POWER August 2017 - 6

SPEAKING OF POWER
Is Natural Gas Threatening
Grid Reliability?
Aaron Larson
f you've been paying attention to the
power markets in recent years, you
know that merchant coal and nuclear
power plants are struggling to compete
against natural gas-fired generation and
renewable resources. For example, PJM
Interconnection-the world's largest
competitive power market-in late May
announced results for its annual capacity
auction. It procured more than 165 GW
for the June 1, 2020, to May 31, 2021,
period with natural gas fueling the largest
share of the cleared capacity (more
than 75 GW).
I
Coal and Nuclear Stumble
It wasn't that long ago that coal-fired
generation dominated the PJM auctions.
In the 2013/2014 capacity auction, for
example, coal cleared more than 60 GW
while gas was less than 50 GW. Since
then, the trend has been nearly straight
down, with only slightly more than 40 GW
of coal capacity clearing the auction in
2020/2021.
The PJM auctions haven't been particularly
kind to nuclear generators either. Exelon's
Three Mile Island (TMI) and Quad
Cities nuclear plants failed to clear the
auction this year. The news had near-immediate
consequences for TMI. The week
after the auction results were released, Exelon
announced it would retire the plant
in September 2019, unless Pennsylvania
enacts policy reforms.
Exelon has had some success getting
states to provide support for struggling
nuclear plants. The New York State Public
Service Commission approved a " Clean
Energy Standard " in August 2016, which
provides subsidies for upstate nuclear
plants. In Illinois, the legislature last
December passed the " Future Energy Jobs
Bill, " which will feed millions of dollars
to Exelon each year to keep the Quad Cities
and Clinton nuclear facilities open.
The measures are being challenged in
court, however, and unfavorable rulings
could jeopardize the future of several
nuclear plants.
6
While nukes often receive backing from
clean energy advocates for their lack of
carbon emissions, coal generators are not
as fortunate. Rather, environmentalists
are generally the most outspoken critics
of coal, often suggesting its use be discontinued
altogether.
Effects on Reliability
Understanding that coal and nuclear generation
face serious retirement threats,
PJM stakeholders raised the question:
Is the grid becoming so dependent on
natural gas and renewable resources that
operational reliability could be adversely
affected? Speaking at the American Society
of Mechanical Engineers (ASME) Power
and Energy Conference in Charlotte, N.C.,
on June 27, Michael Bryson, PJM's vice
president of operations, said, " The unspoken
question of this is 'Is there such a
thing as too much natural gas?' "
To answer the question, PJM conducted
a study designed to evaluate fuel diversity
through the lens of reliability and to identify
a range of resource mixes that could
effectively manage reliability risk.
" One of the things we started out assuming
was that more diversity means
more reliability, " Bryson said. " What we
found out as we looked through our results
was that's not necessarily true. "
In the end, reliability did not depend
so much on a diverse resource mix; it depended
on generator reliability attributes.
PJM's team identified 13 essential reliability
attributes. The attributes were frequency
response, including synchronous
inertia, primary, and secondary frequency
response; voltage control; ramping ability
for regulating margin; ramping ability
for contingency reserve; ramping ability
for load following; fuel assurance as determined
by the ability to maintain economic
maximum energy output for at least
72 hours; fuel assurance through the ability
to store fuel on-site; flexibility to start
and stop more than once in 24 hours; flexibility
to start within 30 minutes following
notification; flexibility to run 2 hours
www.powermag.com
or less per start; black start capability;
lack of environmental restrictions limiting
hours of operation; and high equivalent
availability factor.
PJM then created a matrix and evaluated
each resource type's ability to exhibit
each of the attributes. Hydropower
was judged to be the most reliable resource.
However, natural gas combustion
turbines (CTs) were a close second. In
fact, the only attribute that CTs weren't
judged to at least partly exhibit was onsite
fuel inventory.
Natural Gas Is Highly Reliable
The results from the analysis suggest
that the answer to the initial question of
whether or not the system can be too dependent
on natural gas is " no. " Bryson said
that even as the research team cranked up
coal and nuclear retirements, and added in
more renewables, portfolios composed of
up to 86% natural gas showed no decrease
in reliability.
However, the same can't be said for wind
and solar, which fell to the bottom of the reliability
matrix. " A marked decrease in operational
reliability was observed for portfolios
with significantly increased amounts of wind
and solar capacity, " the report says. Moreover,
most portfolios with solar unforced
capacity of 20% or greater were considered
infeasible because loss of load expectation
criteria were violated at night.
" Just looking at reliability may not be
enough, " Bryson said. " It may be more important
to take that and look at reliability
as kind of a base level and continue to
look at resilience and develop resilience. "
PJM defines resilience as " the capability
of an energy system to tolerate disturbance
and to continue to deliver energy
services to consumers. " The report suggests
that relying too heavily on any one
fuel type may negatively impact resilience
because resources do not provide generator
reliability attributes equally. It sounds
to me like it's time for a resiliency study. ■
-Aaron Larson is POWER's
executive editor.
POWER | August 2017
http://www.powermag.com
POWER August 2017

Table of Contents for the Digital Edition of POWER August 2017
