=sbs&id=33367&id=33368

    However, if you click on the "Energy and Environment" tab and then under the "Greenhouse Gas Emissions" section select "Show: Tailpipe and upstream GHG" you can get the CO2 emissions (in grams per mile) including upstream emissions from the powerplant. The conversion factor is 11.1 kg CO2/gallon gasoline (from the Prius getting 50mpg and 222g/mi when including upstream). You get the following results.

    60kWh:
    230 g/mi (US Average) = 48mpg gasoline car
    120 g/mi (downtown SF) = 93mpg gasoline car

    85kWh:
    250 g/mi (US Average) = 44mpg gasoline car
    130 g/mi (downtown SF) = 85mpg gasoline car
     
  3. Pmacafee

    Pmacafee Member

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    Location:
    San Francisco

    Thanks stopcrazypp; I think I understand most of it but the 85kwh model is advertised as having an EPA rating of 89MPGe. Why do the calculations above come in about the same as the EPA rating if the area is cleaner than the national average?
     
  4. gregincal

    gregincal Active Member

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    Location:
    Santa Cruz, CA
    MPGe has nothing to do with emissions, just how far the car goes on an equivalent amount of energy (regardless of what form the energy takes).
     
  5. stopcrazypp

    stopcrazypp Well-Known Member

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    Again, the 89MPGe (38kWh/100miles) only measures the energy from the EVSE to the wheels. In the 85kWh model's case it means 100.7kWh (38kWh/100miles * 265 miles) of electricity from the EVSE to charge the car for 265 EPA miles.

    So basically the EPA MPGe number only includes energy use from the part in bold:
    Fossil Fuel Extraction -> Transportation -> Powerplant -> transmission lines -> transformer -> electrical panel -> EVSE -> Car -> wheels

    In contrast, the g/mi numbers I posted includes emissions from everything above (from the fossil fuel being extracted from the ground, all the way to it being used to power the wheels on your car).

    To make it more clear for 85kWh model:
    38kWh/100 miles (car) * 658g/kWh (US Avg upstream emissions) = 250 g/mi (US Avg) = 44mpg gasoline car
    38kWh/100 miles (car) * 342g/kWh (SF upstream emissions) = 130 g/mi (SF) = 85mpg gasoline car
     

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