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- in Section 3 the methodology followed to perform the prefeasibility study is discussed, point
by point, in different subsections, specifically devoted to (i) the estimation of energy loads,
(ii) the estimation of distribution costs, aimed at identifying the most promising solutions as
concerns the installation of “DH only”, “DH&DC” or “DC only” networks and the possible
paths of the network, (iii) the identification of reasonable supply temperatures and the type of
pipes to be installed, (iv) the detailed evaluation of investment costs and possible revenues
from selling heat to private/public customers;
- in Section 4 a brief overview of the values achieved by synthetic economic performance
indicators is given, attempting to provide some keen interpretations of the reasons leading to
feasibility or unfeasibility of the examined “CHP + DH/DC” retrofit options.
The methodology is punctually examined, although some description could appear, only at a
first sight, as a simple implementation of consolidated techniques. In fact, the atypical
morphology of the served community (compared to the urban areas usually supplied by
district heating in Europe) contributed to make the whole DH design and evaluation process a
highly non-standardized approach, which required several ad hoc decisions to be taken and
consequently represents an innovative contribution with evident methodological interest; it is
worthwhile observing that no such detailed studies can be found, in literature, as concerns the
design of cogeneration and district heating network in disadvantaged areas like small islands.

THE EXAMINED CASE STUDY: SIX SMALL ISLANDS IN ITALY
Due to their geographical position, many small islands laying into the Italian territory are today
not connected to the national electric grid. In these islands, private companies supply almost the
100% of the consumed electricity by means of local power plants fired by fossil fuels. Present
study belongs to a research project on the feasibility of CHP retrofit actions of these power
generation units to be connected to new distribution networks for fulfilling thermal end-uses in
the neighbours. Currently, most of the power generation units are operated in pure power-
production mode. Due to the very high production cost (related with the cost of fuel shipping and
the moderately low efficiency of diesel engines, compared to large power plants), they receive a
special subsidized feed-in tariff, named “UC4”, for the produced electricity [18]. One of the
analysed hypotheses is that an economic exploitation of a fraction of the waste heat currently
discharged could reduce the cost of power supply in such remote communities.
The islands that have been analysed in this study differ each other for dimension, density of
population and climatic conditions (as shown in Table 1). Lampedusa and Linosa are the most
Southern and host one of the only two Municipalities in Italy laying in the Climatic Zone A (568
Heating Degree Days - HHD). On the other hand, Isola del Giglio is the most northern island of
the sample and it is the only one laying in the Climatic Zone D (2084 HHD) where the winter
heating demand is very relevant.

Table 1. Main data for the analysed islands (coordinates refer to the power plant site)

Climate Population
Island Latitude Longitude HDD Area Inhabitants
Zone density
2
N E [°C] [-] [Km2] [-] [inh./Km ]
Lampedusa 35° 30' 14.9" 12° 37' 13.2" 568 A 20.2 6234 308.6
Linosa 35° 51’ 38’’ 12° 51’ 52’’ 568 A 5.40 433 80.2
Ustica 38° 42' 33.5" 13° 11' 43.4" 717 B 8.09 1309 161.8
Pantelleria 36° 49' 40.4" 11° 56' 04" 717 B 83.0 7364 88.7
Isola del 42° 21' 10° 52' 2084 D 23.8 1299 54.5
Giglio 47.47" 50.04"
Favignana 37° 56' 06.3" 12° 20' 33.3" 814 B 19.8 3975 200.7

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