Thread by @Coyoteblog

1\ Given @ElectrekCo's hot take on how Toyota & Honda don't understand efficiency (via @tool_grinder), I thought it time to return to my old Forbes article from 2010 on the fraud behind the EPA's eMPG figures for electric vehicles. @TESLAcharts $tslaq

2\ Obviously MPG doesn't have much meaning for electric vehicles, but the EPA didn't want to create a 2nd standard & wanted a figure that consumers could use to compare the efficiency among electric, ICE, and hybrid vehicles. Thus they decided to create an eMPG standard for EVs

3\ So they had to convert electrical energy used to gallons of gasoline. They did this be dividing the potential energy or heating value of a gallon of gasoline (115,000 BTUs) by the energy in a KwH of electricity (3412 BTUs) to get a conversion factor of 33.7 gallons per KwH

4\ Using this factor, they can convert miles per KwH of electricity in an electric vehicle to an MPGe that is supposedly comparable to more traditional vehicles.

5\ For those unschooled in science and @elonmusk fanbois (but I repeat myself), this probably all seems fine. But anyone who knows anything about combustion and thermodynamics knows that there is a big problem here.

6\ Specifically, nowhere on the planet is anyone able to convert the full heating value of gasoline (or any fuel) into electricity -- in fact it is impossible to do so by the 2nd law of thermodynamics

7\ In reality, there are inefficiencies. Why didn't the EPA consider these? Well, actually it did. Way back in the Clinton Administration a well-to-wheels methodology was created to base eMPG numbers on the actual amount of fuel it takes to generate that electricity in real life

8\ First, the DOE looked at the electrical generation efficiency, and determined that only 32.8% of the potential energy in the fossil fuel becomes electric energy in the average US power plant, which it further reduced to 30.3% to account for transmission losses.

9\ However, they realized it was unfair to charge electric vehicles for these losses without also charging gasoline-powered vehicles for the energy cost of refining and gasoline distribution. They calculated these as adding 20% to the energy it takes to run a gas-powered car...

10\ ...but rather than reducing existing MPG standards by this amount, they instead gave a credit back to electric vehicles. The 30.3% electric production and distribution factor was increased to a final adjustment factor of 36.5%

11\ This is the number to adjust the pure heating value conversion factor for real world electrical generation efficiencies. Since current eMPG is based on the pure heating value conversion, we can just multiply the eMPG times .365 to get the more realistic well-to-wheels number.

12\ According to the EPA, the top @tesla eMPG number for a 2019 model 3 is 130. We know now that this is a completely meaningless number that assumes drivers can break the 2nd law of thermodynamics

13\ Using the more realistic well to wheels standard that takes into account actual electric generation efficiencies, we multiply 130 by .365 and get a 47.5 eMPG for the best Model 3. A good number, but note that it is LESS than a Prius, whose best number in 2019 was 56 MPG.

14\ Let's anticipate some responses. The first is that I live in an area with lots of solar and renewables so my electricity is using a lot less (or no) fuel. The answer: maybe. What matters is not the average fuel mix in your area, but the marginal fuel --

15\ the fuel that supplies the electricity for the next incremental load. You may live in an area that is 98% hydro power, but if the marginal fuel for incremental demand is natural gas, when you buy your Tesla and charge it, you are adding to natural gas demand.

16\ This issue of marginal fuel source for EV charging is complicated (see one study below) but this study does find that charging at night (which many EV owners do) drives a lot of fossil fuel use even in large renewable areas.
afdc.energy.gov/files/u/public…

17\ The second objection might be that I have solar on my house and I use it to charge my car during the day, so I use zero fuel. And the answer is again, maybe. If you normally sell your excess solar into the grid, you are likely displacing some fossil fuel use

18\ when you instead use the solar yourself, more fossil fuels may have to be burned to make up for the solar electricity you aren't selling to the grid.

19\ Yes, marginal analysis is hard which is why so much media analysis of public policy is garbage.

20\ All this said, EV's are indeed an investment in a future electric economy. It makes no sense for us to fire up a big nuclear program without also migrating to EVs in transportation. Long-term, EVs are a good investment. In the next 5-10 years though, your eMPG number is bogus

21\ So here is that golden oldie from Forbes written on this topic all those years ago. It is a shame that the Obama Administration chose to put its finger on the scale and issue what it had to know was a flawed standard.

forbes.com/sites/warrenme…