I wrote a column recently about crypto – about being uneasy about it – because it isn’t easy to understand or explain it.
Unlike miles-per-gallon, which anyone can understand, MPGe is very hard to understand. Which is why I am uneasy about it. Maybe you ought to be, too.
What is “MPGe”?
It is – supposedly – the electric car analogy of MPG – sans the “e.”
It is – so we are told – the measure of how far an electric can go on a given quantity of electricity. This is already confusing because while everyone understands what a gallon of gasoline or diesel is and also can readily understand that a gallon of it will take you “x” many miles in a given vehicle and that times however many gallons the tank holds gives you an easy understanding of the vehicle’s range, few non-electricians understand what a kilowatt-hour of electricity is much less the various variables involved as regards how far they can take you.
The EPA – the federal “agency,” as these coercive bureaucratic apparats are styled (so as to make it seem as though we are dealing with something that hasn’t got bayonets behind it) defines the MPG equivalent (hence the “e”) of a gallon of gasoline, in terms of the energy locked up in the latter, as being about 33.7 kilowatt-hours (kWh) of electricity.
This figure is then used to gin up numbers that – supposedly – correlate to the easily understood miles-per-gallon (and range) numbers we’re all used to and which we all understand.
And these numbers seem extremely favorable – relative to miles-per-gallon numbers. For instance, the Nissan Leaf rates 111 MPGe, which is to say it goes about 100 miles on the kilowatt-hour equivalent of about a gallon of gasoline. This sounds very appealing – especially now, given the cost of a gallon of gasoline.
But how many kilowatt-hours does it take to go farther than 150 miles – which is the maximum rated range of the Leaf equipped with its standard battery pack? (If you spend another $5,000 over the $27,400 price of the 150-mile range Leaf, you get one that can go supposedly as far as 226 miles, which carries an MPGe rating of 108 MPGe.)
The answer is: More kilowatt-hours than the Leaf’s standard battery pack can store.
And when it comes to storage – EPA is opaque.
Even with its $5k extra battery pack, the Leaf can only store the kilowatt-hour equivalent of the energy needed to travel maybe 226 miles, which is equivalent to about five gallons of gasoline, in terms of the energy contained therein – which will take a 40 MPG-capable car about 200 miles.
But most cars carry around 15 gallons of gas – which stores more energy than any currently available battery pack. Those gallons would take a 40 MPG-capable car about 600 miles, which is a bit shy of twice as far as the highest-range electric cars, such as the Tesla3 with its optional battery pack. EPA says it can store enough energy to theoretically go about 358 miles – and carries a 131 MPGe rating.
But don’t believe it.
Unlike the MPG ratings EPA publishes – which do not vary appreciably according to the weather or the use of accessories such as the AC and heater – the miles-per-gallon-e that your EV will travel will vary, considerably, depending on those factors because use of those accessories uses energy and there’s not very much energy stored in EV battery packs relative to the energy-density stored in 15 or even five gallons of gasoline.
There is nothing analogous – much less equivalent – here.
A Leaf that advertises it can go 150 miles on the kilowatt-hours it can store may only go 100 miles – or 80 – depending on such things as whether it’s freezing cold out and you’re using the heater and the defroster and the lights – and also because it’s cold and battery efficiency goes down, significantly, when it is. Also if it’s very hot – and you’ve got the AC cranked up, to cool you down.
A non-electric car that advertises 40 MPG will not return appreciably less than that. Because if it did – irrespective of the use of accessories – there would be recalls and lawsuits for false advertising. This happened fairly recently to Hyundai, incidentally – and over a relatively slight (less than 5 MPG) difference between the rated (and advertised) mileage and what the cars actually delivered.
With EVs, the range regularly – routinely – varies by 20-40 percent or even more, depending on external factors such as outside temperatures.
There’s something else to understand, too. An EV’s touted maximum range is less than its realistically usable range – because of the necessity of finding a place (and having the time to wait) to instill more kilowatt-hours before the ones remaining in storage in the car’s battery pack are dissipated. It is not the same as running right up to empty in a gas-engined car because of the wait involved in re-instilling even a portion of the kilowatt-hours an EV battery pack can store.
Effectively – as a practical matter – it’s necessary to always keep enough charge in reserve to make it to the next charge. However many miles that is must be deducted from the putative MPGe/range rating.
Well, it ought to be deducted – if the intent were to inform rather than confuse people about how far EVs actually/realistically go on the equivalent of a gallon of gas.
There’s one more thing to understand, too.
The miles-per-gallon achieved by non-electric cars doesn’t go down over time. At least, not for a very long time. Not until the transmission starts slipping – or the engine starts burning oil as well as gas. That usually doesn’t happen for 15-plus years and often for more than 20.
But the advertised range of electric cars decreases as the battery pack’s capacity to store kilowatt-hours reduces as the battery pack is used. Which you have to do, in order to use the electric car.
This will happen faster, the more it is used.
Battery packs age as they are discharged – and then recharged – especially when they are discharged completely, as you’d have to do in order to get the touted maximum range/MPGe’s out of the thing – and regularly “fast” charged with high-voltage kilowatt-hours, which is as hard on battery packs as running a gas engine WOT regularly.
If you’re still not understanding how far an EV can go on so-and-so many kilowatt-hours, it’s because they don’t want you to. If that weren’t true, they’d explain how far it goes – and doesn’t – in a way that anyone could understand.
But then, too many people might do just that.
. . .
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