IEEE Power & Energy Magazine - July/August 2021 - 44

Thirty-four Bruny Island households received
a subsidy to buy a solar battery and an EMS
that supports time-of-use shifting.
Finally, optimal distributed coordination and appropriate
rewards may not be enough: prosumers need to be willing to
participate. Hence, it is essential to understand how prosumers
respond to the idea of providing network support, the
technology, and the rewards, which is why the project had a
dedicated social science team. This group spent many hours
interviewing householders about their experience and gaining
insight into issues that might be encountered with DER
programs in the future (Figure 3).
Residential EMS
Before we could start coordinating batteries, we first needed
to get some batteries into the hands of customers. Approximately
15% of customers had residential solar systems, but
there were no existing battery systems on the island. Similarly,
while some of the local electricians had experience with offgrid
battery installs, few were familiar with the new generation
of grid- and Internet-connected batteries. To stir interest
in the various stakeholders and offset the battery capital costs,
which were still out of reach for most consumers, the project
offered customers a subsidy for new solar battery systems.
Customers selected their installer and through them had
a choice of off-the-shelf hardware (battery, PV panels, and
inverters) and the overall system design. The system cost
was subsidized based on the maximum discharge capacity
of the battery at AU$3,200/kW, with a minimum customer
contribution of AU$2,000 and maximum subsidy of
AU$17,200. The available funding allowed for 34 customers
to receive subsidies and participate in the trials, where
most elected for 5-kW/10-kWh LG Chem batteries, totaling
128 kW/333 kWh in battery capability after factoring in the
inverter limits.
One condition was that the system had to have a compatible
EMS, which would become a key part of the customer
and network coordination. By default, this EMS is capable
of monitoring and forecasting the battery state, solar generation,
household demand, and retail prices as well as optimizing
the battery operation in real time to minimize the
owner's costs. For example, it can charge the battery from
excess solar or during cheap time-of-use price periods and
then offset the load or discharge back to the grid during more
expensive time-of-use prices.
This project expanded this functionality so that the EMS
could additionally respond to price signals from the network,
to provide support when the network needed it and when it
was in the customer's benefit to do so. From the customer's
perspective, the system is fully automated, and the design
of the battery controller means that it will act only when it
provides a direct financial benefit to the customer that outweighs
any opportunity cost.
figure 3. Customers showing their new battery system to the social science team.
(Source: University of Tasmania, Australia; used with permission.)
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ieee power & energy magazine
NAC
With solar, batteries, and priceresponsive
EMSs in the hands of 34
customers, the next challenge was to
develop the algorithms to coordinate
their actions within the strict limits
of the network. For inspiration, we
looked to how generation and load are
coordinated in wholesale electricity
markets. We focused on Australia's
National Electricity Market (NEM),
but the concepts and approach are
similar the world over. The NEM
clears bids from participants offering
to generate and consume power
by solving an optimization problem.
Without network constraints, this is
commonly called economic dispatch;
if the optimization problem explicitly
considers network constraints as
well, it is termed OPF.
july/august 2021
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