Energy and Human Ambitions on a Finite Planet, 2021a

D.3 Electrified Transport 400
It is not impossible 24 to electrify long-haul trucking, but neither is it free
of significant challenges. Certainly it is not as easy <strong>and</strong> convenient as
fossil fuels.
24: Indeed, Tesla offers a Semi capable of
500 mile range, but see this careful analysis
[129] on the hardships.
D.3.4 Buses
Like cargo ships <strong>and</strong> long-haul trucks, public transit buses are on the
go much of the time, favoring solutions that can drive all day <strong>and</strong>
charge overnight. Given the stops <strong>and</strong> breaks, a typical bus may average
30 km/hour <strong>and</strong> run 14 hours per day for a daily range of approximately
400 km. At an average fuel economy of 3.5 mpg (70 L/100 km), each day
requires about 300 L or 220 kg of fuel—no problem for a fuel tank. The
equivalent battery would need to be 4,500 kg (900 kWh; 2.3 kWh/km),
occupying about three cubic meters. Size itself is not a problem: the roof
of the bus could spread out a 0.15 m high pack covering a 2 m × 10 m
patch. Buses typically are 10–15 tons, so adding 4.4 tons in battery is not
a killer.
Electrified transit is therefore in the feasible/practical camp. What makes
it so—unlike the previous examples—is slow travel, modest daily ranges,
<strong>and</strong> the ability to recharge overnight. Raw range efficiency is low, at
2.3 kWh/km, but this drops to a more respectable 0.2 kWh/km per
person for an average occupancy of 10 riders.
For charging overnight, a metropolitan transit system running 50 routes
<strong>and</strong> 8 buses per route 25 <strong>and</strong> therefore needs to charge 400 buses over
6 hours at an average rate of 150 kW per bus 26 for a total dem<strong>and</strong> of
instance.
60 MW—equivalent to the electricity dem<strong>and</strong> of about 50,000 homes.
26: . . . 900 kWh capacity <strong>and</strong> 6 hours to
25: A one-hour one-way route operating
on a 15 minute schedule needs 4 buses in
service in each direction of the route, for
D.3.5 Passenger Cars
charge
Passenger cars are definitely feasible <strong>and</strong> practical for some uses. Typically
achieving 0.15–0.20 kWh/km, the average American car driving
12,000 miles per year (about 50 km/day, on average) would need at least
10 kWh capacity to satisfy average daily driving, but would need closer
to 100 kWh to match typical ∼500 km ranges of gasoline cars.
At a current typical cost of $200–300 per kWh, such a battery costs 27: Thus, long-range electric cars roughly
$20,000 to $30,000, without the car. 27 The most basic home charger runs double the price.
at 120 V <strong>and</strong> 12 A, 28 multiplying to 1,440 W. A 100 kWh battery actually
28: . . . satisfying the 80% safety limit for a
takes closer to 110–120 kWh of input due to 80–90% charge efficiency. 15 A circuit
Dividing 115 kWh by 1.44 kW leaves 80 hours 29 as the charge time.
29: . . . 3.3 days!
Table D.1 provides similar details for this <strong>and</strong> two other higher-power
scenarios.
The middle row of Table D.1 is most typical for home chargers <strong>and</strong> those
found in parking lot charge stations, resulting in an effective charge speed
of about 10 miles per hour, or 16 km/hr. This is a convenient way to
© 2021 T. W. Murphy, Jr.; Creative Commons Attribution-NonCommercial 4.0 International Lic.;
Freely available at: https://escholarship.org/uc/energy_ambitions.