Why Is It So Hard To Get Even Smart People To Think Clearly on Electric Vehicle Efficiency?

A lot of people on Twitter get freaked out when they see football players kneeling for the national anthem, or detect obscure micro-agressions in some online statement.  When I venture onto Twitter, which I am still not sure is good for my mental health, I get freaked out by this:

My initial response on Twitter was "Of course they are if you leave out the efficiency of converting fuel to electricity".  I will explain this response more in this post.

It would be impossible to say that Eric Schmidt is not a smart guy or lacks technical training.  I'd like to think that he would quickly understand his error and say that he would have said it better when he has 280 characters.  But soooo many people make this mistake, including the folks who write the electric vehicle MPGe standards for the government, that it is worth explaining why Mr. Schmidt's statement, as written, is silly.

Let's first look at what the terms here mean.

  • When we say that electric motors are 97% efficient, we mean that the actual physical work produced per unit of time is 97% of the electrical power used by the motor, which equals the current flowing to the motor times its voltage.
  • When we say that the internal combustion engine is 45% efficient, we mean that the physical work we get out of the engine is 45% of the heat liberated from burning its fuel.

By the way, both these efficiency numbers are the top end of current technology running at an ideal speed and percentage load.  In real life, efficiencies of both are going to be much lower.  Of the two numbers, the efficiency number for internal combustion is probably the most generous -- for non-diesel engines in most cars I would be surprised if the actual efficiency was much higher than half this figure.  Even average electric motors will still be in the 80's.

Here is the problem with what he tweeted

The problem with Schmidt's statement on its face is that he is comparing apples and oranges -- he has left out the efficiency in actually producing the electricity.  And for the vast, vast majority of the country, the marginal fuel -- the fuel providing the electricity for the next increment of load -- is going to be natural gas or coal.  His numbers leave out that conversion step, so let's add it in.

Actual power plants, depending on their age and use, have a wide range of efficiency numbers.  For example, a big combined cycle plan is more efficient that a gas turbine, but a gas turbine is useful because it can be started and stopped really quickly to react to changes in load.  Schmidt used leading-edge efficiency numbers so I will do the same.  For a coal plant the best numbers are in the high forties.  For a gas plant, this can reach into the 50's (this site says 60% but that is the highest I have ever seen).  We will take 50% as a reasonable number for a very very efficient power plant.  Power plants, by the way, since they tend to run constantly at ideal speeds and loads can get much closer to their ideal efficiency in real life than can, say, internal combustion engines.

After the electricity is produced, we have to take into account line and transformer losses (and in the case of electric cars the battery charging losses).  This obviously varies a lot but I have always used a figure of 10% losses so a 90% efficiency number.

Taking these numbers, let's convert the 97% efficiency number for electric motors to an efficiency number all the way back to the fuel so it is apples to apples with internal combustion.  We take 97% times 90% transmission efficiency times 50% electricity production efficiency equals 43.6%.  This is actually less than his 45% figure.  By his own numbers, the electric motor is worse, though I think in reality with realistic efficiency numbers rather than best-possible numbers the electric motor would look better.   The hard step where one is really fighting the laws of thermodynamics is the conversion of heat to work or electricity.  So it is amazing that a tiny power plant in your car can even be in the ballpark of giant optimized multi-stage power plants.

Here is why electric motor efficiency is almost irrelevant to getting rid of fossil fuels

Very efficient electric motors are necessary to moving to a non-fossil fuel economy, but not because of small increments in efficiency.  The reason is that large parts of our energy-using technology, mostly vehicles, run on a liquid fuel directly and this distribution for the fuel is already in place.  To replace this liquid fuel distribution system with something else is really expensive.  But there does exist one other energy distribution system that has already been built out -- for electricity.  So having efficient electric motors allows use of non-gasoline energy sources if those sources can be turned into electricity.  For example, there are real advantages to running vehicles on CNG, but there is no distribution system for that and so its use has been limited to large fleets (like city busses) where they can build their own fueling station.  But electric cars can use electricity from natural gas, as well as solar and wind of course that have no other distribution method other than by electricity.

The problem with all this is that most of the barriers to using electricity in more applications are not related to motor efficiency.  For vehicles, the problem is in energy storage density.  Many different approaches to powering automobiles were tried in the early days, including electric and steam powered cars.  The main reason, I think, that gasoline won out was due to energy storage density.  15 gallons of gasoline weighs 90 pounds and takes up 2 cubic feet.  This will carry a 40 mpg car 600 miles.   The Tesla Model S  85kwh battery pack weighs 1200 pounds and will carry the car 265 miles (from this article the cells themselves occupy about 4 cubic feet if packed perfectly but in this video the whole pack looks much larger).  We can see that even with what Musk claims is twice the energy density of other batteries, the Tesla gets  0.22 miles per pound of fuel/battery while the regular car can get 6.7.  More than an order of magnitude, that is simply an enormous difference, and explains the continued existence of internal combustion engines much better than electric motor inefficiencies.

And here is why electric vehicle equivalent MPG standards are still screwed up

I don't really have the energy to write about this again, but because these issues are so closely related I will quote myself from the past.  Suffice it to say that after years of development, the EPA made nearly the exact same mistake as did Mr. Schmidt's tweet.  This Despite the fact that the agency had already developed an accurate methodology and then abandoned it for a flawed methodology that produced inflated numbers for electric vehicles.  There is more than one way for the government to subsidize electric vehicles!

The Fisker Karma electric car, developed mainly with your tax money so that a bunch of rich VC's wouldn't have to risk any real money, has rolled out with an nominal EPA MPGe of 52 in all electric mode (we will ignore the gasoline engine for this analysis).

Not bad?  Unfortunately, it's a sham.  This figure is calculated using the grossly flawed EPA process that substantially underestimates the amount of fossil fuels required to power the electric car, as I showed in great depth in an earlier Forbes.com article.  In short, the EPA methodology leaves out, among other things, the conversion efficiency in generating the electricity from fossil fuels in the first place [by assuming perfect conversion of the potential energy in the fuel to electricity, the EPA is actually breaking the 2nd law of thermodynamics].

In the Clinton administration, the Department of Energy (DOE) created a far superior well to wheels MPGe metric that honestly compares the typical fossil fuel use of an electric vs. gasoline car, using real-world power plant efficiencies and fuel mixes to figure out how much fuel is used to produce the electricity that goes into the electric car.

As I calculated in my earlier Forbes article, one needs to multiply the EPA MPGe by .365 to get a number that truly compares fossil fuel use of an electric car with a traditional gasoline engine car on an apples to apples basis.  In the case of the Fisker Karma, we get a true MPGe of 19.  This makes it worse than even the city rating of a Ford Explorer SUV.


  1. Rob McMillin:

    This is absolutely because people in Silicon Valley are typically CS types who have had no or very limited exposure to real systems engineering. They believe, naively, that all problems will yield solution curves similar to that Gordon Moore found with his famous law (really, a well-behaved axiom). And hardly any of them understand the difference between energy and power.

    I have said this many times in the past, but people who do not know what the Haber process is have no business being anywhere near anything remotely describable as "energy policy".

  2. Jerryskids:

    Not related to fuel efficiency but to efficiency in general, add in the economic and environmental costs of producing and disposing of batteries and things get even worse.

  3. SamWah:

    Those advocating for electric motors believe in handwavium power. They hate oranges.

  4. sl149q:

    Not too mention the time it takes to "fill" a gas tank versus a battery.

    Or that even if we could design a battery that could charge in a similar amount of time it takes to fill a gas tank (i.e. say less than five minutes for a small vehicle), designing a charging station that was safe to use by ordinary drivers would be difficult. The charging system would have seriously dangerous amounts of energy flowing through them.

  5. Sam P:

    The interesting solution of battery exchange has unfortunately not gone anywhere.* Better Place went bankrupt several years ago. Tesla actually had battery exchange on the Model S and built one exchange station, but gave up on it after a year or two.

    * Battery exchange has a major problem: you'd have to standardize the battery at the very time battery technology is changing rapidly.

  6. Duane Hakala:

    And to add insult to stupidity. I caught a news bite last night. Moon Beam is checking on the feasibility of Totally Banning internal combustion vehicles in California within 10 years.

  7. SamWah:

    The only "real" battery-powered cars were in a Heinlein novel (I forget the title) I read some 20-40 years ago. The batteries were called "shipstones"; you drove up, and swapped yours out for a charged one (I don't recall a price for the service, either), and off you went.

  8. Agammamon:

    "It would be impossible to say that Eric Schmidt is not a smart guy or
    lacks technical training. I'd like to think that he would quickly
    understand his error and say that he would have said it better when he
    has 280 characters."

    You would be wrong. No matter how many characters he had, he's starting from bad assumptions - that the 45% number is for the *whole* conversion cycle (fuel to movement) for ICE engines while the electrical number is electricity into the motor vs movement out (not even how much energy is lost through the battery charging alone).

    Its an apples to horseflies comparison. Its comparing real world capitalism to the textbook theoretical version of communism. Its such a simple yet major screwup that tons of people who like to think they are smart make. But smart people don't make that type of error. Certainly no one who is smart *and* has technical training should make.

  9. AtlantaDude:

    Here is a somewhat related analysis. You mention that aside from gasoline, the electrical grid is the only available and ubiquitous energy distribution network. My question was whether it was more efficient to use that electricity to charge batteries, or to use it for electrolysis to pull hydrogen out of water, and then power a hydrogen fuel cell car.

    Hydrogen is not a fuel like gasoline. It takes power to isolate hydrogen, and then the hydrogen can provide power via a fuel cell. So, the hydrogen cycle is less like using gasoline and more like charging and draining a battery. So, how does the hydrogen cycle compare to the lithium-ion battery cycle? I have never found clear answer on the Internet. Here is what I was able to piece together.

    Hydrogen Cycle
    Pulling hydrogen atoms out of water, using current electrolysis methods, requires approximately 60 kwh of electricity to isolate 1 kg of hydrogen. Toyota's hydrogen-powered Mirai automobile gets approximately 60 miles per kg of hydrogen. Therefore, with current technology, 1 kwh from your electrical outlet will move a hydrogen car 1 mile.

    Lithium-Ion Battery Cycle
    Battery chargers are not 100% efficient. Therefore, for every 1 kwh pulled out of your electrical outlet, they battery will get approximately 0.8 kwh worth of charge. Tesla Model S users say they get roughly 3 miles per kwh of battery charge. This translates into 2.4 miles per kwh from your electrical outlet.

    So, based on current technology 1 kwh of outlet power would yield 1 mile in a hydrogen powered car vs. 2.4 miles in a battery powered car.

  10. cc:

    There are other efficiency issues. The batteries in an electric car don't last forever. Most electric cars are not old enough for that price to hit home but people will not be happy when they have to replace them. Tesla has quoted replacement batteries after the 8 year warranty for $8,000 to $12,000, but if the true costs are higher Tesla will be in trouble. So this comes to $1000 to $1500/yr for battery costs (or your used car value plummets at 8 yrs) vs a similar cost for gas (for my cars). That is, I would be saving nothing vs gasoline when taking battery depreciation into account.

  11. mobile:

    Is cost per mile an appropriate comparison? Sure, the ratio of gas-to-electricity prices varies across the country (and across the world). But to a first order, the cost of resources needed to power a car of any kind will take into account all of these issues.

  12. joe - the climate science expe:

    Think about all the electric vehicles trying to escape the next florida hurricane - 200 mile range, all stopping at the one or two charging stations in the county - taking 8 hours to charge up -

  13. jdgalt:

    This needed to be said, and so did AtlantaDude's addition, but even the two of you together didn't capture the whole problem. Electric (and hybrid and H2) vehicles have a third efficiency problem -- the energy cost of manufacturing them is much greater than for a conventional car, *and* their expected lifetime is much less. So if you measure total life-cycle energy cost per mile of driving, I'd be seriously surprised if a Leaf, a Volt, or even a Tesla were half as energy efficient as a regular car.

    This is only one of several reasons why forcing taxpayers to subsidize this technology is a stupid idea. When it reaches energy break-even, it will not need a subsidy; until then it does not deserve one.

  14. jdt:

    I wouldn't buy one of those expensive battery replacements. I would simply visit one of the battery exchange stations mentioned in comments below and pass my defective battery on to the exchange station!

  15. joe - the non climate scientis:

    Mobile - Is cost per mile an appropriate comparison? Yes

    Same with measuring pollution - one of the reasons the EPA has been slow to object to ethanol is the pollution per gallon is slightly less, yet due to the reduced mileage, the pollution per mile is greater.

  16. Richard Kleeman:

    The line losses are far greater than 10%, more like 65% from what I have seen in presentations by electrical engineers working on the grid. As well as that reactive power has to be supplied as well for voltage control. Makes the comparison a lot worse.

  17. Dimitri Mariutto:

    Yet more progress for the venerable ICE:


    To be fair, it is a hybrid engine but still this makes the all electric car less likely to reign anytime soon.

  18. Jaedo Drax:

    Treat Hydrogen production as a by-product created at power plants that need to be run at full bore all the time, during times in which their power isn't required, just Methane as the feed stock instead of water, and build more plants.

  19. AtlantaDude:

    Using spare power plant capacity to produce hydrogen rather than generate electricity assumes that hydrogen storage and transport would be cheaper than electricity storage and transport. I'd like to see an analysis of that, but I imagine that electricity would win on that front as well.

  20. Mike Powers:

    Plenty of work done smugly listing all the missed elements in the electric-vehicle energy chain, but I don't see you providing any of that for gas-burners. I guess all that 91-octane just magically appears in the tank?

    In particular, if you're going to throw "line and transformer losses" into the mix, then you have to address the cost of extracting, shipping, and processing petroleum.

    So you can say "97% and 45% are two different numbers" and you're not wrong, but neither is it correct to say "the proper comparison should be 43.6% to 45%!"

  21. Jaedo Drax:

    true enough... practical fuel cells in cars has been 5 years away for at least the last 30 years; though Ford did build a hydrogen burner as a demo about 14 years ago, that might have been a better path...

    Though in Ontario's case, paying other jurisdictions more than $200/MWh to take our power, and running the nucs at less than full bore, is a stupid way to run an electrical system.

  22. Mike:

    GM designed the batteries in the Volt and Bolt to last 15 to 16 years, which is longer than car bodys last in most parts of the country.

  23. Mike:

    For most usage, overnight charging is sufficient and safe. For long distance, cross country driving you're absolutely correct about this being a limitation of today's EV technology.

  24. Mike:

    LiOn batterys are 100% recyclable. The have always been recyclable - the problem is that most people just throw them away when they dispose of the devices they're in.

  25. Mike:

    While you're killing subsidies, let's kill the $500 Billion annual subsidy governments, at all levels, around the world give to the oil & gas industry. This number is from their own published documents.

    The batteries in the Volt and Bolt (both GM) are designed to last 15 or 16 years of daily charge/discharge cycles. This is longer than most car bodies last. When disposed, the batteries can be dropped out and recycled to make new batteries.

  26. Mike:

    At the low speeds on those evacuation routes, EVs are actually more efficient and that 200 mile range doubles to 400.

  27. Uncle Max:

    Really, it all falls apart on a cost/basis ratio... AND the biggie?? What are we trying to do here? Air pollution is NOT a problem. The Government has put the ppm for pollutants acceptable in the air to stupidly small numbers, where you have to step back and ask, at what point are you done? At what point have we achieved the goal? Ah.. and the answer is never! and that is the rub. The folks driving the debate don't want 100mpg cars. They also don't want cars with engines. They don't want coal plants or nuclear that will power their electric cars. It is a religion ... and ideology. They never say " that's good " and move on. Nope... it's always more. Crush zones... safety cameras, new power plug in stations ( with subsidies! ).. self-driving!... etc. It's a rabbit-hole of unicorns and futuristic BS, and absolutely elitist.

    Lastly... gasoline/diesel is storable energy. Like coal... sitting there.. it has energy stored. Weight to power potential is good too. The power could go out for a month, but if you have stored fuel, you could get around, help others, etc. Electric cars is a dependency loop.. you are dependent on the power company and the Government. You forfeit your ability to move about on whim or on your own account. You are a pleb... no bueno. That's unAmerican.

  28. David:

    Remember that you need virtually all the same cost of extracting, shipping, and processing petroleum (or other fossil fuels) to generate the electricity to power your EV. It seems that it is about a wash for both types of vehicles.

  29. theelephantschild:

    Here in the Seattle area, powerful investors are pushing for making all the highways available only to driverless electric cars. The nasty people who like to drive, or those who don't want an electric car would be out of luck. To reach the Leftist mind, you may have to write more briefly in simpler words, and get into the CO2 as not the cause of global warming, but being fertilizer for plants thingy.

  30. Sooke:

    With lights, AC or heat on, time becomes a more important factor than distance.

  31. Mike Powers:

    Yes, that's the point. He *didn't* include those costs in the calculation for gas-burners. It's *not* a wash.

  32. Dcoronata:

    No discussion on transportation losses on gasoline, no discussion on losses in catalytic practices, nothing on infrastructure for gas delivery... This article is based on the author's piece on Forbes, which is the least science-based "economics" source out there. For all practical purposes, he looks at every single joule in the process of EVs and not a single electron volt for gasoline systems.

  33. Dcoronata:

    What if your E-vehicle is powered by nuclear, or hydro, or renewable energy sources?

  34. Dcoronata:

    As a Mercedes owner and a big fan of their F1 team, I ask you to mention that the 50% efficiency comes through two separate hybrid regeneration systems, costs several million dollars an engine, and is lucky to drive 1000 miles in its lifetime without major overhaul.

  35. Dcoronata:

    The line losses are actually much less than 10% for very high voltage lines- the efficiency of the best steam generators is roughly 60%, this is where the other losses come from. And at ~60%, they are nearly three times as efficient as your car's engine.

  36. Null66:

    except they don't wear out.

  37. jon49:

    The Chevy Bolt gets 119 MPGE or 119 * 0.365 = 43.4 MPGE. Not too bad. And 238 mile range. So, it should have less maintenance since it has only an electric motor, if you drive it right you could probably get away with never changing its breaks, no oil changes. With a price tag of MSRP from $36,620. So, still not in my price range but finally in my mileage range. You could probably even use it as an only car at this point. A car I might actually be able to use. Now to wait 7 years so the price gets in my range too!

  38. Philip Ngai:

    Yes, we already have an electric grid serving most homes in the United States, but that grid is sized for the existing load. If a large portion of those households started charging at 6 kilowatt or 10 kilowatt levels, the existing grid would probably break down.