Plug in Prius - Most Environmentally Friendly Vehicle in Study

So, it turns out that the Climate Central report authors completely ignored a GREET-based analysis of battery manufacturing authored at ANL 9 months ago that finds even lower CO2e emissions than the Notter study.

Summary says:

The study that Climate Central relied on (Hawkins 2012) reported GHG (CO2e) emissions of 22 kg CO2e/kg of battery weight or, in other words, 4.3 times higher CO2e emissions than the GREET report. The ANL GREET report includes an attempted analysis of the discrepancy with the Hawkins study and essentially says it is due to inaccurate and overly generalized data due to the Hawkins study's "top down" calculation approach.

The Climate Central report (along with its other sloppy mistakes) assumed that the Volt battery was LiFePO4 and assigned it an apparent manufacturing CO2 debt of 9,960 pounds. They should have modeled it as being consistent with the LEAF battery and scaled it down to 7,917 pounds (11,516 * (16.5/24)). Of course, they based their numbers on the Hawkins study which was based on LiNMC and other studies show LiNMC manufacturing emits significantly higher CO2e than the manufacturing of the LiMn2O4 cells which most closely match the actual chemistry used in the LEAF and Volt.

The ANL GREET study by Dunn et el. (2012) is based on LiMn2O4 and, at first glance, would appear to imply a Volt pack CO2e debt of under 3,000 pounds or less than 1/3 of the amount assumed by the Climate Central report. If you believe the ANL study, it completely invalidates the Climate Central report conclusions. At the very least, they should acknowledge the ANL study and the wide range of reported battery manufacturing CO2e results and correct their various data and obvious methodology flaws (double-counting CO2e debt in Table 9).

As I said earlier, its time for a do-over!

Unfortunately, the ANL study is presently hiding behind a peer-reviewed journal's pay wall but it is available if you are willing to fork up $35 like I did.

The summary is free:

Impact of Recycling on Cradle-to-Gate Energy Consumption and Greenhouse Gas Emissions of Automotive Lithium-Ion Batteries - Environmental Science & Technology (ACS Publications)

 

Been busy with work so missed most of this thread. Some good discussions. As many have pointed out there are many problems. Too many for this to be given any serious consideration. The biggest errors are in the battery. Jeff pointed out they cited a range then used the highest. But in fact the most recent study from ANL (who do the greet model for many of the other items cited) is even lower than any cited at 5.1, i.e. the model used was more than 4x over the ANL estimate for CO2 production from manufacturing of modern PHEV/EV battery. (see http://pubs.acs.org/doi/abs/10.1021/es302420z for details). (NOTE: I see Jeff just posted this same study.)

But even just using the average battery manufacturing estimates cited would reduce the manufacturing penalty for the volt vs PHV by 4000lb, and using the ANL estimates reduces it by over 6000lb. If one takes the approximation used by ryogajyc (note that 9000/.048=187,500 miles, I don't see how you got the 229K miles). Taking that and and corrects for the errors in manufacturing (i.e. reduces the manufacturing penalty for the volt and PHV to use ANL estimates, then the manufacturing penalty difference is about 2400 lb, which at .048 per mile is only aboit 50000 miles to make it up at 100/0 If one assumes the Utility factor rates of 66% and 28% EV it would take closer to 131K to make up the difference so the PHV still has a edge if one is at the average and stops at 100K miles. But is ignoring the other errors and presuming its grid energy.. if one makes other corrections an buy renewable energy both are cleaner but the Volt is much cleaner and makes up its manufacturing CO2 debt much faster..


Second, they really pump up the PHV and effectively beat up the Volt by assuming all PHEVs are 50/50 gas electric. That obviously favors using a small battery a lot, since they have greatly overestimated the battery's impact and then they give the Volt NO benefit from its bigger battery while giving it a much greater penalty. At the same time it is inflating the assumed benefit from the PHV by assuming a 50:50 EV/ICE ratio which, while possible, is unlikely with its battery. This is a sophomoric error.


Third&fourth they are assuming a fixed grid efficiency but factoring it over a 50K or 100K (neither of which are realistic lifetimes for a modern car). I don't see a viable correction for either assumption.

Fifth their regional analysis ignores that GHG of gasoline also varies significantly. In the mountain west, one of the heavy coal regions, we also use mostly tar-sands based gasoline which is 15-20% higher in GHG.

Sixth, for oil they are citing (hence assuming) wells to wheels, ignoring the very high energy costs of research/discovery/drilling and it also ignores the flaring off of gas while drilling, which is a major issue for the recent discoveries.

So while the PHV is a great car, the study has too many major problems for its conclusions be taken very seriously.

 

As far as I recall, the Climate Central report itself did not acknowledge any disagreement on battery production CO2e. They just chose to use the high-end Hawkins study. You had to go find and read the Hawkins study on your own in order to learn of the wide-ranging CO2e dispute and the other, much lower, reported values from other studies.

 

Sorry, you are correct.. Read too many things and when writing it up I was not being clear which cited the range. Given they cited papers they should have admitted the range and given a rational for choosing an extreme value from that range. Given I had already read the ANL study I was more focused on just how wrong their number of 22 was rather than who said what.

I forgot to mention the ANL study that resulted in 5.1 vs 22 also excluded recycling. It notes that "direct physical recycling of LiMn2 O4 , aluminum, and copper in a closedloop scenario can reduce energy consumption during material production by up to 48%." i.e. by the time my batter is recycled the effective footprint will nearly half of what they projected. They have 8-10 years to get recycling in place ;-)

 

No surprise, Volt owners hate the study, go figure!!!!

DBCassidy

 

I went back and checked my math and I did make a mistake, but it was actually in favor of the Volt. The actual delta is 0.038 lbs CO2e, so 9000/0.038 => 238,842 miles.

A little more actually, at about 63,158.

I double-checked this too and this turns out to be incorrect. At 66% EV for the Volt, the emissions are 0.55 lbs CO2e/mi vs. a 28% Prius Plug-in at 0.49 lbs CO2e/mi, so a Volt could never catch up with a Prius Plug-in in terms of lower CO2e emissions.

I thought so too initially, before I did the math. It turns out the Volt's 37MPG really hurts it's CO2e emissions and as does low electrical efficiency. Put in terms of the 28% utility factor you assumed for the Prius Plug-in, to simply have the same CO2e/mi, a Volt must drive 95% EV, which is pretty optimistic. That's without ever making a dent 2,400-9,000 lbs of CO2e difference in manufacturing emissions.

From the math, the actual error seems to be inflating the benefit of a larger battery which in reality is quickly and easily squandered by gas and electrical energy inefficiency. I'm going to refrain on making a judgments on whether that is sophomoric.

 

Sorry I was rushed when I was writing and it was already getting long so I ended up skipping multiple steps when I was commenting.

Do to the utility factor correctly you cannot use the math model you used, and its also not appropriate to include the manufacturing CO2 which is embedded in Tables 5/6 which is what it seems you used. So where you see a terrible EV efficiency for the Volt, it is because of the way you computed using bad data embedded in the report.


To estimated co2 per EV miles you took taking the reports's estimated Co2 at 50K miles from Table 5, but that presumes 50:50 mix CO2 which inflates the Volts CO2 per mile and decreases the Prius PHV co2 per mile. So when you break out the gas and use it to estimate the EV efficiency you get a bogus number. Since it also includes the inflated CO2 from manufacturing its beyond bogus. The Volt is much less than .48 Co/mile.

To get proper CO2 per EV mile for the you take 1.16 * 35 /100 to get .406 Co2 per EV/mile. (p9 of the report says they use 1.16lb Co per kWh, and the 2013 Volt uses 35kWh per 100). With 100% EV, it would only take 21428 to make up a 2400 lb manufacturing difference with a 50MPG car.

With SAE utility factory for a 38 EV mile PHEV being .66 the overall CO2 per mile with that factor becomes .5059 lb Co2 per mile. And thus with the official utility factor it does catch up with a 50MPG gar which is .518 CO2 per mile. However, I will note that using the proper utility factor and the national average grid, it would be over 200K miles to make up a 2400lb manufacturing difference. So one either needs to be in a green energy region, buy renewable or have a higher EV ration, to keep it green.

If however one does a higher EV rates the manufacturing CO2 difference, is made up quickly even on the national grid. If one considers say 85%EV which is where I am, then the Volt will have .45 CO2 average per mile and the tradeoff versus a 50MPG car is about 36K miles to make up the manufacturing difference of 2400lb. So with higher rates EV even using the 2012 national grid the Volt is greener.

Note the SAE utility factor presumes only 1 charge per day. Many get a second so the average is higher than the actual utility factor. With 80% EV (the median at Volt stats) it takes about 45K miles, and with 74%, the average EV% at Volt stats, it will take about 63K miles to make up 2400lb manufacturing difference.

 

Another alternative for someone who prefers driving a Volt (for example) but wants to meet or exceed CO2 usage emissions of a 50 mpg car is to just drive a little more efficiently than the EPA ratings.

Slow down a little and learn a couple of easy techniques for efficient driving. My 12 month average Volt efficiency is 260 Wh per mile and 46 mpg HV. In order to match the CO2 of a 50 mpg car I just need about a 30% EV ratio on U.S. national average grid power.

With a higher EV ratio and/or cleaner power it just gets better. I'm presently doing around 80% EV and driving on a utility grid with less than half the U.S. average CO2 emissions. My new goal is 85% EV ratio and doing half my EV driving on 100% renewable power by next year.

 

No, I did not include manufacturing CO2e in my calculations. I subtracted the total CO2e @ 50,000 by the total CO2e @ 100,000 miles, which leaves just the CO2e from 50,000 miles.

The number you use in pg. 9 is marked as CO2 emissions, not CO2-equivalent emissions (CO2e) which is what the tables use. CO2e includes the effect of other greenhouse gases as explained in pg. 23, so you can't use that number for an apples to apples comparison.

 

Good point.. I'll note that some will say they get better than 50MPG EPA in their prius, but than again so can volt drivers. I drive the volt far more efficiently the EPA, with an 18 month average of about 27kwh/100m (24/25 in summer 29/30 in winter) -- not as efficient as Jeff but then we get much colder temps in CO. At 85% EV, presuming the national grid and gas CO2, I'm thus at about .313lb Co2 per EVmile and .371 CO2 per average mile or equivalent to about 70MPG, and I made up the 2400 lb manufacturing CO2 difference after only 16500 miles compared to a 50MPG car and after 40K compared to someone getting a lifetime 60mpg out of a Prius. I pay for 100% renewable (wind) energy, i.e. i'm putting some of my fuel cost savings into cleaning up the grid.

 

Ah I see how you removed the manufacturing.

With respect to the number from P9 it does say it is raw CO2, but it is not clear. It says "carbon emissions intensity", and since intensity implies its more than just CO2 especially given the discussion of per-state data which follows it it would seem to be that it follows methodology of the paper. Even looking at the the citations for how to compute their COe2 given data on their website, there is insufficient detail to produce the numbers in their paper. But its unclear what numbers they used for various critical efficiencies. Even more unclear is why the felt the need to compute numbers differently than prior reports. (One can guess for some things, e.g. using G

I like your overall idea of trying to back into their numbers, as it provides a way of checking when the details are lacking. Unfortunately, I cannot see how to back into many of their numbers as the paper is lacking in such details.
For example, given the numbers you computed for "EV" efficiencies, the relative EV efficiency of the Volt and PHV (In terms of CO2e) is .442 vs .48 a ratio of 1.182, i.e. PHV is about 18% more EV efficient in their model. But since CO2e for EV is about EV driving efficiency that should be directly reflected in their EV EPA numbers, which are 35kwh/100m for the volt and and 29hWh/100m (+.2 gallon gas/100m). The EPA pure EV numbers are a ratio of 1.207, i.e. they are not consistent. I could find no meaningful inclusion of the .2 gallons of gas to make them consistent. At some point, given enough inconsistencies and unwarranted assumptions combining with missing details, I just cannot waste more time trying to figure it out.

 

As drinnovation pointed out, the Volt does not have a monopoly being driven efficiently as the 50 MPG car can be driven more efficiently as well. It also neglects the flip side that some buyers buy a Volt or Prius Plug-in purely for HOV access and never plug their vehicle in. For those gas-only PHEV drivers, Volt incurs larger manufacturing and per mile emissions than a Prius Plug-in.

There's a bunch of anecdotal stuff which is great for you guys, but irrelevant unless you can find an equivalent Prius Plug-in driver to compare against or be willing to drive a Prius Plug-in to see how you do with each vehicle side-by-side.

 

Please double-check your math before jumping to the wrong conclusion. The ratio is 1.086, or 8.6% more efficient. The Volt is 0.35 kWh/mi. For the Prius Plug-in, the 0.2 gallons at 51 MPG accounts for 10.2 of the 100 miles, so 29kWh/89.8 mi = 0.32 kWh/mi, so the ratio here is 1.084, which is pretty damn close.

That's a little bit of the pot calling the kettle black... and the kettle might not even be a kettle!

 

Sure, that's why I positioned my statement in terms of someone who enjoys driving a vehicle (Volt, CMAX Energi, Tesla Model S, etc.) but wants to feel that they are meeting some reasonable standard of environmental responsibility on climate change even if the local utility is not low-carbon (of course, you could also throw some solar panels on the roof or pay a little extra for a renewable electricity option in many areas).

I'm saying the answer doesn't have to be "buy a Prius". The answer can also be "enjoy driving the car you want and just drive at least as efficiently as an average Prius driver (48.5 mpg on Fuelly) or EPA 50 mpg".

Sure, you could have bought a Prius and driven it even more efficiently than the average Prius driver and you would be doing that much better for the environment. But, you gotta have fun and enjoy life too. I'm saying there is a choice of a middle ground where you can enjoy driving a Model S (or a Volt or a Prius) and punch the accelerator every once in a while but also drive beyond average efficiency at other times in order to meet some CO2 goals you set for yourself.

I don't know anyone like that but I'm going to make a precarious guess that many people who do that are also driving 80 mph and changing lanes in congested traffic without signaling. Those folks are a lost cause and I'm not going to ruin my life worrying about their car choices.

Nope. I'm happy enough comparing my efficiency to average Prius drivers on Fuelly or to the EPA estimates. I don't feel the requirement to seek out individual Prius Plugin drivers to compare MPGe. Well....actually I did do that back in January with Devprius for the Volt/PiP 7-11 thread here on PriusChat but I did that for fun and out of intellectual interest -- not because I felt that I needed to do it in order to assuage carbon guilt.

PiP/Volt January 7-11 Switcheroo | PriusChat

 

Using the .2 gallons as producing at 51MPG is a dubious approach, since the the car is only doing it during high-demand times. Then again its unclear howmuch the EV is helping at that time. But if that is how they used it, should be explained that way but it was not.

Furthermore, even that way is not consistent. Given your computations:

So sorry to say, the ratio of your estimates is .48/.422 which is 1.13. (I accidentally typed it as .442 in the earlier message)

My posts may have been a bit sloppier than or you (or I) would like, but then again this is not a published paper. And if the kettle is black, the fact that the also black pot is calling it out is natural. We dyslexic pots know black.