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of context-oriented design solutions. A very interesting work by Čulig-Tokić et al. [12] has
presented a comparison between two different district heating systems serving two towns,
Zagreb (Croatia) and Aalborg (Denmark); evident asymmetries were observed in terms of
heat supply sources, total network length, supply temperatures and cost charging criteria for
customers. In the search for the so-called 4th Generation District Heating concept [13],
intended as systems which could operate as smart thermal grids and contribute to
sustainability of energy supply, one of the main trends for the development of new
installations consists in gradually lowering the water supply temperature, so as to reduce heat
losses and increase the overall efficiency of the energy conversion chain. Ommen et al. [14]
have analysed the positive impacts of low supply temperatures, in terms of increased
efficiency of Combined Heat and Power systems eventually supplying the network
(accounting for different power plant technologies), possible inclusion of district heating
booster heat pumps and overall results from the primary energy saving and CO2 emission
viewpoints. Recently, Østergaard and Lund [15] developed a technical scenario where the
assumption of very low supply temperature was formulated to allow exploiting the large
amounts of low temperature geothermal energy and thus converging toward the declared goal
of making the Danish city Frederikshavn a 100% renewable energy city.
The present paper, conversely, is aimed at identifying solutions to increase the overall energy
efficiency in small islands, with a particular focus on six islands in Italy. The ambitious goals
declared in the above referenced works (like the 100% renewable energy scenario) become,
for small islands, absolutely far from realistic. The state of art, as will be clarified in the
following sections, reveals the presence of different very poor energy uses and an extremely
low penetration of renewable sources. Then, the perspective of the research and the aim of the
study is completely different than usual: the feasibility of DH/DC networks will be
investigated only as a means to allow exploiting the enormous amounts of waste heat
currently discarded, with no useful scope, by the power generation units (prevalently based on
diesel generators) that supply electricity to these remote communities. While performing such
pre-feasibility studies, the authors were aware that very unfavourable context conditions could
represent strong barriers to the economic viability to be investigated; in fact, though any
waste heat recovery virtually represents a “zero-cost” energy input to the network, the
extremely low heat/cooling demand density and the difficult orography of the examined
islands could contribute to make any DH/DC-based scenario unfeasible.
The problem of feasibility of district heating in low heat demand density areas is not new in
literature. In the framework of the “Heat Roadmap Europe” projects, Persson et al. [16]
investigated under what conditions the coexistence of heat supply/recovery options and
possible heat consumers can offer a promising context for the feasibility of district heating. In
another work the same authors systematically approached the problem of heat distribution
cost assessment, providing tools and formulas to answer a very common problem in DH
networks planning, i.e. the optimal extension of an urban network toward suburban-periphery
areas where the share of built area gradually decreases [17]. It was pointed out that the
distribution cost can be estimated as an inverse function of the “linear heat density” (ratio
between the heat load and the length of the network branches needed to supply the load) and
it is linearly dependent on the average tube pipe diameter, which ultimately influence also the
cost of civil works for pipes installation. In the present work, these cited approaches are
applied to the different islands, to identify reasonable network geometries and someway
predict the feasibility of DH/DC.
The paper is structured as follows:
- in Section 2 the islands considered in this study are briefly presented, providing sufficient
details about the distribution of energy users, the installed capacity and the estimated waste
heat available;

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