Environmental aspects of Clarity PHEV

Discussion in 'Clarity' started by Ray B, Oct 8, 2018.

  1. Ray B

    Ray B Active Member

    Below is an estimate of the CO2 emissions in metric tons saved by the Clarity PHEV over the highly efficient 2019 Honda Insight.

    I have several disclaimers, notes, and cautions:
    • This is not a full Life Cycle Analysis study (LCA) that covers all environmental impacts, but rather just an educated guess as to the CO2 emissions which dominate most discussions of the environmental impact of passenger cars.
    • I hesitated to post this because I know how it can spiral into mayhem. Please avoid debating politics, climate change, etc. ...this is strictly meant to inform. There are many studies online which cherry-pick data on this topic in order to spin a preferred viewpoint. The intent here is mainly to show what the data is telling us.
    • Estimates are using recent figures for electricity grid emissions for each region, but there are some aspects which can lead to inaccuracies. Local utilities can have varying impact depending on the sources used, and how much power is imported from other states, etc. That is why regional values are used, as the impact of state-to-state variances are affected by power interconnections. If you want you can search your local state's numbers and see if they differ radically from the regional values listed. These numbers also were adjusted to account for transmission and distribution losses.
    • EPA estimates of combined fuel economy were used as a guess on the efficiency. I grant that many people argue about the applicability of these estimates, but I ran the numbers with -20% up to +20% of those estimates for both the Clarity and the comparison car, so the end result did not change much. The column headings show which EPA adjustment was used for each calculation (-20%, 0%, +20%).
    • Another aspect considered was the amount of the lifetime of the PHEV car was spent on EV-only mode: 99% / 90% / 80% / 50%
    • Another variable is whether one anticipates replacing the EV battery during the car's lifetime. The right hand table estimates that.
    • The second table provided is for users who charge the car using ~50% solar PV as the energy source. Why choose 50%? Because I myself have solar PV at home, but only charge at home about half the time, as it is convenient for me to charge at work. If you want the 100% solar result, it would equate to the results for Yukon in the table.
    • I chose the 2019 Honda Insight HEV as the comparison car, because it is one of the best mileage cars on the market and made by the same manufacturer, and although a little smaller, compares well to the Clarity in many respects. It is impossible to get a perfect 1:1 comparison, but if one is interested in the best choice from an environmental perspective, then the Insight HEV certainly is a good contrast car to the Clarity.
    • No BEV (e.g. Nissan Leaf) was used for comparison, as it is likely that the the results would not be radically different than the 99% EV-only mode for the Clarity. Indeed, other PHEV's (Toyota Prius Prime, Chevy Volt, etc.) would likely have very similar results to the Clarity, although one can spend hours researching it.
    • The model developed here does include 'End of Life' (EOL) estimates, but those are very much guesses. The only difference between the PHEV and HEV comes down to the size of the battery and a slightly larger overall car, so the difference boils down to an extra 220 kg CO2 for the Clarity (0.22 tons). It depends on how the battery is recycled, as pyrometallurgical processes result in a net increase in CO2, which hydrometallurgical processes would likely be net negative CO2 (the recycled compounds would displace the raw material CO2 generation). Overall, most LCA results show that the EOL stage has the smallest overall impact on the CO2, and certainly differences between similar cars are negligible.
    • By my research into the numbers, the manufacturing of the battery of the Clarity is estimated to release ~1 metric ton of CO2. This equates to an estimate of the Chevy Volt's battery which is very similar in size.
    • The lifetime of the car was estimated to be 250,000 km (~155,000 miles).
    • For reference, in MA the Clarity will result in 21.6 tons of CO2 over this lifetime assuming 250,000 km, no battery replacement, and averaging the EPA combined fuel economy, when using the EV-only mode 99% of the time. Under similar assumptions, the Honda Insight would result in 33.1 tons of CO2.
    Clairty vs Insight CO2 100 percent grid.png Clairty vs Insight CO2 50 percent solar.png eGRID subregions USA.png
     
    Last edited: Oct 8, 2018
  2. Clarity_Newbie

    Clarity_Newbie Active Member

    Ray B

    Impressive stuff. Less C02 emissions is one of the goals I hoped to achieve with the Clarity.

    Thanks for taking the time and share this study.
     
  3. KentuckyKen

    KentuckyKen Well-Known Member

    Less CO2 goes into the environment and less money leaves your wallet.
    No matter how you look at it, it’s the perfect car for today.
     
  4. Sandroad

    Sandroad Well-Known Member

    So in Michigan the estimate is 745.9 lbs of C02 emitted per KWH of electricity using the state's utilities. That correct?
     
  5. Ray B

    Ray B Active Member

    Yes, the data I used came from this 2014 document: https://www.epa.gov/sites/production/files/2015-10/documents/egrid2012_summarytables_0.pdf, but I just found a newer version from 2016 (https://www.epa.gov/sites/production/files/2018-02/documents/egrid2016_summarytables.pdf) which shows a significant change for Michigan down to 577.5 g CO2/kWh. It doesn't change the overall result but the only magnitude of the difference. It would be now be comparable to the result for Long Island (NYLI). If I find any more big changes I will re-run the numbers and re-post.

    EDIT: When accounting for grid losses (4.49%) it would be 603.4 g CO2/kWh...
     
    Last edited: Oct 9, 2018
  6. Ray B

    Ray B Active Member

    I updated the results using the newer eGRID data from 2016, which added ~3 regions to the list of ones where the Clarity (and in reality most BEVs and PHEVs) produces less CO2 than the 52 MPG 2019 Honda Insight. Rather than post the low quality image I will attach the pdfs to show what regions the Clarity is the better choice for reducing CO2 emissions compared to the Insight, and a second pdf compares it to a garden variety Honda Accord (non-hybrid), in which case the Clarity is the better choice, even in areas that burn a lot of coal to create electricity.

    I also am attaching a simplified map to show areas (in green) where Clarity produces less CO2 than the Insight over its lifetime. Areas in grey are basically a tie, and I put Nova Scotia in pink because although they burn a lot of coal for electricity currently, in a little over a year they will finalize a connection to NFLD to draw hydroelectric power, so it may soon swap to become a PHEV/BEV friendly province.

    NOTE: the map below is only an approximation, since the grid regions don't always follow state boundaries. Refer to the pdfs for the maps that show the results for each specific area, or research your local utility for recent CO2/kWh data (add ~5% for grid losses).

    BEV-PHEV green HEV purple 2016.png
     

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    Last edited: Oct 9, 2018
    RogerB likes this.

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