IEEE Electrification Magazine - September 2015 - 29

around 50-60%, with peak penetration approaching and, in
some instances, reaching 100%. Maintaining grid stability
despite the high level of renewable penetration is made
possible by intelligent deployment of storage. In these minigrid environments, storage is primarily used for frequency and
voltage stabilization and typically requires a combination of
flywheel and/or BESS, high-speed load control, and synchronous compensators to maintain grid stability.
Flywheels are particularly suited to rapidly counteracting
the frequency and voltage variations associated with renewable energy, maintaining power quality in instances of high
renewable penetration. Typically, they comprise a bearingsupported rotor (the flywheel) suspended in a vacuum
chamber. Electricity is stored in the form of kinetic energy
used to spin the rotor, and the kinetic energy can be quickly
converted back into electricity by slowing the spinning disk.

Attempts to maintain power quality in larger grids will
limit the ability to improve renewable penetration, without the proliferation of storage.

Further Reading
Electricity storage. [Online]. Available: https://www.sbc.slb.
com/SBCInstitute/Publications/ElectricityStorage.aspx
Australian PV installations since April 2001. [Online].
Available: http://pv-map.apvi.org.au/analyses
R. Khalilpour and A. Vassallo, "Leaving the grid: An ambition or a real choice?" Energy Policy, vol. 82, pp. 207-221,
July 2015.
B. Hredzak, V. G. Agelidis, and G. Demetriades, "Application
of explicit model predictive control to a hybrid battery-ultracapacitor power source," J. Power Sources, to be published.

Biographies
Case Study: King Island, Tasmania
King Island, off the northwest cost of Tasmania, sits in the
middle of the "roaring forties" and has a population of
around 1,500 people. The island's minigrid is supplied by a
combination of wind (two wind turbines producing
1,700 kW), solar PV (total capacity of 390 kW), and diesel/
biodiesel generators (Figure 8).
Storage is principally supplied by a hybrid lead-acid/
supercapacitor BESS supplying 3 MW of power and storing
1.6 MWh of usable energy. In fact, it was the largest battery
ever installed in Australia at the time. Originally, a VRB was
installed as the preferred BESS technology; however, due to
an operational event, the VRB was eventually decommissioned and replaced by the current lead-acid BESS. Graphite
heat block storage systems and flywheels also supplement
the BESS, and together this has allowed stability at an average of 50% renewable energy penetration on the island,
including instances of peak penetration reaching 100%.

Case Study: Coral Bay, Western Australia
Coral Bay is a small community on the remote northwest
coast of Western Australia, with a permanent population
of around 150 people. The town's minigrid is supplied by
three 225-kW wind turbines with a maximum output in
strong gusts of up to 400 kW. The output of the turbines
varies as the frequency varies, and this provides additional management challenges.
The wind turbines are supplemented by four 320-kW
low-load diesel generators running at 7%, which can start
and synchronize to the grid in approximately 10 s with the
aid of an 18 MW at +/- 500 kW flywheel storage unit,
which has been deployed to stabilize the grid. This has
resulted in stability at 93% renewable energy penetration
(see Figures 9 and 10).
Successful management of very high renewable penetration minigrids can provide a blueprint for higher penetrations in the big grid. However, applying city-level power
quality to remote communities is prohibitively expensive.

Anthony Vassallo (anthony.vassallo@sydney.edu.au) earned
his Ph.D. degree in chemistry from Macquarie University,
Australia. He is a past president of the Australian Institute of
Energy and coleader of the Clean Intelligent Energy Networks in the Faculty of Engineering at the University of Sydney, Australia. He has held the Delta Electricity Chair in Sustainable Energy Development, School of Chemical and Biomolecular Engineering, University of Sydney, since October
2008. He previously held the position of senior principal
research scientist with the Commonwealth Scientific and
Industrial Research Organization, followed by a period of
consultancy to industry and government in the field of sustainable energy technology.
Phil Maker is a senior control engineer at Powercorp,
Darwin, Australia. He has extensive field experience with
high renewable penetration minigrids supplemented by
energy storage. He has been involved with developing,
testing, and commissioning a variety of systems, including life-critical systems.
Tim Dixon earned his bachelor of arts degree (honors)
from the University of Sydney, Australia, where he is currently studying for his master of commerce (international
business) degree. He is with the Australian Energy Research
Institute (AERI) at the University of New South Wales, Sydney. He is responsible for AERI's strategic planning and business development and has previously held positions with
the New South Wales government, with a focus on strategic
policy and international business activities.
Vassilios G. Agelidis is the director of the Australian
Energy Research Institute and a professor of power engineering at the School of Electrical Engineering and Telecommunications at the University of New South Wales,
Australia. He is one of Australia's leading authorities on
efficient electricity grid technologies and power engineering. He has extensive research experience in the field of
smarter grid infrastructure and sustainable energy systems incorporating solar and wind energy sources.

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

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