Plug in Prius - Most Environmentally Friendly Vehicle in Study

Even if the battery carbon footprint is corrected, Volt will not be as clean as a regular Prius, using the average electricity.

You may find a few flaws in it but the overall report is well researched and well written. It is no way flawed and need a redo.

 

Agree.
Before throwing mud, one must realize that - as mentioned in the study- it is difficult to get accurate data from batteries and cars manufacturers on 'state-of-the-art' batteries (for obvious reasons...).

 

I assumed the 50/50 electric/gas mile ratio and 50k/100k mileage tilted the conclusions negatively against a PHEV with a larger battery. The conclusion I jumped to was that a Volt would have less lifetime CO2e emissions than a Prius Plug-in, since it could have a much higher electric/gas mile ratio. So I decided to work backwards from the study numbers to see at what electric/gas mile ratio the Volt beats the Prius Plug-in.

Prius Plug-in
0.81 lbs CO2e/mi @ 50,000 mi => 40,500 lbs
0.64 lbs CO2e/mi @ 100,00 mi => 64,000 lbs
=> 23,500 lbs CO2e / 50,000 mi => 0.47 lbs C02e/mi
=> 17,000 lbs CO2e from manufacturing
25.9 lbs CO2e/g / 50 mi/g => 0.518 lbs CO2e / gas mi => 0.422 lbs CO2e/electric mi

Volt
1.15 lbs CO2e/mi @ 50,000 mi => 57,500 lbs
0.87 lbs CO2e/mi @ 100,00 mi => 87,000 lbs
=> 29,500 lbs CO2e / 50,000 mi => 0.59 lbs C02e/mi
=> 28,000 lbs CO2e from manufacturing
25.9 lbs CO2e/g / 37 mi/g => 0.70 lbs CO2e / gas mi => 0.48 lbs CO2e/electric mi

So the difference between the Volt electric mi and a Prius Plug-in gas mi is: 0.038 lbs CO2e/mi, which is the lbs of CO2e saved every mile that a 100% electric/gas ratio Volt vs. a 0% electric/gas ratio Prius Plug-in. A Volt starts with 9,000 lbs more of CO2e from manufacturing, so 100% electric Volt and 0% electric (100% gas) Prius Plug-in would have be driven driven 236,842 electric miles before a Prius Plug-in did not have less lifetime CO2e than a Volt.

Hm, it turns out I was wrong... I guess that's what I get for doing the math...

 

Not true and not completely true. They are considering more than CO2 as explained on pg. 23, since they are using lbs CO2-equivalent (CO2e) which includes (but is not limited to) methane and nitrous oxide. Nitrous oxide is one of the components of smog.

They actually mention this in an unbiased fashion on pg. 26.:

 

My error...but there is a big difference between CO2 and CO2e and smog. They are still counting emissions as something that creates a GHG. But when considering immediate air quality and the health of someone today smog forming emissions in a city are maybe 1000x as important as some emissions at a far away power plant or car battery factory. I grew up in the LA area breathing the worst of the smoggy air, eyes stinging while playing sports outside etc. Even if the CO2 and CO2e are a wash...it is better to move it out of the cities. That was my point.

Mike

 

Your math looks right but not the premise.

 

The point of explaining my premise was to demonstrate I did not start with the presupposition that the Volt was had a larger lifetime CO2e than the Prius Plug-in, despite being a Prius Plug-in owner which connotes a certain bias demonstrated by other owners.

Anyhow, I already stated that my premise was incorrect. Seems a little impolite to repeat that or perhaps you misread my post.

 

I replied in agreement. Also to sum it up for those gets turned off by a long post with calculation.

It was a great post. The CO2 lbs are in reverse for 50k and 100k miles but the result is right. Perhaps posting error.

 

Inspired by ryogajyc's calculation, I did the same backward calculation for manufacturing emission of Leaf and regular Prius.

Prius - 16,000 lbs
PiP - 17,000 lbs
Leaf - 27,000 lbs
Volt - 28,000 lbs

 

The problem is starting from the results of the paper and working backwards is that the paper's assumptions are in question.
The original Hawkins report, for example, used a 'static' electric motor in its calculations. The problem with that original assumption is that the static motor used was not an automotive motor which, but a 1000kg motor!
This was corrected by Hawkins later, but he still came up with a 110kg motor where the Leaf's is about half of that.

I applaud the working backwards to eliminate the silly 50,000 mile life of EVs, which that does nicely. But there are other glaring errors such as not taking into account battery usefulness after its automotive use.

 

I think it is fine for what it attempts to do, keeping in mind the assumptions and the daunting task if they try to factor in everything.

The truth is individual driving habits will have a big impact on any PHEV. On my normal commute I'd be about 50/50 EV in a PIP, but I can do it 100% EV in a Volt, but my lifetime EV% in my Volt after 50,000 miles is only around 58%, and on those longer trips I'd have been better off with a prius (for purposes of emissions and mpg).

I also have home generated electricity so the grid comparisons are less useful for me, and I have to factor that into a comparison with a non-EV like a conventional prius.

From a decision making standpoint I don't think the differences are significant. If choosing the "highest" rated anything is important to you, you should be prepared to buy a new car every 6 months. Overall I think we can see we need to look at cleaning the grid, reducing manufacturing costs/inefficiencies, and electrifying transportation.

 

I think the most important point it revealed was that, more EV mile is not necessary better. A balance needs to be struck for optimal performance.

Ford Energi comes close with fast refueling feature (gas) for long vacation drives, like PiP but a small cargo is not that practical. Energi also qualifies for more plugin tax credit. PiP gets the least out of all plugins. If the incentives are structured based on social benefits and battery size ignorant, PiP deserves the highest incentive.

 

I agree, but what the paper shows to me is that that balance should not be just between gas and electric, but between manufacturing and consumption, cleaning the grid and the costs of doing so, etc...

Ultimately, I believe total electrification is the only viable long term solution. How we get there should include advances in battery technology to decrease weight, increase energy density, and hopefully minimize manufacturing footprint. It should also include cleaning the grid and trying to do so while keeping electric rates reasonable, and I believe it should look at ways to recycle as much as possible for post-auto applications or reuse in new auto applications (after refurbishment) without the same intensity of mining the raw product. And of course rapid recharging infrastructure.

 

I missed this post before.

Yes, CARB states require hybrids and plugin hybrids to have 10 years / 150k miles warrenty because it is considered part of the tailpipe emission control hardware.

However, there is no such requirement for EVs because they have no tailpipe.

 

Interesting! I have never considered an EV because of the range/charging limitations. Add one more plus for the Prius.

 

It's worse than that, there is no engine warranty either.

 

Are you sure? I think that is a Leaf owner complained of an engine problem that it would be fixed for free for the first million miles...maybe more.

Mike

 

One of the problems that I think many are alluding to is the fact that the study looks at CO2 payback from manufacturing vs the grid power in each state...today. Maybe for a few cars this is correct, but a negative payback will be a small number. The real payback should be based on the delta to the grid when there are many EVs and PHEVs.

IMO, it doesn't really matter much if the total CO2 from the grid+manufacturing in one state goes up or down 1% or 2%. What matters in the long term is the net change. To get a few extra megawatts in a given region/state, where will it come from? Wind, solar, nuke? Or coal? Or, most likely it will be NG over the next few years, primarily.
I don't think it is a good idea to not buy an EV or PHEV just because you live somewhere that happens to be building one of the few additional coal generation plants.

Mike

 

I agree. One should consider the grid mix over the lifetime of the plugin. However, engineering can't be based on hope and faith.

The approach that Toyota took to start with PiP makes the most. Gen2 PiP can scale up EV range as battery price drop, energy density increase and grid gets cleaner.

The best way to decrease battery manufacturing emission is to increase the recharge cycles (durability). You get a smaller pack that can recharge more often and better for the environment. It also turn out that EVs benefit more on short trips than gas due to the lack of engine warmup penalty.

 

Wouldn't that hit Prius and PiP as well?

Leaf has 80kW motor. Prius has 60kW motor and ~20kW generator.