Do you want MPGe or Cost per Mile? MPGe doesn't require knowing the cost of gas or electricity. It's purely a measurement of energy efficiency, cost is not part of the equation. An MPGe display would show: Total Miles Driven / (Gallons Burned + (kWh/33.7)).Allow the driver to enter electric price and gas price and calculate an effective MPG. It is not realistic to ignore the cost of electricity.
MPGe can and is used to compare all electric cars and Tesla's do have an MPGe rating. That's the entire point, to enable normalized comparisons between vehicles using different fuel sources. The Tesla Model S-60 is rated at 95. The Volt is 98, and the Leaf is 115.Displaying "Lifetime MPG" and MPG on the "A" and "B" displays is meaningless because it ignores the cost for electricity. MPGe is a term that is too confusing to understand and explain to people. It also cannot be compared to all electric cars (I don't think a Telsa will ever display MPGe).
I'd like to see the electric car industry agree on units - either miles/KWh or Wh/mile. I like the former because efficiency improves as the number gets bigger.
Yes and no. One could not assign a general combined (gas+elec) MPGe figure to all Volts because, as you say it's based on driving pattern and more specifically the EV%. But, if the vehicle displayed an MPGe number specific for that vehicle based on some given time period, then you could calculate your costs fairly accurately. First assume the Volt will on average get the same MPGe when driving all electric, and likewise will get the same average MPG when driving all gas. With that, any combined MPGe value is really nothing more than a different way of measuring EV% and a given MPGe number can only be achieved by driving a particular ratio of gas and electric.If you are concerned about cost, then the combined MPGe figure, including both gasoline and electricity, is not only confusing but useless. Depending on the driving pattern, there may be more gas and less electricity in that total or more electricity and less gas (especially in a Volt), and gallons of energy are not fungible in different forms. A gallon of gas does not cost the same as a gallon of electricity (or necessarily have the same environmental impact). That's why I don't like MPGe as a combined metric; it doesn't tell you anything.
It seems that the true common denominator is cents/mile, which can be calculated by the car by entering the per-gallon cost when one fills up and the cents/KWh that one typically pays.
Most have little idea of what their cost per mile is. Most have a guess of what their MPG is. All know how much it costs to fill a tank and about how often they need to do it. Start talking MPGe and you might as well get the camera out and take pictures as their eyes roll into the back of their head and drool dribbles from the side of their mouth, haha.I've spent the last 14 months trying to explain to other "villagers" where I live about the various reasons I bought a Volt and people here can't even figure out the "cents-per-mile" part (maybe all the villagers here are simpletons, I live in a rural region of Texas)...
Most have little idea of what their cost per mile is. Most have a guess of what their MPG is. All know how much it costs to fill a tank and about how often they need to do it. Start talking MPGe and you might as well get the camera out and take pictures as their eyes roll into the back of their head and drool dribbles from the side of their mouth, haha.
Combined MPGe would be a bad estimate of EV%, since people can get different electric efficiency and different MPG on different days, depending on how and where they drive and what the weather is like. Certainly, someone isn't going to look at the MPGe on the display and figure out their EV% and how much it costs to drive in their heads. With a pocket calculator they could come up with a guess, but what would be the point? Myvolt.com tells you total miles driven, electric miles driven, gas miles driven, kWh used (not sure whether it is from the battery or taken in through the charge port), and gallons used. That gives you enough to approximate whatever you want as a big picture, and how many cents one trip costs isn't very important.First assume the Volt will on average get the same MPGe when driving all electric, and likewise will get the same average MPG when driving all gas. With that, any combined MPGe value is really nothing more than a different way of measuring EV% and a given MPGe number can only be achieved by driving a particular ratio of gas and electric.
BTW my point is only that if your Volt could somehow tell you MPGe, it would correlate to some EV%. That said, it would be easier and more accurate to have the Volt just simply give you EV% since while the Volt IS capable of precisely measuring miles driven on gas and electric, it IS NOT apparently very good at estimating kWh used (as discussed in many other threads).
I use the same dual-fuel setup in the house. Of course if the system calculated the switchover temp from costs, then you would have to feed it real-time cost data. And we wonder why SW expands to fill available memory & processor cycles.That would be a good addition. In discussions you always end up having to explain the EPA ratings which use a energy equivalent vice a cost equivalent to calculate an effective mpg. Actual cost per mile is what consumers would care about. I have a hybrid furnace and it has the same issue in that I can program a crossover temperature for switching between Natural gas and heat pump but what I would really like is to be able to put the cost of each fuel in and let it manage the crossover based upon which is cheaper to use at a given temperature taking into account the efficiency of each heating method at that temperature.
Yes I agree, and I wasn't suggesting MPGe is a good method for driving a cost calculation. I was only saying it is possible to do, and I don't think it would be a bad estimate. It wouldn't be perfect either, but even accounting for the 3Ts, I think you could get within 5% of actual.Combined MPGe would be a bad estimate of EV%, since people can get different electric efficiency and different MPG on different days, depending on how and where they drive and what the weather is like.
I don't think there is any way to measure the Volt's energy usage exactly without taking some kind of measurements every day and keeping a log by hand (maybe there are some electric meters that will do this if the Volt is the only thing on the meter)
I agree on all counts. MPGe is OK for engineers, not so useful for the common man (or woman). QED.If the primary goal is understanding your cost to drive, then yes MPGe doesn't answer that question very well (at least not without doing a bunch of additional calcs). But from an engineering efficiency perspective, if you are trying to compare vehicles of varying fuel types to determine which one is most efficient at driving a certain distance on a given amount of energy, then MPGe works well. Of course most people don't really care about that.
+1 Exactly. (Prius lets you input the gas price and a reference mpg to get comparison and savings.)Allow the driver to enter electric price and gas price and calculate an effective MPG. It is not realistic to ignore the cost of electricity.