Environmental Engineering Reference
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storage of wind is also possible, it would require much larger storage
volumes [30]. While typical capacity factors for wind farms are approxi-
mately 30 to 40% [31], wind/CAES systems can achieve capacity factors
of 80 to 90% typical of baseload plants [10]. Therefore, the coupling of
wind to energy storage enhances utilization of both existing transmis-
sion lines and dedicated new lines for wind. This can alleviate transmis-
sion bottlenecks and minimize the needs for transmission additions and
upgrades. The cited report indicates that removal of bulk storage (pumped
hydroelectric storage in this case) increases integration costs for wind by
approximately 50% for a wind penetration level of 10%. Also, doubling
of storage capacity lowered integration cost by ~$1.34/MWh in the 20%
penetration case.
The Greenblatt (2005) estimate is based on the assumption that various
land use constraints limit the technical potential for wind to what can be
produced on 50% of the land on which class 4+ wind resources are avail-
able. The technical wind power potential at the global level is also huge.
Considering only class 4+ winds exploited on 50% of the land on which these
resources are available, as in the North American case, Greenblatt (2007) esti-
mated that the global technical wind energy potential is 185,000 TWh/year
on land and 49,400 TWh/year offshore. For comparison, the global electricity
generation rate in 2004 was 17,400 TWh/year.
Capacity factor in this case is on the basis of a constant demand level. The
rated capacity of the wind park will be “oversized” relative to this demand
level and the CAES turbo expander capacity matched to it such that excess
wind can be stored to balance subsequent shortfalls. While it is possible to
produce constant output (i.e., 100% capacity factor) from a wind/CAES plant,
significantly larger storage would be required.
Where transmission capacity is limited, it will be advantageous to site the
storage reservoir and wind turbine array as closely as possible to exploit
the benefits described above. If this is not possible, there is no need to
co-locate the storage system and wind array. Independently siting these com-
ponents would allow added flexibility for simultaneously matching facilities
to the ideal wind resource, storage reservoir geology, and the required natu-
ral gas supplies.
SystemOperation
CAES systems operate in much the same way as conventional gas turbines
except that compression and expansion operations occur independently
and at different times (Figure 5.2). Because compression energy is supplied
separately, the full output of the turbine can be used to generate electric-
ity during expansion, whereas conventional gas turbines typically use
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