IEEE Power & Energy Magazine - January/February 2017 - 24

energy from raw resources to service demands relative to
single-input, single-output power plant designs.
HES provides increased path redundancy between energy
resources and energy services, offering alternative means to
satisfy energy service demands. After the 2005 hurricanes
Katrina and Rita in the Gulf of Mexico, a large percentage
of U.S. natural gas supply was shut down for many weeks.
Although electric and natural gas demand was interrupted
for only a short time in a localized region, electric and natural gas prices rose steeply throughout the nation, and they
did not return to their prehurricane levels for months. An
increased link density due to HES deployment would have
enabled shifting between supplies and products after the
disaster occurred, thus minimizing the price spike.
HES plants are scalable from conventional utility-sized generation to distributed resources (DRs) to meet flexibility needs
at different scales. DRs are connected at the electric distribution
level (consistent with IEEE standard 1547), which means that
for some small-scale applications, the capacity is constrained
by distribution circuits. Distributed HES plants with capacities of 10-100 MW, however, could be connected directly to
the distribution substation rather than the distribution circuit,
which means that their DR potential is less limited. Distribution-substation connections of resources at this capacity maintain the partial benefit of proximity to loads while still retaining
the ability to utilize the transmission system without reversing
flows on distribution circuits. Therefore, wide deployment
throughout a region of many HESs of this scale would satisfy
the operational flexibility necessary for high wind and solar
penetration, enable economic flexibility, and balance the benefits of load proximity with transmission accessibility.
HES deployment can potentially provide both operational and economic flexibility by combining different energy
resources (inputs) and energy services (outputs). However, the
industry is often disaggregated, and many plant users are only
active in one specific market. Therefore, plant owners and companies may not see opportunity arising from a by-product, lack
the skills to expand to new markets, or shy away from the risk of
expanding into unknown markets. Collaboration and research
are essential to develop skills and confidence.

Conclusions
Today, gas turbines are the main flexibility source (next to
interconnectors) for balancing demand and variable supply and
achieving stable grid operation. Gas-fueled power plants typically start up quickly and provide excellent ramping capabilities that cannot be understated. The profitability of gas power
plants is decreasing, however, because operational hours are
dropping and material wear and tear is increasing. Gas turbine
R&D efforts are focused on reducing cycling costs and maximizing flexibility capabilities, but market design that adequately
rewards flexibility is essential to ensure system reliability.
The cyclical operation of gas power plants increases
gas supply variability and requires the increased use of
short-term storage and intraday market trading. Increased
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coordination between gas and electricity infrastructure is
critical due to the different time constants for real-time operation of gas and electricity networks.
Further integrating the energy resources and energy services through HESs can increase both the operational and economic flexibility of an energy system. Various HES designs
are possible that enable the use of existing infrastructures and
meeting local demands. Additionally, the deployment of HES
plants improves system reliability and resilience by increasing link density and enabling the switch between different
supply sources and products. However, collaboration among
sectors and industries is essential to realize this potential.
The gas infrastructure is a major flexibility resource for
the electricity system. A holistic perspective including both
systems captures couplings and interactions, and, if those
are significant, then it reveals integration challenges and
opportunities to further increase the flexibility options

Acknowledgment
Steve Heinen is supported by the Fonds National de la Recherche, Luxembourg (project reference 6018454), and the CITIES project, Denmark (project reference 1305-00027B/DSF).

For Further Reading
COWI and DNV KEMA, "Study on synergies between
electricity and gas balancing markets (EGEBS)," European
Commission for Energy, Brussels, Belgium, Rep. TRENTALOT3-015, Oct. 2012.
"Report on outages and curtailments during the Southwest cold weather event of February 1-5, 2011-Causes and
recommendations," Federal Energy Regulatory Commission
and North American Electric Reliability Corp., Aug. 2011.
"Accommodating an increased dependence on natural
gas for electric power," NERC, Atlanta, GA, 2013.
P. Ostergaard, "Comparing electricity, heat and biogas
storages' impacts on renewable energy integration," Energy,
vol. 37, pp. 255-262, 2012.
M. Qadrdan, M. Chaudry, J. Wu, N. Jenkins, and J. B.
Ekanayake, "Impact of a large penetration of wind generation on the GB gas network," Energy Policy, vol. 38, no. 1,
pp. 5684-5695, Jan. 2010.
N. Szarka, F. Scholwin, M. Trommler, H. Jacobi, M.
Eichhorn, A. Ortwein, and D. Thran, "A novel role for bioenergy: A flexible, demand-oriented power supply," Energy,
vol. 61, no. 10, pp. 18-26, Oct. 2013.

Biographies
Steve Heinen is with University College Dublin, Ireland.
Christian Hewicker is with DNV Energy, Germany.
Nick Jenkins is with Cardiff University, United Kingdom.
James McCalley is with Iowa State University, United States.
Mark O'Malley is with University College Dublin, Ireland.
Sauro Pasini is with Enel Thermal Generation, Italy.
Simone Simoncini is with Enel Thermal Generation, Italy.
p&e
january/february 2017

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