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Mechanical Technology — July 2016
9
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Special report
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Above:
ABB’s Longmeadow facility now has
a 750 kWp, monocrystalline rooftop PV
system connected to a microgrid.
Above right:
A PowerStore
TM
battery-based
grid stabilising system takes up the load
immediately when the grid goes down.
Right:
The dc power from the panels is
passed through a single PVS 800 630 kW
ABB inverter to generate the ac supply.
and greener power solution
“So while microgrids can be grid con-
nected, as we see at our demonstration
plant here in Longmeadow, they are also
100% ‘islandable’. Here, we have grid-
connected power, PV solar generation,
the battery and diesel generation all
interconnected via a common ring and
automatically managed by the Microgrid
Plus distributed control system (DCS).
The unique feature of ABB’s microgrid
control system is that it has a distributed
network of controllers allowing for redun-
dancy, expandability and maintenance to
take place without interrupting genera-
tion of power.
“As soon as an outage is detected,
the PowerStore provides the reference
for off-grid generation. Then, when the
grid comes back on line, the PowerStore
resynchronises, which will cause the off-
grid generation sources to follow. The grid
can then be safely brought back into the
supply mix,” he adds.
Key features of microgrids
The core purposes of ABB’s microgrid
solutions is power security and grid
resilience. Since no single generation
option is able to offer this all of the
time, it makes sense to combine power
generation sources to make sure power is
always available. “While seamless power
changeover is not always necessary, it is
now a primary part of our offering and is
often essential,” Duarte suggests.
“Probably the largest microgrid market
is in the USA, where you would think
they have no need of it. Why? Because
of the increasing occurrence of natural
disasters, which tend to take out the grid
and cripple the affected community. To
minimise the impact of such events, the
power needs to be restored immediately
and microgrids are being installed on a
redundancy basis to back up the grid in
high-risk areas. Typically these are large
systems of between 10 to 100 MW,
but there is no capacity limit since the
technology involves the management
and coordination of generation, not the
generation itself,” he informs
MechTech
.
A second objective is to achieve the
lowest possible levelised cost of energy
(LCOE) from a combination of generation
sources. “Levelised cost of energy is a
stream of equal payments, normalised
over the expected energy production
period, that would allow a project owner
to recover all costs – including financing
and an assumed return on investment
over a predetermined financial life. This
value is expressed as a tariff per kWh of
generation,” he explains, adding, “gener-
ally calculated for a 20-year life.”
With this information, ABB’s Microgrid
Plus DCS is able to optimally combine
available generation sources to meet
prevailing load demand at the lowest
possible cost.
And the third important imperative