IEEE Electrification Magazine - September 2015 - 27

financial viability is currently very low. However, the
intelligent use of multiple storage systems in the 10-50MWh range can be effectively used to reduce or eliminate network congestion and may allow deferral of significant capital expenditure such as expensive line
upgrades and augmentation. These smaller-scale storage
systems may be modular and of the same type, of different sizes and technologies, centrally located, or distributed throughout the network.
Regardless of the type and location of the storage assets
utilized, it is important that they are used only when it is economically beneficial to do so. The average wholesale value of
electricity can be an order of magnitude lower than peak
retail tariffs, so securing sufficient revenue to cover the cost
of storage assets can be challenging.
However, intelligent dispatch of storage based on real-time
price signals can allow storage assets to dispatch energy only
when the price in the NEM is above the
life-of-asset price of electricity generated by the asset. That is, the price
received for electricity must be greater
than the depreciation of averaged
value, based on reduction in life of the
asset incurred by a dispatch event.

Figure 6. Equipment for the hybrid energy-storage research project at
the Australian Energy Research Institute, University of New South
Wales, Australia. (Photo courtesy of T. Dixon.)

AEMO/Dispatch Engine
Dispatch Target:
∗

PDT

Applying Hybrid Energy
Storage Solutions Through
Intelligent Control
Just as electricity from storage must
be dispatched only when market
conditions make it profitable to do
this, the type and characteristics of
storage assets must be taken into
account and matched to demand to
prolong the life of those assets
(Figure 6). It is commonly accepted
that there is no one generation technology suited to all applications, and
so it is with storage technologies. For
example, the lithium-ion (Li-ion)
battery is relatively cheap to produce, and its characteristics are well
known and largely predictable given
it is a mature technology. However,
Li-ion performance is sensitive to
temperature, and repeated deep discharging can significantly reduce the
number of cycles the battery can
withstand, reducing the overall life
very quickly. Conversely, supercapacitors are able to quickly and
deeply charge and discharge without
suffering the ill effects experienced
by lithium-based batteries. On the
downside, they are unable to provide
a stable power supply over a long

Power Availability Offers
Based on Day-Ahead
and Intra-Hour Forecast

PV Power Plant Control Level
PˆPV

References:
∗

Measurements:
SoCVRB, SoCSCB

∗

PPV, PVRB,
∗

PSCB,

Converters' Control Level
References:
∗

∗

Measurements:
IVRB, VVRB, ISCB,
VSCB, VDC

∗

IPV, IG, IVRB,
∗

∗

VVRB, ISCB,VSCB,

Grid

PV Array

+
PV Power Plant
VRB

SCB

Figure 7. The topology of a hybrid energy-storage and control system in combination with
a solar PV array.

IEEE Electrific ation Magazine / S EP T EM BE R 2 0 1 5

Table of Contents for the Digital Edition of IEEE Electrification Magazine - September 2015