This is called plucking the low hanging fruit. Battery tech has now
reached the point in which these types of fixes can be implemented.
This was a problem that was recognized in the late nineteenth century
and underscores just how slow progress can be.
We will be doing the same thing in our EVs were again it is all about
battery technology.
The really good news is that we are really getting there. A storage
build out along with smart power management will easily double the
output of our installed base.
A decade of energy investment is paying of handsomely.
Smart grid leads to
more efficient electric trains
By Brian Dodson
00:05 July 11, 2012
Electric commuter
trains, while quiet and fast, have one glaring inefficiency – when
they brake at a station, the energy of the moving train is lost, even
when the motors are electrically reversed. Capturing the electrical
energy generated during braking is simple, but efficiently
redistributing it through the power grid is not. The result, in too
many systems, is that the braking energy is simply wasted. Now an
energy storage project in Philadelphia aims to capture and
efficiently utilize that braking energy, providing a clear view into
the potential of the forthcoming smart grid.
In a conventional
electric train, the electrical energy generated while stopping is fed
immediately into the third rail (or the overhead power lines). The
problem is that the third rail has a very limited capacity for
absorbing a sudden flood of electrical energy. As a result, the
voltage of the third rail rises considerably. However, the third rail
voltage is controlled within narrow limits to avoid system
instabilities. If the voltage rises too much (as when slowing at a
passenger stop), the excess energy must be dissipated. The third rail
is then connected to a resistive load, and the braking energy is
converted into waste heat.
In essence, the power
grid of the electric train system does not have sufficient
capacitance to absorb the braking energy while staying within
acceptable voltage, frequency, and phase limits (these are AC
systems, so a bit more complicated than if the systems were DC). The
Southeastern Pennsylvania Transportation Authority (SEPTA) has
embarked on a pilot project to better absorb and reuse braking
energy. Their engineering studies showed that while practical
banks of ultracapacitors cannot provide sufficient additional
capacity, banks of lithium-ion batteries can. The power is not only
recovered efficiently, but is fed back into the regional power grid
rather than remaining confined within the commuter train's third rail
system.
The SEPTA pilot
project captures the braking energy of trains through a large scale
battery storage system. The braking energy is then fed into the
regional transmission organization, which coordinates movement of
wholesale electricity in 13 eastern states and the District of
Columbia, where it is sold to neighboring power grids in the
frequency regulation market.
The frequency
regulation market sells power from a local grid that is generating
too much power to a local grid which is not generating enough. This
is called frequency regulation because a generator that is overloaded
slows down, and an underloaded generator speeds up, while the entire
network of grids has to provide power at the same frequency and phase
to avoid hot and dead spots in the local grids.
SAFT Batteries Max20
containerized Li-ion battery bank (Photo: SAFT Batteries)
The SEPTA project
takes a different path. Located in a substation that serves five or
six stations on SEPTA's elevated train line, it senses when the track
voltage is too high (about 800 volts), and pulls energy from the
third rail, storing it in a large-scale lithium-ion battery (the
MAX20 Intensium Max containerized battery bank) from Saft Batteries.
The MAX20 can store and deliver power at a 1.5 MW rate, and has a
storage capacity of about 500 kWh – roughly equal to 280 Toyota
Prius battery packs. When the voltage of the third rail falls too
low, the battery pushes current into the third rail. This negative
feedback mechanism leads to a stable operating point for the smart
grid and efficient reuse of the braking energy.
The operating software
balances the simultaneous processes of regenerative capture,
regulation performance, and energy market participation by selecting
in which market to participate based upon market pricing, battery
state of charge, and availability of regenerative energy from the
trains.
“We are excited to
be a part of this groundbreaking achievement,” said Audrey
Zibelman, CEO and President of Viridity Energy, the designer of the
operating software. “In a smart grid world, two‐way digital
information exchange opens up new horizons. By harnessing the
regenerative braking power of the trains and empowering SEPTA to
become a virtual power generator that can provide valuable and
environmentally responsible service to the electric grid, we can
fulfill the promise of interconnected systems on the grid and behind
the meter responding dynamically to reliability and economic signals
to strengthen the grid.”
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