IEEE Power & Energy Magazine - November/December 2021 - 96

In Colorado, a winter (nonpeak season) reliability concern
has emerged. What is currently a summer-peaking system
is projected to change significantly in the next 10 years.
In 2021, the summer net load peak occurs during hours of
high solar production. The spread between summer and winter
net load peaks is more than 1,200 MW (Figure 7), signaling
a significant capacity overhang.
The difference between the summer peak resource
need and rest of the year means that, in 2021, planning to
a summer peak load provides enough capacity to cover the
entirety of the year. With solar energy being built largely
to serve a summer peak, the winter reliability event grows
in importance.
In 2030, the summer net peak load has shifted later
in the day after solar energy has dissipated, while the
nature of the winter peak is unchanged. Solar energy is
a poor performer in the winter months due to short days,
and, while wind energy is stronger, on average, in the
winter than summer, there are days when wind energy is
nearly nonexistent.
This foretells a new critical scenario-the winter doldrums.
The 2030 summer net load peak is 6,055 MW,
and the winter net load peak is 5,631 MW, resulting in
a capacity overhang of just more than 400 MW. Other
resources not considered in this analysis could make
the mismatch even worse. Public Service of Colorado's
control and cycling of residential air conditioning
compressors contribute 220 MW of demand flexibility
available only during summer peaks, further reducing
the needed capacity overhang between summer and
winter. Future electrification loads, such as electrified
winter heating loads, will also exacerbate winter reliability
concerns.
Conclusion
The recent records in VRE shares have underscored challenges
with VRE integration. The main challenges encountered
for the pioneering countries and regions are summarized
as follows:
✔ avoiding VRE curtailments
✔ dealing with zero or negative market prices
✔ reduced hydropower flexibility due to constraints on
the water-energy nexus and the occurrence of transmission
congestion
✔ ensuring frequency stability, system strength, and minimum
fault levels
✔ addressing the long-term reliability with resource adequacy.
The
ongoing and planned mitigation measures include
increasing flexibility, reinforcing transmission capability,
and adding new operational constraints. The need is now
apparent for a new suite of reliability services and methods
to assess future resource adequacy. The increasing levels of
VRE create a need for both new and modified reliability services
as well as VRE to help provide those services.
Acknowledgments
Rodrigo Moreno acknowledges the support of Claudio Silva
and the financial support of ANID through grants Fondecyt/1181928
and Instituto Sistemas Complejos de Ingeniería
PIA/APOYO AFB180003.
For Further Reading
" Quarterly Energy Dynamics, " AEMO Quarterly. Accessed:
Aug. 25, 2021. [Online]. Available: https://aemo.com.au/
library/major-publications
L. A. Barroso, F. Munoz, B. Bezerra, H. Rudnick, and
G. Cunha, " Zero-marginal-cost electricity market designs:
Lessons learned from hydro systems in Latin America, "
IEEE Power Energy Mag., vol. 19, no. 1, pp. 64-73, 2021.
doi: 10.1109/MPE.2020.3033398.
H. Rudnick, L. A. Barroso, R. Moreno, R. Ferreira, and
E. Pereira, " Facilitating the integration of renewables in
Latin America: The role of hydropower generation and other
energy storage technologies, " IEEE Power & Energy Mag.,
vol. 15, no. 5, pp. 68-80, Sept. 2017.
Holttinen et al., " Design and operation of energy systems
with large amounts of variable generation, " IEA
Wind Task 25 Summary Rep., 2021. [Online]. Available:
https://iea-wind.org/task25/t25-publications/
Biographies
Hannele Holttinen is with Recognis, Vantaa, 01630,
Finland.
Andrew Groom is with Australian Energy Market Operator,
Melbourne, 3000, Australia.
Eoin Kennedy is with EirGrid, Dublin, D04 FW28,
Ireland.
Dan Woodfin is with the Electric Reliability Council of
Texas, Taylor, Texas, 76574, USA.
Luiz Barroso is with PSR Energy Consulting, Rio de
Janeiro, 22250-040, Brazil, and Institute for Research in
Technology, ICAI, Comillas Pontifical University, Madrid,
28015, Spain.
Antje Orths is with Energinet, Fredericia, 7000, Denmark.
Kazuhiro Ogimoto is with Tokyo University, Tokyo, 1138654,
Japan.
Caixia Wang is with State Grid Energy Research Institute,
Beijing, 102209, China.
Rodrigo Moreno is with the University of Chile and Instituto
Sistemas Complejos de Ingeniería, Santiago, 8370451,
Chile, and Imperial College, London, U.K.
Keith Parks is with Xcel, Colorado, USA.
Thomas Ackermann is with Energynautics, Darmstadt,
64293, Germany.
p&e
96
ieee power & energy magazine
november/december 2021
https://aemo.com.au/library/major-publications https://aemo.com.au/library/major-publications https://www.iea-wind.org/task25/t25-publications/
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