POWER June 2014 - 74

ELECTRIC POWER 2014 ROUNDUP
The Dynamic Challenge of
Integrating Variable Resources
All aspects of system operations are tested by unique challenges as more variable
energy resources are connected to the grid.
Sonal Patel
T
he share of non-hydro renewables in
total U.S. power generation shot up to
6.5% in 2013 from 2.4% in 2003, according
to the Energy Information Administration
(EIA). The past five years alone have
been specifically marked by a growth spurt
for wind and solar power-so-called " variable
energy resources " because the power they
produce is less predictable compared to power
from conventional technologies. Combined,
wind and solar power generation soared to
4.4% of the nation's total generation in 2013,
compared to 1.49% in 2009 (Figure 1).
But, while the growth of these variable
resources is " a blessing for the planet and
for people, " it poses myriad challenges for
grid operators who must deal with inherent
swings, or ramps, in power output, said ABB
Director of Marketing Francisco Tacoa at the
ELECTRIC POWER 2014 renewables track
session on integrating renewables.
Generators, too, are being forced to tackle
a host of issues, he said. These include factoring
in the need for more flexible generation
resources, meeting demand for real-time
energy requests, and evolving plant key performance
indicators to accommodate variable
renewables. Then they must minimize
damage to assets not designed for intermittency,
run power plants not designed for
highly variable generation, and coordinate an
automated and wide generation dispatch.
These issues will only gain more urgency
in the future, Tacoa noted. Backed by renewable
portfolio standards (RPS) and federal
tax incentives, more than 50 GW of wind
capacity is projected to be installed in the
Western Interconnection while about 20 GW
are expected to be installed in the Eastern Interconnection
by 2020.
An Energy Imbalance Market
Tacoa outlined an interesting proposal in the
Western Interconnection to address the anticipated
increase in variable generation over
the next several years that calls for its smaller
balancing authority areas (BAAs) to pool
their variable and conventional generation
resources to improve operational efficiency
over a wider area. This sub-hourly, real-time
" Energy Imbalance Market (EIM) " would
provide centralized, automated, and regionwide
generation dispatch for imbalances. A
working group comprising several western
BAAs, the Western Governors Association,
and a number of other stakeholders is making
plans to link the entire Western Interconnection
to the EIM.
1. A growth spurt. Compared to 2009, the share of U.S. renewable generation that is not
conventional hydropower has increased 2.5%. From 2009 to 2013, wind generation increased
from 74 TWh to 167 TWh, while solar generation grew from 891 GWh to 9.2 TWh. Source: EIA
■ Wind ■ Solar ■ Geothermal ■ Wood biomass ■ Other biomass ■ Other renewables
The idea is gaining backers on a smaller
scale, too: In mid-April, MidAmerican Energy's
newly purchased NV Energy filed
a request with the Nevada Public Utilities
Commission to voluntarily participate,
starting in October 2015, in a regional
5-minute EIM agreed to in 2012 by the
California Independent System Operator
(CAISO) and MidAmerican's northwestern
utility PacifiCorp. NV Energy has said its
EIM participation could benefit all participating
parties in the range of $9.2 million
to $29.4 million annually.
Nevertheless, the EIM concept isn't without
its critics. Beyond concerns about exorbitant
startup costs, cost shifting, and new
reliability problems, the American Public
Power Association points out that an EIM
has the potential to quickly evolve into a
regional transmission organization-which
historically " developed incrementally, with
continual additions of more complex and
costly centralized market features. " And, it
says, an EIM could suffer similar problems:
complex and costly market-pricing mechanisms,
price volatility, and an absence of
cost-effective measures to ensure resource
adequacy. (See " tablet " sidebar next page.)
The proposed Western Interconnection
EIM " does not require any formal coordinated
unit commitments, but it does not preclude
it down the road, " said Tacoa.
There also are other options to balance
generation and load in BAAs, he said, including
area-control error pooling, advanced
dynamic scheduling, or an intra-hour transaction
accelerator platform.
2009
Share of total
generation:
4%
(156 TWh)
74
2010
Share of total
generation:
4.5%
(180 TWh)
2011
Share of total
generation:
5%
(208 TWh)
2012
Share of total
generation:
5.7%
(232 TWh)
2013
Share of total
generation:
6.5%
(266 TWh)
www.powermag.com
More Flexible Generation
Resources
For generators, the growth of variable generation
has underscored the need for more
flexible generation resources, Tacoa said,
and if two key considerations were to be
identified, they are speed and efficiency. Gas
turbines are at least 20% more efficient than
steam boilers, which can take up to 12 hours
to warm up. And, while today's gas turbines
POWER | June 2014
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POWER June 2014

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