Integrated modelling review - Modelling Distributed Energy Resources in Energy Service Networks - page 25

both thermal and electric demands. End-user heat demand consideration is impor-
tant since CHPs play a large role in urban energy blueprints; however, gas network
modelling is commonly omitted despite heat loads adding another dimension to the
problem [131]. Most significant references in power systems are found under virtual
power plants [132] and micro-grids [133].
The virtual power plants framework was introduced in 1997, consisting of a
joint effort by market-driven embedded generators to provide efficient energy ser-
vices [134]. The theory establishes suitable interfaces among the local components,
adequate generation control strategies and optimal use of the available capacity.
By adding these properties, virtual power plants become a visible force of flexible
customer-oriented energy service provision. Specific aspects of virtual power plants
research promote the adoption of CHP technologies and analyse the interactions with
energy markets [135]. Hence, research has focused on unit commitment generation
programs to maximise DER portfolio [136]. This type of analysis permits to assess
DER capability to buy and sell electric power close to spot market prices as well as
the chance to offer ancillary services [137].
Micro-grids [138] are local entities that coordinate DER technologies in a con-
sistently decentralised way, thereby reducing the control burden on DNOs and instead
expects a localised level of coordination from the assets. Micro-grids have the ability
to work in either grid-connected or islanded modes [139]. This implies that the con-
nection point between a micro-grid and the main grid may not necessarily be active
at all times. It could be the case that the connection does exist but is normally open,
closing only in particular events such as an internal outage or because it is finan-
cially advantageous to establish an energy trade with the main grid [140]. Within
this context, committing a unit usually means bringing online multiple small genera-
tors instead of large power plants [141]. The difference is related not only to the size
but also to the complexity of the management behind each action. Thus, for logistics
to work properly advanced applications of power electronics, protection schemes and
control systems are required [69], leading to the idea that a power-sharing framework
aimed at enhancing financial benefits in a micro-grid is likely to rely on a strong com-
munication infrastructure [142]. Nevertheless, research has instead mainly focused
on developing strategies that minimise fuel consumption [143] or that evaluate optimal
techno-economical operation [90,144].
2.2.2 Integrated energy transportation systems
A single integrated framework approach for addressing the cohesion of a regional
power grid by considering the interdependencies it has with other systems was pub-
lished in 2003 [145]. The high-level analysis merges electric, natural gas and coal
systems as analogous interconnected network flow models. In addition, this novel
model considers functionalities for each system, such as supply, demand, storage and
transportation. The purpose of the research is to evaluate the economic efficiencies
of the energy flows in the integrated energy system, from the fossil fuel suppliers to
the electric load centres [146]. The authors represent the various energy systems as
networks comprising nodes and arcs that possess capacity and efficiency constraints.