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Sustainability 2017, 9, 106 10 of 19

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Sustainability 2017, 9, 106
type of magnet has been chosen thanks to its prominent features. In fact, neodymium–iron–boron
magnets are able to produce a strong and long lasting magnetic field, without any electrical energy
Obviously, the time variation of the magnetic field, due to the vertical alternate motion of the devices
request. Obviously, the time variation of the magnetic field, due to the vertical alternate motion of the
produced by the wave source, produces the electromotive forces in the electric circuit.
devices produced by the wave source, produces the electromotive forces in the electric circuit.

Figure 10. Graphic representation of a DEIM Point Absorber.
Figure 10. Graphic representation of a DEIM Point Absorber
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.

Figure 11. Cross section of the inner buoy of the DEIM Point Absorber.
Figure 11. Cross section of the inner buoy of the DEIM Point Absorber.
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