Environmental Engineering Reference
In-Depth Information
3.8 Energy Storage
3.8.1 Introduction
Energy storage devices capable of being topped up during periods of low demand and drained
during periods of high demand would aid enormously the frequency control problem. Pumped
storage schemes are classical but very expensive examples of such devices. Storage devices,
if suitably cheap and effi cient could be of benefi t to the integration of high levels of RE source
penetration, although if such devices were to be present in a power system they would be of
operational benefi t to traditional energy sources as well.
Income may be derived from an energy store by charging it when the local electricity value
is low and discharging it when the value is high, but the level of income critically depends
on the round trip effi ciency and how this compares with the system electricity cost differen-
tial. If, at times, the grid at the point of connection of the embedded renewable generation
cannot absorb the entire output of the generator a local storage device could prevent curtail-
ment. Whether this is an economically viable strategy depends, among other things, on the
capital cost, the round trip effi ciency and the operation and maintenance costs of the device.
Another source of income from such devices results from the supply of ancillary services,
for example reactive power, voltage and frequency control, and emergency power during a
power outage. It is clear that assessing the economic benefi t of storage is not a simple matter
and that if renewable energy sources have low capital costs it may be more effective to curtail
output whenever a surplus exists, rather than attempt to store the surplus.
3.8.2 Storage Devices
As mentioned above, storage technologies depending on their characteristics may aid the
integration of renewables, and they could assist the operation/control of a power system over
the range of timescales discussed in Section 3.4.6. Conventional technologies include:
1 .
The large hydro
is an 'old' renewable but whenever available could facilitate the take-up
of variable renewable sources by suitable timing of water release.
2 .
Compressed air storage
has been talked about for some time and involves the storage
of compressed air in disused underground cavities, e.g. exhausted salt mines. At present
it is uncertain how economically and technologically viable this technology is.
3 .
Pumped hydro
is an excellent energy storage technique as far as the maturity of technol-
ogy is concerned, but few attractive sites exist and upfront capital costs are very high.
Less conventional technologies include:
4 .
Hydrogen
can be produced by the electrolysis of water using energy from a renewable
resource. It can then be 'burnt'
2
as fuel to generate electricity. Alternatively it can be
piped as a gas or liquid to consumers to be used locally providing both electricity and
heating in a total energy scheme, or it can be used for transport. The combustion of
2
Literally burnt or oxidized in a fuel cell.
