Powering Freight & Transportation - Power Systems Design

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Powering Freight & Transportation
Figure 2. Maxwell’s BOOSTCAP ® HTM125 module.
trams and metros, all of which benefit
from the adoption of a hybrid power
train approach. Consequently, primary
energy demand and maintenance costs
can be considerably reduced.
The obvious energy storage device
might be a rechargeable battery. However,
such technology shows evidence
of some serious limitations in freight and
transportation applications. Batteries
are heavy in weight, large in size, slow in
charging rate and high in maintenance
costs due to reduced cyclic capabilities.
Furthermore, battery technology suffers
from degraded performance at low temperatures.
Today, heavy transportation application
engineers are considering alternative
energy storage technology - the ultracapacitor.
Ultracapacitors, or doublelayer
capacitors, provide high charge
acceptance, high-efficiency, high cycling
stability, and excellent low-temperature
performance.
Ultracapacitors are therefore the
perfect component to store the heavy
transportation vehicle’s kinetic energy
during frequent braking events. In comparison
to battery chemical reaction,
energy storage in ultracapacitors is
based on an electrostatic reaction with
an extremely short time constant. For
an ultracapacitor, the energy storage
begins as soon as electrons are available.
During the acceleration phase of
the vehicle, the previously stored energy
can be re-injected into the application
thereby avoiding important absorp-
tion in network primary energy. Due to
the extremely low internal resistance of
ultracapacitors, the losses are reduced
to a minimum and the energy transfer
efficiency is maximized. Furthermore,
ultracapacitors can be cycled more
than 1 million times without experiencing
substantial performance degradation.
Additionally, ultracapacitors are
environmentally friendly because they
do not contain heavy metals and can
therefore be recycled easily. Finally, and
perhaps most importantly, ultracapacitors
offer more than 10 times the power
of batteries, which, when translated into
functional application characteristics,
Figure 3. Bombardier’s Mitrac Energy Saver trains use Ultracapacitor technology
for energy storage.
Power Systems Design October 2008
www.powersystemsdesign.com
Powering Freight & Transportation
Figure 4. Still’s Hybrid forklift equipped with Maxwell’s Ultracapacitors modules.
provides higher performance in terms
of acceleration of a vehicle, an essential
goal of such applications.
Ultracapacitors for Heavy Transportation
Applications
Heavy transportation vehicles, such as
trains trams and metros, place particular
demands on energy storage devices.
Such devices must be very robust and
reliable displaying both long operational
lifetimes and low maintenance requirements.
Further, the devices must operate
efficiently under harsh conditions
including handling high peak currents,
high duty cycle and frequent deep discharging.
Maxwell Technologies, has
addressed these issues with its BOOST-
CAP ® HTM125 module for ultracapacitor-based
braking energy recuperation
and torque assist systems in transportation
applications. Operating at 125V, the
new module can store more energy per
unit volume, deliver more power per unit
volume and weight and perform longer
than any other commercially available
ultracapacitor solution.
The HTM125 module is based on
Maxwell’s MC power cell, rated at 3000
Farads, which individually has a very low
internal resistance, resulting in excellent
efficiency during charging and discharging.
Up to 12 modules may be linked in
series to deliver as much as 1500V per
system. One key factor in the energy
storage systems is the thermal management.
Using Maxwell's ultracapacitor
modules, which incorporate efficient
cooling systems, allows higher continuous
currents up to 150A, and 750A as
a peak (750A during 1 second @ 10%
duty cycle), without compromising the
reliability.
Ultracapacitor products have been
fully tested and qualified in light rail
applications over many years. As an
example, Bombardier's LRV (Light Rail
Vehicle) prototype has been in passenger
operation since 2003 in Germany
and has recorded energy savings up to
30% at around 300,000 load cycles per
year. This success has now resulted in
Bombardier delivering Mitrac Energy
Saver trains utilizing ultracapacitor technology
for energy storage for operation
in the city of Heidelberg.
Ultracapacitors for Heavy-Duty
Equipment
In the lifting, hoisting, and excavating
equipment markets, typical characteristics
of the energy storage demands
include deep discharge cycling coupled
with high duty cycle requirements.
Cost is also a significant factor
in the implementation of
an energy storage option. In
heavy duty equipments, the
cost of the unit is outweighed
by the durability, reliability and
productivity factors. The initial
cost of equipment is extremely
high and this means that an
elevated initial investment cost
is returned faster for a higher
performance, reliable and durable
system.
Maxwell’s heavy duty
equipment solutions are the
most flexible energy storage
solution to power cranes,
straddle-carriers, RTG, stackers,
forklift, utility trucks, and
other earth moving and mining
equipments. With the help of
the company’s ultracapacitor
products, harbor crane
manufacturers are providing
innovative solutions to port
authorities delivering savings
of up to 30% on diesel consumption
realized through both braking energy
recovery and downsizing of diesel
engines. The substantial reduction in
terms of CO 2 emissions is also a significant
advantage for the harbor's authorities
in today’s climate where global
warming and levels of gas emissions
are becoming an increasingly greater
concern.
In lifting applications, studies have
shown that new generations of forklifts
equipped with Maxwell's ultracapacitor
products can increase the autonomy
and life of the equipment’s battery system
by more than 25%, thereby reducing
the cost of downtime and maintenance.
The time for efficient and environmentally
friendly energy storage and management
has come and Maxwell’s
ultracapacitor solutions have proven
themselves to fulfil this requirement.
These solutions are an essential part
in today’s innovative, efficient hybrid
system for public transportation and
heavy industrial applications allowing an
increase in power efficiency and a reduction
in fuel consumption and global
CO2 emissions.
www.maxwell.com
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