How will the Chevrolet Volt be better than a Toyota Prius plug-in hybrid?

In my experience, the large majority of the time that my Volt is running in CS mode on gasoline is on highway-dominated segments. Only a small part of my total CS miles are driven on city streets since the larger battery entirely takes care of most daily commute driving. I sometimes use the Volt's "Mountain Mode" as a crude "hold" mechanism to retain about 16 miles of battery range for the city driving at my destination after I exit the highway. What mostly matters to me for gasoline is highway miles and the Volt's 40 mpg highway estimate closely matches most of Toyota's and other manufacturer's hybrid models other than the Prius (and now Plug-in Prius) which float up at the top of the EPA ratings by themselves with 48 mpg. On a monthly basis, my personal average CS gasoline use rate is around 41-43 mpg.

Speaking of Mountain Mode, the larger retained battery buffer will fill any power output gaps needed from the Volt's 1.4L gas engine when accelerating up long mountain climbs so you get the full 149 HP.

 

That is true to a point.

I live on the East coast and have never even taken the Volt on what passes for mountains here. However the buffer will give you the full combined power for a while, but it may used up on really long steep climbs. There are no climbs like that near me, but I believe there are out in the Rockies.

Once used up you'd be back to just the ICE power.

 

Supposedly, the additional retained buffer has been sized to allow full power driving up the most severe mountain passes. Even on long mountain climbs there are notable flat and even momentary downhill sections where the 1.4L engine can catch up and refill at least part of the buffer.

I recently returned from a 3000 miles road trip through the Northwestern areas of the U.S. And Canada. I had myself plus 3 adult passengers and our luggage in the car while crossing mountain passes along Mt. Shasta and also the California-Oregon border and had no problems at all.

You don't need Mountain Mode for ordinary mountains.

 

Since MPG(e) does not include power plant waste, you cannot honestly weight MPG(e) the same as MPG.

I know dumb nice person americans have trouble grasping this point, but I'm giving you more credit.

 

Which is Exactly why I bought an Edsel, and a Pacer, and an Aztec... oh, yeah, that wasn't good. But you have to admit, that stainless steel cow catcher look on the Volt is kinda kitschy. Chevrolet Volt and Acura TL, separated at birth?

 

Interesting paper. It compares PHEV20 and PHEV40, both are blended plugins (like PiP). The majojr differences between PHEV40 used in this paper vs. the Volt are the following:

Electric motor power (kW): 48 vs. 111
Curb Weight (kg): 1,567 vs. 1,715
Electricity consumption (Wh/mi): 157 vs. 360

It is clear that Volt is heavier and uses much more electricity with the more powerful electric motor. It will be harder on the battery for sure.

It also validates the blended PHEV durability (15 years life) despite multiple recharges per day with careful battery management.

Is there similar study for "EREV" type PHEV like the Volt?

 

1. please mind the language
2. please don't debase into disparaging comments regarding race, religion, or national origin

MPGe does not account for power plant waste, but MPG accounts for upstream waste how?

Lets assume we're talking about WV coal and Saudi oil. I believe it is more efficient to mine coal in WV (american jobs) and train it to my local power plant, than to drill in a desert on the other side of the planet, pipe and tanker it into US, then refine it. Electric delivery has energy losses in the lines, gas delivery needs to be trucked out to the stations and then you have to drive there to go get it.

You probably didn't mean energy though, you probably meant emissions, burning the coal is dirtier for sure. Locally about 40% of my electricity is emission free nuclear so that helps a little, and I'm installing PV on the roof which will give me a lot of zero emission driving. But thats a little removed from mpg comparisons between different vehicles.

Define what argument you want to make and be clear about it so we can discuss if you wish.

 

The key issue related to power is the so-called 'C' rate at which the battery is discharged. Volt drivers are rarely going to be drawing the full 111 kW. The vast majority of power draw will probably be well under 60 kW and most of that will be less than 30 kW. That means a discharge rate of 1C to 3C since the Volt battery is 16 kWh.

Meanwhile, the Prius Plug-in battery will be routinely discharging at 4C to 6C+ at its apparent maximum output rate of 27 kW (36 HP). At 27 kW, the Volt battery would be putting out less than 2C.

Battery studies show significant aging differences between a discharge of 2C and 6C.

 

That seems high. Any source for that data?

PiP's gas engine is pretty efficient starting from 8kW load and we know PiP is designed to pull both power sources. Continuous high C draws should kick the gas engine in, to prolong the PHV battery pack. AKA synergy affect when gas and electric work together.

This is not the case with the Volt. It is designed to only use the battery pack at all cost first.

 

The model is showing at-the-battery consumption on some unknown driving sequence, which you are comparing to EPA at-the-wall actual test results (multiplied by 0.7). A better number for the Volt would be 252, or even 176Wh/mi, which is the raw at-the-battery EPA test result.

I'm quite impressed with their model's 95 Wh/mi PHEV20 though. What's the PiP's utilization percentage? The pre-prod (2.8kWh available) should have been good for 30 miles!

We read it completely differently. It validates that lots of deep cycles kill your battery (strictly, carbon/NCA chemistry), which comes as no surprise. It also appears that they included charge rate but not discharge rate in their evaluation, which seems odd.

I don't understand why they didn't report PHEV-40 "opportunity charged" vehicles. Surely it's just another run of the simulation engine.

I'll bet there's a good one at GM, since they're the ones on the hook to warranty the thing. *shrug* Toyota probably has a few internal docs that are much better than that study too.

 

We don't know yet but 3rd party conversion (specifically Hymotion L5) estimates 30-40 miles blended range from 4kWh usable energy. That's 100-133 Wh/mi.

That's why I think the production PiP will have blended range higher than the pure 15 EV miles.

 

I don't know what Toyota's production Prius Plug-in "battery versus gas" blending strategy will be but I suspect that many owners will have their own driving strategy which seeks to minimize gas engine startup while there is still charge energy remaining in the battery.

Here is a presentation from ANL that covers power requirements for the various common international test driving cycles. In particular, see the collection of graphs on page 11.

http://www.autonomie.net/docs/5 - P...onent Requirements/impact_of_drive_cycles.pdf

 

The Prius and PIP will cap battery draw at 28 kw. I don't know if this is sustained. From Jim's link


This is the highway test that EPA uses. I count about 24% of the distance requiring ICE.

 

That is the problem with "blended." I have a Hymotion converted Prius, and running strictly electric, which is 31 mph or slower, and for about 5 or 10 miles maximum (due to driving conditions, not depletion of the battery), I will see about 230 Wh/mi. With "blended," you can stretch it out to 30 miles, or about 150 Wh/mi. (I have never gone farther than 32 miles on "blended.") Or with "blended" you can still be at 220 Wh/mi.. It all depends on how you're driving, if you're running the A/C, etc.

And, what I have found is that the A/C really depletes the electricity reserves. Where I can go 20 miles without A/C, with the A/C it might be as low as 14 or 15.

 

By the way, this entire discussion of power control strategy in testing to eke out a higher MPG(e) highlights the stupidity of it all. A low battery capacity PHEV is going to deplete the charge to empty between most recharging opportunities. End of story.

 

at 49 mpg in gas mode, i find it hard to believe that anyone could think that the Prius is charging as well

 

that is strange. in my Leaf, the heat uses more than 4 times the power of the A/C. the A/C really has a minimal hit on range. Heat can take as much as 25-30% of the range if cold enough

 

^^ Not strange, heating from an ICE is free.
This is one of the hidden treats owners of EVs and *EVs like the Volt get to find out when the first winter rolls around: the EPA only tests in balmy conditions.

 

I see about 33% under 20 kW and 49% under 30 kW which implies greater than 50% requiring ICE. Once the gas engine starts up it may take a few seconds to decide to turn back off after a peak power draw has finished so it may actually stay running on gas longer than the graph implies.

The 27 kW maximum battery output on the PiP may well be at maximum SOC and the peak allowed power output might drop as the battery is discharged. That is what happens on a battery manufacturer's cell specification chart but the PiP 27 kW battery output limit may have different characteristics imposed by Toyota's design goals.

It's possible that when the PiP battery is under 50% SOC that the maximum power it will draw from the battery is significantly lower than 27 kW.

 

^^ Jeff,
I just realized that the sum of the bars from 0 kw till the red line is 72%. Why not close to 100% ?