IEEE Electrification Magazine - September 2015 - 64

VIEWPOINT

Energy Storage
in the Future Grid
By Benjamin Kroposki

NE OF THE MAIN CHALlenges with the electric
power system today is that
it is relatively difficult and expensive
to store electricity. Electricity is best
used immediately after it has been
generated and transmitted to the
loads. In the current power system,
energy storage is typically provided
on the primary fuel side of generation. This could be in the form of uranium fuel rods for nuclear plants,
coal piles for coal plants, underground or tank storage for natural
gas and oil, or water reservoirs for
hydrostations.
Once these primary energy sources are converted into electricity, the
main technologies for electricity storage used in the grid today include
pumped hydro and battery energy
storage. Currently, the United States
has about 25 GW (approximately 2.3%
of total electric production capacity)
of electricity storage capacity, 95% of
which is pumped hydro. Pumped
hydro is one of the best systems for
large-scale energy storage (typically
1-3 GW) because of the physical
amount of storage it can provide, but
it has siting limitations. Stationary
batteries are very flexible energy-storage solutions and can be deployed in
various scales, with most being under
30 MW. Current research on energy
storage focuses on developing costcompetitive energy-storage technologies, validated reliability and safety,

Digital Object Identifier 10.1109/MELE.2015.2447994
Date of publication: 1 September 2015

an equitable regulatory environment,
and industry acceptance.

A Look at the Future Grid
The future grid will contain increasing amounts of variable generation
from wind and solar energies. These
sources produce power based on the
availability of solar and wind
resources. Integration of these technologies at a significant scale will
require a much more flexible grid
that can respond quickly to the variability and uncertainty of the generation source. This will require a new
operational paradigm, where storage
plays an increasing role and loads are
responsive and follow available generation. Energy storage can improve
the operating capabilities of the grid
and address issues with the timing,
transmission, and dispatch of electricity. It can also regulate the quality
and reliability of the power generated by traditional and variable sources of power.
Another possibility is the use of
plug-in electric vehicles (PEVs) to provide a variety of grid services. PEVs
may prove to be very low-cost electricity-storage devices because the
majority of the capital investment in
the energy-storage sector is focused
on vehicle applications, which have
seen significant cost reductions. PEV
charging and discharging have been
identified as a possible balancing
resource that could be made available
to grid operators. This could represent
a low-cost, highly controllable, and
rapidly responding storage device

I E E E E l e c t r i f i c ati o n M agaz ine / SEPTEMBER 2015

located near load centers that could
be highly valuable to grid operators.
One challenge with traditional energy storage in a grid with significant
amounts of wind and solar is the total
amount of storage that may be needed
to not curtail the variable generation
and throw away free energy. Pumped
hydro is a good option for this largescale storage, but new sites are not being
developed as rapidly as the amount of
wind and solar that is coming online.
As we examine the role of energy
storage in the power system, we
must also be cognizant that there
may be more cost-effective methods
to provide similar types of services
than what classical electricity storage
can provide through the concepts of
energy-systems integration (ESI) and
virtual storage. ESI is the optimization of energy across multiple energy
domains and physical scales. This
includes ideas like using excess wind
energy to power electric boilers and
dump energy into district heating
systems. This type of ESI is currently
being used in Denmark to make the
best use of excess wind energy and
store this energy for future use.
Another example of ESI is the use of
excess wind and solar to produce
hydrogen via electrolysis. The hydrogen can then be used to fill fuel-cell
vehicles, run fuel cells for power
applications, or be combined with
carbon to create synthetic methane or
natural gas. This can then be stored in
existing natural gas pipelines and
(continued on page 62)

Table of Contents for the Digital Edition of IEEE Electrification Magazine - September 2015