Energy Saving in Public Transport Using Renewable Energy - MDPI

sustainability Article

Energy Saving in Public Transport Using Renewable Energy Vincenzo Franzitta *, Domenico Curto, Daniele Milone and Marco Trapanese Department of Energy, Information engineering and Mathematical models (DEIM), University of Palermo (UNIPA), 90128 Palermo, Italy; [email protected] (D.C.); [email protected] (D.M.); [email protected] (M.T.) * Correspondence: [email protected]; Tel.: +39-091-238-61941 Academic Editors: Francesco Asdrubali and Pietro Buzzini Received: 24 September 2016; Accepted: 9 January 2017; Published: 13 January 2017

Abstract: Hydrogen produced by renewable sources represents an interesting way to reduce the energetic dependence on fossil fuels in the transportation sector. This paper shows a feasibility study for the production, storage and distribution of hydrogen in the western Sicilian context, using three different renewable sources: wind, biomass and sea wave. The objective of this study is the evaluation of the hydrogen demand, needed to replace all diesel supplied buses with electrical buses equipped with fuel cells. An economic analysis is presented with the evaluation of the avoidable greenhouse gas emissions. Four different scenarios correlate the hydrogen demand for urban transport to the renewable energy resources present in the territories and to the modern technologies available for the production of hydrogen. The study focuses on the possibility of tapping into the potential of renewable energies (wind, biomass and sea wave) for the production of hydrogen by electrolysis. The use of hydrogen would reduce significantly the emissions of particulate and greenhouse gases in the urban districts under analysis. Keywords: hydrogen; wind; biomass; sea wave; mobility

1. Introduction Among the actions that the Kyoto Protocol indicates in order to reduce CO2 emissions, innovative technologies are promoted, in particular based on the exploitation of renewable energy sources (RES). All RES (expect geothermal) are related to solar radiation: annually the earth’s surface receives about 885 billion GWh of solar energy. This huge amount of energy is equivalent to 6200 times the primary energy consumed by humankind in 2008 [1]. For this reason, the RES could theoretically satisfy the entire energy demand of human settlements. Nevertheless, the existing energy systems are dominated by technologies based on fossil fuels, producing the emissions of greenhouse gases and polluting the environment [2]. Within this economically managed part of the energy sector, renewable energy sources currently provide about 25% of the energy supplied [3]. Energy use and resource depletion does not, of course, constitute the primary goals of any society or individual within a society. For example, average Europeans or Japanese use about half as much energy as the average North American, but have a living standard similar to the North American citizens. This underlines the fact that the living standard and welfare depends on having primary (food, shelter, relations) as well as secondary standards of individual preference fulfilled and this can be done in different ways with different implications for energy use [3]. In the last years, the interest of research and policy has been focused on a new system able to exploit energy from nature or economical sources of energy. Electricity generation from clean, safe and sustainable energy sources is nowadays a priority for many industrialized countries to meet increased energy demand and to reduce CO2 emissions. The residential and industrial sector modified their fundamental structure, for example with the Sustainability 2017, 9, 106; doi:10.3390/su9010106

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adoption of clean and sustainable improvements. In fact, another field that European Government of clean and sustainable improvements. In fact, another field that European Government studies with studies with more attention is mobility. Numerous researches have demonstrated that the number of more attention is mobility. Numerous researches have demonstrated that the number of vehicles in vehicles world to is expected the next 30 years, which couldnegative have serious negative the worldinisthe expected double into thedouble next 30inyears, which could have serious consequences consequences for energy security and The the climate. this is the growingfor demand cars in for energy security and the climate. cause ofThe thiscause is theofgrowing demand cars infor countries countries such as Brazil, China, India, South Korea, Mexico, Poland, Russia and Thailand as the people such as Brazil, China, India, South Korea, Mexico, Poland, Russia and Thailand as the people there there seek to increase their individual mobility they become prosperous seek to increase their individual mobility whenwhen they become moremore prosperous [4]. [4]. Figure 1 shows the correlation between the number of vehicles owned by people and the per capita income.

Figure 1. Correlation the per per capita capita income income and and the the number number of of personal personal vehicles vehicles owned. owned. Figure 1. Correlation between between the

The most common effect of this above-mentioned amount is the increasing air pollution. The most common effect of this above-mentioned amount is the increasing air pollution. Therefore, Therefore, some new possible solutions should be investigated. Hydrogen is an energy carrier with some new possible solutions should be investigated. Hydrogen is an energy carrier with great potential great potential for clean, efficient power in stationary, portable and transport applications. It is for clean, efficient power in stationary, portable and transport applications. It is envisaged as a envisaged as a significant element of the future fuel mix for transport, enhancing energy security, significant element of the future fuel mix for transport, enhancing energy security, reducing oil reducing oil dependency, greenhouse gas emissions and air pollution. Hydrogen allows a wide dependency, greenhouse gas emissions and air pollution. Hydrogen allows a wide diversification of diversification of energy sources. In combination with fuel cells, it can also improve energy efficiency energy sources. In combination with fuel cells, it can also improve energy efficiency in transport in transport and contribute strongly to mitigating climate change—especially when produced by and contribute strongly to mitigating climate change—especially when produced by renewable renewable primary energy sources. Hydrogen and fuel cell technologies were identified amongst the primary energy sources. Hydrogen and fuel cell technologies were identified amongst the new energy new energy technologies needed to achieve a 60% to 80% reduction in greenhouse gases by 2050. technologies needed to achieve a 60% to 80% reduction in greenhouse gases by 2050. Recent studies Recent studies show the possible advantages of hydrogen’s introduction on bus fleet. Shaheen et al. [5] show the possible advantages of hydrogen’s introduction on bus fleet. Shaheen et al. [5] showed that showed that greater levels of exposure to hydrogen-fueled vehicles lead to higher levels of hydrogen greater levels of exposure to hydrogen-fueled vehicles lead to higher levels of hydrogen acceptance and acceptance and that early adopters tend to feel safer when using the technology, leading to significant that early adopters tend to feel safer when using the technology, leading to significant improvements improvements in public awareness. Langford et al. [6] presented Knoxville Area Transit (KAT) as a in public awareness. Langford et al. [6] presented Knoxville Area Transit (KAT) as a case study to case study to support the transition of a medium sized transit agency to full conversion to hydrogen support the transition of a medium sized transit agency to full conversion to hydrogen fuel, describing fuel, describing requirements for hydrogen bus fleets, production, storage, refueling and requirements for hydrogen bus fleets, production, storage, refueling and maintenance facilities. maintenance facilities. In the past decade, there have been several projects demonstrating the In the past decade, there have been several projects demonstrating the feasibility of hydrogen bus feasibility of hydrogen bus infrastructure, vehicles and operating procedures. Another interesting infrastructure, vehicles and operating procedures. Another interesting benefit regarding hydrogen’s benefit regarding hydrogen’s production, is that it can be obtained from a variety of sources, such as production, is that it can be obtained from a variety of sources, such as fossil fuels or water, etc. fossil fuels or water, etc. Technologies for the production of hydrogen from fossil fuels (steam Technologies for the production of hydrogen from fossil fuels (steam reforming, partial oxidation, reforming, partial oxidation, gasification) are, as mentioned, mature and widely used (more than 95% gasification) are, as mentioned, mature and widely used (more than 95% of the hydrogen produced of the hydrogen produced today comes from these processes). As for its production from renewable today comes from these processes). As for its production from renewable sources, this comes from sources, this comes from such sources as biomass or water. Currently, the European Parliament passed a law on hydrogen vehicles’ homologation in an effort to protect the environment in urban centers.

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such sources as biomass or water. Currently, the European Parliament passed a law on hydrogen Thehomologation law applies not to the of fuel cell vehicles also to the development of vehicles’ in only an effort todevelopment protect the environment in urbanbut centers. hydrogen filling stations and the necessity of producing in sustainable ways [7]. Hydrogen The law applies not only to the development of fuel hydrogen cell vehicles but also to the development of can be produced from biomass through several thermochemical such as [7]. gasification or hydrogen filling stations and the necessity of producing hydrogen inprocesses, sustainable ways Hydrogen pyrolysis and biological processes. Oneseveral of the thermochemical possible renewable energysuch sources to be used or to can be produced from biomass through processes, as gasification produce and hydrogen is water, through electrolysis orrenewable thermochemical processes. thistopaper, we pyrolysis biological processes. One of the possible energy sources to beInused produce consider is thewater, hydrogen production based on the electrolysis process, since it requires only the the hydrogen through electrolysis or thermochemical processes. In this paper, we consider electrical energy supply, thaton can beelectrolysis easily satisfied by using renewable energy sources. hydrogen production based the process, sinceseveral it requires only the electrical energy The following Section 2 analyzes the energy of wind, supply, that can be easily satisfied by using severalpotential renewable energybiomass sources.and sea wave sources in the western SicilianSection context. In order the to exploit wave source, anbiomass energy converter is presented. The following 2 analyzes energythe potential of wind, and sea wave sources The 4 evaluates the hydrogen demand in order to replace thean diesel-powered buses in Trapani in theSection western Sicilian context. In order to exploit the wave source, energy converter is presented. with electrical buses equipped with demand fuel cells.inThe three different sources are considered for The Section 4 evaluates the hydrogen order to replace theenergy diesel-powered buses in Trapani the hydrogen production. Finally, environmental evaluation is presented. with electrical buses equipped with an fueleconomic cells. Theand three different energy sources are considered for the hydrogen production. Finally, an economic and environmental evaluation is presented. 2. Renewable Energy Sources in Trapani 2. Renewable Energy Sources in Trapani 2.1. Wind Source 2.1. Wind Source Firstly, we analyze the wind resource. In Sicily, this source is characterized by high potential Firstly, the wind resource. In Sicily,from this source characterized by high levels levels and we theanalyze production of electrical energy wind isturbines represents [8]potential nowadays an and the production of electrical energy from wind turbines represents [8] nowadays an important important percentage of the overall electrical energy production in loco [9]. Wind source was percentage the overall electrical energy production in loco [9]. Wind source accurately studied accurately of studied by CESI (Centro Elettrotecnico Sperimentale Italiano) andwas Physics Department of by CESI (Centro Elettrotecnico Sperimentale Italiano) and Physics Department of University of Genova. University of Genova. Thanks to these studies, the Italian Wind Atlas (Atlante Eolico Italiano) is now Thanks to these the Italian Eolico Italiano) is now available [10]: it electrical is a very available [10]: studies, it is a very useful Wind onlineAtlas tool,(Atlante that can be used to evaluate the theoretical useful online tool, that can be used to evaluate the theoretical electrical energy production from wind energy production from wind turbines. The web page reports a GIS (Geographic Information System) turbines. The web reports GIS (Geographic Information System) map, in which map, in which the page average windaspeed at different levels from the soil is expressed: 25 m,the 50 average m, 75 m, wind speed at different levels from the soil is expressed: 25 m, 50 m, 75 m, 100 m from the soil. In this 100 m from the soil. In this work, we consider only the average wind speed at 50 m from the soil, work, we consider only the average wind speed at 50 m from the soil, because the particular type of because the particular type of wind turbine selected will be able to work at this distance. Greater wind turbine selected be abletotointroduce work at this distance. distances involve thewhile necessity to distances involve thewill necessity a higher andGreater more visible wind turbine, shorter introduce a higher and more visible wind turbine, while shorter distances reduce the electrical energy distances reduce the electrical energy production. Moreover, the authors focused their attention on production. the in authors their on the on-shore wind with source in order to not the on-shoreMoreover, wind source order focused to not use seaattention areas, which will be exploited a Point Absorber, use sea areas, will be 3. exploited withthe a Point Absorber, proposed in the Section for 3. Moreover, the proposed in which the Section Moreover, Italian laws are a serious obstacle the potential Italian laws are a serious obstacle for the potential installation of off-shore wind farms. Figure 2 shows installation of off-shore wind farms. Figure 2 shows the average wind speed in Sicily at 50 m above the average wind speed in Sicily at 50 m above ground level. ground level.

Figure 2. Average wind speed in Sicily at 50 m above ground level. Figure 2. Average wind speed in Sicily at 50 m above ground level.

Particularly, most of the Sicilian lands are characterized by an average wind speed comprised between 5 and 6 m/s. Additionally, the province of Trapani presents higher values, comprised


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Sustainability 2017, 9, 106 Particularly, most

4 of 19 of the Sicilian lands are characterized by an average wind speed comprised between 5 and 6 m/s. Additionally, the province of Trapani presents higher values, comprised between between 6 and 7 m/s, with a maximum of 8 m/s in the coastlines. This is due to the higher fetch in 6 and 7 m/s, with a maximum of 8 m/s in the coastlines. This is due to the higher fetch in which the which the wind is able to blow. So, Trapani is an excellent place to adequately exploit the wind source. wind is able to blow. So, Trapani is an excellent place to adequately exploit the wind source. Figure 3 shows the GIS map of the annual theoretical energy production by wind in Sicily. Most Figure 3 shows the GIS map of the annual theoretical energy production by wind in Sicily. of Sicily shows an average production between 1500 and 2000 MWh/MW, while the values shown in Most of Sicily shows an average production between 1500 and 2000 MWh/MW, while the values the province of Trapani remain higher. It is marked by values comprised between 2000 and 2500 shown in the province of Trapani remain higher. It is marked by values comprised between 2000 and MWh/MW, with a maximum of 3000 MWh/MW in the coastlines. Prudently, an average value of 2000 2500 MWh/MW, with a maximum of 3000 MWh/MW in the coastlines. Prudently, an average value MWh/MW is fixed in this text. of 2000 MWh/MW is fixed in this text.

Figure Figure 3. 3. Energy Energy production production in in Sicily Sicily at at 50 50 m m above above ground groundlevel. level.

2.2. 2.2. Biomass Biomass Source Source As resource, wewe consider the installation of a power plant with ratedapower As regards regardsthe thebiomass biomass resource, consider the installation of a power planta with rated of 1.2 MW (electrical output). output). The biomass power station composed of eight small ORC (Organic power of 1.2 MW (electrical The biomass powerisstation is composed of eight small ORC Rankine units, eachunits, one having a rated electrical output equaloutput to 150 kW [11]. kind[11]. of plant (OrganicCycle) Rankine Cycle) each one having a rated electrical equal to This 150 kW This is ableoftoplant use several biomass, forof example straw, pruning straw, residues of olives and vineyards. kind is able types to useofseveral types biomass, for example pruning residues of olives Before the use, the biomass is dried and converted and vineyards. Before the use, the biomass is driedinto andwoodchips converted and into pellets. woodchips and pellets. The The annual annual biomass biomass consumption consumption of of the the power power plant plant isis estimated estimated at at about about 13,600 13,600 t/year, t/year, considering lower heating heatingvalue value(LHV) (LHV)equal equaltoto1717 MJ/kg, electrical efficiency fixed to 16% considering a lower MJ/kg, an an electrical efficiency fixed to 16% and and a boiler efficiency fixed to 85% a boiler efficiency fixed to 85% [11].[11]. Based toto identify a suitable sitesite forfor thethe installation of Based on onthe theinformation informationgiven givenbelow, below,we wewill willtrytry identify a suitable installation aofbiomass power plant, in in thethe city ofof Trapani. a biomass power plant, city Trapani.The Thebiomass biomasscatchment catchmentarea areaisisselected selectedaccording according to to these conditions: conditions: these

•

collectionof ofatatleast least50% 50%ofofbiomass biomassfrom fromstraw, straw, sufficient cover 30% biomass demand collection sufficient to to cover 30% of of thethe biomass demand of of the power plant; the power plant; collectionof of at at least least 50% 50% of of biomass biomass from from pruning pruning residues residues of of olives olives and and vineyards, vineyards, sufficient sufficient to to • collection cover 70% of the biomass demand of the power plant. cover 70% of the biomass demand of the power plant. The analysis firstly evaluates the territory of Trapani, having a surface of 3555 ha at the northern The analysis firstly evaluates Trapani, a surface hathe at the northern part of the town and 25,500 ha atthe theterritory southernofpart. The having following Figureof4 3555 shows land uses in part of the town and 25,500 hagreatest at the southern part. The following 4 shows the land uses in the the territory of Trapani. The part of the territory is used Figure for cultivation, in particular 42.8% territory of Trapani. The greatest part of the territory is used for cultivation, in particular 42.8% for for extensive farming and 31.8% for vineyards. extensive farming and 31.8% for vineyards.


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Figure4.4.Land Land uses uses in in Trapani Trapani city. Figure city.

Table 1 reports productionin inthe theterritory territoryofofTrapani. Trapani. With Table 1 reportsthe themain maindata dataabout about the the biomass biomass production With thethe term “biomass equivalent”,we weconsider consider aa biomass having fixed to to 1717 MJ/kg. term “biomass equivalent”, havingaalower lowerheating heatingvalue value fixed MJ/kg. Table1.1.Agriculture Agriculture residues residues in Table in the the territory territoryofofTrapani. Trapani. Type of Cultivation

Type of Cultivation

Extensive cultivation Vineyard pruning Olive pruning Extensive cultivation Total biomass equivalent

Surface Surface Occupied [ha]

Occupied 11,545.60 [ha] 8592.73 1631.93 11,545.60 21,770.26

Productivity Moisture Fraction Moisture Productivity [t/ha] [%] 3.0[t/ha] 2.8 2.1 3.0

Fraction 50[%]

Lower Heating Value Lower Heating [MJ/kg] Value 14 [MJ/kg] 17

Dry Residue

Dry[t/Year] Residue [t/Year] 34,636.80 12,029.82

40 -

2056.23 1417 34,636.80 17 42,610.48 Vineyard pruning 8592.73 2.8 50 17 12,029.82 Olive pruning 1631.93 2.1 40 17 2056.23 As shown in Table 1, the total available biomass is enough to satisfy17 the biomass demand of Total biomass equivalent 21,770.26 42,610.48 -

the power plant, in the case of complete interception. However, this hypothesis is unrealistic, in fact, the fraction of collected biomass generally does not exceed 50%. Furthermore, in order to reduce the As shown in Table 1, the total available biomass is enough to satisfy the biomass demand of the volumes of biomass storage, the biomass input from extensive crops must be reasonably limited to power plant, in the case of complete interception. However, this hypothesis is unrealistic, in fact, the 30% of the energy requirements of the power plant, due to the low calorific value and the low density fraction of collected biomass generally does not exceed 50%. Furthermore, in order to reduce the of straw bales that increase the costs for the collection, transport and storage. volumes of biomass storage, the biomass input from extensive crops must be reasonably limited to Table 2 shows the results of this first hypothesis: the available biomass from straw is abundant, 30% of the energy requirements of the power plant, due to the low calorific value and the low density while the biomass from the pruning of olives and vineyards is not enough to cover the demand of the of power straw bales plant.that increase the costs for the collection, transport and storage.

Table 2 shows the results of this first hypothesis: the available biomass from straw is abundant, while the biomass from thebiomass pruning of territory olives and vineyards is not required enoughby topower coverplant. the demand of Table 2. Available in the of Trapani and biomass the power plant. Lower Heating Value Available Biomass Biomass Demand Surplus Figure 5 Cultivation shows the distribution of several cultivations in the territory of Trapani. The map shows Type of [MJ/kg] [t/Year] [t/Year] [t/Year] also that the territory of Trapani is14contained in a range of 30 km from4954 the ATM (Azienda Trasporti Extensive cultivation 17,318 12,364 e Mobilità) bus depot, so this location can be a potential site for the installation of the biomass power Vineyard pruning 17 6015 −2477 9520 plant andOlive hydrogen pruning production. 17 1028 Table 2. Available biomass in the territory of Trapani and biomass required by power plant

Figure 5 shows the distribution of several cultivations in the territory of Trapani. The map shows also that the territory of Trapani is contained range of 30 km from Biomass the ATMDemand (Azienda Trasporti Lower Heating Valuein aAvailable Biomass Surplus e Type of Cultivation

[MJ/kg]

[t/Year]

[t/Year]

[t/Year]

Extensive cultivation

14

17,318

4954

12,364

Vineyard pruning

17

6015

Olive pruning

17

1028

9520

−2477


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Mobilità) bus depot, so this location can be a potential site for the installation of the biomass power Sustainability 9, 106 production. plant and2017, hydrogen

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Figure 5. Culture distribution in the territory of Trapani. Figure 5. Culture distribution in the territory of Trapani.

However, since the availability of biomass in the Trapani area is not enough to cover the demand However, since of biomass in the Trapani areaof is the not area enough to cover the demand of the power plant, it the willavailability have to accept to increase the radius of biomass interception. of the power plant, it will have to accept to increase the radius of the area of biomass interception. For this reason, the analysis is extended to the province of Trapani. For this reason, the analysis is extended to the province of Trapani. In order to respect the conditions for the identification of the biomass harvesting area and to In order to respect the conditions for the identification of the biomass harvesting area and to contain the collection and transportation costs, the analysis is conducted considering the available contain the collection and transportation costs, the analysis is conducted considering the available resources in a radius not more than 70 km from the potential site of the power plant. resources in a radius not more than 70 km from the potential site of the power plant. Table 3 reports the available dry biomass residue in the province of Trapani. This area is divided Table 3 reports the available dry biomass residue in the province of Trapani. This area is divided in in concentric zones, km and andthe thecenter centerfixed fixed location of the ATM bus depot, concentric zones,with withaastep step of of 10 10 km inin thethe location of the ATM bus depot, as as shown in Figure 6. The map shows a heterogeneous mix of crops (olive, vineyard and straw) within shown in Figure 6. The map shows a heterogeneous mix of crops (olive, vineyard and straw) within a a radius of 10 km, rather than vineyards and extensive cultivations that are more widespread. The radius of 10 km, rather than vineyards and extensive cultivations that are more widespread. The major major crops of olives are concentrated the region radius ranging and 50 km. crops of olives are concentrated in the in region havinghaving a radiusa ranging betweenbetween 40 and 5040km. Figure 7 reports the available biomass resource as a function of the distance from the ATM bus Table 3. of Available drybiomass residues in province, by demand type of cultivation. depot. Fixing the fraction collected toTrapani 50%, the biomass from extensive cultivation can be satisfied with a collection radius ranging between 5 and 10 km, while the biomass demand Available Dry Biomass Residue [t/Year] from olives and vineyards Distance [km] cropping can be satisfied with a collecting radius ranging between 15 and Olives Vineyards 20 km, as shown in Figure 8. Extensive Cultivations 10 17,960.94 3419.84 3782.56 20 49,686.60 2232.81 17,312.36 Table 3. Available dry residues in Trapani province, by type of cultivation. 30 50,465.28 2424.83 27,370.39 40 55,058.61 3308.38 35,798.84 Available Dry Biomass Residue [t/Year] 50Distance [km] 33,338.85 20,569.28 Extensive Cultivations12,020.64 Olives Vineyards 60 10,155.51 1677.83 3940.85

10 20 30 40 50 60

17,960.94 49,686.60 50,465.28 55,058.61 33,338.85 10,155.51

3419.84 2232.81 2424.83 3308.38 12,020.64 1677.83

3782.56 17,312.36 27,370.39 35,798.84 20,569.28 3940.85


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Figure in Trapani Trapaniprovince. province. Figure 6. 6. Culture Culture distribution distribution in

Figure 7 reports the available biomass resource as a function of the distance from the ATM bus depot. Fixing the fraction of collected biomass to 50%, the biomass demand from extensive cultivation can be satisfied with a collection radius ranging between 5 and 10 km, while the biomass demand from olives and vineyards cropping can be satisfied with a collecting radius ranging between 15 and 20 km, as shown in Figure 8. Figure 6. Culture distribution in Trapani province.

Figure 7. Available biomass in the province of Trapani, as a function of the distance from the ATM bus depot.

Figure Trapani, as as aa function function of ofthe thedistance distancefrom fromthe theATM ATM Figure7. 7. Available Available biomass biomass in in the the province province of of Trapani, bus depot. bus depot.


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Figure Biomasssurplus surplusasas a function ofdistance the distance of the ATM bus depot, in the province Figure 8. 8. Biomass a function of the of the ATM bus depot, in the province of Trapani. of Trapani.

2.3. Sea Wave Source 2.3. Sea Wave Source Sea wave source represents nowadays an unused renewable source, despite the high levels Sea wave source nowadays an assumes unused renewable source, despite the high levels of exploitable energyrepresents [12]. This consideration greater importance, especially in this caseof exploitable energy [12]. This consideration assumes greater importance, especially in this case study study of the province of Trapani. In fact, as exposed in [12], the higher levels of wave energy in the ofMediterranean the provinceSea of are Trapani. In fact, exposed in [12], the higher levelswith of an wave energy in the identified in theaswestern coasts of Sardinia and Sicily, average off-shore Mediterranean Sea are identified in[13]. the western of Sardinia with an average offwave power greater than 5 kW/m So, thesecoasts particular sites areand the Sicily, best ones along the Italian shore wave power greater than 5 kW/m [13]. So, these particular sites are the best ones along the coastline in order to use the new conversion device here proposed. The main parameters through Italian in order to use new conversion device proposed. The main which coastline wave energy is defined arethe significant wave height Hs here (measured in meters); peakparameters period Tp through which wave energy is defined are significant wave in height meters); (measured in seconds); and main direction D p . The first oneheight represents(measured the average ofpeak the period (measured inwhile seconds); and main . Theoffirst one represents the height highest third of waves, the second onedirection is highest value the period measured inaverage the recording oftime. the highest third of waves, while the second is highest the Ondametrica period measured in the These parameters were collected thanks to one the wave buoysvalue of theofRete Nazionale (RON), which from 1989. Additionally, the data obtained buoys were recording time. operated These parameters were collected thanks to the wave through buoys ofthe the wave Rete Ondametrica used to confirm values carried out by1989. simulating software, which windthrough data as input. In Nazionale (RON),the which operated from Additionally, the data used obtained the wave this way, it was possible to describe wave energy potential along the Sicilian coastline in more detail. buoys were used to confirm the values carried out by simulating software, which used wind data as Furthermore, the use of GIS technology (see Figure 9) is able to identify simultaneously the wavein input. In this way, it was possible to describe wave energy potential along the Sicilian coastline source and Furthermore, the restricted areas inof which this source (see will Figure not be 9) exploited example, due to the more detail. the use GIS technology is able to(for identify simultaneously presence of particular maritime Particularly, Figure 9 shows the the wave source and theenvironmental restricted areasand in which thisconstraints). source will not be exploited (for example, due of maritime constraints along the islands of Favignana, Marettimo and Levanzo. According topresence the presence of particular environmental and maritime constraints). Particularly, Figure 9 shows to the averageofwave potential, the coastlines the province of Favignana, Trapani can be divided into parts: the presence maritime constraints alongofthe islands of Marettimo andtwo Levanzo. the northern southern part. The firstthe onecoastlines is globallyofcharacterized wave power According to and the the average wave potential, the provincebyofa Trapani can comprised be divided between 5 and 6 kW/m, while the second one is characterized by values comprised between and into two parts: the northern and the southern part. The first one is globally characterized by a6wave 7 kW/m. In this text, an annual wave power of 5 kW/m is cautiously fixed for the northern part of the power comprised between 5 and 6 kW/m, while the second one is characterized by values comprised coastlines between 6 and and 67 kW/m kW/m.for In the thissouthern text, an part. annual wave power of 5 kW/m is cautiously fixed for the Moreover, the main wave direction is [12], thanks northern part of the coastlines and 6 kW/mnorth-west for the southern part. to the exposition to the wider fetch. The Moreover, correct position of the wave buoys array will have [12], to consider characteristic, inthe order to avoid the main wave direction is north-west thanks this to the exposition to wider fetch. interference phenomena. Finally, wave source appears to be higher during the winter season and lower The correct position of the wave buoys array will have to consider this characteristic, in order to avoid during the summer season. The issue to the variability of this source be overridden interference phenomena. Finally, waveconnected source appears to be higher during the can winter season and through the use of appropriate storage tanks. lower during the summer season. The issue connected to the variability of this source can be overridden through the use of appropriate storage tanks.


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Figure 9. Average power (measured in kW/m) in the western coastlines of Sicily. Figure 9. Average power (measured in kW/m) in the western coastlines of Sicily.

3. The Point Absorber for the Exploitation of Sea Wave Source 3. The Point Absorber for the Exploitation of Sea Wave Source The Point Absorber here proposed is an innovative wave energy converter designed and The Point here proposed is an innovative wave energy converter designed developed by theAbsorber Department of Energy, Information engineering and Mathematical models (DEIM) and developed by the of Department of Energy, Information engineering andwave Mathematical models (DEIM) of the University Palermo. This machine is able to directly convert energy into electrical of the University of Palermo. This machine is able to directly convert wave energy into electrical output without the use of intermediate devices [14], such as toothed wheels, transmission belts or output without the use oforintermediate devices suchtoasconvert toothed wheels, transmission belts or pressurized fluids (water oils). Moreover, it will[14], be able wave energy independently pressurized fluids (water or oils). it will be able toon convert wave energy independently from its propagation direction. ThisMoreover, new technology is based an innovative small-scale prototype from of apropagation linear generator projected at theis DEIM The Wave Energy Converter its direction. Thisand newrealized technology based laboratory. on an innovative small-scale prototype of a (WEC) is shown in Figure 10. It is fundamentally composed of two floating buoys. The external linear generator projected and realized at the DEIM laboratory. The Wave Energy Converterbuoy (WEC) is (yellowin one) is the10. capture device, becausecomposed it intercepts alternate motion. shown Figure It is fundamentally of the twocontinuous floating buoys. Thewave external buoyThis (yellow motion is transferred inside the central buoy (green in the picture), which one) is the capture device, because it intercepts the continuous alternate wavecontains motion. the Thislinear motion is generators, thanks to acentral connecting (blue The external has athe nominal of 10 transferred inside the buoyrod (green in rod). the picture), whichbuoy contains lineardiameter generators, thanks meters, while the internal one has a nominal diameter of 2 m. The working stroke of the linear to a connecting rod (blue rod). The external buoy has a nominal diameter of 10 m, while the internal generators is about diameter 4 meters: of so,2 the WECworking will produce energy [15] also is inabout bad weather one has a nominal m. The strokeelectrical of the linear generators 4 m: so, the conditions (which usually represents the most energetic sea state). Additionally, most of the WEC will produce electrical energy [15] also in bad weather conditions (which usually represents the conversion device is under the sea level in order to avoid a significant visual impact. The presence of most energetic sea state). Additionally, most of the conversion device is under the sea level in order to a red light in the upper part of the WEC, at different heights in meters, makes it visible up to several avoid a significant visual impact. The presence of a red light in the upper part of the WEC, at different nautical miles away. Each of the eight linear generators presents a nominal power of 10 kW, for a heights in meters, makes it visible up to several nautical miles away. Each of the eight linear generators total nominal power of 80 kW. The particular size of the conversion device has been chosen in order presents a nominal power of 10 kW, for a total nominal power of 80 kW. The particular size of the to optimize the electrical energy production according to the wave climate along the western coast of conversion deviceinertia has been chosen order optimize the energyweight production according Sicily. The greater of the inner in buoy andtothe presence ofelectrical a hemispherical in its lower to the wave climate along the western coast of Sicily. The greater inertia of the inner buoy and the part guarantee the correct vertical positioning of the conversion device. presence of a hemispherical weight inone) its lower partthe guarantee the vertical positioning Furthermore, a jumper buoy (blue connects lower part ofcorrect the inner buoy to the weightsof the conversion device. located in the seabed, through heavy chains. The role of this jumper buoy is very important: in fact, Furthermore, a jumper one) the lower part of the the damage inner buoy to the weights it is able to maintain the fourbuoy lower(blue chains in connects vertical position, avoiding of the seabed located in the seabed, through heavy chains. role in of the thisupper jumper very and its precious flora and fauna. Two springs areThe located andbuoy lowerispart of important: the inner in fact, is able any to maintain in vertical damage of the case, it avoiding damage ofthe thefour innerlower buoy chains due to bad weather,position, as shownavoiding in Figure the 11. Each linear generator is composed of two parts: statorTwo and the translator. The firstin one represents the lower magnetic seabed and its precious flora andthe fauna. springs are located the upper and part of circuit, andcase, it is avoiding composedany of two plate packs The copper are weather, arranged as in the hollows and 11. the inner damage of thesteel. inner buoy duecoils to bad shown in Figure present a three-phase connection, is the connection the the national grid. The The first second is Each linear generator is composedthat of two parts: the statorofand translator. one one represents composed of 132 neodymium–iron–boron permanent magnets fixed in a plate realized in a nonthe magnetic circuit, and it is composed of two plate packs steel. The copper coils are arranged in the magneticand material, bakelite, which also has a highthat electrical this particular type hollows present a three-phase connection, is the resistance. connectionMoreover, of the national grid. The second of magnet has been chosen thanks to its prominent features. In fact, neodymium–iron–boron magnets one is composed of 132 neodymium–iron–boron permanent magnets fixed in a plate realized in a are able to produce a strong and long lasting magnetic without any electrical energythis request. non-magnetic material, bakelite, which also has a highfield, electrical resistance. Moreover, particular


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Sustainability 2017,has 9, 106been chosen thanks to its prominent features. In fact, neodymium–iron–boron 10 of 19 type of magnet 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 Graphicrepresentation representation a DEIM Point Absorber. Figure 10. Graphic of aofDEIM Point Absorber

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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 Crosssection sectionofofthe the inner buoy of the DEIM Absorber. Figure 11. 11. Cross inner buoy of the DEIM PointPoint 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


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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 Natural gas Electrical Total

44 0 4 48

1,274,350 115,850 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


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reports the overall annual distance covered by the hydrogen bus fleet, the corresponding hydrogen demand and the avoided diesel consumption, in the four scenarios. Table 5. Distance covered by hydrogen fleet and fuel request in four hydrogen penetration scenarios. Penetration Rate [%]

Distance Covered by Hydrogen Fleet [km]

Avoided Diesel Consumption [L/Year]

Hydrogen Request [kg/Year]

25 50 75 100

318,587 637,175 955,762 1,274,350

127,435 254,870 382,305 509,740

79,647 159,294 238,941 318,588

A compensatory approach will be proposed: the conversion devices will be installed in the best sites of Trapani’s province without territorial or marine constraints, while the production and storage of hydrogen is useful to be realized near the transport company’s venue. The presence of the storage tanks will be helpful to compensate the fluctuations of the electrical energy production and, in this way, the hydrogen generator will be able to work optimally. The electrical energy request to produce 1 kg of H2 has been set equal to 56.3 kWh [22], through the electrodialysis technology. Furthermore, the electrical energy consumption for the storage of 1 kg of H2 in compressed form has been set equal to 3.35 kWh [23], for a global request of 59.65 kWh/kg of H2 . Table 6 reports the evaluation of the electrical energy demand related to the production and storage of hydrogen in the four different scenarios. Table 6. Electrical energy demand in the four hydrogen penetration scenarios. Penetration Rate [%]

Electrical Demand to Produce H2 [GWh/Year]

Electrical Demand to Store H2 [GWh/Year]

Total Electrical Demand [GWh/Year]

25 50 75 100

4.49 8.97 13.50 17.94

0.27 0.53 0.80 1.07

4.75 9.50 14.25 19.00

As shown before, in this study, we consider the following renewable energy sources: biomass, wind and sea wave. As regards the biomass source, we consider the installation of several ORC units, each one having a rated electrical power of 150 kW; in particular, in the 100% scenario, eight ORC units will be installed, with an overall installed power of 1.2 MW. In order to exploit the wind source, we selected wind turbines, having a rated power of 330 kW. The rotor has a horizontal axis, installed about 50 m from the ground. In the 100% scenario, 10 wind turbines will be required. Finally, as regards sea wave source, we consider the installation of a wave farm composed of 20 DEIM point absorbers. Figure 12 shows the electrical energy production by renewable source; Figure 13 shows the number of units by renewable source in the four hydrogen penetration scenarios. In every scenario, we have a modest surplus of electrical energy, which can be sold on the electrical network. The sizing of the renewable energy plants is realized, with the hypothesis of annual balancing. During the year, of course, it is possible that the energy production by renewable sources could exceed the electrical energy demand of the hydrogen station or on the contrary the renewable production could be not enough to cover the energy demand. In every case, the role of balancing between electrical energy production and energy consumption by hydrogen station will be assigned to the electrical grid.


13 of 19 13 of 19

absorbers. 2017, Figure 12 Sustainability 9, 106

shows the electrical energy production by renewable source; Figure 13 shows 13 of 19 absorbers. Figure 12 shows the electrical energy production by renewable source; Figure 13 shows the number of units by renewable source in the four hydrogen penetration scenarios. the number of units by renewable source in the four hydrogen penetration scenarios.

Figure 12. 12. Electricalenergy energy production produce store 2, by renewable energies (biomass, Figure to to produce andand store H2 , H by energies (biomass, wind Figure 12. Electrical Electrical energyproduction production to produce and store H2,renewable by renewable energies (biomass, wind and sea wave). and sea wave). wind and sea wave).

Figure 13. Number of units required to satisfy the electrical demand, by scenario. Figure to satisfy satisfy the the electrical electrical demand, demand, by by scenario. scenario. Figure 13. 13. Number Number of of units units required required to

In every scenario, we have a modest surplus of electrical energy, which can be sold on the In every scenario, we have a modest surplus of electrical energy, which can be sold on the 4.2. Avoided Emissions electrical network. The sizing of the renewable energy plants is realized, with the hypothesis of electrical network. The sizing of the renewable energy plants is realized, with the hypothesis of annual During the year, of with course, it is possible the province energy production renewable Thebalancing. replacement of diesel buses hydrogen busesthat in the of Trapaniby represents a annual balancing. During the year, of course, it is possible that the energy production by renewable sources could exceed the electrical energy demand of the hydrogen station or on the contrary the big opportunity to reduce significantly the production of pollutants in urban areas, especially due to sources could exceed the electrical energy demand of the hydrogen station or on the contrary the renewable production could be not of enough to cover demand. In every case, the role of public transport. The centralization the storage andthe theenergy presence of specialized workers represent renewable production could be not enough to cover the energy demand. In every case, the role of other important advantages. The emission factors used in this text are shown in Table 7 [17]. These are: CO2 , CO, PM10 , NMVOC and NOx , expressed in g/km.

The replacement of diesel buses with hydrogen buses in the province of Trapani represents a big opportunity to reduce significantly the production of pollutants in urban areas, especially due to public transport. The centralization of the storage and the presence of specialized workers represent other important advantages. The emission factors used in this text are shown in Table 7 [17]. These Sustainability 2017, 9, 106 14 of 19 are: CO2, CO, PM10, NMVOC and NOx, expressed in g/km. Table the province province of of Trapani. Trapani. Table 7. 7. Emission Emission factors factors used used for for public public transport transport in in the Pollutants Pollutants CO2 CO2 CO CO PM10 PM 10

NMVOC NMVOC NO x x NO

Emission Factors [g/km] Emission Factors [g/km] 1132.797 1132.797 5.992 5.992 0.879 0.879 1.642 1.642 17.92717.927

The avoided emissions are obtained by multiplying these emissions factors by the kilometers covered by the diesel buses in every scenario. Obviously, the biggest item is represented represented by by CO22, but important role in order to reduce global the avoided emissions of the other pollutants have also an important warming [24]. 14 shows showsthe theavoided avoidedemissions emissionsfor forthe thebest best scenario (penetration rate equal to 100%). Figure 14 scenario (penetration rate equal to 100%). In In order to reach this prestigious goal, all three renewable resources are necessary, obtaining order to reach this prestigious goal, all three renewable resources are necessary, obtaining a variegated energy mix.

Figure best scenario scenario (100% (100% of of hydrogen hydrogen penetration penetration rate). rate). Figure 14. 14. Avoided Avoided emissions emissions in in the the best

Finally, the following Table 8 reports the avoided emission in the four different hydrogen Finally, the following Table 8 reports the avoided emission in the four different hydrogen penetration scenarios. penetration scenarios. Table 8. Avoided emissions for public transport in the province of Trapani. Penetration Rate Scenario [%]

Distance Covered by Hydrogen Fleet [km]

25 50 75 100

318,587 637,175 955,762 1,274,350

Avoided Emissions [t/Year] CO2

CO

PM10

NMVOC

NOx

361 722 1083 1444

1.91 3.82 5.73 7.64

0.28 0.56 0.84 1.12

0.52 1.05 1.57 2.09

5.71 11.42 17.13 22.85

4.3. Economic Analysis In this section, we report the economic analysis in the 100% hydrogen penetration scenario. Except for the sea wave farm, in literature, much information about the items of investment, operative and


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maintenance costs can be found. The evaluation of the investment costs for hydrogen production can be easily realized, because all components are already used in the chemical industry. In order to evaluate the economic viability, the discounted cash flow is calculated in two different hypotheses: A.

B.

In this hypothesis, we take into account the initial investments of the biomass power plant, wind farm, wave farm, and hydrogen station. As virtual annual income, we consider the avoided purchase of fossil fuel. In this hypothesis, we consider only the installation of the hydrogen station, run by purchasing electrical energy from the grid. Similarly, as virtual annual income, we consider the avoided purchase of fossil fuel.

The discounted cash flow is evaluated by the following equation: n

DCF = − I0 −

∑

i=1

Ii

(1 + τ ) i

+ Fc f uel − Ecenergy

n

∑

i=1

1 + ε 1 + τ

i (1)

Where I0 is the initial investment, Ii the annual costs for operative and maintenance costs, F is the avoided annual diesel consumption, E is the annual energy required to produce hydrogen (this term is considered only in the hypothesis B), c f uel and cenergy represent respectively the unitary costs of electrical fuel (1.40 €/L) and energy (170 €/MWh), τ is the discount rate and ε is the discount rate in the energy sector. According to [25,26], τ is fixed to 1% and ε to 3%. Table 9 reports the main items of initial investments for the installation of the wind farm. In particular, the costs are evaluated considering the installation of 10 wind turbines, each one having a rated power of 330 kW [27,28]. The unitary costs are expressed in function of the installed power. Table 9. Initial costs of the wind farm. Item Cost

€/kW

€

Wind turbine Grid connection Constructions Others Total

1652 354 236 118 2360

5,451,600 1,168,200 778,800 389,400 7,778,000

Similarly, Table 10 reports the main items of initial investments for the installation of the biomass power plant. We consider the installation of eight ORC (Organic Rankine Cycle) units, each one having a rated electrical output of 150 kW [11,29]. Table 10. Initial costs of the biomass power plant. Item Cost

€/kW

€

ORC unit Grid connection Constructions Others Total

2440 150 270 50 2910

2,928,000 180,000 324,000 60,000 3,492,000

Table 11 reports the initial costs for the installation of a wave farm, composed of 20 DEIM points absorber, each one having a rated power of 80 kW.


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Table 11. Initial costs of the wave farm. Item Cost

€/kW

€

On-shore transformers and grid Cables Mooring Building/facilities Installation work Sea wave energy converters Total

18 12 75 150 35 2500 2790

28,800 19,200 120,000 240,000 56,000 4,000,000 4,464,000

Finally, Table 12 reports the initial costs estimated for the realization of the hydrogen station. The unitary costs are expressed in function of daily production capability of hydrogen [30]. In particular, as reported in Table 5, the annual hydrogen demand estimated is equal to 318,588 kg/year. Fixing the annual availability to 0.97 and considering an increase in the total capacity of 20%, the hydrogen station has a rated capability of about 1080 kg/day. Table 12. Initial costs of the hydrogen station. Item Cost

€/kg Day

€

Building Compressor Electrolyzer Vessel Others Total

310 330 1320 1050 50 3060

334,740 356,336 1,425,345 1,133,797 53,990 3,304,209

As regards the operative and maintenance costs, we consider the values reported in Table 13. Table 13. Operative and maintenance costs.

Wave farm Wind farm Biomass power plant Hydrogen station

Unitary Costs

Annual Costs

55 €/(kW-year) 47 €/(kW-year) 98 €/(kW-year) 48 €·day/(kg-year)

€181,500 €155,100 €117,600 €52,068

Figure 15 shows two important results: the production of hydrogen by an own-power plant supplied by renewable sources is not economically viable (at least in the absence of incentives) because the avoided cost of diesel purchase does not pay the initial investment in a reasonable period; the hypothesis B shows that the purchase of electrical energy for the production of hydrogen is very high, in fact, in just five years the two different scenarios have the same discounted cash flow. For these reasons, we simulate a third hypothesis, characterized by a greater power plant by renewable sources, in order to sell the electrical surplus and reduce the breakeven time of the project. In this hypothesis (C), we fixed the installed power by biomass (for reasons of availability of this resource) and increased the installed power by wind and sea wave. In particular, the power produced by wave and wind plants was doubled (6.6 MW for the wind farm and 3.2 MW for sea wave). Thanks to the selling of the electrical energy surplus, in the last hypothesis, the breakeven time is about 14 years (see Figure 16). Of course, the breakeven time can be further reduced through the introduction of an incentive [31].


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Figure 15. Discounted cash flow in the two different hypotheses.

For these reasons, we simulate a third hypothesis, characterized by a greater power plant by renewable sources, in order to sell the electrical surplus and reduce the breakeven time of the project. In this hypothesis (C), we fixed the installed power by biomass (for reasons of availability of this resource) and increased the installed power by wind and sea wave. In particular, the power produced by wave and wind plants was doubled (6.6 MW for the wind farm and 3.2 MW for sea wave). Thanks to the selling of the electrical energy surplus, in the last hypothesis, the breakeven time is about 14 years (see Figure 16). Of course, the breakeven time can be further reduced through the introduction of an incentive [31]. Discounted cash cash flow in the two different hypotheses. Figure 15. Discounted

For these reasons, we simulate a third hypothesis, characterized by a greater power plant by renewable sources, in order to sell the electrical surplus and reduce the breakeven time of the project. In this hypothesis (C), we fixed the installed power by biomass (for reasons of availability of this resource) and increased the installed power by wind and sea wave. In particular, the power produced by wave and wind plants was doubled (6.6 MW for the wind farm and 3.2 MW for sea wave). Thanks to the selling of the electrical energy surplus, in the last hypothesis, the breakeven time is about 14 years (see Figure 16). Of course, the breakeven time can be further reduced through the introduction of an incentive [31].

FigureFigure 16. Discount cashcash flow in the hypotheses C. 16. Discount flow in the hypotheses A A and and C. 5. Conclusions 5. Conclusions The availability of biomass, wave the province of of Trapani Trapani shows that thethe useuse of of The availability of biomass, windwind and and sea sea wave in in the province shows that these resources for the electrolytic hydrogen production would allow the replacement of the entire fleet these resources for the electrolytic hydrogen production would allow the replacement of the entire of urban buses powered by diesel with an equal number of hydrogen vehicles. From the environmental fleet of urban buses powered by diesel with an equal number of hydrogen vehicles. From the point of view, this project allows the abatement of several greenhouse gases, in particular, in the best environmental view, this 16. project allows the abatement of several greenhouse gases, Discount cash flow in the hypotheses A are and C. tons scenariopoint (100% of replace ofFigure diesel buses), the annual avoided emissions 1444 of CO , 7.64 tons in 2

of CO, 1.12 tons of PM10 , 2.1 tons of NMVOC and 22.85 tons of NOx . 5. Conclusions From the economic point of view, the project—in absence of an incentive—presents a very long breakeven time, incompatible with theand lifetime of the plants. A possible solution is the The availability of biomass, wind sea wave in the province of Trapani shows thatoversizing the use of of wind and seafor wave plantshydrogen in relation to the electrical forreplacement hydrogen production, in these resources thepower electrolytic production woulddemand allow the of the entire

fleet of urban buses powered by diesel with an equal number of hydrogen vehicles. From the environmental point of view, this project allows the abatement of several greenhouse gases, in


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order to sell the surplus of energy into the electrical grid. In this way, with a double installed power of wind and sea wave farms, the breakeven time is about 14 years. The introduction of an incentive related to the annual distance covered by hydrogen buses and/or the selling of electrical surplus can be a successful way to reduce the breakeven time, making this project feasible. Author Contributions: All authors contributed to writing the article on equal terms. All authors read and approved the final manuscript. Conflicts of Interest: The authors declare no conflict of interest.

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