How EPA calculates MPGe of plug-in hybrid ?

[HTSS_TR]

How EPA calculates gas mileage of plug-in hybrid in the form of MPGe ?

Example: The 2017 Toyota Prius Prime claims 120 MPGe.

But, on one 11.3-gallon tank of regular-grade gasoline and a full electric charge, the 2017 Prius Prime anticipates a class-leading estimated total driving range of over 600 miles.

If this is the case then it should be no more than 60 MPG. Where is the 120 MPGe coming from ?

May be the MPGe is calculated for drivers that stay within the battery range all the time ? For Prius Prime battery range is about 20 miles.


https://www.yahoo.com/autos/first-look-2017-prius-prime-132000175.html

 

[Ethan1]

Here is a quide to MPGe

 

[OneEyeJack]

The methods don't matter because whatever the EPA says is law and there is no review and no second guessing them. They don't answer to ordinary citizens and to cross them is to be guilty. It's the same with other government agencies like the BLM.

 

[Nate1979]

MPGe is listed for electric only driving and there should be a separate value listed for running on gas only.

 

[earlyre]

Originally Posted By: HTSS_TR

May be the MPGe is calculated for drivers that stay within the battery range all the time ? For Prius Prime battery range is about 20 miles.

you know...90% of the time, that 20 mi range would be more than sufficient for me....

 

[raytseng]

Originally Posted By: HTSS_TR
How EPA calculates gas mileage of plug-in hybrid in the form of MPGe ?

Example: The 2017 Toyota Prius Prime claims 120 MPGe.

But, on one 11.3-gallon tank of regular-grade gasoline and a full electric charge, the 2017 Prius Prime anticipates a class-leading estimated total driving range of over 600 miles.

If this is the case then it should be no more than 60 MPG. Where is the 120 MPGe coming from ?

May be the MPGe is calculated for drivers that stay within the battery range all the time ? For Prius Prime battery range is about 20 miles.


https://www.yahoo.com/autos/first-look-2017-prius-prime-132000175.html


Let's use your same logic to just crack your first step out of it, if you don't want to read the article.

By your logic of it going 600miles over 10gallon, and if you want to rate it 60mpg, that means you are taking a case of NEVER plugging it in except for the one time per fillup.

But it's got a plugin feature and if you use that, it's going to get you a number higher than 60, otherwise you'd just have a regular hybrid that you can't plug in.

 

[splinter]

Sat shotgun in a friend's '16 Prius yesterday.

He's a very successful conservative electrical engineer btw...stereotypes aren't always applicable.

Dash readout claimed ~104-mpg over many miles. He stated manual hand calculations were actually quite close. Wow!

 

[A_Harman]

Originally Posted By: Ethan1
Here is a quide to MPGe


Nice link.

Here's a quote from one of the references:
Quote:
The EPA calculates that 33.7 kilowatt-hours of electricity is the equivalent to one gallon of gas, so an electric or hybrid vehicle that uses 29 kWh per 100 miles would get a combined 115 MPGe rating.


This is not actually as difficult to understand as some people would make out.

Gasoline has an energy content of 43MJ/kg. Gasoline has a density (give or take a few percent) of 744.5 kg/m^3 * 1 m^3/264 gallons = 2.82 kg/gallon (pardon the mixing of measurement systems!), so the energy contained in one gallon of gasoline is 43 MJ/kg * 2.82 kg/gallon = 121.3 MJ/gallon.

A kilowatt*hour is a unit of energy, equivalent to 1000 Watts consumed for a period of 1 hour. A kilowatt is 1000 Joules per second. So a kilowatt*hour is equivalent to 1000 J*hour/sec * 3600 sec/hour = 3,600,000 J = 3.6 megaJoules.

121.3 MJ/gallon / 3.6 MJ/kW*hr = 33.7 kw*hr per gallon energy equivalent. Therefore, it's an equivalence based on the energy stored in one gallon of gasoline.

Now, how the energy storage rating of batteries is determined...

 

[hatt]

Looks like MPGe is a made up useless number for the consumer to stare at on the window sticker.

 

[HTSS_TR]

Originally Posted By: Nate1979
MPGe is listed for electric only driving and there should be a separate value listed for running on gas only.

For the Prius Prime the battery provides 20 miles of driving, if a driver daily commute is 200 miles he/she would be able to go 20 miles on battery(after fully charged over night) and 180 miles with gasoline engine.

So the 120 MPGe is virtually useless figure for this particular driver.

The MPGe is useful figure for pure EV such as Nissan Leaf, Tesla ... but not for plugin hybrid.

For plugin hybrid the fuel consumption should use different formula, such as fully charged batter and full tank of gas and driven until the car stopped. Divided distance by gallons used to get MPGe, and this is the minimum. For drivers with shorter distance he/she would get better MPGe if the vehicle is plugin every night.

 

[Nate1979]

Originally Posted By: HTSS_TR
Originally Posted By: Nate1979
MPGe is listed for electric only driving and there should be a separate value listed for running on gas only.

For the Prius Prime the battery provides 20 miles of driving, if a driver daily commute is 200 miles he/she would be able to go 20 miles on battery(after fully charged over night) and 180 miles with gasoline engine.

So the 120 MPGe is virtually useless figure for this particular driver.

The MPGe is useful figure for pure EV such as Nissan Leaf, Tesla ... but not for plugin hybrid.

For plugin hybrid the fuel consumption should use different formula, such as fully charged batter and full tank of gas and driven until the car stopped. Divided distance by gallons used to get MPGe, and this is the minimum. For drivers with shorter distance he/she would get better MPGe if the vehicle is plugin every night.


Plug in hybrid should have both an MPG and MPGe rating. MPGe is supposed to be for electric only operation and has nothing to do with operation when using the gas motor. There should be an MPGe rating, MPG rating, and then a mixed rating based on EPA drive cycle test.

Example:
2015 Chevy Volt: 38 miles EV only, 37 mpg on gasoline, and 98 MPGe on electricity
2016 Chevy Volt: 53 miles EV only, 42 mpg on gasoline, and 106 MPGe on electricity

With this information anyone should be able to get an estimate MPG for their actual drive cycle.

 

[KrisZ]

EPA used to run tests and probably still does, where they would pump pure diesel exhaust gasses into the lungs of children and homeless people. Why on earth would anybody expect them to do something useful for a change, like come with a proper electricity consumption rating for EVs?

 

[hatt]

Originally Posted By: Nate1979
Originally Posted By: HTSS_TR
Originally Posted By: Nate1979
MPGe is listed for electric only driving and there should be a separate value listed for running on gas only.

For the Prius Prime the battery provides 20 miles of driving, if a driver daily commute is 200 miles he/she would be able to go 20 miles on battery(after fully charged over night) and 180 miles with gasoline engine.

So the 120 MPGe is virtually useless figure for this particular driver.

The MPGe is useful figure for pure EV such as Nissan Leaf, Tesla ... but not for plugin hybrid.

For plugin hybrid the fuel consumption should use different formula, such as fully charged batter and full tank of gas and driven until the car stopped. Divided distance by gallons used to get MPGe, and this is the minimum. For drivers with shorter distance he/she would get better MPGe if the vehicle is plugin every night.


Plug in hybrid should have both an MPG and MPGe rating. MPGe is supposed to be for electric only operation and has nothing to do with operation when using the gas motor. There should be an MPGe rating, MPG rating, and then a mixed rating based on EPA drive cycle test.

Example:
2015 Chevy Volt: 38 miles EV only, 37 mpg on gasoline, and 98 MPGe on electricity
2016 Chevy Volt: 53 miles EV only, 42 mpg on gasoline, and 106 MPGe on electricity

With this information anyone should be able to get an estimate MPG for their actual drive cycle.
What important information does the MPGe number provide? Shouldn't the number use a unit of coal, or some other method of actual electric generation, as the equivalent?

 

[Nate1979]

^^^^MPGe is electrical generation equivalent in number the driver might understand (gallon of gas). It is a measure of efficiency basically as it is a measure of the average distance traveled per unit of energy consumed. Whether that unit of energy is produced by natural gas or coal doesn't matter in the calculation.

If you look at the EPA sticker on the Chevy Volt it is very detailed and includes various scenarios for miles driven.

https://en.wikipedia.org/wiki/Fuel_economy_in_automobiles#/media/File:Chevy_Volt_EPA_Fuel_Economy_Official_Label.png

So, if you look at the actual sticker you get a lot of detail. I think the story in the original post is just a headline number. The real details would be on the EPA sticker.

 

[hatt]

Quote:
MPGe is electrical generation equivalent


Where? We can't convert all of a gallon of gasoline's energy into electrical energy, in the real world. MPGe is a useless number unless it accounts for for electrical generation and distribution losses. If you're running gas you need to know how much gas is used. If you're running electric you need to know how much electric is used.

 

[Nate1979]

Originally Posted By: hatt
Quote:
MPGe is electrical generation equivalent


Where? We can't convert all of a gallon of gasoline's energy into electrical energy, in the real world. MPGe is a useless number unless it accounts for for electrical generation and distribution losses. If you're running gas you need to know how much gas is used. If you're running electric you need to know how much electric is used.


MPGe tells you how much electric energy your car is using. No different than the energy that your car uses from gasoline. The EPA sticker number considers MPG as tank to wheel calculation and for MPGe it is wall to wheel. Neither MPG nor MPGe consider upstream energy usage. It is basically a number that indicates to the consumer how much gas or electricity their car is using that leads directly to their wallet. Nothing to do with total energy consumption in the entire supply chain.

 

[A_Harman]

Originally Posted By: Nate1979
Originally Posted By: hatt
Quote:
MPGe is electrical generation equivalent


Where? We can't convert all of a gallon of gasoline's energy into electrical energy, in the real world. MPGe is a useless number unless it accounts for for electrical generation and distribution losses. If you're running gas you need to know how much gas is used. If you're running electric you need to know how much electric is used.


MPGe tells you how much electric energy your car is using. No different than the energy that your car uses from gasoline. The EPA sticker number considers MPG as tank to wheel calculation and for MPGe it is wall to wheel. Neither MPG nor MPGe consider upstream energy usage. It is basically a number that indicates to the consumer how much gas or electricity their car is using that leads directly to their wallet. Nothing to do with total energy consumption in the entire supply chain.


MPGe is not really "wall-to-wheel" energy usage. It is only based on the energy present in a fully charged battery. To get wall-to-wheel, the actual amount of kW*hrs to charge the battery would have to be measured in the electron hose going to the car.