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Electric Vehicles
Positive and Negative Attributes
Slide 5 of 13
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Notes:
I dont think theres any doubt that we can expect to see widespread use of
electric vehicles in the future, both battery-electrics and hybrids - certainly within the
time frame that we are discussing, and probably sooner. I might have to come back in
a few years and eat those words because there are still significant problems that have to
be solved. But from this perspective in time, its difficult to imagine a
future without electric cars.
In my opinion, the electric power system, at least from a conceptual standpoint, is the
ideal automobile power system. The torque characteristics and wide speed band of the
electric motor make it ideal for propulsion, and generally, a multi-ratio transmission is
unnecessary. Also, the energy loop is inherently bi-directional, so the energy used
for acceleration can be reclaimed on deceleration using the same hardware. You
cant do that with a liquid fuel without resorting to a separate system like a
flywheel or an electrical generation and storage system. In the case of BEVs, the
vehicle itself has zero tailpipe emissions and operates at more than twice the onboard
energy efficiency of a conventional ICE-vehicle. And despite the talk about their
high costs, a battery-electric car is potentially a very cheap vehicle to build. It
has an elegant simplicity thats very appealing - conceptually, mechanically, and
from a manufacturing standpoint. But there are a couple of spots on the wall.
The first problem with BEVs is the limited energy capability of the battery. The
second problem, which is less talked about, has to do with the practical limitations of
pulling into a local service station for a quick fill-up of electrons. I think the
problem of limited energy capability has good prospects for being solved, but Im not
too optimistic about the prospects for solving the quick-recharge problem - and Im
referring to the ten-minute fillup, not the one- or two-hour recharge. The
battery-electric car will probably never equal the fast fill-up of todays liquid
fueled cars (on a time/energy-dump basis). At least thats the way it looks
through my paradigm of technical feasibility.
Assuming an energy efficiency equal to that of the EV1, a 300-mile range BEV would need
energy stores on the order of 65 kW-h. A ten-minute, 65 kW-h energy dump at 70%
efficiency (conversion and battery efficiency) would imply an input of over 1800 amps at
300 volts. If we account for the lighter batteries of an advanced EV, the same range
might be provided with a 45 kW-h battery, which would then reduce the ten-minute recharge
to 1280 amps at 300 volts. Considering the limitations of conductors, batteries, and other
associated realities, Im not very optimistic about the prospects for a truly
quick-recharge system for BEVs - at least not one that would equate to what we have with
liquid fueled vehicles.
Although BEVs could ultimately approach the range of todays cars, they will
probably remain mostly limited to overnight recharging at home, with perhaps some topping
off done at remote recharging sites.
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