Coyote Blog, Electric Cars, Energy Efficiency, Energy Losses, Environmental Protection Agency, EPA, Eric Schmidt, Fossil fuels, MPG Conversion Factor, MPGe, Storage Density, Tesla, Transmission Losses, Warren Meyer
Electric cars don’t save much energy over gas-burners if at all, at least for now. Warren Meyer’s recent Coyote Blog post on this topic is aptly titled “Why Is It So Hard To Get Even Smart People To Think Clearly On Electric Vehicle Efficiency“. Meyer begins by quoting the following tweet from Google smarty Eric Schmidt, which typifies the general level of public awareness regarding the supposed energy savings from electric cars produced by Tesla and many others:
“Electric motors are the unsung hero of clean energy – the latest are 97% efficient, vs. 45% for internal combustion.“
Meyer emphasizes these major points:
- the efficiency with which source fuels are converted to physical work via electric and gas-burning cars is more comparable than Schmidt’s tweet suggests;
- differences in energy density weigh heavily in favor of fuel-burning vehicles.
- the so-called miles-per-gallon equivalent (MPGe) calculated by the U.S. Environmental Protection Agency (EPA) is a sham.
First, Schmidt’s tweet is accurate only if the discussion is confined to simple conversion of energy to physical work performed by the respective engines. The tweet ignores energy losses that occur prior to that conversion: electricity must be generated with far less than 100% efficiency, mainly by burning coal and natural gas. In an earlier Forbes article, Meyer compares this situation to a distorted comparison of two refrigerator installers:
“In both cases the customer lives in a fourth floor walkup. The first installer finds the refrigerator has been left on the street. He has to … haul the appliance up four flights of stairs. After that, relatively speaking, the installation is a breeze. The second installer finds his refrigerator has thoughtfully been delivered right to the customer’s door on the fourth floor. He quickly brings the unit inside and completes the installation. So who is a better installer?“
The fact is that both gas-burning and electric vehicles rely heavily on fossil fuels. And, in addition to losses in the generation process, there are other losses of energy attributable to electric cars: transmission of power involves a significant energy loss, as does charging batteries and storage itself. Meyer considers only the extra losses from production and transmission of electricity in the following comparison:
“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….“
Meyer qualifies this comparison, as some of his assumptions are of the “best outcome” variety, but contrary to Schmidt’s assertion, gasoline and electric engines are reasonably comparable in terms of energy efficiency.
Some contend, however, that power losses in electricity transmission are much larger than the 10% Meyer assumes (see the comments on his post). Battery charging involves a loss of perhaps 20%. And a replacement for a Tesla battery, post 8-year warranty, is $8,000 – $12,000, an additional storage “cost” that is virtually non-existent for gas-powered vehicles. Beyond a certain point in its life, that cost will have an impact on a Tesla’s resale value. Moreover, some contend that the production of electric vehicles is more energy-intensive, putting them in an energy efficiency hole right from the get-go.
Meyer then takes up the notion of storage density as an explanation for why early experiments with electric cars were essentially abandoned:
“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…“
Meyer notes in the Forbes article that the EPA calculates its MPG conversion factor for electric vehicles by dividing BTU’s in a gallon of gas by the BTUs in a kilowatt hour: 33.7 KwH per gallon. Thus, the EPA multiplies an electric car’s miles per KwH by 33.7 to arrive at the so-called MPG equivalent: MPGe. But as we’ve seen above, the conversion factor ignores the generation and transmission of electricity required at the front end, and the associated energy losses that occur before a single KwH is released by a Tesla battery.
Despite what we hear from the EPA, Tesla, and other interests today, electric cars have not really overcome these disadvantages, at least not yet. The EPA’s MPGe estimates are vastly inflated. Perhaps if they were accurate, these vehicles would not have to rely so heavily on taxpayer subsidies to be competitive. By extension, the presumed environmental benefits of electric cars are nonexistent at this stage of development. I’m certain that Eric Schmidt and many other smart people are capable of understanding these nuances, but they might be too busy tripping over their politics to bother.