Environmental Engineering Reference
In-Depth Information
5.5.1.1 Pumped storage
The most widely established large-scale form of energy storage is hydroelectric
pumped storage (see Section 5.2). Typically, such plant operates on a diurnal basis -
charging at night during periods of low demand (and low priced energy) and
discharging during times of high or peak demand. A pumped storage plant may have
the capacity for 4-8 hours of peak generation with 1-2 hours of reserve, although in
some cases the discharge time can extend to a few days. Round-trip efficiency is
typically around 75 per cent. Worldwide capacity is almost 100 GW, with facilities
ranging up to 2,000 MW. The high construction costs, long development times and
environmental considerations (most feasible locations are already being exploited)
suggest that future growth in this area will be limited. Traditionally, pumped storage
is utilised for energy management and the provision of standing reserve, but more
recent installations possess the ability to provide frequency support and operate at
partial capacity (Donalek, 2003).
Hydroelectric plant typically have fast ramp-up and ramp-down rates, pro-
viding strong regulating capabilities, and their marginal generation cost is close to
zero. In many countries, a natural synergy exists between hydroelectric generation/
pumped storage and wind power. Clearly, if hydro generation is being replaced by
wind energy then emission levels will not be directly affected, but the hydro energy
can be transformed into potential energy stored for later use. As an example, during
periods of high wind power production, network congestion can occur in both
Sweden and Norway. The existing hydroelectric plant can reduce their output,
using the reservoirs as storage, to avoid wind energy curtailment (Tande and
Vogstad, 1999; Matevosyan and S ¨der, 2003). Similarly, in Portugal, most of the
wind farms are located in the north of the country, close to existing hydroelectric
plant (Pe¸as Lopes, 2005). However, the major load centres of Lisbon and Porto lie
to the south, potentially leading to future congestion problems in the transmission
network. A critical concern for the interconnected Iberian system is that a network
disturbance may cause a sudden loss of wind generation, leading to an influx of
power from neighbouring regions and an overload of the limited interconnection
capacity between Portugal and Spain, and between Spain and France. The large
differential in payment for wind energy between valley hours and off-valley hours
in Portugal does suggest, however, that a pumped storage arrangement could
become economically viable (Castronuovo and Pe¸as Lopes, 2004). On a much
smaller scale, pumped storage has also been proposed in the Canary Islands to
mitigate wind variability using existing water reservoirs (Bueno and Carta, 2006).
5.5.1.2 Secondary batteries
Rechargeable lead-acid and nickel-cadmium batteries have been used widely by
utilities for small-scale backup, load levelling, etc. The largest (nickel-cadmium)
battery installation is a 45 MW, 10 MWh installation in Fairbanks, Alaska built in
2003, and designed to provide a guaranteed 27 MW for at least 15 minutes fol-
lowing local power outages. For similar reasons, the largest (20 MW, 14 MWh)
lead-acid system was installed by the Puerto Rico Electric Power Authority in
1994, and later repowered in 2004. However, given the fairly toxic nature of the
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