Environmental Engineering Reference
In-Depth Information
4.1.3 Disadvantages of PHES
A major disadvantage of PHES facility is its dependence on specifi c geological
formations, because two large reservoirs with a suffi cient hydraulic head between
them must be located within close proximity to build a PHES system. As well as
being rare, these geological formations normally exist in remote locations such
as mountains, where construction is diffi cult and the power grid is not present,
although large wind farm sites may provide a useful modern alternative. Finally,
in order to make a PHES plant viable it must be constructed on a large scale.
Although the cost per kWh of storage is relatively economical in comparison to
other techniques, this results in a very high initial construction cost for the facility,
therefore deterring investment in PHES, e.g. Bath County storage facility in the
United States which has a power capacity of 2100 MW cost $1.7 billion in 1985.
4.1.4 Future of PHES
Currently, a lot of work is being carried out to upgrade old PHES facilities with
new equipment such as variable speed devices which can increase capacity by
15-20% and effi ciency by 5-10%. This is more desirable as energy storage capac-
ity can be added without the high initial construction costs. Prospects of building
new facilities are limited due to the “high development costs, long lead times and
design limitations” [3]. However, a new concept that is showing a lot of theoretical
potential is UPHES, discussed in the next section.
4.2 Underground pumped-hydroelectric energy storage
An UPHES facility has the same operating principle as PHES system: two res-
ervoirs with a large hydraulic head between them. The only major difference
between the two designs is the locations of their respective reservoirs. In conven-
tional PHES, suitable geological formations must be identifi ed to build the facil-
ity, as discussed earlier (see Section 5.1). However, UPHES facilities have been
designed with the upper reservoir at ground level and the lower reservoir deep
below the earth's surface. The depth depends on the amount of hydraulic head
required for the specifi c application (see Fig. 4).
4.2.1 Applications of UPHES
UPHES can provide the same services as PHES: load levelling, frequency regu-
lation, and peak generation. However, as UPHES does not need to be built at a
suitable geological formation, it can be constructed anywhere with an area large
enough for the upper reservoir. Consequently, it can be placed in ideal locations to
function with wind farms, the power grid, specifi c areas of electrical irregularities,
etc. The fl exibility of UPHES makes it a more attractive option for energy storage
than conventional PHES, but its technical immaturity needs to be addressed.
4.2.2 Cost of UPHES
The capital cost of UPHES is the deciding factor for its future. As it operates in the
same way as PHES, it is a very reliable and cost-effective storage technique with
Search WWH ::
Custom Search