POWER May 2016 - 32

DISTRIBUTED ENERGY RESOURCES
How Are Distributed Energy
Resources Affecting Transmission
System Operators?
Courtesy: Independent Electricity System Operator (IESO)
Distributed energy resources (DERs) may be a competitive concern for traditional
electric generators, but for independent system operators, DERs offer both benefits
and challenges. Here's what POWER learned about how system operators are responding
to DERs.
Aaron Larson
W
hat are distributed energy resources
(DERs)? For many people, rooftop
solar is the first thing that comes
to mind, but when you ask that question of
an independent system operator (ISO)-the
folks who coordinate, control, and monitor
North America's electric transmission grid-
the answer you get is likely to include much
more than just rooftop solar.
They will also mention small-scale
wind or biomass generation, energy storage,
plug-in vehicles, demand response,
energy efficiency programs, and even some
natural gas- and diesel-fueled reciprocating
engines. In fact, in the Electric Reliability
Council of Texas (ERCOT) region, fossilfueled
distributed generation (DG) makes
up the majority of DERs. (For more on the
big picture of DERs, see " Evolving Roles
for the Grid and Generation " in this issue or
online at powermag.com.)
Although each ISO or regional transmission
operator (RTO) seems to have its own
32
DER definition, for most it includes generation
resources on the distribution system
(normally less than 69 kV) that are typically
connected to end-use customers and located
behind the customer's meter. Some ISOs
have size limitations for DERs, such as less
than 5 MW in New England, but the one
definitive descriptor is that the resources do
not generally participate in the ISO markets.
(Although this is changing. See " U.S. Microgrid
Market Development " in this issue or at
powermag.com.)
And therein lies one of the biggest challenges
for ISOs: The DERs are not visible to
them. ISOs operate the transmission grid and
have a limited view of the distribution network
(see the sidebar " How Does the North
American Electric Grid Work? " ). DERs simply
reduce the amount of energy that would
otherwise have been needed from other resources
on the regional power grid. In other
words, they make demand appear lower than
it actually is.
www.powermag.com
CAISO: A Pioneer in DER
Integration
California offers a natural starting point for any
discussion involving DERs. The state leads the
nation with 489,778 interconnected solar photovoltaic
(PV) net energy-metering systems
installed, with a total capacity of 3,868 MW as
of March 23, 2016. California also has a fairly
aggressive self-generation incentive program,
which provides support for the installation of
clean and efficient DERs, including wind turbines,
microturbines, fuel cells, advanced energy
storage systems, and more.
Although statistics on residential and nonresidential
(Figure 1) solar installations are
recorded and maintained by the state, the
California ISO (CAISO) told POWER that it
does not perform any analysis of retail sales
growth of DERs and said it doesn't speculate
on trends. It said behind the end-use customer
meter resources are passive, so they do
not participate in the ISO market and are not
visible to CAISO.
POWER | May 2016
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POWER May 2016

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