Tailpipe Emissions and Beyond

Well, the last thread along these lines, I seem to recall getting some harsh comments for saying that electric vehicles offered very modest CO2 savings, right now, for the US grid average. (And I own a Prius Hymotion conversion, so this wasn't a theoretical point for me). For Virginia, I calculated something like a 30% reduction in CO2/mile, relative to a stock Prius. These EPA numbers seem to show about half that level of savings for the US grid average. (So, nyah, I guess.) If you live in an area with a clean local grid, great. If not, not so much.

There's always the argument that the grid will get sufficiently cleaner, over the life of the vehicle, that current-year savings substantially understate lifetime savings. That appears reasonable, although prior to this past year, the "decarbonization" of the grid was moving pretty slowly, about 1% per year. But if a car lasts (say) a decade, even if I'm not going to own it for the decade, I'd want to trend the grid carbon number down at some plausible rate, for the predicted vehicle life, to get an accurate snapshot of what I'm doing with the current purchase decision.

Then there are the guys with grid-connected solar who argue that their EV miles are carbon-free. Not so, incremental electrical use of grid-connected systems should get "scored" for CO2 output at the local grid rate. But it's all-but-impossible to get them to see the logic of that. Not even going to try on that one. But since I understand that, putting in grid-connected PV is not a way to alter the Prius-versus-EV comparison for carbon footprint of each additional mile.

Anyway, I looked for something with a little better savings than what the EPA is showing/many people had calculated previously.

Electric bicycles have little footprint in use, but they really aren't a substitute.

But electric motorcycles looked pretty interesting. They'll do highway speeds, you can get 50-100 mile range. And where these EVs are getting 3 mi/KWH, manufacturers are claiming 12 to 15 mi/KWH for motorcycles. Seemed like, with the right weather, and willingness to take the increased risk, they offered a substantial CO2 savings for solo travel, relative to a Prius or an EV.

 

USB: Something is wrong with your chart as it shows the Prius PHV < 200, but the EPA site shows it at 210 for the national average.


Note this is using Greet 2010, which is based on 2007 emissions data.. and so its already "old" in terms of how green the grid has gotten in the past 5 years.

Interesting to note the EPA added the line

"Purchasing ​

green power​

could lower your CO​

2​

emissions. ​

Tell me more.​

"
But provide no computation for that..

I agree with chogan2 that using PV Solar or wind is not "zero" GHG, as there is generally some grid-tie usage/loss, but I do consider it overall to be carbon offsetting and hence justifiable to consider it very low net GHG while in EV mode. After all they consider "upstream" costs in equlivence not direct usage too. However I understand that computing that depends on the individual, their provider and more details than EPA probably wants to cosnider.

 

Good info and I would point out that I presume EPA is using ideal (non-winter) conditions to show EV's at their very best case scenario. For example, Consumer Reports had noted last year they measured 2 mile/Kwhr for a Volt in winter with heat vs. the normal 3 mile/Kwhr.

 

EPA is likely using the overall test averages which mix city/highway hot/cold and for PHEV EV and ICE.

 

Good info and I would point out that I presume EPA is using non-winter conditions to show EV's at their very best case scenario.

Since I am often accused of beating around the bush, let me just clearly say what I am trying to say.
For winter mode Volt, multiply the EPA carbon by 3/2 = 1.5 x 260 ~= 390.
Of course winter mode does not represent full year, but there is a +correction to be made (IMHO).
Herein I am assuming mileage per KwHr drops down to 2 in winter from 3 per Consumer Reports last year.
Summer mode too w/ air cond I assume EV takes a carbon hit?

 

Your presumptions of EPA doing it to "show EVs at their very best" is simply wrong. The EPA is trying to estimate average normal usage, not best case. If you want to claim that a correction is needed, you'll need a better starting point that assuming the reported was the best case. The EPA already applied corrections during their estimations, e.g. the Volt actually went more than 45 EV miles, but they "corrected" it down to 35 EV miles via the various correction factors.

Where did you find CR saying 2kWr? They reported EV range of from a low of 23-28 in winter to over 50 in summer. They reported an average of 2.93 miles/kWh (which is 33kWh/100 miles, while the EPA reports 36kWh/100 miles). but I never saw a report with different numbers for winter/summer.

 

...my reference is the CR April 2011 Volt First Look article, however, I cannot find my copy right now.

 

I remember reading segments on-line from the CR hack piece. I am sure you read and remember it correctly. Some facts on the ground though are YMMV. The epa is an objective test, while CR tested in a bad case conditions, then people try to compare to EPA. With a PHEV like the volt or prius phv, no one is left stranded by a worst case scenario.

The epa does indeed take the test results and reduce fuel consumption by 30%. This makes these plug-ins regularly beat estimates in good conditions, but they can fall bellow. Best test is side by side testing.

 

One wonders the carbon footprint in the winter for the Volt.

In order to get cabin heat, does not the ICE need to be running?

DBCassidy

 

The carbon footprint for Volt in winter is worse in my view depending on elec power sources.
According to the Union of Concerned Scientists, EV can be as low 33 MPG equivs on fossil fuel basis.
But I think in winter (heat) on or summer (air cond on) for Volt that could get down to about 20 MPG equivs.
However, the Volt owners are disputing me on this, they say the EPA takes into account EV heat/air cond losses in their CO2 footprint analysis. I am not convinced but it's a stand-off pending more info on EPA calc techniques.

 

I think I am one of those Volt owners you are referring to. However, I never said that the EPA takes Hvac losses into effect.
I did say that I suspect that they do, based on the fact that I get higher than their EV range 2/3rds of the year and less the other third.
Like you, I would like to see more info on their testing. But their numbers definitely aren't 'best case' and definitely aren't 'worst case'.

 

You've got to remember YMMV. In a warm place like I live in, winter is the easy time of year on cars, and most plug-in owners choose to charge with non carbon intense wind. In a place like indiana with cold winters and a coal intense grid its probably going to produce more ghg. Certainly even there, we are substituting coal for oil, which with good public policy allow for more money to change the grid.

The 2012 volt used the city and highway tests
Detailed Test Information
The results are then multiplied by a fudge factor of 70% to account for higher speeds, airconditioning, and heating.

The 2013 tesla S used all 5 tests, so the 2012 phevs may be doing all five tests now also.

 

AG I like it but sounds like conventional gaso vehicles are certainly debited for winter, summer, high speed cycles. Think you are saying Volt did not do this testing but they had a fudge factor. I am going by Consumer Reports they said they saw 2 mile/kwhr in winter in a Volt with heat on, and they saw 3 mile/kwhr no heat. Whereas the 3 mile/kwhr is approx equal to 100 MPGe. You are suggesting the 3 mile/kwhr (100 MPGe) already includes a reduction factor for heat/cool cycles.

 

Some current cars are actively tested for all 5 cycle models (one with heat, one with AC), but many are still tested on 2 cycle with a fudge factor. EPA is switching all over to the 5-cycle model but in 2012 it was still optional.

And if you want to consider CR data, remember they rate the the Prius at 44mpg and rate most "EPA 33MPG" cars at 26-27. And be careful about rounding if 2.3 becomes 2 and 2.7 becomes 3.. its much less of a difference. (Again I did not see the articule to which you are refering).

 

Green is not a good term to use, as it is poorly defined. Some may find it greener to use abundant domestic energy instead of a more scarce source that we are importing and rapidly depleting. In these cases the phev is more sustainable with a greater carbon footprint. How do you choose which is more green - sustainable or co2? It all depends on the amount. I suppose you could make a utility function, but even here there would be wide disagreement. Many don't find any of these cars green, only a little less brown than their alternatives.

I think the term you want is lower in ghg emissions if you choose not to use renewable electricity. Full sentance with the lawyer words -

In 48 states the prius will produce less ghg emissions than the volt, assuming X% electric miles and the epa mileage estimates, if the volt owner chooses not to use renewable electricity. YMMV This is according to the 2007? grid, and the grid maybe more or less carbon intense in that state in the future.