Environmental Engineering Reference
In-Depth Information
Background
Compressed air energy storage (CAES) is a low cost technology for storing
large quantities of electrical energy in the form of high-pressure air. It is
one of the few energy storage technologies suitable for long duration (tens
of hours), utility scale (hundreds to thousands of megawatts) applications.
Several other energy storage technologies such as flywheels and ultraca-
pacitors can provide short duration services related to power quality and
stabilization but are not cost effective options for load shifting and wind
generation support [1,2].
The two principal technologies capable of delivering several hours of
output at a plant-level output scale at attractive system costs are CAES and
pumped hydroelectric storage (PHES) [3-8]. Although some emerging bat-
tery technologies may provide wind-balancing services as well, typical
system capacities and storage sizes are an order of magnitude smaller than
CAES and PHES systems (~10 MW, <10 hours) with significantly higher capi-
tal costs.
PHES does not require fuel combustion and has more field implementa-
tion than CAES, but is economically viable only at sites where reservoirs
at differential elevations are available or can be constructed at manageable
cost. Furthermore, the environmental impacts of large-scale PHES facilities
are becoming more complex, especially where preexisting reservoirs are not
available and sites with large, natural reservoirs at large differential eleva-
tions where environmentally benign, inexpensive PHES facilities can be
built are increasingly rare.
In contrast, CAES can use a broad range of reservoirs for air storage and
has a more modest surface footprint, giving it greater siting flexibility rela-
tive to PHES. High pressure air can be stored in surface piping, but for large-
scale applications, developing storage reservoirs in underground geologic
formations such as solution-mined salt, saline aquifer, abandoned mine, and
mined hard rock are typically more cost effective. The widespread availabil-
ity of geologies suitable for CAES in the continental United States suggests
that this technology faces far fewer siting constraints than PHES—especially
important for deploying CAES for wind balancing.
One of the main applications for CAES is for the storage of wind energy
during times of transmission curtailment and generation onto the grid dur-
ing shortfalls in wind output. Wind balancing requires large-scale, long
duration storage, fast output response times, and siting availability in wind-
rich regions. Prior studies indicate that suitable CAES geologies are widely
available in the wind-rich Great Plains of the U.S. Furthermore, CAES is able
to ramp output quickly and operate efficiently under partial load condi-
tions, making it suitable for balancing fluctuations in wind energy output.
Finally, the low greenhouse gas (GHG) emissions rate of CAES makes it a
good candidate for balancing wind in a carbon constrained world. Several
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