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A handful of other energy storage strategies have likewise been around
for several years but have thus far proven to be limited in their usefulness.
Compressed air systems, which have existed for decades but are relatively
few in number, fall into this category of storage strategies. Compressed
air systems involve the use of excess electricity to compress and pump
air into sealed underground reservoirs. These systems can then produce
electricity at a later time by slowly releasing the compressed air to rotate
systems are relatively energy-inefficient and are usable only in areas with
suitable geographic features. These and other limitations prevent them from
contributing in a major way to energy storage challenges in many regions.
Spinning flywheel technologies, which use devices similar to a spinning
top toy to store energy, have also existed for many years. Because flywheels
are subject to fewer geographic constraints than pumped storage facilities
or compressed air systems and are usable on a much smaller scale, they
have shown some promise as a potentially valuable energy storage strategy
in certain contexts. However, because they are presently capable of storing
energy for only relatively short periods of time, flywheels are unlikely to
ever become a dominant means of energy storage.
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Fortunately, new energy storage technologies are beginning to emerge
that provide reasons to hope for real progress on this front. For instance,
a molten salt energy storage system is helping to store energy generated
at the Solana project—a large concentrating solar plant near Gila Bend,
the plant reflect sunlight to heat large tanks of molten salt. These molten
salt tanks are specially designed to retain much of their heat, enabling them
to continue producing steam-generated electricity for several hours after
the sun has set. Although these innovations are only available in certain
settings, they have the potential to reduce the intermittency of power
supplies at some utility-scale solar energy projects.
“Smart” battery system technologies are another bright spot in the energy
storage realm. These systems seek to smooth out the intermittency of
distributed solar energy systems or to reduce the variability of an electricity
customer's demand. Researchers are increasingly exploring ways to better
integrate energy storage systems with solar arrays so that the arrays can
companies are beginning to market distributed energy storage systems to
businesses operating in areas where electricity prices fluctuate throughout
the day, surging to expensive levels during periods of peak demand. Energy
storage systems can allow businesses in these areas to purchase less power
during peak use periods and thereby reduce their electricity bills.
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Utility mandates for energy storage—policies patterned after renewable
portfolio standards that effectively require utilities to invest in energy storage
systems—have the potential to be a valuable tool for promoting advance-
ments in energy storage technologies. In late 2013, California became the
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