Integrated modelling review - Modelling Distributed Energy Resources in Energy Service Networks - page 27

The system components are represented by using input-output models, similar
to a black box approach, describing the energy interactions by means of efficiency
and conversion factors. Hence, the relationships among the components are mod-
elled through coupling matrices [153]. Analysis of energy transfers in the systems
is performed through several optimal power flow formulations which objective func-
tions mainly focus on optimum design and operation strategies [129]. Lately, the
energy hub framework analysis has been expanded by considering new technologies
such as PHEVs and thermal storage, thus depicting interactions of multiple assets
[128,154,155].
Although results from this string of research are not yet conclusive, initial efforts
have tended to expose the influence DER technologies can have on locational marginal
prices as well as impacts on gas and electricity networks. Anyhow, since the infras-
tructure modelling does not focus on current characteristics ( e.g. employing direct
current lines a.k.a. direct current (DC) power flow), its results lack the technical data
that is commonplace and valuable to DNOs and other stakeholders.
Some key contributions from the energy hub framework are [156]:

Establishing a general and comprehensive approach of modelling conversion
and storage for multiple energy carriers;

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Proposing a flexible combination of different energy carriers with DER technolo-
gies that have the potential to reduce overall energy cost and emissions.

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2.2.4 Integrated natural gas and electricity studies
In a deregulated environment, energy markets have been unbundled allowing util-
ities to invest at any stage of the commodity delivery process ( i.e. generation,
transmission, distribution and retail) [71]. Unsurprisingly, some energy players are
actively involved in both natural gas and electricity sectors ( e.g. EDF, E.ON, Ener-
gias de Portugal and Iberdrola) [157-160]. Based on these circumstances multiple
stakeholders have the opportunity to expand their zone of influence. Therefore, it is
logical to assume that integrated resource studies have to be identified and quantified
so that utilities can benefit from their investments while also enhancing final end-use
of energy [28].
Research concerning integrating natural gas and electrical network studies is
scarce in the literature. Most of the existing publications regarding this particular
interaction focus on issues at a transmission level. The abundance of literature at high-
voltage and -pressure levels is because the 'dash for gas' for centralised generation
is a more mature subject than at a distribution level [161]. Nonetheless, distribu-
tion networks require addressing this research field as well, since urban areas will
most likely suffer a 'dash for gas' of their own due to high penetration of CHP tech-
nologies [15]. Similarly, where possible, interactions with heat networks are deemed
necessary.
Publications that have approached combined gas and electric network analysis
have focused on the following issues:

Influence of natural gas infrastructure layout on planning electric power genera-
tion [66,162-165];

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