Environmental Engineering Reference
In-Depth Information
microgrid formation; in addition, customer storage can be used to improve reliability or
save money.
With high penetration of variable resources like wind and solar, electricity storage
technologies could help to enhance the flexibility, efficiency, and resilience of the grid.
Energy storage is particularly valuable for leveling the costs of electricity generation
because the cost of producing electricity varies considerably based on the time of day
and the level of electricity demand. With storage, energy can be stored during low-cost
times of day and then used to generate electricity during more expensive, peak-demand
times. Storage can also help maintain power quality on the grid by providing ancillary
services to ensure power quality and system function. The expansion of energy storage
could minimize the need to build additional power plants and additional transmission lines
to meet infrequent peak demand (California PUC
2010
).
Pumped hydro is one important energy storage technology that can be applied at a
large scale (100s to 1000s of MWs) and can be released quickly in response to a sudden
demand for more power. Pumped hydro relies on low-cost electricity to pump water from a
low-level reservoir to a higher-elevation reservoir. Once the water is at the higher-elevation
reservoir it can generate electricity on demand by releasing the water back to the
lower-level reservoir, letting gravity power drive the turbine to generate electricity. More
than 127,000 MW of pumped hydro is in operation today globally, with over 20,000 MW
in the United States.
Another approach to electricity storage that uses similar logic is compressed air energy
storage, which is often used with natural gas-fired turbines. Low-cost electricity can be
used to compress air to a high-pressure underground media (porous rock formations,
depleted gas/oil fields, or caverns). When the pressurized air is released it reduces the
amount of natural gas required to generate electricity. There are just a handful of
compressed air energy storage plants in operation today, in Alabama, Texas, and Germany.
Others have been proposed, but the relatively high costs and specific geological
requirements have made more widespread use difficult (St. John
2013
).
Battery technology is evolving rapidly and has great potential for energy storage in
various types of applications. Several different large-scale rechargeable batteries are
currently available, including sodium sulfur,lithium ion,andflow batteries. Energystorage
batteries strive to scale up the same mechanisms used by rechargeable batteries used in
cars, computers, and other applications, but remain costly.
Perhapsthemosttraditional typeofenergystoragetechnologyistheflywheel,amassive
spinning disk on a metal shaft. Electricity is used to spin the disk, and braking of the
rotating disk powers an electric motor to retrieve the stored energy. The size of the disk
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