IEEE Power & Energy Magazine - January/February 2017 - 44

solutions that strike a balance among cost, reliability, and
the environment, while accounting for energy affordability,
overall stainability (which pertains not only to carbon emissions but also involves the use of natural resources such as
water), and social acceptability. The latter includes visual
impacts, safety and privacy concerns, and thermal (dis)comfort, to name just a few.

Shifting Supply and Demand
Across Spatiotemporal Scales
From an operational perspective, the coordinated and seamless control of various energy infrastructures represents a
significant change, which favors a local view that renders
city quarters, residential neighborhoods, and industrial areas
the fundamental building blocks of the integrated energy
system. Along with the growing role of distributed energy
resources (DERs), the envisioned control architectures is
based on a multi-area view, whereby the local neighborhoods
and districts are driving factors in a bottom-up approach.
Benefits such as the integration of higher levels of renewable energy resources, increased reliability and improved
efficiency in power systems, and significant savings in, e.g.,
water, heating/cooling, and gas system operations can be
achieved by uncovering (and capitalizing on) the intrinsic
flexibility that emerges from an integrated operation of multiple energy systems at multiple spatiotemporal scales. Flexibility can generally be seen as a system's ability to provide
secure and economical supply-demand balance across spatial and temporal scales by leveraging and seamlessly coordinating various controllable assets. In the context of future
low-carbon power systems, major flexibility challenges are
associated with

✔✔ the integration of variable and uncertain renewable

energy sources
✔✔ low-inertia operational settings, with the consequent
impacts on the frequency-response task
✔✔ the high cost of utility-level and community-level energy storage systems.
In this respect, multi-energy systems could represent a key
option to provide flexibility in future power systems owing
to their untapped potential to shift supply and demand across
energy vectors and networks-and, in doing so, across spatiotemporal scales-by exploiting energy storage in the form
of energy, heat, or gas storage.
For example, coupling combined heat-and-power (CHP)
plants with electric heat pumps (EHPs) can introduce opportunities for an energy-shifting arbitrage between gas and
electricity to supply electricity, heat, and cooling to end
users, something that is particularly useful in the presence of
variable renewable energy. The presence of thermal energy
storage (TES)-which may come at a much lower cost than
electricity energy storage but can provide similar services
in the context of multi-energy systems (a process that overall might be considered a form of "virtual" storage)-could
provide further possibilities for energy-shifting flexibility.
Similarly, considering the natural interaction between gas
and electricity networks, there are major flexibility opportunities that can be exploited via coordinated control, as
explained later in the article.

The Concept of Energy Hubs

Figure 1 exemplifies a complex system of interconnected
infrastructures providing basic electricity, heat, gas,
and water services to end customers. The physical couplings
among systems could, for instance,
be represented in mathematical terms through the so-called
"energy hub" formalism-a geAdjacent
ner ic, sca lable, a nd modula r
Systems Solar
modeling approach that offers the
Industrial
Area
flexibility to capture energy-conversion factors at various spatial
Residential
H1
H2
scales. In particular, the mathArea
ematical model associated with
Pumped Hydro
the energy hub shown in Figure 2
(Storage)
could offer representations of the
interdependencies among energy
carriers at the household, commercial, and energy-district levels and facilitate the formulation
H3
H4
Commercial
Wind
of (and solutions for) control/opArea
timization schemes to control
Water
Heating
Natural Gas
Electricity
co-generation and tri-generation
plants in distribution settings, as
well as gas-to-power and powerfigure 1. A complex system of systems providing basic electricity, heat/cooling, gas,
to-gas
and hydro facilities at the
and water services to end customers. Dark areas designated Hi (energy hubs) represent
transmission
level.
locations and facilities where the various infrastructures are coupled.

44

ieee power & energy magazine

january/february 2017



Table of Contents for the Digital Edition of IEEE Power & Energy Magazine - January/February 2017

IEEE Power & Energy Magazine - January/February 2017 - Cover1
IEEE Power & Energy Magazine - January/February 2017 - Cover2
IEEE Power & Energy Magazine - January/February 2017 - 1
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IEEE Power & Energy Magazine - January/February 2017 - Cover3
IEEE Power & Energy Magazine - January/February 2017 - Cover4
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