Wind energy storage technologies - Wind Power Generation and Wind Turbine Design - page 700

Energy devices required for load management must be in the 1-100+ MW range
as well as possessing fast response characteristics.
5.2 Spinning reserve
Spinning reserve is classifi ed under two categories:
1. Extremely fast response spinning reserve : power capacity that is kept in the
state of 'hot-stand-by'. As a result it is capable of responding to network
abnormalities quickly.
2. Conventional spinning reserve : power capacity that requires a slower response.
Energy storage devices used for spinning reserve usually require power ratings of
10-400 MW and are required between 20 and 50 times per year.
5.3 Transmission and distribution stabilization
Energy storage devices are required to stabilise the system after a fault occurs on
the network by absorbing or delivering power to generators when needed to keep
them turning at the same speed. These faults induce phase angle, voltage and fre-
quency irregularities that are corrected by the storage device. Consequently, fast
response and very high power ratings (1-10 MW) are essential.
5.4 Transmission upgrade deferral
Transmission line upgrades are usually separated by decades and must be built to
accommodate likely load and generating expansions. Consequently, energy storage
devices are used instead of upgrading the transmission line until such time that it
becomes economical to do so. Typically, transmission lines must be built to handle
the maximum load required and hence it is only partially loaded for the majority
of each day. Therefore, by installing a storage device, the power across the trans-
mission line can be maintained constant even during periods of variable supply
and demand. Then when demand increases, the storage device is discharged pre-
venting the need for extra capacity on the transmission line to supply the required
power. Therefore, upgrades in transmission line capacities can be postponed. Stor-
age devices for this application must have a power capacity of kW to several hun-
dreds of megawatts and a storage capacity of 1-3 h. Currently the most common
alternative is portable generators; with diesel and fossil fuel power generators as
long-term solutions and biodiesel generators as a short-term solution.
5.5 Peak generation
Energy storage devices can be charged during off-peak hours and then used to
provide electricity when it is the most expensive, during short peak production
periods.