sustainability

Article Energetic Sustainability Using Renewable Energies in the Mediterranean Sea

Vincenzo Franzitta *, Domenico Curto and Davide Rao

Department of Energy, Information and Mathematical Models, UNIPA (University of Palermo), Palermo 90128, Italy; [email protected] (D.C.); [email protected] (D.R.) * Correspondence: [email protected]; Tel.: +39-091-238-61941

Academic Editor: João P. S. Catalão Received: 26 August 2016; Accepted: 7 November 2016; Published: 10 November 2016

Abstract: The paper is focused on the analysis of the electrical energy sector in the Maltese islands, focusing on the employment of Renewable Energies in order to increase its energy independence. The main renewable source here proposed is wave energy: thanks to its strategic position, will be able to generate electrical energy through the use of an innovative type of Wave Energy Converter (WEC) based on the prototype of linear generator designed and developed by the University of Palermo. This new technology will be able to cut down the electrical energy production from traditional power plants and, consequently, the greenhouse gas emissions (GHG). Wave energy source and off-shore photovoltaic (PV) technology are proposed here. Particularly, the installation of 18 wave farms, for a total installed capacity of 130 MW, will generate about 5.7% of Malta’s energy requests in 2025, while the installation of 60 MW of off-shore PV will generate about 4.4%.

Keywords: wave energy; ; Mediterranean Sea; WEC; point absorber; Malta

1. Introduction Electrical energy is an essential requirement to satisfy the needs of human beings, such as the production of goods and services. Despite the technological developments, in remote areas or in small islands, the electrical energy production is based on outdated technologies, powered by fossil fuels. This way of producing energy generates negative effects for the environment, like pollution of air, water and soil, as well as the generation of noise [1]. In this context, many small islands in the world are almost completely powered by old diesel generators [2]. The fuel is usually shipped from the mainland and long underwater cables sometimes connecting the small islands to the mainland [3]. Due to these reasons, on small islands, such as in remote areas, the electrical power production shows higher operating costs and losses than on the mainland [4]. The use of Renewable Energy Sources (RES), in particular wind, solar, biomass and also sea waves, will produce the reduction of energy dependence from fossil fuels and the improving of the efficiency of the electrical grid [5]. The RES also contributes to the reduction of greenhouse gas (GHG) emissions and environmental pollution. Samsø, a small island in Denmark, is a famous example of a community, electrically linked to the mainland and totally powered by renewable sources (wind in particular). Many islands around the world are working on important projects in order to achieve energetic independence from fossil fuels, thanks the utilization of renewable energy sources. Some examples are: Maldives, Graziosa (Portugal), Gotland (Sweden), the Canary Islands (Spain) and Sumba (Indonesia). In other countries, several studies have investigated the possibility of constructing small stand-alone electrical grids, powered only by renewable energy sources [6–10]. Zhao et al. [6] proposed a micro grid electrical system for Dongfushan Island, located in Zhejiang Province, in the eastern part of China. The system proposed is composed of solar panels, wind

Sustainability 2016, 8, 1164; doi:10.3390/su8111164 www.mdpi.com/journal/sustainability Sustainability 2016, 8, 1164 2 of 16 turbines, diesel generators and a battery storage system. The optimization is realized by using a genetic algorithm that minimizes the life cycle cost and maximizes the production of electrical energy by renewable resources. Similarly, using the HOMER (Hybrid Optimization Model for Electric Renewable) tool, Ma et al. [7] investigated a particular solution based on a hybrid solar-wind system with battery storage. The study is applied on a small island in Hong Kong. The electrical energy is produced by photovoltaic arrays and wind turbines. The direct current output is used to satisfy the electrical demand. If the energy produced is greater than the request, the energy surplus is accumulated in battery. Conversely, if a deficit occurs, the battery is discharged. If the electrical production by RES is excessive, such as to not allow the accumulation in the battery, the surplus of energy is directed to a dump load. An inverter system is necessary to connect the power plants by RES and the battery to the electrical grid, which works in alternative current. In other study, Ma et al. [8] analyzed a different solution for the storage energy system, proposing a hydroelectric pumped storage, supported by a battery storage system. Using the HOMER tool, Bin et al. [9] studied the electrical energy demand of Hainan Island, located in the southern part of China. This region is rich of renewable resources (hydro, wind, solar). However, the electrical energy production is mainly based on coal. Hainan has natural gas reserves and is electrically connected to the mainland by a submarine interconnector (transmission capacity 600 MW). The study shows the energy potential of available renewable sources, in particular that it is possible to avoid the building of other plants, thanks to the employment of renewable sources. In other interesting study, Petrakopoulou [10] simulated a hybrid power plant to satisfy the electrical demand of Skyros, a small Greek island, located in the middle of Aegean Sea. The system proposed is composed by solar thermal and photovoltaic, hydroelectric generators and wind turbines. In this way, it is possible accumulate solar energy in thermal storage system, reducing the daily fluctuation of electrical power production by solar sources. In this paper, we focus our attention on the Malta archipelago, where the electrical energy production is currently almost totally based on fossil fuel. After the ratification of the Kyoto Protocol, the European Union is committed to reducing its GHG emissions by 8% of 1990 levels [11]. According to the European Directive 2009/28/EC (Annex I), Malta is obliged to generate 10% of its energy from RES in gross final consumption by 2020 [12]. Malta’s target is considerable, although it is lower than other European Countries, because Malta presents quite particular conditions, such as other Mediterranean islands: high population density, a growing primary energy consumption and a low free surface to install new plants. In order to achieve the environmental and energetic targets [13], Malta will have to use all available renewable sources [14]. Moreover, Malta’s electrical grid needs several developments, in order to minimize the electrical problems caused by randomness of many RES, such as wind and solar [15]. Taking into account the peculiarities of Malta, in this paper, we analyze a new frontier of renewable energy sources: sea wave. As known from literature, sea wave energy is extremely underused, despite its great energy potential [16,17]. Furthermore, sea wave energy presents many advantages for small islands—in particular, the installation of plants not requiring land employment and that the energy converters present a very limited visual and environmental impact [18]. According to this vision, the following Figure1 shows a possible future structure of Malta’s electrical grid. Every available RES will be used to produce electrical energy [19]. In order to match the electrical load and the electrical production by RES, new innovative storage systems have to be developed. Sustainability 2016, 8, 1164 3 of 16 Sustainability 2016, 8, 1164 3 of 16

Figure 1. Electrical grid with main renewablerenewable energy source and storage systems.systems.

This work analyzes the sea wave source in Malta’sMalta’s archipelago, exploitable to generate electrical energy through the useuse ofof anan innovativeinnovative devicedevice thatthat directlydirectly convertsconverts thethe mechanicalmechanical energy of seasea waveswaves intointo electricalelectrical output,output, minimizingminimizing thethe energeticenergetic conversionconversion losses.losses. This system is based on an innovativeinnovative prototypeprototype designed designed and and developed developed by theby Departmentthe Department of Energy of Energy and Information and Information Models (DEIM)Models of(DEIM) the University of the University of Palermo of Palermo (Italy). (Italy). This paperpaper shows shows a preliminarya preliminary evaluation evaluation of electrical of electrical energy productionenergy production through the through installation the ofinstallation wave farms of basedwave onfarms DEIM based converters on DEIM along conver the Malteseters along coasts. the In Maltese this system, coasts. photovoltaic In this system, panels canphotovoltaic be integrated, panels increasing can be integrated, the electrical increasing output. the electrical output.

2. Maltese Maltese Archipelago Archipelago Malta’s Country is an archipelago, inin thethe middle ofof thethe MediterraneanMediterranean Sea.Sea. It is located at about 80 km south from Sicily, Sicily, 333 333 km km north north from from Libya Libya and and 284 284 km km east east from from Tunisia. Tunisia. The The capital capital city city is isValletta, Valletta, having having the the geographical geographical coordinates coordinates 35°53 35◦53′N–14°350N–14◦35′E.0E. It Itis is situated situated in in the the largest islandisland (also(also calledcalled Malta)Malta) ofof thethe archipelago.archipelago. Malta covers an overall area ofof 316316 kmkm22; thus, it is one ofof thethe smallest European countries. The The Maltese archipelago is characterized by a very highhigh populationpopulation density (1318 inhabitant/kminhabitant/km22,, 2012). 2012). The The state state of of Malta Malta has has a a population population of of about about 416,515 inhabitants (in(in 2012),2012), andand aboutabout 416,515416,515 livelive onon thethe principalprincipal islandisland [[20].20]. The Maltese archipelago archipelago is is composed composed of of several several islands, islands, but but essentially essentially only only three three of them of them are arepopulated: populated: Malta Malta Island Island (245.8 (245.8 km2), kmGozo2), (67.1 Gozo km (67.12) and km Comino2) and Comino (2.8 km2 (2.8) are km shown2) are in shown Figure in2. FigureThe archipelago2. The archipelago also includes also includes18 uninhabited 18 uninhabited smaller smallerislands; islands; some of some them of are: them Manoel are: Manoel Island Island(“Il-Gż (“Il-GiraManoel”,z˙iraManoel”, in Maltese in Maltese language, language, 0.3 km 0.32), km St2 ),Paul’s St Paul’s Island Island (“G (“Gżejjerz˙ejjer ta’ ta’ San San Pawl” Pawl” or “Selmunett”,“Selmunett”, inin Maltese, Maltese, 0.101 0.101 m 2m),2 Cominotto), Cominotto (“Kemmunett” (“Kemmunett” in Maltese, in Maltese, 0.099 0.099 km2), km Filfla2), Filfla (0.02 km(0.022), andkm2), Fungus and Fungus Rock (“Il- RockG˙ eblatal- (“Il-ĠGeblatal-˙ eneral”,Ġeneral”, in Maltese, in 0.007Maltese, km 20.007). Malta’s km2). islands Malta’s are islands mainly are rocky, mainly with terracedrocky, with fields, terraced dry vegetation, fields, dry rock vegetation, and limestone. rock and The limestone. highest Maltese The highest peak isMaltese Ta’ Dmejrek, peak is with Ta’ 253Dmejrek, m (830 with feet from253 m sea (830 level, feet located from sea near level, Dingli). located Maltese near coastsDingli). are Maltese fairly indented coasts are with fairly several indented bays. Inwith Maltese several Country, bays. In lakes Maltese and permanent Country, lakes rivers and are absent,permanent although rivers there are areabsent, some although inland waterways, there are havingsome inland fresh waterways, water during having all year, fresh at water Lunzjata during Valley all inyear, Gozo, at Lunzjata at l-Imta Valleyh¯ leb and in Gozo, San Martin, at l-Imta andħleb at Ba¯andhrijanear San Martin, Rasir-Ra¯ andh ateb Ba [20ħrijanear]. Rasir-Raħeb [20]. Sustainability 2016, 8, 1164 4 of 16 Sustainability 2016, 8, 1164 4 of 16

Figure 2. View of the Maltese archipelago.

In order to overcomeovercome the limitedlimited availability of water on the inhabitedinhabited islands of Malta, six desalination plants are installed, two of which areare alwaysalways on.on. Due to its latitude and the central location in the MediterraneanMediterranean Sea, the Maltese climateclimate is Subtropical–Mediterranean, so winters and summers areare temperate.temperate. TheThe rainfall rainfall happens happens usually usually in in autumn autumn and and winter winter season, season, about about 578 578 mm mm per year.per year. The The main main yearly yearly temperature temperature is about is about 23 ◦ C23 in°C the in daytimethe daytime and and 16 ◦ C16 at°C night. at night. January January is the is coldestthe coldest month, month, while while August August is the is hottest. the hottest. The main The yearlymain yearly temperature temperature of the seaof the is 20 sea◦C, is ranging 20 °C, fromranging 15 ◦fromC in February15 °C in February to 26 ◦C into August.26 °C in Winters August. in Winters Malta are in usuallyMalta are mild, usually but, duringmild, but, the during winter months,the winter it tendsmonths, to getit tends pretty towindy get pretty from wi windndy from blowing wind from blowing the northeast. from the northeast. In Malta’s Malta’s archipelago, archipelago, thanks thanks to to the the latitude, latitude, the the solar solar radiation radiation is very is very high, high, with withabout about 3000 3000sunlight sunlight hours hours per year. per year. The Thedaylight daylight hours hours range range from from a minimum a minimum of 5.2 of 5.2 h during h during December December to toa amaximum maximum of of12 12 h in h inJuly July [21]. [21 The]. The Maltese Maltese woods woods were were cut cutdown down centuries centuries ago, ago, so the so only the only trees trees that thatsurvive survive nowadays nowadays are the are olives, the olives, citrus, citrus, carob carobtrees, trees,pine, fig pine, trees fig and trees tamarisk. and tamarisk. On Gozo On and Gozo Malta, and Malta,the hills the are hills cultivated are cultivated for vegetables for vegetables and grapes. and grapes. The economy is essentially based on tourism, which generates around 15% of Gross Domestic Product (GDP). Other important sectors are foreign trade, electronics, manufacturing, shipyard and pharmaceutical industry.industry. Italy Italy is amongis among the mainthe main trading trading partners. partners. As a result As ofa theresult limited of the freshwater limited sources,freshwater Maltese sources, food Maltese production food production is very low, is satisfying very low, only satisfying 20% of only the national 20% of the needs. national needs. Transport, publicpublic administration administration and and industry industry are are the mainthe main sector, sector, employing, employing, respectively, respectively, 28.6%, 26.6%28.6%, and26.6% 15.7% and of15.7% the total of the workforce. total workforce. Fishing Fishing and agriculture and agriculture are marginal are marginal sectors sectors [20]. [20].

3. Electrical Electrical Energy Energy Production Production in in Malta Malta In Malta’s archipelago, the electrical power production is almost completely based on fossil fuel power plants. For For example, example, in in 2005, 2005, the the entirely entirely electrical electrical energy energy production production was was generated generated from from oil oil[22], [22 and,], and, at the at the same same time, time, the the transport transport sector sector was was fully fully based based on on petroleum. petroleum. Furthermore, Furthermore, on the Maltese archipelago, the fossil fuels (natural gas, o oilil or col) are totally absent; therefore, all of these sources mustmust be be obtained obtained from from other other countries, countries, which which are often are characterized often characterized by geopolitical by geopolitical instability. instability.The Enemalta Corporation (EMC) (City, Country) is the owner of all Maltese thermoelectric power plantsThe [23 Enemalta]. Electrical Corporation energy is mainly(EMC) generated(City, Country) at the Delimarais the owner Power of all Station Maltese (with thermoelectric an installed power ofplants 444 MW),[23]. Electrical located onenergy the southeastern is mainly generated part of Malta. at the TheDelimara power Power station Station is composed (with an of conventionalinstalled power steam of turbines444 MW), (2 ×located60 MW), on openthe southeastern cycle gas turbines part (2of× Malta.35 MW), The one power combined station cycle is plantcomposed (110 MW)of conventional and four stroke steam medium turbines speed(2 × 60 diesel MW), engines open cycle (144 gas MW, turbines operating (2 × in 35 a MW), combined one combined cycle plant (110 MW) and four stroke medium speed diesel engines (144 MW, operating in a combined cycle mode with one steam turbine). In the past, another important plant was installed at Sustainability 2016, 8, 1164 5 of 16 Sustainability 2016, 8, 1164 5 of 16 thecycle Marsa mode plant with (with one an steam installed turbine). power In theof 155 past, MW another, 2010), important but, nowadays, plant was is in installed a decommissioning at the Marsa phaseplant [23]. (with Therefore, an installed the power total traditional of 155 MW, installed 2010), but, capacity nowadays, was about is in 599 a decommissioning MW, while the renewable phase [23 ]. powerTherefore, plants the capacity total traditional does not installedexceed 14 capacity MW [24]. was In about Figure 599 3,MW, the electric while the grid renewable of the archipelago power plants of Maltacapacity is shown. does not exceed 14 MW [24]. In Figure3, the electric grid of the archipelago of Malta is shown.

FigureFigure 3. 3. TheThe electrical electrical grid grid on on Malta’s Malta’s archipelago archipelago [23]. [23].

InIn order order to to overcome overcome thethe growinggrowing requestrequest for for electrical electrical energy, energy, the the Malta–Italy Malta–Italy Interconnector Interconnector was wasinaugurated inaugurated in April in April 2015, 2015, connecting connecting the Italian the Italian station station located located in Ragusa in Ragusa (Sicily) (Sicily) to the to Maltese the Maltese station stationlocated located in Malta in at Malta QaletMarku, at QaletMarku, Baharic-Caghaq. Baharic-Caghaq. This interconnector This interconnector is composed ofis acomposed submarine cable,of a submarinehaving a length cable, abouthaving 120 a km.length The about system 120 works km. The in a highsystem voltage works alternating in a high currentvoltage (220alternating kV) and currentis capable (220 of kV) a bidirectional and is capable flow of ofa bidirectional electrical power, flow with of electrical a maximal power, flow with rate ofa maximal about 200 flow MW rate [21 ]. ofThe about electrical 200 MW distribution [21]. The gridelectrical in Malta distribution is achieved grid on in four Malta voltage is achieved levels, which on four are: voltage 132 kV; levels, 33 kV; which11 kV; are: and 132 400/230 kV; 33 V.kV; The 11 frequencykV; and 400/230 of the V. supply The frequency of electrical of energythe supply in Malta of electrical is 50 Hz, energy like thein MaltaEuropean is 50 electricalHz, like the grid. European electrical grid. FigureFigure 4 showsshows thethe trend trend of of electrical electrical energy energy consumption consumption by sourcesby sources in Malta in Malta during during the period the period1971–2015 1971–2015 [25]. This [25]. trend This istrend characterized is characterized by an importantby an important increase increase from 300 from GWh/year 300 GWh/year in 1971 in to 19712257 to GWh/year 2257 GWh/year in 2015. in 2015. As shown As shown in the in figure,the figure, the electricalthe electrical interconnector interconnector between between Malta Malta and andSicily Sicily has significantlyhas significantly changed changed the electrical the electrical energy energy production production in Malta: in inMalta: fact, duringin fact, the during year 2015,the yearthrow 2015, the throw interconnector, the interconnector, Malta has Malta imported has imported 1054 GWh, 1054 which GWh, is almost which halfis almost as much half as as consumed much as consumedin the same in the year; same the year; remaining the remaining energy demandenergy demand in Malta in was Malta satisfied was satisfied by oil plantsby oil plants (1099 GWh),(1099 GWh),biofuels biofuels (9 GWh) (9 andGWh) photovoltaic and photovoltaic plants (95plants GWh) (95 [26GWh)]. Despite [26]. Despite the huge the collapse huge collapse of electrical of electricalenergy production energy production by fossil by fuel fossil (oil) fuel and (oil) the increaseand the ofincrease energy of production energy production by solar plants,by solar the plants, use of therenewable use of renewable sources is sources very low, is very compared low, compared to European to European Countries. Countries. FigureFigure 5 shows the distribution of electrical en energyergy consumptions to to fi finalnal users users in in the years 2000,2000, 2007 2007 and and 2014. 2014. As As shown shown in in the the picture, picture, in in the the three three reference reference years, years, self-consumption self-consumption by by industriesindustries represents represents only only 5%–6% 5%–6% of total of total consumption. consumption. The residential The residential sector sector stably stablyconsumes consumes 28%– 29%.28%–29%. The electrical The electrical energy energy consumed consumed by industries by industries has been has progressively been progressively downsized, downsized, going from going 504from GWh 504 (which GWh (which represents represents 27% in 27% 2000) in to 2000) 413 toGWh 413 (18% GWh in (18% 2014). in 2014).Conversely, Conversely, the commercial the commercial and public service has increased the electrical consumption, going from 504 GWh (26% in 2000), to 663 Sustainability 2016, 8, 1164 6 of 16 Sustainability 2016, 8, 1164 6 of 16 GWh (29% in 2007) and 940 GWh (42% in 2014). Electrical consumption is absent in the public Sustainability 2016, 8, 1164 6 of 16 andtransport public sector; service other has sectors increased such the as electrical fishing, agriculture consumption, andgoing forestry from are 504 negligible GWh (26% [25,26]. in 2000), to 663 GWhGWh (29%(29% inin 2007)2007) andand 940 GWh (42% (42% in in 2014). 2014). Electrical Electrical consumption consumption is absent is absent in the in public the public transporttransport sector; sector; other other sectors sectors such such as as fishing, fishing, agriculture agriculture and forestry forestry are are negligible negligible [25,26]. [25,26 ].

Figure 4. Electricity consumptions by sources in Malta (1971–2015) [25]. FigureFigure 4. Electricity 4. Electricity consumptions consumptions byby sourcessources in in Malta Malta (1971–2015) (1971–2015) [25]. [25].

Figure 5. Distribution of electrical energy consumption to final users [25,26]. Figure 5. Distribution of electrical energy consumption to final users [25,26]. 4. Sea WaveFigure Energy 5. ResourcesDistribution of electrical energy consumption to final users [25,26]. 4. Sea WaveThe Energy use of wave Resources energy is able to reduce energetic dependence of Mediterranean islands from 4. Sea Wave Energy Resources fossil fuels. This important target presents different advantages, such as the reduction of The use of wave energy is able to reduce energetic dependence of Mediterranean islands from Theimportations use of waveof exogenous energy fossil is able fuels to from reduce unst energeticable countries, dependence the abatement of Mediterranean of greenhouse gas islands fossil fuels. This important target presents different advantages, such as the reduction of fromemissions fossil fuels. (especially This importantCO2 emissions), target and presents the creation different of a working advantages, industry such strongly as thelinked reduction to the of importations of exogenous fossil fuels from unstable countries, the abatement of greenhouse gas importationsterritory. ofNowadays, exogenous wave fossil energy fuels represents from unstable a renewable countries, source totally the abatement unused in Malta, of greenhouse despite its gas emissions140 km (especially of coasts. COMoreover,2 emissions), the ratio and of theterritorial creation waters of a toworking the land industry area in Maltastrongly is very linked high, to the emissions (especially CO2 emissions), and the creation of a working industry strongly linked to the territory.approximately Nowadays, 10, wave with 3000energy km 2represents of territorial a watersrenewable [27]. sourceThis means totally that unused the exploitable in Malta, areas despite are its territory. Nowadays, wave energy represents a renewable source totally unused in Malta, despite 140 kmcharacterized of coasts. byMoreover, a great extension, the ratio with of aterritorial great total watersenergetic to potential the land that area can inbe Maltaproperly is usedvery in high, its 140 km of coasts. Moreover, the ratio of territorial waters to the land area in Malta is very high, order to produce electrical 2output thanks to appropriate conversion devices. The additional approximately 10, with 3000 km2 of territorial waters [27]. This means that the exploitable areas are approximatelyadvantage 10,is linked with 3000to the km preservationof territorial of the waters limited [ 27Maltese]. This soil means from that the theinstallation exploitable of further areas are characterized by a great extension, with a great total energetic potential that can be properly used in characterizedpower plants. by a great extension, with a great total energetic potential that can be properly used in order to produce electrical output thanks to appropriate conversion devices. The additional order to produceDuring this electrical time, several output studies thanks focused to appropriate their attention conversion on the devices. assessment The of additional the wave energy advantage advantage is linked to the preservation of the limited Maltese soil from the installation of further is linkedpotential to the in preservation the Mediterranean of the limited Sea. Indeed, Maltese a soilgood from confirmation the installation of the ofenergy further theoretically power plants. power plants. Duringextractable this from time, sea several waves studiesis fundamental focused in their orde attentionr to increase on the interest assessment about of this the important wave energy During this time, several studies focused their attention on the assessment of the wave energy potentialrenewable in the Mediterraneansource and the Sea.improvement Indeed, a goodof new confirmation technologies of of the conversi energyon. theoretically Different studies extractable potential in the Mediterranean Sea. Indeed, a good confirmation of the energy theoretically from sea waves is fundamental in order to increase the interest about this important renewable source extractable from sea waves is fundamental in order to increase the interest about this important and the improvement of new technologies of conversion. Different studies demonstrated that the renewable source and the improvement of new technologies of conversion. Different studies Sustainability 2016, 8, 1164 7 of 16 off-shore wave energy resources near the northwest European coasts are the higher ones [28], while the MediterraneanSustainability 2016 is, 8, characterized1164 by quite lower values. However, this particular condition7 involves of 16 different advantages: the calmer sea state defines less rigorous conditions for those Wave Energy Convertersdemonstrated (WECs) that that the will off-shore be employed wave energy off-shore, resources with near a lower the northwest risk of failure European due tocoasts breakdown are the or higher ones [28], while the Mediterranean is characterized by quite lower values. However, this malfunctions. A calmer sea state avoids an excessive oversizing of WECs too. Particularly, the central particular condition involves different advantages: the calmer sea state defines less rigorous locationconditions of Malta for in those the SicilianWave Energy Channel Converters determines (WECs) a favorablethat will be wave employed climate off-shore, in order with to a createlower the first commercialrisk of failure wave due farmsto breakdown in the Mediterranean or malfunctions. Sea. A calmer sea state avoids an excessive oversizing Theof WECs in situ too. measurements Particularly, alongthe central Maltese location coasts of was Malta realized in the withSicilian a single Channel Datawell determines Waverider a buoy (Datawell,favorable wave Haarlem, climate The in order Netherlands), to create the which first wascommercial installed wave about farms 2 km in westthe Mediterranean of the Gozo coastline, Sea. at a depthThe of 200in situ m [measurements29]. The use ofalong wave Maltese buoys coasts has was a fundamental realized with role a single in order Datawell to obtain Waverider some of the firstbuoy data (Datawell, about wave Haarlem, potential The withNetherlands), an experimental which was measurement installed about campaign. 2 km west However, of the Gozo they are usuallycoastline, too expensive, at a depth so of they 200 m are [29]. used The only use of in wave the first buoys part has of a anfundamental assessment, role especially in order to in obtain order to some of the first data about wave potential with an experimental measurement campaign. However, validate software data. The Gozo wave buoy was able to define the wave climate in Gozo and in the they are usually too expensive, so they are used only in the first part of an assessment, especially in northwestern part of the Maltese archipelago, while it was hopeful to know the wave energy potential order to validate software data. The Gozo wave buoy was able to define the wave climate in Gozo alongand all the in the coasts. northwestern Additionally, part of maintenance the Maltese costsarchipelago, usually while reduce it was the measurementhopeful to know period the wave to some years.energy In the casepotential of Gozo’s along waveall the buoy, coasts. measurements Additionally, were maintenance performed costs from usually 14 September reduce 2011the to 13 Septembermeasurement 2012 [period29], recording to some the years. wave In climate the case during of Gozo’s the seasons. wave buoy, measurements were Theperformed main parameters from 14 September that define 2011 to wave 13 September energy resource2012 [29], recording are: significant the wave wave climate high duringHs and the the main periodseasons.T m. The first one is measured in meters, the second one in seconds. For each sea state, using 1025The kg/m main3 forparameters the density that defineρ and wave 9.807 energy kg/m resource3 for the are: gravitational significant wave acceleration high andg [29 the], the correspondingmain period wave . powerThe first is one calculated is measured through in meters, this expression: the second one in seconds. For each sea state, using 1025 kg/m3 for the density and 9.807 kg/m3 for the gravitational acceleration [29], the corresponding wave power is calculated through this expression:kW  P = 0.49H2T . (1) s m m = 0.49 . (1) Finally, the annual average wave power must be multiplied by 8760 h (hours in one year) in Finally, the annual average wave power must be multiplied by 8760 h (hours in one year) in orderorder to have to thehave total the energy,total energy, expressed expressed in MWh/year. in MWh/year. The The next next step step consists consists in thein the use use of theof the SWAN (SimulatingSWAN Wave (Simulating Nearshore) Wave modelNearshore) hindcast model three-hourly hindcast three-hourly fields, which fields, is characterizedwhich is characterized by 89,701 by grid point89,701 around grid the point Maltese around islands the Maltese [29]. This islands model [29]. is This particularly model is particularly advantageous advantageous with propagation with problemspropagation from deep problems water from up todeep the water coasts. up Both to th buoye coasts. data Both and buoy SWAN data dataand haveSWAN highlighted data have an importanthighlighted seasonal an variabilityimportant seasonal of sea wavevariability power of sea along wave Maltese power coasts.along Maltese Wave powercoasts. Wave is characterized power by highis characterized values during by high winter values season, during which winter decrease season, which in autumn decrease and in spring,autumn whileand spring, the minimum while valuesthe are minimum recorded values in summer. are recorded Moreover, in summer. winter waveMoreover, power winter is more wave than power double is more the annualthan double average, the annual average, visible in Figure 6 and obtained from the data reported in [29]. visible in Figure6 and obtained from the data reported in [29].

Figure 6. Seasonal wave power from buoy and SWAN model data in Gozo. Figure 6. Seasonal wave power from buoy and SWAN model data in Gozo. Sustainability 2016, 8, 1164 8 of 16

Therefore, mean power values obtained with SWAN model data are very similar to those obtainedTherefore, with meanthe wave power buoy, values although obtained slightly with SWAN lower. model Furthermore, data are very this similar seasonal to thosetrend obtained can be withuseful the because wave buoy,it is opposite although to slightly the solar lower. trend Furthermore, and the two thistrends seasonal may offset trend each can be other. useful because it is oppositeFinally, to Figure the solar 7 reveals trend and that the the two most trends advantageous may offset eachlocations other. are the western coasts of the islands,Finally, caused Figure by 7the reveals northweste that thern most prevalent advantageous direction locations of sea wave. are the An western annual coastsaverage of thepower islands, of 5 kW/mcaused is by considered the northwestern here, which prevalent is a good direction value of du seae wave.to the Anhigh annual depth averageof the seabed power even of 5 kW/mnear the is coast.considered here, which is a good value due to the high depth of the seabed even near the coast.

FigureFigure 7. SeasonalSeasonal wave wave power power along along the the Maltese islands for the SWAN model domain [[29].29].

5. DEIM Point Absorber 5. DEIM Point Absorber This work proposes an innovative WEC, nowadays at the design step, designed by the This work proposes an innovative WEC, nowadays at the design step, designed by the Department Department of Energy and Information Models (DEIM) of the University of Palermo [30]. Figure 8 of Energy and Information Models (DEIM) of the University of Palermo [30]. Figure8 shows a shows a representation of a particular type of Point Absorber, a technology proposed thanks to its representation of a particular type of Point Absorber, a technology proposed thanks to its ability to ability to convert wave potential in electrical output directly, without the use of pressurized liquids convert wave potential in electrical output directly, without the use of pressurized liquids (such as (such as oils or waters) or other intermediate devices [31]. Moreover, it is able to work adequately oils or waters) or other intermediate devices [31]. Moreover, it is able to work adequately with any with any direction of wave propagation, which is a really important characteristic [32]. direction of wave propagation, which is a really important characteristic [32]. Sustainability 2016, 8, 1164 9 of 16 Sustainability 2016, 8, 1164 9 of 16

Figure 8. Three-dimensional (3D) representation of the DEIM converter. Figure 8. Three-dimensional (3D) representation of the DEIM converter.

The DEIMDEIM converterconverter proposed proposed here here has has a nominal a nomi sizenal ofsize 80 kW.of 80 In kW. order In to order reduce to the reduce designing the anddesigning developing and developing costs for different costs for sizes different of systems, sizes aof modular systems, approach a modular is applied.approach In is fact, applied. the electrical In fact, converterthe electrical is made converter from eightis made linear from generators, eight linear each ge onenerators, with a each nominal one sizewith of a 10nominal kW. It consistssize of 10 of kW. two floatingIt consists buoys, of two independent floating buoys, of each independent other [33]. The of external each other one (yellow[33]. The buoy) external intercepts one (yellow the sea waves,buoy) whileintercepts theinternal the sea one waves, (green while buoy) the contains internal all ofon thee (green eight linear buoy) generators. contains Theall of alternate the eight motion linear of thegenerators. sea waves The is transferredalternate motion from the of externalthe sea buoywaves to is the transferred internal one from thanks the toexternal the connecting buoy to rods the (pinkinternal rods). one thanks to the connecting rods (pink rods). A hemispherical weight is installed in the lowest part of the central buoy, guaranteeingguaranteeing good stability to the system and itsits verticalvertical position.position. This hemispherical weight is connected to a jumper (purple sphere) throughthrough aa bigbig chain,chain, whilewhile the same jumper is connected to four moorings, placed on the seabed.seabed. In In this this way, way, the fourthe chainsfour chains connecting conne mooringscting moorings and the jumperand the are jumper constantly are maintainedconstantly inmaintained a vertical in position, a vertical avoiding position, the riskavoiding due tothe the ri scrapingsk due to of the the scraping seabed [ 34of]. the An seabed intermittent [34]. redAn lightintermittent is positioned red light on theis positioned top of the buoy,on the making top of visiblethe buoy, the WECmaking up visible to several the nauticalWEC up miles to several away. Thenautical capture miles buoy away. has The a useful capture diameter buoy has of 5 a m, useful while diameter the working of 5 strokem, while of thethe generatorworking stroke is about of 4the m. Thisgenerator length is also about allows 4 m. the This production length also of electricityallows the in production most agitated of andelectricity energetic in most sea states. agitated and energeticThe innovativesea states. aspect of the project is related to use of a particular type of linear electrical generatorThe innovative that converts aspect the mechanicalof the project energy is related of sea wavesto use intoof a electricalparticular output type of without linear theelectrical use of brushesgenerator or that other converts mechanical the mechanical devices. energy of sea waves into electrical output without the use of brushesThe or linear other generatorsmechanical are devices. composed two parts: the translator and the stator. The first part containsThe 132linear neodymium-iron-boron generators are composed permanent two magnetsparts: the used translator to generate and thethe magnetic stator. The field first without part anycontains electrical 132 energyneodymium-iron-boron consume. The second permanent one contains magnets the used coils, to with generate a three-phase the magnetic connection, field representingwithout any theelectrical magnetic energy circuit. consume. In order The to second control theone motioncontains of the translators coils, with avoiding a three-phase possible damageconnection, from representing bad weather the conditions, magnetic twocircuit. end In stop order springs to control are installed the motion inside of thetranslators central buoyavoiding [35]. Figurepossible9 representsdamage from a cross bad sectionweather of conditions, the conversion two en buoy,d stop in springs which the are eight installed linear inside generators the central are visible,buoy [35]. with Figure the connecting 9 represents road a and cross the section two end of stroke the conversion springs. buoy, in which the eight linear generators are visible, with the connecting road and the two end stroke springs. Sustainability 2016, 8, 1164 10 of 16 Sustainability 2016, 8, 1164 10 of 16

Figure 9. Cross section of the inner buoy of the DEIM Point Absorber. Figure 9. Cross section of the inner buoy of the DEIM Point Absorber. Several experiments were conducted in a DEIM laboratory on a small scale linear converter, in orderSeveral to evaluate experiments the energetic were performances.conducted in a Depending DEIM laboratory on the loadon a conditions,small scale thelinear machine converter, is able in toorder convert to evaluate into electric the energetic energy even performances. 70%–80% ofDepend mechanicaling on energy the load in conditions, input. the machine is able to convertIn this into work, electric as a precautionary energy even 70%–80% level, the of energetic mechanical previsions energy are in basedinput. on an average efficiency, fixedIn to 50%.this work, as a precautionary level, the energetic previsions are based on an average efficiency, fixed to 50%. 6. Scenarios 6. ScenariosThe strategic position in the middle of the Mediterranean Sea and the quite high wave energy potentialThe strategic make Malta position one of in the the best middle sites of for the the Me employmentditerranean of Sea the and innovative the quite Point high Absorber wave energy here proposed.potential make Moreover, Malta one DEIM of the WEC best will sites be for able the to employment increase energetic of the innovative independence Point of Absorber this country, here currentlyproposed. atMoreover, a very low DEIM level. WEC The will optimal be able collocation to increase of theenergetic installation independence sites will of be this in choosingcountry, accordinglycurrently at differenta very low standards, level. The in order optimal to not collocation influence of the the main installation maritime routessites will and be activities in choosing such asaccordingly fishing [36 different]. It is important standards, to sayin order that fishingto not doesinfluence not have the main a main maritime role in theroutes Maltese and economy,activities andsuch the as off-shorefishing [36]. installation It is important of buoys to (several say that kilometers fishing does away not from have the a coast) main will role contribute in the Maltese to the reductioneconomy, ofand visual the impactoff-shore from installation the mainland. of buoys Additionally, (several kilometers the development away from of renewable the coast) energy will systemscontribute can to produce the reduction direct economicof visual impact benefits, from with the the mainland. creation ofAdditionally, new jobs, related the development to installation of andrenewable maintenance energy ofsystems power can plants. produce Figure direct 10 shows econom theic projections benefits, with until the 2035 creation of annual of new electrical jobs, energyrelated requestto installation [GWh] and and maintenance maximal peak of power requestplants. Figure [MW] in10 Malta.shows Thethe projections projections until are realized 2035 of consideringannual electrical a growing energy rate request equal to [GWh] 1% per and year ma in theximal base peak case power scenario request and 0.5% [MW] per yearin Malta. in the The low caseprojections scenario are [37 realized]. considering a growing rate equal to 1% per year in the base case scenario and 0.5%According per year in tothe the low base case case scenario scenario, [37]. in 2025, the estimated electrical request will be about 2500According GWh/year. to For the the base following case scenario, evaluation, in 2025, we th usee estimated this value electrical as reference. request Here, will wave be sourceabout 2500 and off-shoreGWh/year. photovoltaic For the following (PV) technology evaluation, are proposed.we use this The value installation as reference. of 18 waveHere, farms wave based source on and the off-shore photovoltaic (PV) technology are proposed. The installation of 18 wave farms based on the 80 kW DEIM Point Absorber along the western coast of Malta and Gozo, for a total installed capacity Sustainability 2016, 8, 1164 11 of 16 Sustainability 2016, 8, 1164 11 of 16 of80 130 kW MW, DEIM will Point generate Absorber about along 141,900 the western MWh/year. coast This of Malta production and Gozo, represents for a total 5.7% installed of the capacityoverall electricalof 130 MW, energy will generaterequests in about 2025. 141,900 The energy MWh/year. produc Thistion productionis obtained representswith an overall 5.7% ofefficiency the overall of 40%,electrical multiplying energy requeststhe diameter in 2025. of Thethe energycut-off productionbuoy by the is obtainedlocal sea withwave an power. overall Moreover, efficiency ofevery 40%, wavemultiplying farm will the consist diameter of ofthree the cut-offlines of buoy 30 WEC. by the The local distance sea wave between power. each Moreover, WEC every(about wave 10 m) farm is equalwill consist to twice of the three diameter lines of of 30 the WEC. device The itself distance (5 m). between Thus, a eachsingle WEC wave (about farm 10covers m) is an equal area to with twice a lengththe diameter of 300 m of theand device a width itself of 30 (5 m).m. At Thus, the asame single time, wave the farm installation covers an of area off-shore with a PV length technology, of 300 m forand a atotal width installed of 30 m. capacity At the sameof 60 MW, time, will the installationgenerate about of off-shore 108,300 PVMWh/year technology, [27]. for This a total production installed representscapacity of 4.4% 60 MW, of the will overall generate electrical about energy 108,300 pr MWh/yearoduction in [27 2025.]. This Therefore, production the represents overall electrical 4.4% of productionthe overall by electrical sea wave energy and off-shore production photovol in 2025.taic Therefore, sources represents the overall the electrical 10.1% in production 2025. by sea wave and off-shore photovoltaic sources represents the 10.1% in 2025.

Figure 10. Projections until 2035 of Maltese electrical energy requests and peak requests [28]. Figure 10. Projections until 2035 of Maltese electrical energy requests and peak requests [28].

Thanks to the large extension of territorial sea and the high daily solar radiation in Malta [27], Thanks to the large extension of territorial sea and the high daily solar radiation in Malta [27], the off-shore PV technology would be correctly integrated with the sea wave one. This solution will the off-shore PV technology would be correctly integrated with the sea wave one. This solution will increase the installed power in a fixed area, improving the electrical energy output. Finally, considering increase the installed power in a fixed area, improving the electrical energy output. Finally, the most recent CO2 emission factor for the Delimara power plant estimated in [38], wave sources considering the most recent CO2 emission factor for the Delimara power plant estimated in [38], can avoid 68,700 tons/year of CO2 emissions, while the off-shore PV one is 52,300 tons/year, for an wave sources can avoid 68,700 tons/year of CO2 emissions, while the off-shore PV one is 52,300 accumulative reduction of about 121,000 tons/year. tons/year, for an accumulative reduction of about 121,000 tons/year. 7. Economic Assessment 7. Economic Assessment The first preliminary economic assessment of wave farm is presented. Two possible scenarios The first preliminary economic assessment of wave farm is presented. Two possible scenarios are analyzed: the first concerns the construction of 18 wave farms, each one having 90 DEIM point are analyzed: the first concerns the construction of 18 wave farms, each one having 90 DEIM point absorbers; the second includes the integration of photovoltaic panels on wave converters. absorbers; the second includes the integration of photovoltaic panels on wave converters. In both scenarios, the discounted cash flow is evaluated, according the following equation: In both scenarios, the discounted cash flow is evaluated, according the following equation: n n i Cannual (1+1 + ε) DCF = −C0 − + Iannual , (2) = − −∑ i+∑ ,i (2) i=1(1+1 + τ) i=1 (1+1 + τ) wherewhere C0 isis the the initial initial investment, investment, Cannual isis the the annual annual operativ operativee and and maintenance maintenance costs, costs, Iannual isis thethe annual annual income income generated generated from from energy energy selling, selling, τ is is thethe discountdiscount rate,rate, andand εis is the the discount discount rate rate in inenergy energy systems. systems. In In order order to to simplify simplify the the evaluation, evaluation,C annualand andIannual are are considered considered stable stable in thein theyears. years. According According to [to39 ,[39,40],40], τ is fixed is fixed to 1% to and1% andε to 3%. to 3%. TableTable 11 showsshows thethe mainmain cost cost items items required required to to install install the the wave wave farms. farms. The The costs costs are are expressed expressed for forinstalled installed power. power. Table Table2 shows 2 shows the additionalthe additional costs co requiredsts required to integrate to integrate the photovoltaicthe photovoltaic system system into intosea wavesea wave energy energy converters, converters, increasing increasing the overallthe overall installed installed power power [41]. [41].

Sustainability 2016, 8, 1164 12 of 16

Table 1. Estimated costs for the installation of wave farms.

[€/kW] [€] Onshore transformers and grid 18 2,332,800 Cables 12 1,555,200 Mooring 75 9,720,000 Building/facilities 150 19,440,000 Installation work 35 4,536,000 Sea wave energy converters 2500 324,000,000 Total 2790 361,584,000

Table 2. Additional costs to integrate photovoltaic panel (PVP) on wave farms.

[€/kW] [€] PVP purchase 1500 90,000,000 PVP installation on sea wave 150 9,000,000 Total 1650 99,000,000

Table3 reports the estimation of annual operative and maintenance costs of point absorbers, expressed as costs per installed power. Table4 shows the additional costs for maintenance of solar panels.

Table 3. Annual operative and maintenance costs of wave farms.

[€/kW] [€] Purchased components 1.80 233,280 Repair & maintenance 1.25 162,000 Technical consulting service 0.70 90,720 Transport by water 0.25 32,400 Engineering service 0.15 19,440 Commercial and industrial equipment 0.15 19,440 Analytical laboratory instrument 0.10 12,960 Others 0.85 110,160 Total 5.25 680,400

Table 4. Additional operative and maintenance costs of PVP.

[€/kW] [€] Purchased components & maintenance 1.80 233,280

Finally, Table5 shows the annual income from energy selling. In this evaluation, the selling energy price is fixed to 80 €/MWh [42].

Table 5. Annual income.

Selling energy prize [€/MWh] 80 Sea wave energy production [MWh] 141,900 Income by sea wave [€] 11,352,000 Photovoltaic energy production [MWh] 108,300 Income by photovoltaic [€] 8,664,000

Using Equation (2), Figure 11 shows the Discounted Cash Flow, assuming the realization of the wave farm without the integration of solar photovoltaic. According to this evaluation, the breakeven time is estimated to be equal to 24–25 years, as shown in the following figure. Sustainability 2016, 8, 1164 13 of 16

SustainabilitySustainability 20162016,, 88,, 1164 1164 1313 of of 16 16

FigureFigure 11. 11. DiscountDiscount Cash Cash Flow Flow of of sea sea wave wave farms farms without without solar solar photovoltaic. photovoltaic. Figure 11. Discount Cash Flow of sea wave farms without solar photovoltaic. Assuming the realization of the wave farm with the integration of solar photovoltaic, the Assuming the realization of the wave farm with the integration of solar photovoltaic, the economic economic evaluation shows significantly changes. As shown in Figure 12, the breakeven time is evaluationAssuming shows the significantly realization changes.of the wave As shown farm inwi Figureth the 12 integration, the breakeven of solar time photovoltaic, is estimated to the be estimated to be equal to 19 years. This change is linked to the lower cost of photovoltaic solar economicequal to 19 evaluation years. This shows change signif is linkedicantly to changes. the lower As cost shown of photovoltaic in Figure solar12, the technology, breakeven which time has is technology, which has been commercially mature from several years. estimatedbeen commercially to be equal mature to 19 from years. several This years. change is linked to the lower cost of photovoltaic solar technology, which has been commercially mature from several years.

Figure 12. Discount Cash Flow of sea wave farms with solar photovoltaic. Figure 12. Discount Cash Flow of sea wave farms with solar photovoltaic. Figure 12. Discount Cash Flow of sea wave farms with solar photovoltaic. ItIt should should be be noted noted that that the the costs costs of of realization realization of of sea sea wave wave converters converters is is the the item item cost cost with with the the greatestgreatest impact, impact, which which is is due due to to the the fact fact that that technology technology is is currently currently at at a a prototypal step. Assuming Assuming It should be noted that the costs of realization of sea wave converters is the item cost with the that,that, with with development development of of technology, technology, the the building costs will reduce to 1500 €€/kW/kW (the (the same same price price greatest impact, which is due to the fact that technology is currently at a prototypal step. Assuming assumedassumed for for photovoltaic photovoltaic panels), panels), the the breakeven time decreases to 13 years. In In addition, addition, other other that, with development of technology, the building costs will reduce to 1500 €/kW (the same price variablesvariables can can have have a a strong strong effect effect in in this evaluation evaluation.. As As stated stated in in the the previous previous section, section, the the energetic energetic assumed for photovoltaic panels), the breakeven time decreases to 13 years. In addition, other efficiencyefficiency is fixed fixed conservatively toto aa lowerlower value.value. ImprovingImproving the the electrical electrical efficiency efficiency of of the the machine, machine, of variables can have a strong effect in this evaluation. As stated in the previous section, the energetic ofcourse, course, the the electrical electrical output output increases increases and, consequently,and, consequently, the income the income from energy from sellingenergy also selling increases. also efficiency is fixed conservatively to a lower value. Improving the electrical efficiency of the machine, increases.Furthermore, Furthermore, the previous the assessmentprevious assessment does not takedoes intonot take account into theaccount presence the ofpresence any incentive of any of course, the electrical output increases and, consequently, the income from energy selling also incentivemechanisms. mechanisms. Assuming Assuming an energy an selling energy prize selling with incentives—forprize with incentives—for example, 240 example,€/MWh—the 240 increases. Furthermore, the previous assessment does not take into account the presence of any €/MWh—thebreakeven time breakeven falls to fivetime years. falls to This five incentivized years. This incentivized prize is supposed, prize is considering supposed, considering that this value that is incentive mechanisms. Assuming an energy selling prize with incentives—for example, 240 thisvery value lower is thanvery incentivizedlower than incentivized prizes used prizes in Italy used for photovoltaic in Italy for photovoltaic panels during panels the firstduring years the of first the €/MWh—the breakeven time falls to five years. This incentivized prize is supposed, considering that yearsmechanism of the mechanism “Conto Energia” “Conto [43 Energia”]. [43]. this value is very lower than incentivized prizes used in Italy for photovoltaic panels during the first years8. Conclusions of the mechanism “Conto Energia” [43]. 8. Conclusions The sea wave energy potential has been evaluated along the Maltese coasts. According to 8. ConclusionsThe sea wave energy potential has been evaluated along the Maltese coasts. According to our our evaluation, the installation of 18 wave farms, based on DEIM converters, could produce evaluation, the installation of 18 wave farms, based on DEIM converters, could produce 141,900 141,900The MWh/year.sea wave energy In addition, potential by has installing been evaluated off-shore along photovoltaic the Maltese panels coasts. on DEIMAccording converters, to our MWh/year. In addition, by installing off-shore photovoltaic panels on DEIM converters, another evaluation,another 108,300 the installation MWh/year couldof 18 bewave produced. farms, based The total on electricalDEIM converters, production could from off-shoreproduce systems141,900 MWh/year. In addition, by installing off-shore photovoltaic panels on DEIM converters, another Sustainability 2016, 8, 1164 14 of 16 could amount to 250,200 MWh/year, which represents the 10.1% of the electricity demand expected for 2025. The economic assessment shows that the breakeven time is currently high because this technology is currently at a prototypal step. However, with the introducing economic incentive, this technology becomes economically sustainable, allowing a more rapid commercial development. The correct use of Renewable Energies will contribute to reducing the dependence of Maltese islands on exogenous fossil fuels, limiting the emissions of greenhouse gases due to the energy sector and global warming. Obviously, the installation of wind turbines and photovoltaic panels on Malta’s archipelago can produce a very significant part of electrical energy demand. Thanks to the presence of the Malta–Sicily interconnector, the system (not evaluated in this paper) plays a secondary role in the electrical energy, until the electrical energy production by RES becomes predominant.

Author Contributions: All authors contributed equally. Conflicts of Interest: The authors declare no conflict of interest.

Nomenclature

Hs Significant wave height [m] Tm Main period [s] P Power per front wave [kW/m] ρ Sea water density [kg/m3] g Gravitational acceleration [m/s2] DCF Discounted Cash Flow [€] C0 Initial investment [€] Cannual Annual operative and maintenance costs [€] Iannual Annual income generated from energy selling [€] τ Discount rate [%] ε Discount rate in energy systems [%]

References

1. Qoaider, L.; Steinbrecht, D. Photovoltaic systems: A cost competitive option to supply energy to off-grid agricultural communities in arid regions. Appl. Energy 2010, 87, 427–435. [CrossRef] 2. Di Dio, V.; Franzitta, V.; Milone, D.; Pitruzzella, S.; Trapanese, M.; Viola, A. Design of Bilateral Switched Reluctance Linear Generator to Convert Wave Energy: Case Study in Sicily. Adv. Mater. Res. 2013, 860–863, 1694–1698. [CrossRef] 3. Franzitta, V.; Milone, A.; Milone, D.; Trapanese, M.; Viola, A. A Procedure to Evaluate the Indoor Global Quality by a Sub Objective-Objective Procedure. Adv. Mater. Res. 2013, 734–737, 3065–3070. [CrossRef] 4. Antoine, B.; Goran, K.; Neven, D. Energy scenarios for Malta. Int. J. Hydrog. Energy 2008, 33, 4235–4246. [CrossRef] 5. Franzitta, V.; Milone, D.; Trapanese, M.; Viola, A.; Di Dio, V.; Pitruzzella, S. Energy and Economic Comparison of Different Conditioning System among Traditional and Eco-Sustainable Building. Appl. Mech. Mater. 2013, 394, 289–295. [CrossRef] 6. Zhao, B.; Zhang, X.; Li, P.; Wang, K.; Xue, M.; Wang, C. Optimal sizing, operating strategy and operational experience of a stand-alone microgrid on Dongfushan Island. Appl. Energy 2014, 113, 1656–1666. [CrossRef] 7. Ma, T.; Yang, H.; Lu, L. A feasibility study of a stand-alone hybrid solar-wind-battery system for a remote island. Appl. Energy 2014, 121, 149–158. [CrossRef] 8. Ma, T.; Yang, H.; Lu, L. Feasibility study and economic analysis of pumped hydro storage and battery storage for a renewable energy powered island. Energy Convers. Manag. 2014, 79, 387–397. [CrossRef] 9. Bin, Y.; Jie, T.; Qiang, L. Feasibility analysis of renewable energy powered tourism island—Hainan, China. J. Renew. Sustain. Energy 2012, 4.[CrossRef] Sustainability 2016, 8, 1164 15 of 16

10. Petrakopoulou, F. On the economics of stand-alone renewable hybrid power plants in remote regions. Energy Convers. Manag. 2016, 118, 63–74. [CrossRef] 11. Trapanese, M.; Viola, A.; Franzitta, V. Design and Experimental Test of a Thermomagnetic Motor. AASRI Procedia 2012, 2, 199–204. [CrossRef] 12. Franzitta, V.; Milone, A.; Milone, D.; Pitruzzella, S.; Trapanese, M.; Viola, A. Experimental Evidence on the Thermal Performance of Opaque Surfaces in Mediterranean Climate. Adv. Mater. Res. 2013, 860–863, 1227–1231. [CrossRef] 13. Milone, D.; Pitruzzella, S.; Franzitta, V.; Viola, A.; Trapanese, M. Energy Savings through Integration of the Illumination Natural and Artificial, Using a System of Automatic Dimming: Case Study. Appl. Mech. Mater. 2013, 372, 253–258. [CrossRef] 14. Franzitta, V.; Milone, A.; Milone, D.; Pitruzzella, S.; Trapanese, M.; Viola, A. A Case Study to Evaluate the Indoor Global Quality. Adv. Mater. Res. 2013, 864–867, 1054–1058. [CrossRef] 15. Trapanese, M.; Franzitta, V.; Viola, A. The Jiles Atherton model for description of hysteresis in lithium battery. In 2013 Twenty-Eighth Annual IEEE Applied Power Electronics Conference and Exposition (APEC); IEEE: Piscataway, NJ, USA, 2013; pp. 2773–2775. 16. Colucci, A.; Boscaino, V.; Cipriani, G.; Curto, D.; di Dio, V.; Franzitta, V.; Trapanese, M.; Viola, A. An inertial system for the production of electricity and hydrogen from sea wave energy. In Ocean 2015—MTS/IEEE Washington; IEEE: Piscataway, NJ, USA, 2015; pp. 1–10. 17. Antonio, F.D.O. Wave energy utilization: A review of the technologies. Renew. Sustain. Energy Rev. 2010, 14, 899–918. 18. Viola, A.; Franzitta, V.; Curto, D.; Di Dio, V.; Milone, D.; Rodono, G. Environmental Impact Assessment (EIA) of Wave Energy Converter (WEC). In OCEANS 2015—Genova; IEEE: Piscataway, NJ, USA, 2015; pp. 1–4. 19. Trapanese, M.; Franzitta, V.; Viola, A. Description of hysteresis of Nickel Metal Hydride Battery. In IECON 2012—38th Annual Conference on IEEE Industrial Electronics Society; IEEE: Piscataway, NJ, USA, 2012; pp. 967–970. 20. Wikipedia, Malta. 2016. Available online: https://en.wikipedia.org/wiki/Malta (accessed on 20 October 2016). 21. Weather and climate in Malta and Gozo (malta.com). Available online: http://www.malta.com/en/about- malta/weather-climate (accessed on 20 October 2016). 22. European Commission (EC). Malta Renewable Energy Fact Sheet (2008). Available online: https://www. energy.eu/renewables/factsheets/2008_res_sheet_malta_en.pdf (accessed on 20 October 2016). 23. EneMalta plc, “Enemalta”. Available online: http://www.enemalta.com.mt/ (accessed on 20 October 2016). 24. Renewable Energy Scenarios in Islands (RESI), “RESI Map”. Available online: http://www.resiproject.eu/ site/map/ (accessed on 20 October 2016). 25. International Energy Agency (IEA). Malta. Available: https://www.iea.org/countries/non-membercountries/ malta/ (accessed on 20 October 2016). 26. National Statistics Office. Malta and European Statistical System, Electricity Generation: 2006–2015; European Statistical System: Brussels, Belgium, 2016. 27. Trapani, K.; Millar, D.L. Proposing offshore photovoltaic (PV) technology to the of the Maltese islands. Energy Convers. Manag. 2013, 67, 18–26. [CrossRef] 28. Sørensen, H.C.; Chozas, J.F. The Potential for Wave Energy in the North Sea. In 3rd International Conference and Exhibition on Ocean Energy (ICOE-2010); ICOE: Bilbao, Spain, 2010; pp. 1–6. 29. Drago, A.; Azzopardi, J.; Gauci, A.; Tarasova, R. Assessing the Offshore Wave Energy Potential for the Maltese Islands. In The ISE Annual Conference 2013; University of Malta: Qawa, Malta, 2013. 30. Trapanese, M.; Franzitta, V.; Viola, A. A dynamic model for hysteresis in magnetostrictive devices. J. Appl. Phys. 2014, 115, 1–4. [CrossRef] 31. Franzitta, V.; Viola, A.; Trapanese, M. Design of a transverse flux machine for power generation from sea waves. J. Appl. Phys. 2014, 115.[CrossRef] 32. Marvuglia, A.; Messineo, A. Using Recurrent Artificial Neural Networks to Forecast Household Electricity Consumption. Energy Procedia 2012, 14, 45–55. [CrossRef] 33. Volpe, R.; Messineo, A.; Millan, M.; Volpe, M.; Kandiyoti, R. Assessment of olive wastes as energy source: Pyrolysis, torrefaction and the key role of H loss in thermal breakdown. Energy 2015, 82, 119–127. [CrossRef] 34. Cannistraro, G.; Cannistraro, M.; Galvagno, A.; Trovato, G. Preliminary Design Study of a CHP Plant in Service for an Hotel Accomodation. In Congress WSEAS 2016; WSEAS: Venice, Italy, 2016. Sustainability 2016, 8, 1164 16 of 16

35. Cannistraro, G.; Cannistraro, M.; Galvagno, A. A Innovative System for Monitoring Local Pollution in Urban Areas. In Congress WSEAS 2016; WSEAS: Venice, Italy, 2016; pp. 45–52. 36. Cannistraro, G.; Cannistraro, M.; Cannistraro, A.; Galvagno, A.; Trovato, G. Reducing the Demand of Energy Cooling in the CED, ‘Centers of Processing Data’, with Use of Free-Cooling Systems. Int. J. Heat Technol. 2016, 34, 498–502. [CrossRef] 37. IPA. Fuel Optimization Study to Enemalta, Malta. 2010. Available online: https://mfin.gov.mt/en/home/ enemalta/Documents/Enemalta_FMA_Final_Report_2010-11-19.pdf (accessed on 20 October 2016). 38. European Commission (EC). National Allocation Plan for Malta 2005–2007; European Commission: Luxembourg, 2004. 39. Tasso bce. Available online: http://www.euribor.it/tasso-bce/ (accessed on 4 November 2016). 40. Steinbach, J.; Staniaszek, D. Discount Rates in Energy System Analysis Discussion Paper; BPIE: Berlin, Germany, 2015. 41. Gielen, D. Solar Photovoltaics; IRENA: Abu Dhabi, UAE, 2014. 42. Price Level Index for Household Final Consumption Expenditure (HFCE). 2015. Available online: http://ec.europa.eu/eurostat/statistics-explained/index.php/File:Price_level_index_for_household_ final_consumption_expenditure_(HFCE),_2015,_EU-28=100_V2.png (accessed on 4 November 2016). 43. Ciabattoni, L.; Grisostomi, M.; Ippoliti, G.; Longhi, S. Fuzzy logic home energy consumption modeling for residential photovoltaic plant sizing in the new Italian scenario. Energy 2014, 74, 359–367. [CrossRef]

© 2016 by the authors; licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC-BY) license (http://creativecommons.org/licenses/by/4.0/).