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C total  C CHP retr .  C abs .ch .  C pipes  C spec .el .  C civ .  C instal .  C subst . (7)
where:
- CCHP retr. indicates the cost for the CHP retrofit of the diesel engines. This retrofit essentially
requires installation of shell and tube heat exchangers for high temperature recovery from hot
gases (unit cost in the order of 100-120 €/kW) and plate heat exchangers for low temperature
recovery from the jacket cooling water circuit (unit cost in the order of 110-130 kW);
- Cabs.ch. indicates the cost for the absorption chillers. The inclusion of this cost component in the
financial evaluation, which is of course pertinent only in the two cases (Lampedusa and
Pantelleria) where space cooling requests are also covered, suggests that the existence of some
Energy Performance Contract (like the so-called “shared savings”) between the company and the
supplied customers is assumed;
- Cpipes is the cost of the required length of the main and branch pipes. Several catalogues from
different manufactures were examined [32,33], to develop useful correlations between the
diameter of the pipe and the cost per unit length (Eq. (8) and (9)):

pre
2


c pipes ins . steele  0. 002 ND  0. 123 ND  16. 73 [€/m] (8)
polyethile
2


c pipes ne  0. 0011 ND  0. 6128 ND  16. 73 [€/m] (9)

Both the above correlations provide a reasonable estimation of the unit cost of pipes over the
range of diameters ND (25 mm, 150 mm).
- Cspec.el. represents the cost for special elements such as junction boxes, TEE junctions and
expansion joints;
- Cciv. represents the cost for civil works;
- Cinstal. represents the installation cost of the DH network;
- Csubst. represents the total cost of substations (inclusive of heat exchangers, energy metering and
control equipment). This cost is excluded from the total cost for the scenario (adopted only in
Pantelleria) that assumes connection costs covered by the private customers.
All these costs were estimated on the basis of average cost figures. Details on the value of each
specific cost fraction are not provided for sake of brevity; in Table 5 the capital investments
calculated for the whole project (including CHP retrofit and installation of DH network and
related equipment) are presented.

Table 5. Capital investment for the whole “CHP retrofit + DH network” project in each island

Total investment for the
Island
whole project [M€]
Lampedusa 6.628
Favignana 4.422
Pantelleria 3.061
Ustica 1.235
Giglio 0.961
Linosa 0.602

As concerns the net annual revenues, they were calculated as difference between the incomes
from heat selling activity and the operating costs (which are usually available broken down into a
number of different components). Basing on data available in literature, this last term is at-a-flat-

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