IEEE Power & Energy Magazine - May/June 2014 - 32

figure 5. GE/GNB and Metlatkla Power and Light battery
energy storage system in Alaska. (Reprinted with permission from George Hunt, GNB/Exide.)

transmission and distribution assets due to localized ev
concentration or loading factors not directly related to just
peak demand, such as limiting transformer cool-down during off-peak periods. replacing overloaded transformers,
reconfiguring heavily loaded distribution circuits, and building new substations may be needed in areas that experience
sudden increases in ev charging loads. these system modifications and equipment additions/upgrades are expected to
be manageable and reasonably small relative to the cost of
the evs and the charging infrastructure if charging patterns
are managed. smart vehicle charging strategies will be critical to avoid potentially dramatic increases in generation,
transmission, and distribution capacity requirements.

Energy Storage
the grid is the ultimate "just-in-time" system, instantaneously serving customer load with generation that is precisely dispatched and controlled to match the load. energy
storage presents the capability to relax this constraint. historically, the power system has been designed and controlled
to manage variability in load by increasing or decreasing
the output of generation. Wind and solar power exacerbate
the variable power needed from the rest of the generation.
however, sudies by the authors suggest that the variability
of wind and solar power, when more than 30% of the annual
energy is generated by these resources, can be managed by
the grid. Generally, the significant wind and solar variability smoothing effect observed over large areas (similar to
that of the load smoothing effect of a neighborhood relative
to that of a single home) does not necessitate the need for
energy storage. however, the grid is demanding more flexibility. this is manifesting in a greater need for frequency
regulation and reserves. Wind turbine manufacturers have
responded to this trend and advanced wind turbine technology to better manage variations in wind power output. For
example, Ge is currently offering a hybrid wind turbine with
integrated battery energy storage that can competitively selfsupply incremental ancillary services, given suitable power
market structures.
While storage has not yet found widespread use in the
grid, a long list of potential applications for storage has been
cited. applications that require substantial energy ratings
range from capturing lower cost energy to displace higher
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cost energy at a later time, price arbitrage, or shifting energy
from one time to another to avoid overloading equipment.
in general, these applications do not currently offer strong
value propositions as the cost of energy-storage technologies
is high relative to energy prices and conventional approaches
for managing overloaded equipment. it is the applications
that demand the sudden injection or removal of energy of
short durations that seem to offer the greatest value. niche
applications already exist, and more are emerging. isolated
systems with very high electricity costs also tend to have
relatively high regulation and reserve requirements. meeting
some of these ancillary service requirements with energy
storage rather than high-cost fossil fuel generation has the
potential to be highly economical. For utilities operating in
regions of the united states where there are no organized
power markets, the evaluation of energy storage versus other
sources of operational flexibility needs to be done on a costavoidance basis, rather than from ancillary service market
revenues. For example, in the 1990s, Ge worked with GnB/
exide technologies to build a battery storage system in metlakatla, alaska, to reduce the use of expensive diesel-fired
generation. the system is shown in Figure 5. the roughly
us$2 million battery system reduced the diesel fuel bill by
more than us$6 million over its 12 years of operation.
even in large grids, storage can be an alternative provider
of regulation. the application of storage in this case is not
driven by necessity but must be economically competitive
with generation flexibility. Power market prices for frequency regulation vary daily and seasonally. During periods
of scarcity, prices can be high. the cost of storage for frequency regulation is approaching the average current prices
for regulation in some energy markets. it remains to be seen
if energy storage, without subsidies, can be truly competitive
in the regulation application.
more applications are also being observed. urban centers experiencing line or transformer overloads, with no
room available for new equipment, may benefit from storage
located closer to the loads to avoid expanding the substation
or reconfiguring the lines. in september 2013, the california Public utilities commission issued a proposed Decision adopting energy storage Procurement Framework and
Design Program to address the policies and mechanisms for
the procurement of electric energy storage pursuant to california assembly Bill (aB) 2514. one of the objectives is to
employ storage technology to help maximize existing generation and transmission investment and operation, integrate
renewables, and minimize GhG emissions. the framework
sets forth the storage targets for the investor-owned utilities
and the procurement requirements for other load-serving
entities in california, the procurement mechanisms, and the
program evaluation criteria.
ultimately, storage is another resource that can provide
the grid with flexibility. as the grid evolves, flexibility
requirements are likely to increase, and traditional sources
of flexibility may be displaced. as the cost of storage
may/june 2014

Table of Contents for the Digital Edition of IEEE Power & Energy Magazine - May/June 2014