During the Obama Administration a
regulation was passed requiring all automobile manufacturers to achieve
an average efficiency for all their vehicles of 54 miles per gallon by
the year 2025. President Trump recently canceled the ordinance
recognizing such a requirement could never be reached without
sacrificing the safety of the drivers which we will attempt to explain. A
simple tutorial requiring a little arithmetic follows, and the fallacy
of the benefits of electric cars will slowly dissolve.
The energy in gasoline is not
appreciated. An automobile that gets 40 miles per gallon uses only six
tablespoons of gasoline traveling each mile. As good as that sounds,
cars cannot be perfectly efficient. There must be friction resistance
just to get them going and there is no avoidance of aerodynamic
resistance. Sports cars tend to have smoother machined parts that does
reduce friction and account for the greater cost. This is true in
bicycles as well. On a bicycle your body will feel the difference
between a $500 bicycle and a $2500 bicycle.
In a car there is a practical
limitation to achieving higher burn temperatures in the engine in order
to increase thermodynamic efficiencies for converting chemical energy to
mechanical energy. Higher burn temperatures are accomplished in Diesel
engines, but the higher temperatures also requires a heavier engine
block. They are super efficient for trucks, trains and ships where the
cargo weights are large. More weight eventually means lower miles per
gallon for autos.
There is an efficiency calculation
that applies to all normal personal vehicles. It is energy per unit
distance per unit weight. For example, it may be stated in
kilowatt-hours (kWh) per mile (mi), per ton (t) (2000 pounds). The
majority of all consumer purchased gasoline-fueled cars utilize about
0.65 kWh/mi/t. Some of the heavier, more efficient cars,(less friction
from high performance parts) achieve close to 0.6 kWh/mi/t, which is
nearly an 8% improvement. That tonnage must include the weight of the
driver and whatever he/she is transporting.
A gallon of gasoline will normally
produce 34 kWh of energy. Divide the 34 kWh by the highway miles per
gallon (mpg), and then divide by the “curb weight” in tons and add a
tenth of a ton (200 pounds) for the driver to that curb weight. A car,
for example, that achieves 38 mpg and has a curb weight of 2600 pounds
achieves 0.64 kWh/mi/t. That is an excellent car. If the car weighs more
(and good luxury cars weigh more than 3400 pounds), the technological
advantages must be enhanced to achieve kWh/mi/t values of 0.60 to 0.65.
For the same high standards of
engineering, and 54 miles per gallon that was being required by the
Obama administration, the car’s curb weight must be limited to less than
2000 pounds. That’s a bitter reality. Many good engineers strongly
believed the Obama effort to get cars to 54 mpg, was to put it bluntly,
going to create death traps.
Enter the all-electric car. It is
deceptive to employ “miles per gallon EQUIVALENTS” as being comparable
to the true miles per gallon for a gasoline (or a gasoline-battery
hybrid) engine. Purveyors of all electric cars, treat the electricity
that flows into their batteries from the wall socket at home or from a
charging station as if it were a faucet of free energy.
An accountant would be fired for such
an omission. For each 10 kWh that flows from the socket, there are
about 33 kWh of stored chemical energy in the coal or natural gas that
must be burned back in the local power plant. The kWh that is used in
the correct application of an efficiency calculation is supposed to be
the ultimate source of the energy, not a deceptive free gallons
equivalent coming from the socket.
So the 110 to 120 MPG equivalent
values that we are so often told for electric vehicles turns out to be
only 37 to 40 MPG equivalent for all the source energy. One can claim
110 MPG equivalent, only if one has his/her own solar collection system
with battery storage, and charging facilities. Tesla doesn’t dare
suggest that buyers should buy the car PLUS the solar unit. Without this
pairing, there is only a very slight reduction in carbon dioxide
emissions.
The latest push to have electric
cars with longer range, has resulted in the elimination of mpg quotes in
the range of 110 to 120 MPG equivalents. In fact MPG is now rarely even
mentioned, only the extended ranges. So much battery weight is being
added that the reduction in engine weight of an electric car is no
longer a valid positive argument. The true source energy per mile per
ton may become lower, but only because the total tonnage has increased.
Eight hundred pounds of extra battery weight to increase range, for
example, is the equivalent of carrying four extra passengers at all
times. The additional battery weight is not the equivalent of useful
cargo.
The gasoline-battery hybrids (without
plug-in) such as the Prius are definitely more efficient. They can
achieve close to 0.5 kWh/mi/t, when reaching 50 miles per gallon. The
Prius is definitely not a sport car. It has low weight and near-minimum
required power. It is superbly engineered to achieve the goals of high
miles per gallon (low source energy per mile), and one pays considerably
more for it than for any similar sized gasoline powered car.
With the longer range all-electric
(battery) car, designers will never achieve a total weight that
approaches 0.5 kWh of source energy per mile per ton.
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