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coal EV -vs- petrol car

Discussion in 'Energy, Environment, and Policy' started by dpeilow, Aug 30, 2009.

  1. dpeilow

    dpeilow Moderator

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  2. raymond

    raymond Member

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    Quick back-of-the-envelope calculation seems to agree with the Danes:

    244 miles (392km) on 70kWh. For coal (0.95 [1] kg CO2/kWh) this comes down to 70*0.95/392 = 169gr/km. This is less than for a Porsche Boxster (222 gr/km tank-to-wheel [2]), but much more than a Prius (89 gr/km).

    Using gas (0.60 kg/kWh) instead of coal reduces Roadster well-to-wheel emissions to 107gr/km. This means you have to include wind/solar/nuclear in the mix to get the CO2 emissions down below that of a Prius.

    This is not what I have been led to believe (implicitly?) by Tesla Motors. What am I doing wrong?


    1: CO2 Emissions Report gives 2.117 pounds/kWh for coal in the US in 1999.
    2: well-to-tank is approx. 12% of tank-to-wheel so the 222/89 figures for the Boxster and Prius should really be 252/101 to be more fair.
     
  3. dpeilow

    dpeilow Moderator

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  4. raymond

    raymond Member

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    Greenhouse Gas Conversion Factors | Carbon Trust says:

    The University of Strathclyde (Glasgow) says

    Can somebody please point me to the reliable part of the web, please? These numbers vary hugely! Why would the grid be so horribly inefficient? These figures almost indicate that the best way to charge your roadster is to have it toed by a diesel car and let the Roadster's regen do the work.

    Should this be continued in a separate thread? Is this a "big thing" or am I comparing apples to oranges?
     
  5. dpeilow

    dpeilow Moderator

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    So the Carbon Trust's data = 96g/km and the Glasgow University data = 86g/km.

    By the way, the Danish grid, despite their wind power industry, is 75% coal. That may explain things.
     
  6. Cobos

    Cobos S60 owner since 2013

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    I'm not sure about the reliable part of the internet, but I usually use OhmExcited's rapport about this issue.
    With this a pure coal driven grid and a EV is not better for CO2 than a Pruis. But for most actual grids with different sources the EV comes out on top. And as Martin Eberhard so nicely put it, the EV is the extreme flexfuel car.

    Cobos
     
  7. stopcrazypp

    stopcrazypp Well-Known Member

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    #7 stopcrazypp, Aug 30, 2009
    Last edited: Aug 30, 2009
    In general, I found the rule of thumb is an EV on all coal will be cleaner than the equivalent normal gas car for sure, but not necessarily vs a hybrid.

    So it's wrong when they say an EV is dirtier than a "normal car". I don't consider hybrids such as the Prius as normal cars since you give up performance.

    However, coal is still a very dirty source in general, both in terms of GHG and also other pollutants like mercury and sulfur. Which is why it makes sense to move away from coal as we upgrade our grid. It's encouraging there's a trend of lower coal usage in the US.
    http://www.eia.doe.gov/cneaf/electricity/epm/epm_sum.html


    I think what Tesla Motors does is to compare efficiency. I'm not sure if they ever directly say the Roadster is twice as clean as the Prius, but I'm sure I heard them say it's twice as efficient. They just take the energy in a gallon of gas (34.7kWh/gallon) and convert the Roadster's efficiency number to mpg. This comes up with 100-135mpg plug-to-wheel. So that's where they get the Roadster is twice as efficient as a Prius. They aren't technically lying since the car IS twice as efficient as a Prius if you consider the input/output of energy for the two cars; as an automaker they aren't responsible for and can't control anything else, such as the powerplants where you get electricity.

    So what Tesla does isn't a well-to-wheel kind of comparison, but rather a gas pump/plug-to-wheel kind of comparison.

    For people in the US, I usually recommend this tool to figure out whether you are better off with a hybrid or an EV/plug-in (IMHO every country should have a similar tool if they want to be serious about plug-ins or EVs):
    How clean is the electricity I use? - Power Profiler | Clean Energy | US EPA

    From here, I get the US average emissions is 1329lbsCO2/MWh -> 0.60kg/kWh which corresponds to your 107gr/km.

    Where I live (in California), I get 724lbsCO2/MWh -> 0.33kg/kWh which means 60gr/km for the Roadster in California.

    So those driving a Roadster in California is polluting 35-40% less than a Prius (depending which generation of Prius). Not quite half, but not too bad for such a quick sports car.

    There are some states that use a lot more coal and for those states it doesn't make as much sense to have EVs until they get cleaner. Coal heavy states like Wyoming (can try zip 82082), North Dakota (58203), West Virginia (24985) for example has 70+% coal and 1800+lbsCO2/MWh.
     
  8. raymond

    raymond Member

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    OhmExcited's rapport uses old (wrong) data on the Roadster from an outdated white paper giving energy use as 206 W.hr/mi. Real data (70 kWh for 244mi) gives 287 W.hr/mi (39% more than the white paper).

    The high (higher than I had expected) carbon footprint is due to dirty coal and inefficiencies of the grid, and indeed there is nothing Tesla Motors can do about that.

    Conclusion: we need to clean up the grid if we want to reduce CO2 emissions.


    PS: I'm still curious to find out how much energy really is required to fill up a 56kWh battery under real world conditions. During winter the temperature in my garage is typically less than 10C (at night even less than 5C), so that might be an ideal time to charge because the A/C won't need to run (often). How much of a difference does this make? And what about charging at 30A vs 70A? Do we have any data on that?
     
  9. Cobos

    Cobos S60 owner since 2013

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    Yes I'm pretty sure the 70kWh data is for using the quick charger, which I suppose for most Roadster users is not relevant. If they drove under 50 miles that day using the slowest charging method will yield better efficiency. For people with charging both at home and at work there hardly should be any need for using high-power charging. Which again means the CO2 output is very dependant on both how you drive and how you charge an EV.

    And as we are discussing these numbers, shouldn't we include the production and distribution costs for gasoline to be fair. The ICE car manufacturers supply tank-wheels consumption numbers, the Roadsters tank(battery)-wheels consumption of CO2 is 0.00 :)

    Cobos
     
  10. raymond

    raymond Member

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    That's the 0.88 in my earlier calculation. ICE numbers should be devided by approx. 0.88 to get well-to-wheel numbers.
     
  11. Cobos

    Cobos S60 owner since 2013

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    Are you sure about that 0.88 factor? What kind of oil extraction method is that? I'm pretty sure that's not North Sea oil extraction? How about the refining, to be fair we need to account for the electricity used as well in the refining of the oil and use similar coal-based grid there. It seems to me the problem with these kind of comparisons is that it's hard to find hard data on any of these numbers.

    Cobos
     
  12. Serge

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    These numbers are strange as "grid" CO2 emissions (0.537 kg/kWh) are almost twice that of the "dirtiest" component, which is coal at 0.330 kg/kWh. As noted, grid transmission losses are minor. So why such a big discrepancy?

    To compare with the U.S., let's look at the old (2000) DOE report
    Coal is 2.117 lbs/kWh = 0.961 kg/kWh
    U.S. Grid Avg is 1.350 lbs/kWh = 0.613 kg/kWh.

    So perhaps the overall grid (and U.S. component) numbers hold water and corroborate the .6 kg/kWh reported by stopcrazypp. On the other hand, let's double check that 0.089 kg/km value for Prius.

    According to U.S. EPA CO2 emissions resulting from burning a gallon of gasoline equal 8.8 kg / gallon. Assuming a combined 50 miles-per-gallon rating for 2010 Prius we have:

    8.8 kg / 50 miles = 0.176 kg/mile or 0.109 kg/km (tank-to-wheel).

    So, a generic conclusion is that Roadster powered from the grid emits about the same amount of CO2 as the Prius. A more accurate comparison would take into account the regional/local electric supply mix.
     
  13. dpeilow

    dpeilow Moderator

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    If we are talking about adding in well-to-wheel emissions for ICE cars, should we not add mine-to-plant emissions for coal too? Just a thought.
     
  14. stopcrazypp

    stopcrazypp Well-Known Member

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    For the DOE's analysis, they have 83% as the refining and distribution efficiency for gasoline. Electric and Hybrid Vehicle Research, Development, and Demonstration Program; Petroleum-Equivalent Fuel Economy Calculation | Federal Register Environmental Documents | USEPA I think that just includes refining and distributing to gas stations.

    From the sound of things, the DOE doesn't include the losses from extracting the oil from the ground and getting it to the refinery, so that's why we don't include mine-to-plant emissions. As for the reason, it might be because they are negligible compared to the other losses. I guess it is not true "well-to-wheel," but it's probably close enough.

    88% refining efficiency seems about right if you don't include distribution:
    http://www.transportation.anl.gov/modeling_simulation/GREET/pdfs/energy_eff_petroleum_refineries-03-08.pdf

    I found a document that shows the extraction losses for petroleum really are negligible:
    http://www.transportation.anl.gov/pdfs/TA/166.pdf

    I couldn't find anything for coal, so I'm not sure if it's similar or not.
     
  15. vfx

    vfx Well-Known Member

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    What about decades of thousands searching the entire planet for oil? Expensive satellites, cutting edge geology, pincushinging the ocean floors, and then the cleanup afterwards Then what about those multi billion dollar ocean platforms that get destroyed in storms and well fires that burn for years?

    Any of that stuff included?
     
  16. Cobos

    Cobos S60 owner since 2013

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    I'm pretty sure that depends a lot on HOW the oil is extracted. From tar sands the whole argument is very skewed in the direction of EVs, while Saudi wells on solid ground are a lot easier. Taking the North Sea oil platforms they usually cost several billion dollars to construct and require helicopters to transport people and tankers to transport product away from them. Actually just paying the price for the platform I'm sure there's a few resources being spent there.

    Cobos
     
  17. dpeilow

    dpeilow Moderator

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    This was an interesting programme: BBC - BBC Two Programmes - Coast, Series 4, Norway: Lillesand to Svalbard

    The gas processing plant was taking gas extracted by devices on the sea bed and filtering out water and sand before sending it to the UK. It required a lot of power to do so.

    When the guy from Shell was asked if he was worried that it would be gone in 40 years, the reply was basically "we don't worry, we have hydro power".

    By the way, the osmotic power idea was interesting.
     
  18. SByer

    SByer '08 #383

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    I'm also going to claim that for the portion of the EVs power that overlaps the amount of electricity needed to produce that gallon of gas that we need to use the pollution rate of that gas production, and NOT the general grid mix - the pollutants rate of that >=7.5kWh/gal seems to be much lower than the rate for the grid in most parts of the country, and by substituting completely for that gas, that cleaner mix of electricity could be fed onto the grid instead.

    Yes, it adds yet another set of shakey estimates to things, but this continuous comparison of the dirtiest grid mix for EVs against optimistic gas wells-to-wheels estimates just doesn't pass the sniff test.
     
  19. Serge

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    Maybe in part because it is not an accurate comparison. Such dirty grid exists only in WV and a handful of other locales. Unless somebody points out an error in my calculations an EV powered from such grid is as clean (CO2 wise) as a Prius. Most people's actual carbon-footprint will be lower. In addition, utilities have an option of purchasing electricity from renewable (carbon-neutral) sources. One can always produce own renewable energy. Such options simply do not exist for owner of a gasser.

    This challenge reminds of [ultimately] futile attempts to compare an ER-EV like the Volt to a regular gasser by using only 1 parameter (mpg). New technology requires new approaches.
     
  20. dpeilow

    dpeilow Moderator

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    #20 dpeilow, Sep 3, 2009
    Last edited by a moderator: Mar 13, 2016
    Not strictly true, but it's a bit less practical...

     

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