Prime vs Volt Fuel Economy

MPGe DOES NOT equal MPG

A graph of carbon emissions per distance would be interesting, but it would vary by each users electricity source(s).
Perhaps three graphs: Clean, NG and coal. Most people could use either one of the graphs or eyeball themselves somewhere in between two of the graphs.

I would use 1 lb/kWh for NG and 2 lbs/kWh for coal.

Some grid utilities are transparent enough to report their fractional sources. The other (perhaps even more valid) approach is to use NG if charging during the day and coal if charging during the night based on typical marginal emissions for most of the US.

 

Yes, sometimes there is.

What you are saying is valid on the macro scale.
On the neighborhood scale, behind the transformer for the neighborhood it is quite easy.
Because the voltage being delivered too the transformer from the grid is higher than the voltage on the neighborhood side, electricity won't travel from the neighborhood side to the grid side of the transformer if there is any other choice.

 

Yes, it does, for what it was designed to measure.
MPGe measures the energy content (in kWh) of gasoline.

It is not designed to measure CO2 content.

 

If you have multiple sources and multiple nodes, which you do in every non-trivial grid, you really don't know where things go even if you know the current in every conductor, which you never do. This is because of nodes. When you inject current into a node, you can't tell how much went one way or another if there are multiple current sources, which there always are on any non trivial grid.

The entire Western interconnect is synchronized and the flows are only known at the largest scale and through pathways that often have multiple routes.

 

My former comment still stands.
I may not know which of my neighbors is getting my excess solar power, but I do know that as long as there isn't more excess than my entire neighborhood is using, it is all being used within my neighborhood.

 

Here are graphs for carbon pollution by distance using clean energy, natural gas, or coal as the electricity source:

I used EPA values

 

Intuitively, that makes sense. It just happens to be wrong. In slang, "all electrons are identical". Your "power" could be flowing out and other power is flowing in in greater amounts. You can't tell.

 

Look at what the OP did with MPGe

 

I did, what the OP did with MPGe is correct, as long as you are measuring the efficiency of the use of two different types of energy.

When you start trying to use MPGe to measure CO2 emissions is where you get in trouble.

 

Look again, and read his captions. He is calculating miles per gallon of liquid fossil fuel. If he was calculating btu/mile you would be right, but that would be fairly useless, don't you agree ?

 

Here is the tabular data used for the graphs posted above. I find it easier to use because we have mixed uses for the car: most days under 25 miles and 90 mile trips 2-3 times a week. The numbers are Lbs of CO2 per distance.

 

I went back again to the OP to check again.

Here it is...

The original post is talking about fuel efficiency, not carbon intensity.
The graph has "miles" along the X axis and "fuel efficiency" along the y axis.
No where does it mention CO2, carbon intensity, or green house gases.

Fuel efficiency, when electricity and gasoline are both used, needs to be converted to a single unit that can be compared at different mileages.
This could be BTUs, Joules, kWh or whatever you like.

So when measuring fuel efficiency, MPGe and mpg are the same thing. MPGe is simply a conversion of miles per (energy content in one gallon of gasoline). Or, miles per 33.7kWh.
MPGe, however, is completely inappropriate to measuring carbon intensity.

 

He is talking about liquid fuel per mile, as his captions show.

 

I don't agree.

Petroleum is primary energy, electricity is not.

 

Guys, you are both splitting hairs here.

MPGe is a measurement of fuel efficiency.
It doesn't matter if that fuel is gasoline, electricity or hydrogen.

MPGe allows the direct comparison of the efficiency, nothing else.
It doesn't measure CO2, nor cost, it measures how far the car will go on a unit of energy. The unit chosen is one gallon of gasoline, which has a mathematical equivalence to 33.7 kWh or (I believe) one kg of hydrogen.

The OPs graph is 100% valid, in measuring energy efficiency.

 

If I put a gallon of gasoline into a power plant, it'll produce a lot less than 33.7kWh of electricity - more like 8-12kWh. To make 33.7kWh from gasoline would take something like 2.5-4 gallons.

That's why such a comparison is fought with pitfalls.

 

No one, ever, claimed that you could.
If you thought MPGe meant that, you misunderstand the definition.

The "e" is a mathematical conversion and accurately compares the inherent energy in a gallon of gas in kWh or hydrogen or potato chips or whatever you like. The MPG part tells you how far that particular model car will go on a standardized test.

 

The implication of the chart in the OP is that MPG and MPGe are directly - and algebraically - compatible. But they aren't because of this reason. This should be pretty obvious from the fact that they are so different numerically for the same car.