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Sustainability 2017, 9, 106 11 of 19

Several tests have been realized on a small scale prototype at the DEIM laboratory, showing
interesting results [16,17]. In particular, the electrical efficiency ranges from 50% to 75%, according to
the values of the peak period and significant height of the sea wave.
Prudently, in this text, an overall efficiency of 50% is fixed, according to the experimental data
obtained on the prototype, but it is clear that continuous studies about this WEC will be able to improve
this percentage.
A DEIM Point Absorber can be used in multiple array in off-shore wave farms along the western
coastline of the province of Trapani. In this way, it is possible to minimize the exploited areas and, at
the same time, to increase significantly the installed power.

4. A Case Study: Replacing the Diesel Fleet of Urban Buses with Hydrogen Fuel
Urban buses represent one excellent example for the introduction of hydrogen fuel into urban
mobility. We could find some benefit of this choice, such as the centralization of supply systems; regular
paths; weight reduction compared to vehicles for private transport. In general, all manufacturers have
focused on the polymer electrolyte cell (PEMFC, Proton Exchange Membrane Fuel Cell), that meets
the requirements for use in road vehicles. Low temperature PEMFCs are characterized by a conversion
efficiency of about 50%–60%, even at sizes of a few kilowatts [18,19]. Greater conversion efficiency can
be realized with high temperature PEMFC, however this technology shows difficulties in a vehicular
application, in particular the fuel cell must be firstly heated to the nominal temperature range in order
to work properly. For this reason, a cold start of high temperature PEMFCs is not applicable [20].
PEMFCs have zero pollutant emissions when fueled directly with hydrogen, produced by renewable
energy sources. There are some advantages, such as the high power density, the lack of corrosive fluids,
a simple structure. We present an adoption of this system (PEMFCs) to the urban bus of Trapani, that
is a city on the west coast of Sicily in Italy. The Municipal territory is inhabited by little more than
70,000 people spread over a vast area of 271 square kilometers. The urban buses have a central role in
its mobility. Table 4 shows data of the ATM (Transport Company) of Trapani.

Table 4. Comparison between theory and experiment.

Statistical Data ATM Trapani Traveled [km]
Diesel 44 1,274,350
Natural gas 0 -
Electrical 4 115,850
Total 48 1,390,200

The principal aim of this work is the gradual replacement of diesel with hydrogen produced by
renewable sources, such as wind, biomass and sea wave (examples presented in this work). We will
represent four different scenarios of the total annual kilometers of the urban fleet. The hydrogen
demand will be satisfied by the electrical energy production from renewable sources. In the final part,
we are going to evaluate the avoided emissions of hydrogen buses and an economic analysis.

4.1. Scenarios
The aim of this work is the replacement of diesel buses with hydrogen buses in the entire province
of Trapani. Moreover, this important goal can be achieved thanks to the use of a renewable energy
mix, including biomass, wind and sea wave sources. In particular, the last one can be useful, exploited
with the innovative conversion device proposed by University of Palermo. Different scenarios will
be proposed, in order to show the electrical energy requests to satisfy the production of hydrogen as
the energy carrier. These scenarios comprise a penetration respectively of 25%, 50%, 75% and 100% of
the total annual kilometers of the urban fleet. In this text, the diesel consumption in the urban areas
has been set equal to 0.4 l/km, while the hydrogen one has been set equal to 0.25 kg/km [21]. Table 5