This Nova Bus Rapid Transit Series (RTS) bus uses a dual battery system, which combines a high-power density lithium-ion battery with a
high-energy density sodium metal halide battery.
READY TO
CHARGE INTO THE
REAL WORLD?
Dual battery systems designed to combine energy density, storage capacity
to make electric vehicles better suited to commercial applications
BY BILL SIURU, PHD, PE
For a long time, electric vehicles have been touted as poten- tially significant contenders in
the consumer and commercial transportation industries. A number of
automotive and commercial vehicle
manufacturers, including Freightliner
and Navistar, have already begun
delivering medium-duty electric trucks
and chassis in limited numbers.
But for all that time, skeptics have
pointed to energy storage as the
Achilles heel of e-vehicles. Most
battery systems come with a trade-
off between power they can sup-
ply — which determines vehicle
performance — and energy storage,
which determines operating range.
Since low battery weight is impera-
tive in electric vehicles, power is
defined by its specific energy or
power density. That power-to-weight
ratio is typically expressed as k W/kg.
Likewise, energy storage is defined
by a battery’s specific energy/ener-
gy density or energy-to-weight ratio,
typically k Wh/kg.
GE’s Durathon sodium
metal halide batteries
are part of the dual battery system, which GE
plans to test in a composite bus this year.
