Adding extra battery to 2014 PiP

In this world, for every downhill ride, isn't there always a corresponding uphill climb? I fail to see any advantage there.

 

Of course. In both a PiP and a standard Prius, on the way up you'll be burning gas and getting the same mpg. The difference is that the PiP will be collecting energy the whole way down, while the standard Prius battery will quickly reach a full charge and waste the rest of the energy turning the engine or generating heat from the friction brakes.

It's pretty straightforward.

 

I still don't really get where you are going. Sure MPG in HV mode is pretty much a wash, so if you never charged the battery there would be no significant efficiency benefit or loss. However MPGe in EV mode is significantly better than MPG in HV mode, so you can go significantly farther on the electric BTU equivalent of a gallon of gas. By blending the two you will increase overall energy efficiency the more EV you can use. MPG will of course increase (less gasoline used per mile) but more importantly so will MPGe (less total energy used per mile).

Again from the same ANL data:
Total Energy Consumed to complete UDDS cycle
2013 PiP EV: 1208.6 Wh = 4125 BTU
2013 PiP HV/EV: 1013.4 Wh + 0.026 gal = 6415 BTU
2013 PiP HV: 0.102 gal = 11634 BTU
2010 Prius: 0.098 gal = 11219 BTU

Ultimately, the relevance of these metrics really depends on what you care about and what kind of driving you do. There isn't one right answer. If your motivation is primarily to use less gasoline period (say for energy independence reasons) then MPG is what you care about. If your motivation is primarily efficiency (using less energy overall) then MPGe is most relevant. If your motivation is primarily environmental (IE pollution and/or GHG reduction) then both MPG and MPGe are relevant and you will have to factor in your local electricity generation pollution factors. If you care mostly about cost savings, again both MPG and MPGe are relevant along with local energy costs. There is certainly an added complexity in dual fuel vehicles vs. single fuel in that MPGe is highly distance/ratio dependent. Since that will vary significantly from person to person, I still believe the EPA MPGe rating has value as a basis for a fair comparison over a typical usage condition. However it does take a lot more effort to estimate how your actual average MPGe will compare to the standard cycle, and good information to calculate from is not always readily available.

Rob

 

Well you are full of It!!!!I know different, my PIP gets 56 mpg no matter what you say it is or isn't what ever it is!!!@!@

 

Actually the hybrid mileage is greater in several situations where the extra battery capacity will capture energy that is lost in the standard Prius hatchback. For me on a trip to Baltimore MD from Columbus OH, I get 56 mpg in the PIP(2014) vs 52 in my hatchback(2010). Whatever you want to belive beyond that is up to you.

 

56 MPG, is 56 miles from a gallon of gasoline. No one is arguing that. It's when someone says "I'm getting 90 mpg when I plug in," that what I have a problem with. Or when they start on a big hill and don't count the trip back up.

MPGe when properly defined, is a good description of what's happening. It's covering a distance on a given amount of fuel, PLUS a further distance from an electric power source. Unfortunately, sometimes that definition gets mixed up a little. I think if you read my post again, it may be a bit more clear that's what I meant.

 

I think the important thing that many people miss is that MPGe has nothing specifically to do with electricity. In a gasoline ICE, or non-plugin gasoline hybrid MPG=MPGe, because all of the energy comes from gasoline. It is perfectly accurate to say my 2005 Prius is currently averaging 50MPGe. That's important to realize, because then you can see that a plug-in averaging 100MPGe really is going twice as far on the same amount of energy. And that it doesn't matter if a vehicle gets 100MPGe on electricity alone, or 100MPGe by blending fuels, or somehow gets 100MPG on gasoline alone. All three are equally efficient with regard to the amount of total energy required to travel a given distance. Understood that energy efficiency is not the bottom line for everyone, but that is what MPGe tells you.

Agreed that saying a plug-in vehicle is getting 90MPG and not accounting for the electricity used is meaningless with regard to energy efficiency. But for some, energy efficiency is not the goal. If their goal is to simply use less gasoline, for reasons other than cost, pollution, etc, then it really is 90MPG to them.

FWIW the ANL data says the PiP in HV is a few percent worse on both the highway and city cycle tests, but interestingly is a few percent better on the arguably more realistic US06 "aggressive driving" cycle. I think its fair to say they are about the same, with the data showing some support for folks real world observation that the PiP can be a little better in HV mode compared to the non-plugin Prius.

 

and lithium helps too!

 

Here is a quote that defines the MPGe discussion as used by the EPA:

MPGe works well as a shorthand, but it doesn't tell the whole story. Let's look at how the EPA calculates MPGe.

The agency needed some way to compare two very different power sources. Gasoline and electricity use completely different units (gallons versus kilowatt-hours) so you can't just shove them into the same formula. Then someone came up with a very clever solution: If you burned a gallon of gasoline, it would generate 115,000 British thermal units of heat. So, how much electricity would it take to generate the same amount of heat? Answer: 34 kilowatt-hours (kWh). We now have our connection. One gallon of gasoline produces the same amount of energy as 34 kWh.

Unless you have a car that uses both electricity and gasoline or a full EV than the number (MPGe) is a waste of time. Miles per KWH is a much better measure of efficiency because you can them multiply your cost of electricity per kwh and you have a meaningful value for comparison. On the ICE only vehicle or a hybrid that can't be plugged in it is only MPG of gas that is meaningful. Just multiply by the cost of gas and you can them compare. Of course the EPA messes that up to by using a special combination of so much gas ICE operation plus so much EV ect.. then by their math the have a new meaningless EPA value.

So for me it miles per kwh vs MPG, that is the streight forward comparison.

 

I agree it is a clever solution, and it works very well to explain how a plug-in hybrid utilizes energy. For that reason, they don't really fit in casual discussions, or at least they often portray an incorrect impression.

 

Exactly.