Wind energy storage technologies - Wind Power Generation and Wind Turbine Design - page 702

6 Comparison of energy storage technologies
To begin a brief comparison of the storage technologies within each category is
discussed. These include: large power and storage capacities (PHES, UPHES,
CAES); medium power and storage capacities (BES, FBES); large power or stor-
age capacities (SCES, FES, SMES) energy storage systems (HESS, TESS, EVs).
This is followed by an overall comparison of all the storage technologies.
6.1 Large power and energy capacities
The only devices capable of large power (>50 MW) and energy capacities (>100
MWh) are PHES, UPHES and CAES.
New PHES facilities are unlikely to be built as upgrades continue to prove suc-
cessful. Once upgrades have been completed on existing PHES facilities, like all
large-scale energy storage technologies the potential for PHES will depend heav-
ily on the availability of suitable sites. It is widely believed that there are a limited
number of suitable sites available for PHES. However, recent studies completed
have illustrated the potential for seawater PHES [6, 34] as well as the potential for
many more freshwater PHES sites than originally anticipated [35]. Therefore, if
results continue in this fashion, PHES may only be constrained by economics and
not technical feasibility, indicating that it could become a very important technol-
ogy as fuel prices continue to rise in the future.
In theory UPHES could be a major contender for the future as it operates under
the same operating principals as PHES: therefore, almost all of the technology
required to construct such a facility is already available and mature. In addition,
sites for UPHES will not be located in mountainous, isolated regions where con-
struction is diffi cult and expensive. However, UPHES will still have unique site
constraints of its own as it will require a suitable underground reservoir. Until such
time that an extensive investigation is completed analysing the availability of such
reservoirs, the future of UPHES will be uncertain.
Finally, the attractiveness of CAES depends on your opinion regarding the
availability of gas and once again, the potential for suitable locations. It is a fl exi-
ble, reliable, and effi cient technology but it still needs gas to operate and an under-
ground storage reservoir for the compressed air. Consequently, like PHES and
UPHES, the potential for CAES will depend heavily on the availability of suitable
locations. However, in addition the future of CAES may be decided based on the
future availability of gas within an energy system. CAES by its nature is capital
intensive and hence a long-term commitment. Therefore, if the energy system con-
sidering CAES has long-term ambitions to eliminate a dependence on gas, then
this should be accounted for when analysing the feasibility of CAES.
In conclusion, it is evident that large-scale energy storage facilities all share one
key issue: the availability of suitable locations. However, based on recent studies,
suitable sites for PHES may be more prominent than originally anticipated. There-
fore, until such time that the other large-scale storage technologies can display a
similar potential for new facilities, it is likely that PHES will continue to lead the
way in this category.