POWER January 2020 - 41

POWER TRANSITIONS
4. U.S. electric generation energy source profile for the seven-day period of Aug. 14-20, 2019.
Source: EIA
a significant role in the U.S. power generation
program. There should not be a
rush to close coal plants, nuclear units,
or other technologies without evaluating
the available data and supporting infrastructure.
When politics, technological
changes, transmission and distribution
system design, fuel cost, and self-interest
are added to the equation, decisions
concerning the generation mix become
even more complex.
While coal-powered generation has
been declining over the past 10 years and
will likely continue to decline under economic,
political, and environmental pressures,
it remains a vital part of the U.S.'s
energy generation base. The impact of
coal in the generation mix must be evaluated
on a micro basis (daily or seasonal),
not on an annual basis. Without coal generation
for two extreme weather days in
2019-Jan. 30, the peak winter day that
year, resulting from a polar vortex event
striking much of the country, and July 19,
the peak summer day, with a heat wave
engulfing the nation-the U.S. system
demand for power could not have been
maintained, which would have resulted
in severe consequences.
In this rapidly evolving power genera5.
U.S. electric generation energy source profile for the seven-day period of Jan. 25-31, 2019.
Source: EIA
from wind and only 1.3% from solar.
The California ISO received 22.4% of its
power from solar, while many other areas
generated less than 1% from solar
on the hottest day of the year. Consider,
in July 2019, the price of natural gas for
power generation was about $2.20/Mcf,
which was about the same price as in
1998. The residential gas consumption
in July was about 12% of what it was
in January, which means gas was more
readily available for power generation.
Some regions have low nuclear capacity,
which factors significantly into the
generation mix. Coal is the prime generation
source for the Midwest and
Central U.S.
ERCOT provides additional hourly generation
details that are not provided in
the EIA database. ERCOT breaks out gas
usage in generation between combined
cycle units and other gas-fired power
plants. ERCOT also provides biomass
generation data. For July 19, ERCOT data
shows that 15% (91.8 GWh) of the gas
January 2020 | POWER
used in ERCOT's system was by sources
other than combined cycle units. Based
on this information, it can be assumed
that the bulk of this other generation was
simple cycle gas turbines used for rapid
ramping to compensate for variations in
wind and solar generation.
Most simple cycle gas turbines have
tested heat rates of about 11,300 Btu/
kWh, which is higher than the average
coal-fired power plant heat rate of 10,300
Btu/kWh. An
important
environmental
point is that most simple cycle gas
turbines do not have selective catalytic
reduction systems for NOx
control. Furthermore,
additional infrastructure work
must be done on the U.S. transmission
system to allow energy generated by renewables
to be moved into areas where
renewable generation is limited.
A Complex Power System
The analysis shows that on a day-to-day
and region-by-region basis, coal, gas,
nuclear, solar, hydro, and wind all play
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tion world with more and more power
being generated from variable renewable
energy sources, it remains import
ant to have readily available, baseloaded
generation, and coal is still a key component
in that mix. The U.S. generation
system needs to have the flexibility to
adjust to extreme weather episodes,
such as polar vortex events, hurricanes,
droughts, and other localized issues including
power outages.
To maintain economic leadership,
the U.S. requires an electric power
system that is energy independent of
international tensions, with a cost that
promotes economic growth. Tax credits
are causing an unnatural balance in
the power system. The U.S. needs a
balanced energy policy that considers
the environment, economics, regional
needs, security of supply, and system
capacity requirements. In addition to
transmission improvements, additional
work must be implemented in coalfired
plants to improve their heat rate
while cycling. Without performance
improvements to coal plants, there will
be additional closures. ■
-Anthony Licata is a partner with Licata
Energy & Environmental Consultants
Inc. Thanks to Paul Cleri, PE; Dr. Connie
Senior; Arnold Feldman; and Frank Michell
for their input on this article.
41

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POWER January 2020

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