El Hierro Renewable Energy Hybrid System: a Tough Compromise

energies

Review El Hierro Renewable Energy Hybrid System: A Tough Compromise

Grazyna˙ Frydrychowicz-Jastrz˛ebska

Department of Electrical Engineering, Poznan University of Technology, Piotrowo 3a Street, 60-965 Pozna´n,Poland; [email protected]; Tel.: +48-61-665-2388 or +48-66-163-4997

Received: 23 September 2018; Accepted: 15 October 2018; Published: 18 October 2018

Abstract: The Gorona del Viento project was characterized in this article, concerning its implementation, as well as several years of exploitation in an isolated location, namely on the El Hierro island. The hybrid system includes a wind farm and a pumped storage power plant, which acts as an energy storage, and all are equipped with a control system. The planned strategy assumed a configuration based on 100% wind energy supply. However, the system does not guarantee the anticipated effectiveness. The problems with the lack of energy self-sufficiency are partly the result of changes in the project made already during construction, in particular because of the mismatch of the water reservoir’s capacity and the wind turbines’ energy production efficiency. This results in the necessity to limit the wind farm capacity to ensure grid stability and hence requires supplementation of energy from the diesel generator. The author compared the object to analogical ones which employ different technological solutions and presented potential suggestions as to improve the existing state and achieve the reliability of the system’s operation.

Keywords: renewable energy sources; energy self-sufﬁciency; hybrid system; energy storage; isolated locations

1. Introduction Over the last twenty years, a number of initiatives related to the introduction of energy self-sufficiency in isolated locations have been observed [1–11]. Such attempts were successfully made on the islands of the Atlantic, Pacific, and Indian Oceans [1], the Azores, the Canary Islands, the Greek Islands, the Caribbean, Tokelau (New Zealand), Bornholm, Samsø (Denmark), the Galápagos Islands (Ecuador), Bonaire (Little Antilles, the Netherlands), American Samoa Islands, and many others. This is in addition to those in the center of the European continent, e.g., in Feldheim near Berlin (a separate system). The new solutions are, in most cases, based on hybrid systems of renewable energy sources. Reference [2] reviews the research in the field of the design, optimization, operation, and control of renewable hybrid energy systems in isolated locations, and Reference [3] presents an analysis of the energy potential of isolated systems (with particular reference to wind energy) in relation to their population. The importance of hybridization and energy storage was also emphasized. Reference [4] contains information concerning energy solutions on El Hierro, Bornholm, Samso, Iceland, and Corvo. Assessment of the power system of the insular structures from the point of view of sustainable development and reliability and the feasibility of their implementation for the areas of Madeira, Porto Santo, Hawaii, Canary Islands (El Hierro, Lanzarote), Menorca, Azores Peak, and Vancouver Island were carried out in Reference [5]. The authors suggest worldwide cooperation between islands in the field of energy self-sufficiency and RES (Renewable Energy Sources). Analogous considerations with regard to the Azores and Canary Islands, as well as Danish and Greek islands are contained in Reference [6].

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Reference [7] assessed the isolated electricity network and goals proposed in the Canary Islands energy plan (PECAN), taking into account the average cost and risk associated with different alternatives to electricity generation. In order to increase efficiency (even by 30%), authors additionally suggest the use of natural gas. Current and future (until 2050) action plan in this area was presented in Reference [8]. Reference [9], on the other hand, presented the program of introducing RES in the Azores from 2007 to 2018. The smallest of the archipelago islands, Corvo, is planned to be powered exclusively from RES [4,9]. Reference [10] concerned the Greek islands of Crete, Kythnos, Ikaria, and Agios Efstrations. An interesting solution was applied on Ikaria (thermal, PV (photovoltaic), wind, and hydro with storage in two locations). The island of Agios Efstrations is planned to achieve 100% energy self-sufficiency only from RES. In Reference [11], the importance of assessing the technical and economic feasibility of isolated wind energy systems is emphasized. Because of the instability of the RES (the availability of their potential depends on many factors), a reserve conventional source and a storage are often introduced into the system [4]. Reference [12] proposed a novel method of optimizing the efficiency of battery energy storage systems. Four optimal objective functions have been taken into account, such as minimum energy storage capacity, minimum load dump, the maximum lowest deflection frequency, and minimum disruption duration indicator. An overview of possible solutions for electricity storage is presented in References [13–18] including pumped hydro storage, flywheel, superconducting magnetic energy storage (SMES), supercapacitors, battery energy storage system (BESS), pumped heat electrical storage (PHES), and compressed air energy storage (CAES), whereas in References [13,14,16–18], the subject of the integration of storage systems with RES and application possibilities in insular systems were considered. Energy storage can increase the reliability of the microgrids. Reference [14] indicates that pumped hydro storage currently dominates in total installed power capacity storage (with 96% out of the total of 176 gigawatts installed globally until mid-2017); authors also considered the possibility of using flow batteries. Reference [17] suggests periodic use of electric car batteries for cooperation with RES.

2. Selected Applications in Other Isolated Locations Studies have demonstrated that in the majority of locations, the achievement of the full energy self-sufficiency is an unrealistic purpose; the average annual percentage of renewable energy sources in the energy balance is estimated at the level between 30 and 80%, e.g., in case of Graciosa Island, 65% is the estimated percentage [19,20]. However, RES energy self-sufficiency is possible on Tokelau, which is supplied with solar energy exclusively, and which distributes the energy surplus to the neighbouring islands [21]. It is also possible in in Feldheim [22], with the rich RES assortment and the largest accumulator in Europe [23], and on Samsø [24], which exports the wind energy surplus. Bornholm and Samsø may take advantage of the power supply from land by means of an underwater cable. In other isolated regions, the energy scarcity must be supplemented by the energy obtained from diesel oil, transported from the continent, which results in financial outlays and external costs [4,24,25]. The problem of the lack of self-sufficiency can be partly eliminated by the strict observance of the energy supply and demand balance; the storage of surpluses; the smart energy management as it in the case of Bornholm, Samsø, and in Feldheim [4]; and in hybrid power plants with intelligent software, with the participation of VESTAS, e.g., in Spain, Poland, and Australia, the latter one with the target value of 1.2 GW [26]. Similar activities are introduced in the Canary Islands. The purpose is to ensure the full energy self-sufficiency of the archipelago by the year 2050. Furthermore, there are plans to provide energy connections using an underwater cable between the islands to ensure an energy balance, e.g., between the islands of El Hierro, La Palma, and La Gomera [8]. Energies 2018, 11, 2812 3 of 20

The role of integration between individual energy sources is emphasized in Reference [27] on the example of São Miquel in the Azores. The considerations concern the heat and power plant, two geothermal power plants, a hydroelectric plant, a wind farm, and a conventional source. The possible inclusion of a photovoltaic installation in the system was also analyzed. An innovative serial model has been proposed for the main energy plan on the São Miguel Island. Based on the algorithm, it has been shown that optimizing and maximizing the integration of renewable energy sources reduces fuel consumption, production costs, and greenhouse gas emissions. The Terceira system is difficult to implement because of the greater variety of cooperating RES and the necessity of their integration. For the year 2018, based on the estimated scenario of energy demand and supplies, geothermal energy, wind energy, thermal energy, and recovery of energy from bio-waste were taken into consideration. In the case of Terceira, a detailed analysis of different storage solutions was conducted. It was demonstrated that the optimal storage of energy will be ensured using a pumped hydro storage. The cost of PHS (Pumped Hydro Storage) is much lower than in the case of battery-based solutions [28]. Reference [29] presents the integration of components: wind, diesel, and hydro turbines in the Flores Island. The addition of the FESS (flywheel energy storage system) improved the stability and allowed the higher penetration of energy from renewable sources, and as a consequence of this, a reduction in the consumption of oil. The system was evaluated after one year of its operation. Other hybrid systems in the isolated locations are also supplemented with energy storage, e.g., Graciosa (3.2 MWh lithium-ion storage in the Younicos system) connected with the PV power plant (1 MW) and a wind farm (4.5 MW) [19]; Tokelau (energy storage in a lead-acid battery, a total of 1344 batteries) [21]; and Feldheim (lithium-ion battery with a total capacity of 10 MW and a power of 10.8 MWh) [23]. In the hybrid system, which consists of three wind turbines and two sets of PV modules in San Cristóbal, the Galápagos Islands (Ecuador), from the moment of commissioning in October 2007 up to and including 2015, the average percentage of wind energy reached 29.2%, when compared to diesel’s 70.8%. The reduction in the CO2 emissions during the above-mentioned period was 21,254 tonnes. The lowest share of diesel in the energy generation was observed in the years 2012 and 2015. In the wind farm on the Galápagos Islands, lead-acid and lithium-ion batteries were used to balance the load. The Galápagos project also covers two 6 kWp PV installations, which generated 136,000 kWh of energy, as well as new transmission lines and advanced control systems that allow the integration and cooperation of the entire system [30]. Initially, the Bonaire system did not cover the FESS, and the aim was the achievement of the wind penetration rate at the level of 40–45%. In the absence of energy, a diesel generator with bio-oil from marine algae is used [31]. In the seven-island archipelago of American Samoa, electricity is obtained from wind, solar, geothermal, and biomass energy. Tesla installed two powerpack battery systems and implemented the island network control software, which is to control the integrated 13.6 MWh system of energy production and storage [32,33]. The Greek Ikaria relies on the wind–water system with two water storages (3.1 MW and 1 MW), located in different towns [4,10]. Each of the solutions requires specific conditions and uses different renewable energy sources, though on the Atlantic islands, the wind energy is by far the most popular [8,9]. It is also important to select the storage capacity properly, while the installation per se should not be over-dimensioned Examples of wind farms on the Atlantic islands are presented in Figure1. Energies 2018, 11, x FOR PEER REVIEW 3 of 20

possible inclusion of a photovoltaic installation in the system was also analyzed. An innovative serial model has been proposed for the main energy plan on the São Miguel Island. Based on the algorithm, it has been shown that optimizing and maximizing the integration of renewable energy sources reduces fuel consumption, production costs, and greenhouse gas emissions. The Terceira system is difficult to implement because of the greater variety of cooperating RES and the necessity of their integration. For the year 2018, based on the estimated scenario of energy demand and supplies, geothermal energy, wind energy, thermal energy, and recovery of energy from bio‐waste were taken into consideration. In the case of Terceira, a detailed analysis of different storage solutions was conducted. It was demonstrated that the optimal storage of energy will be ensured using a pumped hydro storage. The cost of PHS (Pumped Hydro Storage) is much lower than in the case of battery‐based solutions [28]. Reference [29] presents the integration of components: wind, diesel, and hydro turbines in the Flores Island. The addition of the FESS (flywheel energy storage system) improved the stability and allowed the higher penetration of energy from renewable sources, and as a consequence of this, a reduction in the consumption of oil. The system was evaluated after one year of its operation. Other hybrid systems in the isolated locations are also supplemented with energy storage, e.g., Graciosa (3.2 MWh lithium‐ion storage in the Younicos system) connected with the PV power plant (1 MW) and a wind farm (4.5 MW) [19]; Tokelau (energy storage in a lead‐acid battery, a total of 1344 batteries) [21]; and Feldheim (lithium‐ion battery with a total capacity of 10 MW and a power of 10.8 MWh) [23]. In the hybrid system, which consists of three wind turbines and two sets of PV modules in San Cristóbal, the Galápagos Islands (Ecuador), from the moment of commissioning in October 2007 up to and including 2015, the average percentage of wind energy reached 29.2%, when compared to diesel’s 70.8%. The reduction in the CO2 emissions during the above‐mentioned period was 21,254 tonnes. The lowest share of diesel in the energy generation was observed in the years 2012 and 2015. In the wind farm on the Galápagos Islands, lead‐acid and lithium‐ion batteries were used to balance the load. The Galápagos project also covers two 6 kWp PV installations, which generated 136,000 kWh of energy, as well as new transmission lines and advanced control systems that allow the integration and cooperation of the entire system [30]. Initially, the Bonaire system did not cover the FESS, and the aim was the achievement of the wind penetration rate at the level of 40–45%. In the absence of energy, a diesel generator with bio‐oil from marine algae is used [31]. In the seven‐island archipelago of American Samoa, electricity is obtained from wind, solar, geothermal, and biomass energy. Tesla installed two powerpack battery systems and implemented the island network control software, which is to control the integrated 13.6 MWh system of energy production and storage [32,33]. The Greek Ikaria relies on the wind–water system with two water storages (3.1 MW and 1 MW), located in different towns [4,10]. Each of the solutions requires specific conditions and uses different renewable energy sources, though on the Atlantic islands, the wind energy is by far the most popular [8,9]. It is also important Energiesto2018 select, 11 ,the 2812 storage capacity properly, while the installation per se should not be over‐dimensioned 4 of 20 Examples of wind farms on the Atlantic islands are presented in Figure 1.

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(c) (c) FigureFigure 1. Examples 1. Examples of wind of wind farms farms in isolated in isolated locations: locations: (a) Gran(a) Gran Canaria, Canaria, (b) ( Tenerife,b) Tenerife, and and (c) ( Terceira.c) Photo:FigureTerceira. G. Jastrz˛ebska. 1. Photo: Examples G. Jastrz of windębska. farms in isolated locations: (a) Gran Canaria, (b) Tenerife, and (c) Terceira. Photo: G. Jastrzębska. 3. Biosphere3. Biosphere Reserve Reserve and and Gorona Gorona del del Viento Viento Project Project 3. Biosphere Reserve and Gorona del Viento Project On 10On January 10 January 2007, 2007, the Europeanthe European Commission Commission presented presented the the ClimateClimate and and Energy Energy Package Package to to the On 10 January 2007, the European Commission presented the Climate and Energy Package to memberthe states, member which states, concerned which concerned a decrease a decrease in the in emission the emission of greenhouse of greenhouse gases gases and and an an increase increase in the thein the member share ofstates, renewable which energyconcerned sources a decrease in the finalin the energy emission consumption of greenhouse and effectiveness.gases and an increase share of renewable energy sources in the ﬁnal energy consumption and effectiveness. in theThe share locations of renewable isolated energy in terms sources of energy in the finalinclude energy El Hierro consumption (Isla del and Meridiano), effectiveness. the smallest Theamong locationsThe the locations Canary isolated isolated Islands, in in terms recognised terms of of energy energyby UNESCO includeinclude in El El the Hierro Hierro year (Isla2000 (Isla del as del Meridiano),a biosphere Meridiano), thereserve smallest the and smallest amongamonggeological the Canary the park, Canary Islands,and Islands, in the recognised La recognised Restinga byregion, by UNESCOUNESCO a marine in in reserve the the year year was 2000 isolated 2000 as asa (Figurebiosphere a biosphere 2). reserve reserve and and geologicalgeological park, park, and and in the in the La La Restinga Restinga region, region, a a marinemarine reserve reserve was was isolated isolated (Figure (Figure 2). 2).

(a) (b) (a) (b) Figure 2. El Hierro UNESCO Biosphere Reserve: (a) Roque de la Bonanza, (b) juniper tree at El FigureFigureSabinar 2. El Hierro 2.under El Hierro the UNESCO influence UNESCO Biosphere of strongBiosphere Reserve:wind. Reserve: Photo: (a) G. Roque(a )Jastrz Roque deębska. lade Bonanza, la Bonanza, (b )(b juniper) juniper tree tree at at El El Sabinar underSabinar the inﬂuence under the of influence strong wind. of strong Photo: wind. G. Photo: Jastrz˛ebska. G. Jastrzębska. The area of El Hierro is mountainous, and the landscape is diverse because of pine forests with Thesteep areaThe cliffs ofarea (on El of Hierrothe El Hierroshore, is mountainous, theis mountainous, area reaches and and1500 thethe m landscapeabove sea islevel) is diverse diverse and because geological because of pineformations of pine forests forests with with steep cliffssteeprock basins (oncliffs the (on[34–39]. shore, the shore, The the island area the area reaches is scarcelyreaches 1500 populated1500 m abovem above during sea sea level) thelevel) entire and and geological year;geological the area formationsformations of 278 km with with2 is rock rockinhabited basins by [34–39]. 7000–10,000 The islandpeople is (36 scarcely people populated per km2). during the entire year; the area of 278 km2 is basins [34–39]. The island is scarcely populated during the entire year; the area of 278 km2 is inhabited inhabitedInitially, by 7000–10,000 the energy demandpeople (36 of peoplethe island per waskm2 ).secured by electricity produced from diesel oil. by 7000–10,000 people (36 people per km2). The oilInitially, in the theamount energy of 6000demand tonnes of theper island year was was transported secured by toelectricity the island produced with a tanker from diesel(the costs oil. Initially,Theamounted oil in the the to energy EURamount 2,000,000) demandof 6000 [4]. tonnes of the per island year was was transported secured by to electricitythe island with produced a tanker from (the costs diesel oil. The oilamounted in theAccording amount to EUR to the of2,000,000) 6000 plans, tonnes by[4]. the year per 2050, year all was the transported islands of the to archipelago the island will with be 100% a tanker supplied (the costs amountedwith Accordingrenewable to EUR 2,000,000) toenergy the plans, sources. [4 ].by the The year strategy 2050, provides all the islands for the of 20% the archipelagoshare of RES will in the be energy100% supplied balance withby the renewable year 2020 energy and by sources. the year The 2030, strategy this share provides will be for 58% the [8].20% share of RES in the energy balance by theThe year aspects 2020 and listed by thein theyear first 2030, section, this share i.e., willself ‐besufficiency 58% [8]. and ecology, as well as financial considerations,The aspects justified listed inthe the introduction first section, of a i.e., new self energy‐sufficiency model onand the ecology, island ofas Gorona well as del financial Viento considerations,[40]. Its task would justified be to the satisfy introduction the needs of of a thenew inhabitants energy model by means on the of island renewable of Gorona energy del sources. Viento [40].There Its were task plans would to beinstall to satisfy a wind the farm needs in combinationof the inhabitants with theby meansexisting of UNELCO renewable‐ENDESA energy sources. (This is There were plans to install a wind farm in combination with the existing UNELCO‐ENDESA (This is

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According to the plans, by the year 2050, all the islands of the archipelago will be 100% supplied with renewable energy sources. The strategy provides for the 20% share of RES in the energy balance by the year 2020 and by the year 2030, this share will be 58% [8]. The aspects listed in the first section, i.e., self-sufficiency and ecology, as well as financial considerations, justified the introduction of a new energy model on the island of Gorona del Viento [40]. Its task would be to satisfy the needs of the inhabitants by means of renewable energy sources. There were plans to install a wind farm in combination with the existing UNELCO-ENDESA (This is cooperation of two companies: Empresa Nacional de Electricidad—ENDESA and Union Electric Company—UNELCO)Energies 2018, 11, x FOR system PEER REVIEW and the pumped hydro storage, which was supposed to fulfil5 of 20 the role of an energy storage in the case of wind energy scarcity. cooperation of two companies: Empresa Nacional de Electricidad—ENDESA and Union Electric TheCompany—UNELCO) topography of the islandsystem and is advantageous the pumped hydro for storage, the completion which was of supposed this investment. to fulfil the Therole peak of an extinctof volcanoan energy wasstorage the in suitable the case of place wind for energy the locationscarcity. of wind turbines. The geographical location of the islandThe guaranteed topography high of the wind island levels is advantageous of 7.24–8.42 for m/s the [completion40,41]. The of highest this investment. wind speed The peak of 30.8 m/s was recordedof an extinct in 2017 volcano [40]. An was additional the suitable advantage place for the was location the possibility of wind turbines. of using The the geographical La Caldera crater as a naturallocation (upper) of the reservoirisland guaranteed of the hydro-electric high wind levels power of 7.24–8.42 plant m/s [40 [40,41].]. The highest wind speed of 30.8 m/s was recorded in 2017 [40]. An additional advantage was the possibility of using the La The first projects related to the integration of the wind park with the pumped hydro storage were Caldera crater as a natural (upper) reservoir of the hydro‐electric power plant [40]. developed inThe the first 1980s. projects related to the integration of the wind park with the pumped hydro storage Referencewere developed [42] refers in the to 1980s. an innovative strategy of operation on the El Hierro island and obtaining a reliable andReference efficient [42] energy refers system to an innovative working exclusivelystrategy of operation using RES. on the The El advantages Hierro island of and connecting a pumpedobtaining storage a reliable power and plant efficient to stabilize energy system the power working supplied exclusively by using a wind RES. farm The advantages are presented. of The connecting a pumped storage power plant to stabilize the power supplied by a wind farm are solution allows for the regulation of the system and store large amounts of energy, and consequently presented. The solution allows for the regulation of the system and store large amounts of energy, reducesand dependence consequently on reduces conventional dependence fuel. on Energy conventional stored fuel. during Energy windy stored periods during windy can be periods transformed into electricitycan be transformed when the into load electricity exceeds when the currentthe load energyexceeds the generated current energy from generated the wind from by meansthe of a hydraulicwind turbine. by means The of results a hydraulic of the turbine. presented The results research of the can presented be extrapolated research can to be other extrapolated networks to in order to estimateother the networks needed in percentage order to estimate of conventional the needed percentage power in of the conventional system, depending power in the on system, the available depending on the available wind power. The terrain intended for the investment is shown in Figure wind power. The terrain intended for the investment is shown in Figure3. 3.

Figure 3.FigureEl Hierro 3. El Hierro UNESCO UNESCO Biosphere Biosphere Reserve Reserve with landform landform and and technical technical documentation, documentation, Photo: Photo: G. Jastrzębska. G. Jastrz˛ebska. The selected concept is innovative. The pumped hydro storage does not provide ”support” for the wind energy, it is rather the wind energy that ensures the pumped hydro‐accumulation, allowing the functioning of the hydroelectric plant as the source of the load [43,44].

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The selected concept is innovative. The pumped hydro storage does not provide ”support” for theEnergies wind 2018 energy,, 11, x FOR it is PEER rather REVIEW the wind energy that ensures the pumped hydro-accumulation, allowing6 of 20 the functioning of the hydroelectric plant as the source of the load [43,44]. The technicaltechnical feasibility feasibility study study was was performed performed and the and optimal the optimal conﬁgurations configurations of wind generators, of wind hydraulicgenerators, turbines, hydraulic and turbines, devices and for devices volumetric for volumetric placement placement were determined. were determined. The support The from support the Europeanfrom the European Union as wellUnion as as the well central as the and central local authorities and local authorities was gained. was The gained. location The of thelocation investment of the co-ﬁnancedinvestment co from‐financed the budget from ofthe the budget El Hierro of the Island El Hierro Council Island (65.82%), Council Endesa (65.82%), (23.21%), Endesa The (23.21%), Canary IslandsThe Canary Institute Islands of Technology Institute of (7.74%) Technology and the (7.74%) Autonomous and the CommunityAutonomous of Community the Canary Islands of the Canary (3.23%) wasIslands planned (3.23%) in was the La planned Caldera in Valverde the La Caldera district Valverde [4,40]. district [4,40]. The Gorona del Viento CompanyCompany waswas establishedestablished inin thethe yearyear 2004.2004. Construction works were started in the year 2009 upon obtaining a permit from thethe locallocal authoritiesauthorities and conducting the environmental clearance [[40].40].

4. System Arrangement and Operations Details The ﬁnallyfinally integratedintegrated system system consisted consisted of of the the wind wind farm, farm, the the hydroelectric hydroelectric power power station, station, and and the pumpedthe pumped storage storage system. system. The wind The farmwind was farm located was atlocated a distance at a of distance 2.5 km from of 2.5 the km hydroelectric from the planthydroelectric [45]. It mustplant be[45]. mentioned It must be here mentioned that this here is the that ﬁrst this such is projectthe first in such the powerproject scale in the given power in megawattsscale given [in40 megawatts]. [40]. Figure4 4 presents presents the the planned planned layout layout of of the the facilities. facilities.

Figure 4.4. InformationInformation board board presenting presenting implementation implementation of the of Gorona the Gorona del Viento del ProjectViento withProject planned with locationplanned oflocation the objects. of the Photo: objects. G. Photo: Jastrz˛ebska. G. Jastrzębska.

The farm consists of ﬁve ENERCON E-70 turbines (ENERCON GmbH, Name of the Company The farm consists of five ENERCON E‐70 turbines (ENERCON GmbH, Name of the Company dealing with wind energy plant) with a total installed power of 11.5 MW. Electricity obtained directly dealing with wind energy plant) with a total installed power of 11.5 MW. Electricity obtained from wind is used for the needs of the inhabitants and for the water desalination plant [4,40,45]. directly from wind is used for the needs of the inhabitants and for the water desalination plant [4,40,45]. One advantage of the ENERCON E‐70 solution is that wind energy converters are started with a special storm control feature. This slows down the turbine, owing to which it can still function at high wind speeds. The turbine switches off only at a wind speed higher than 34 m/s (10‐min average [46].

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Energies 2018, 11, x FOR PEER REVIEW 7 of 20 One advantage of the ENERCON E-70 solution is that wind energy converters are started with a Table 1 contains the values of construction‐operational parameters for ENERCON E‐70 wind special storm control feature. This slows down the turbine, owing to which it can still function at high turbines, used at Gorona del Viento on El Hierro [46]. wind speeds. The turbine switches off only at a wind speed higher than 34 m/s (10-min average [46]. Table1 contains theTable values 1. Parameters of construction-operational of ENERCON E‐70 E4 parameters wind turbines. for ENERCON E-70 wind turbines, used at Gorona del Viento on El Hierro [46]. Parameter Unit Value Tablerated 1. Parameters power of ENERCONkW E-70 E4 wind2300 turbines. hub ‐ steel tube concrete Parameter Unit Value hub height m 64 rated power kW 2300 rotor diameter m 71 hub - steel tube concrete 1 bladehub heightmaterial ‐ mGRP 64 numberrotor diameter of blades ‐ m 713 bladeswept material area -m2 GRP39591 rotationalnumber ofspeed blades (var.) rpm - 6–21 3 swept area m2 3959 cut out wind speed m/s 28/34 2 rotational speed (var.) rpm 6–21 cutwind out zone wind (DIBt) speed ‐ m/s 28/34III 2 windwind zoneclass (DIBt) (IEC) 3 ‐ - IIII A remotewind class monitoring (IEC) 3 -IA‐ ENERCON SCADA remote monitoring - ENERCON SCADA 1 fibreglass, epoxy resin, built in lighting protection, 2 with ENERCON storm control, 3 classification 1 2 3 accordingfibreglass, to epoxy IEC resin, (International built in lighting Electrotechnical protection, Commision),with ENERCON has storm four control, classes definingclassification the accordingintensity to IEC (International Electrotechnical Commision), has four classes defining the intensity of turbulence. SCADA: Supervisoryof turbulence. Control SCADA: and DataSupervisory Acquisition, Control informatic and Data system Acquisition, that supervises informatic the course system of a that technological supervises or productionthe course process. of a technological or production process.

FigureFigure5 5 shows shows the the characteristics characteristics of of the the turbine turbine power power versus versus wind wind speed. speed.

FigureFigure 5.5. Power characteristics of the ENERCON E-70E‐70 turbine as a functionfunction ofof windwind speed,speed, ownown elaborationelaboration basedbased onon ReferenceReference [[47].47].

TheThe secondsecond part part of of the the system, system, the the pumped pumped hydro hydro storage storage with awith total a power total ofpower 11.3 MW, of 11.3 included MW, fourincluded Pelton four turbines, Pelton each turbines, with each the unit with power the unit of 2.83 power MW of connected 2.83 MW withconnected alternators with alternators with a power with of 3.3 MVA. They are the development of the “spray wheel,” in which the blades were set at an angle a power◦ of 3.3 MVA. They are the development of the “spray wheel,” in which the blades were set at ofan 90 angletowards of 90° towards the jet. In the order jet. In to order increase to increase the efficiency, the efficiency, special profiledspecial profiled blades in blades the shape in the of shape two combinedof two combined buckets buckets were used. were Theseused. These were impulsewere impulse turbines, turbines, therefore, therefore, the pressure the pressure at the at inlet the inlet and outletand outlet of the of rotor the was rotor the was same. the In same. connection In connection with the decision with the to disconnectdecision to the disconnect diesel generator, the diesel the Peltongenerator, turbines the Pelton were modified turbines towere operate modified as rotary to operate phase shiftsas rotary (compensators), phase shifts (compensators), and their generators and suppliedtheir generators the required supplied short-circuit the required power short and‐ passivecircuit power power and to the passive grid. After power the to disconnection the grid. After of the dieseldisconnection generator, of theythe diesel were supposed generator, to they take were over thesupposed control to of take voltage over and the frequency control of [40 voltage]. Another and optionfrequency of frequency [40]. Another control option is proposed of frequency in Reference control [ 48is ].proposed The performed in Reference simulations [48]. The confirmed performed the justnesssimulations of the confirmed measures the taken. justness The natural of the measures crater of an taken. extinct The volcano natural was crater used of as an the extinct reservoir. volcano It is was used as the reservoir. It is situated 650 m higher than the artificial reservoir (714.5 m above sea

EnergiesEnergies 2018,, 11,, x 2812 FOR PEER REVIEW 88 of of 20 20 level). The lower reservoir with a capacity of 150,000 m3 is located near the area of the diesel power plantsituated Llanos 650 mBlancos higher [45]. than the artiﬁcial reservoir (714.5 m above sea level). The lower reservoir with a 3 capacityFigure of 150,0006 shows m theis draft located of the near project. the area of the diesel power plant Llanos Blancos [45]. Figure6 shows the draft of the project.

FigureFigure 6. SketchSketch of of the the project project implemented by by the the ABB ABB (ASEA (ASEA Brown Brown Boveri) Boveri) concern concern on on the the island island ofof El Hierro with location of the wind–hydro power plant facilities (own elaboration). Signs: (1) (1) La La × CalderaCaldera hydroelectrichydroelectric tank; tank; (2) (2) wind wind farm farm 5 5ENERCON; × ENERCON; (3) pumping (3) pumping station; station; (4) hydroelectric (4) hydroelectric station × station4 Pelton; 4 × Pelton; (5) bottom (5) bottom tank; (6) tank; pump (6) station;pump station; (7) electrical (7) electrical substation substation with mutual with connectionmutual connection between betweena wind farm, a wind hydroelectric farm, hydroelectric station and station pump and station; pump and station; (8) Llanos and (8) Blancos Llanos diesel Blancos power diesel plant. power plant.Selected parameters of the upper reservoir of the hydroelectric power plant are listed in Table2.

SelectedTable parameters 2. Structural of the and upper operational reservoir parameters of the hydroelectric of the upper hydropower power plant plant are [listed45]. in Table 2.

Table 2. StructuralParameter and operational parameters Unit of the upper hydropower Value plant [45]. 3 1 reservoirParameter capacity Unitm 379,634 desalinatedValue water the height of the summit 2 m 715 3 1 reservoirlower crater capacity height m m 379,634 desalinated 698 water the compactingheight of the the summit bottom 2 m - 2 mm geomembrane715 HDPE 2 lowerwaterproofing crater height m - geomembrane698 PVC 3 3 compactingflow the bottom ‐ m /s 2 mm geomembrane2 HDPE 2 waterproofing1 initially 550,000, ‐ 2 high density polyethylene,geomembrane3 polyvinyl chloride. PVC 3 flow m3/s 2 The upper reservoir1 initially has 550,000, two drain 2 high inlets, density both polyethylene, made of S355NL 3 polyvinyl steel chloride. and 530 m long. The suction from the lower reservoir took place through a steel culvert embedded in concrete, with a diameter of 1 m andThe lengthupper ofreservoir 188 m. has two drain inlets, both made of S355NL steel and 530 m long. The suctionThe from parameters the lower of thereservoir lower reservoirtook place are through described a steel in Table culvert3[45 ].embedded in concrete, with a diameter of 1 m and length of 188 m. The parametersTable 3.ofStructural the lower and reservoir operational are described parameters in of Table the lower 3 [45]. hydropower plant. Parameter Unit Value Table 3. Structural and operational parameters of the lower hydropower plant. reservoir capacity 1 m3 150,000 the heightParameter of the barrier Unit m Value 23 reservoirwater capacity level 1 m3 m 150,000 15 waterproofing 2 mm geomembrane HDPE 2 the height of the barrier m 23 1 2 waterat level 56 m above sea level,m high density polyethylene.15 waterproofing 2 mm geomembrane HDPE 2 The pumping station was characterised by the power of 6 MW (2 × 1.5 MW, connected with a 1 at 56 m above sea level, 2 high density polyethylene. variable speed drive and −6 × 0.5 MW, powered via induction motors. Adjustment of the power factorThe was pumping by means station of capacitors). was characterised The hydro by system the power also of included 6 MW two(2 × transformers,1.5 MW, connected 12 MVA with each a variable(20/6 kV), speed and drive four compensationand −6 × 0.5 MW, capacitors powered with via a unitinduction power motors. of 350 kVA,Adjustment connected of the to 6power kV busbars. factor

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was by means of capacitors). The hydro system also included two transformers, 12 MVA each (20/6 kV), Another system component responsible for electricity generation in the system is the diesel unit and four compensation capacitors with a unit power of 350 kVA, connected to 6 kV busbars. (a conventional source that supplements the energy scarcity from renewable sources). The Central Another system component responsible for electricity generation in the system is the diesel unit Diésel de Llanos Blancos plant had the maximum capacity of 12.73 MW with the utilization factor (a conventional source that supplements the energy scarcity from renewable sources). The Central of 38.2%. It consisted of diesel groups with powers ranging between 0.775 MW and 1.9 MW, and Diésel de Llanos Blancos plant had the maximum capacity of 12.73 MW with the utilization factor of was38.2%. fitted It consisted with alternators, of diesel groups transformers, with powers and control ranging devices between [49 0.775]. According MW and 1.9 to ReferenceMW, and was [18], the maximumfitted with capacityalternators, was transformers, estimated to slightlyand control exceed devices 10 MW. [49]. According to Reference [18], the maximumThe investment capacity was comprised estimated the to slightly ABB Distributed exceed 10 ControlMW. System (whereby its sensors responded withinThe 5 sinvestment from the signal comprised informing the ABB about Distributed waning Control of the wind), System as (whereby well as the its sensors old and responded new grids [4]. withinThe 5 s costs from ofthe the signal generation informing of about electricity waning on of the the Canary wind), Islandsas well as were the old high and due new to grids the necessity [4]. of combinationThe costs of ofthe different generation technologies of electricity during on the itsCanary production. Islands were This high required due to the the assurance necessity of of the technicalcombination control of different with greater technologies complexity, during both its the production. mains frequency This required and voltage, the assurance and a greater of the power reserve.technical However, control with the highestgreater complexity, costs were generated both the mains by the frequency use of the dieseland voltage, oil, and and the a costs greater of wind energypower reserve. generation However, in this regionthe highest are twice costs aswere low generated [41]. The annualby the use demand of the ofdiesel the island oil, and for the electricity costs is estimatedof wind energy preliminarily generation at thein this level region of 35 are GWh twice (average as low load [41]. ofThe 4 MW).annual A demand possible of increase the island in the for load, causedelectricity by anis estimated increase in preliminarily the demand forat the energy level up of to 35 50 GWh GWh (average has been load taken of into4 MW). account. A possible There were predictionsincrease in the that load, El Hierro caused wouldby an increase be the first in the region demand in the for world energy that up to would 50 GWh be 100%has been self-sufficient taken withinto account. regard to There its energy were predictions needs [35, 50that,51 El]. Hierro would be the first region in the world that would be 100%After self preliminary‐sufficient with simulations, regard to theits energy planned needs strategy [35,50,51]. for El Hierro required the preparation of the energyAfter system preliminary which wouldsimulations, rely 100% the planned on wind strategy energy, for partly El Hierro supplied required to the the grid preparation after the conversionof the energy system which would rely 100% on wind energy, partly supplied to the grid after the conversion to electricity and partly converted into the energy stored in the pumped hydro storage. In the original to electricity and partly converted into the energy stored in the pumped hydro storage. In the original version, it was assumed that 80% of wind energy would be used to pump in the water. However, it version, it was assumed that 80% of wind energy would be used to pump in the water. However, it was was found that the conversion of the kinetic energy of wind into potential water energy would be the found that the conversion of the kinetic energy of wind into potential water energy would be the cause of cause of losses reaching even 40%, which was a consequence of both the pumping process and the losses reaching even 40%, which was a consequence of both the pumping process and the efficiency of efficiencythe water turbines. of the water Therefore, turbines. the final Therefore, version assumed the final that version only assumedabout 20% that of wind only energy about was 20% to of be wind energydirected was to the to grid be directed indirectly to through the grid the indirectly pumped hydro through storage the pumped [40]. hydro storage [40]. Figure 7 presents the the information information table table regarding regarding the the respective respective investment investment stages. stages.

Figure 7. 7. InformationInformation board board presenting presenting implementation implementation of the of theGorona Gorona del delViento Viento Project. Project. Photo: Photo: G.JastrzG.Jastrz˛ebska.ębska.

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Energies 2018, 11, x FOR PEER REVIEW 10 of 20 FigureFigure8 shows 8 shows the the wind wind farm farm in in the the El El Hierro Hierro energy energy system.system. Figure 8 shows the wind farm in the El Hierro energy system.

FigureFigure 8. Wind8. Wind power power plant plant in in the the El El Hierro Hierro hybrid power power system system where where four four of of the the five ﬁve turbines turbines are are shown. Photo: G. Jastrzębska. shown.Figure Photo: 8. Wind G. Jastrz˛ebska. power plant in the El Hierro hybrid power system where four of the five turbines are shown. Photo: G. Jastrzębska. DuringDuring the the implementation implementation of of the the project,project, the upper reservoir reservoir in in the the volcanic volcanic basin basin revealed revealed the the weaknessweaknessDuring of of rock rock the formations, formations, implementation which which of brought brought the project, thethe threatthreat the upper of a disastrousreservoir disastrous in leakage. leakage.the volcanic basin revealed the TheweaknessThe problems problems of rock with with formations, the the leak-tightness leak ‐whichtightness brought ofof thethe the reservoir threat oflocated located a disastrous at at the the height leakage. height of of 600 600 m ma.s.l. a.s.l. (above (above sea level) also occurred earlier in the case of the Laguna de Barlovento facility in La Palma. At that sea level)The also problems occurred with earlier the inleak the‐tightness case of theof the Laguna reservoir de located Barlovento at the facility height inof La600 Palma. m a.s.l. At(above that time, a membrane made of plasticized polyvinyl chloride (PVC‐P) was used. Nineteen years after the time,sea a membrane level) also madeoccurred of plasticized earlier in the polyvinyl case of the chloride Laguna (PVC-P) de Barlovento was used. facility Nineteen in La Palma. years after At that the installation, it was subjected to a comprehensive testing programme, which covered quantitative installation,time, a membrane it was subjected made of to plasticized a comprehensive polyvinyl testing chloride programme, (PVC‐P) was which used. covered Nineteen quantitative years after tests the tests as well as the optical and scanning electron microscopy. The test results document the good as wellinstallation, as the optical it was and subjected scanning to electron a comprehensive microscopy. testing The testprogramme, results document which covered the good quantitative condition conditiontests as ofwell the as geomembrane the optical and with scanning initial electrondegradation microscopy. processes The [52]. test Detailed results documenttesting using the thegood of thenumerical geomembrane modelling with for initialthe case degradation of the reservoir processes in an [52 old]. Detailed flooded testingquarry usingwas described the numerical in modellingcondition for theof the case geomembrane of the reservoir with ininitial an olddegradation ﬂooded quarryprocesses was [52]. described Detailed intesting Reference using [the53]. Referencenumerical [53]. modelling The impact for of the the case processes of the in reservoir the water in‐bearing an old layerflooded on thequarry change was in describedthe water in The impact of the processes in the water-bearing layer on the change in the water level was taken levelReference was taken [53]. into The account. impact of the processes in the water‐bearing layer on the change in the water into account. levelFigure was 9taken presents into theaccount. view of the upper reservoir of the hydroelectric plant. Figure9 presents the view of the upper reservoir of the hydroelectric plant. Figure 9 presents the view of the upper reservoir of the hydroelectric plant.

Figure 9. The upper reservoir of the hydropower plant. Photo: G. Jastrz ębska.

FigureFigure 9. The 9. The upper upper reservoir reservoir of theof the hydropower hydropower plant. plant. Photo: Photo: G. G. Jastrz˛ebska. Jastrzębska.

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On the island of El Hierro, in the situation of the threat of leakage, the capacity of the upper reservoir was reduced from 550,000 m3 to 379,634 m3 (Table2). The maximum water level reached 12 m. In addition to the reduction in the capacity, both reservoirs were provided with waterprooﬁng made of PVC foil [45]. Their possible repair could be made under water [51]. On 27 June 2014, the project was ofﬁcially inaugurated.

5. System Operation Efficiency Since 27 June 2014, the island has been supplied experimentally from renewable energy sources. One year later, the energy system began its standard operation including test stages. On 9 August 2015, for two consecutive hours, the wind farm generated the energy that secured the demand of inhabitants using only RES. This was the first success of the new investment. It was assumed that the wind energy surplus was to be used to supply pumps such that water could be delivered from the lower reservoir to the upper reservoir. The filled upper reservoir was used as the energy storage [4,36]. As stated above, on the island of El Hierro, the wind speed reached a significant value, often even up to 13 m/s. The measuring data come from the monitoring system at the airport. The wind park is 3 km away from the airport; it is located on a hill and used the energy obtained at a greater height (the height of the terrain above sea level and the mast height of 64 m); thus, the energy (directly proportionate to the wind speed in the third power) was greater here. However, there were windless periods which even covered 10-day cycles in this region, e.g., January or October 2016 [54,55]. Reference [54] presents examples of wind speed charts. A similar solution was implemented on the island of Foula, in the Shetland archipelago and until July 2016, on the Japanese Okinawa Island. The solution on the island of Foula worked rather ineffectively, which was related to the temporary shut-downs of wind turbines during the breeding period of the birds living on the Island [56]. The Yanbaru power station in Kunigami, intended for the storage of seawater, was dismantled after seventeen years of operation as the electricity demand did not increase as expected [57]. El Hierro had a significant potential for energy self-sufficiency based on RES. The applied solution was unique. However, the size of the upper reservoir was determined by the geological conditions of the previously selected wind park area and the capacity of the La Caldera crater. The process of optimisation of its selection should be conducted as one of the first stages in the planned project, after the determination of the energy demand on the island. The reservoir capacity was adapted to the existing volcanic basin. The energy accumulation capacities, already significantly reduced in the project, were drastically decreased as a result of the rock formation weakness, which caused a considerable mismatch of the system components, and as a consequence of this, the lack of stabilization of the grid operation. A critical reference to this issue was made in Reference [43]. However, it must be taken into account that even if the initially-designed storage capacity was ensured (550,000 m3), the use of full wind power would not be possible. At present, it is estimated that the reservoir capacity should be at least 2.5 times greater than the one that has been assumed. If there is no wind, the hydroelectric plant can satisfy the needs of the inhabitants for no more than 48 h (some sources claim that it is actually 12 h), using the accumulated energy. Based on the three-year period of monitoring of the operation of the system on the island of El Hierro, it was concluded that RES did not cover 100% of the demand. The current deficiencies of the wind energy and the energy stored in the reservoir, whose capacity is too small, were supplemented from the diesel generator. However, according to the assumptions, it was only supposed to be used in exceptional circumstances. However, a closer analysis of the monitoring results allowed us to conclude that the anticipated integration of hybrid system components was slow but effective. In the year 2016, the operator conducted tests, which were aimed at such selection of the respective system components as to ensure the optimal operation and stabilisation of the network. His painstaking efforts brought results. Energies 2018, 11, 2812 12 of 20

The trend for RES’s contribution to the island’s energy economy was clearly growing. The average share of RES in energy production in the second half of 2015 was 19.4%, and in 2016, it was 40.7%. The press office of Red Electrica stated that in 2017, thanks to cooperation with Gorona del Viento, it was possible to increase the share of energy produced from RES on El Hierro to 46.5%. In 2017, the best results were obtained in July, namely 79.4% [55,58]. The average RES share in the first half of 2018 increased to 59.67%. In addition, the successes of the island’s short-term energy self-sufficiency with RES alone were recorded. In August 2016, two periods were observed when 100% of the required electricity was generated from renewable energy sources (in 79 h total), and the average monthly percentage of energy from the RES was 55.6%. It was higher than in the similar period of the previous year. On the other hand, during that period, the share of RES in the energy generation was lower than in July 2016 (65.9%); there were breaks in the wind “delivery”. In 2018, the first period of supplying el Hierro with power exclusively from RES began at 11:20 p.m. on 15 January and lasted until 9:30 p.m. on 21 January, where next one, at the turn of January and February, covered 18 days. Very favorable results were obtained in the summer months of 2018, especially in July [58]. On 3 July at 3:20 a.m., the system support by the diesel generator turned out to be unnecessary until 6:00 p.m. on 13 July. The diesel was disconnected again on 15 July at 00:10 a.m. until 1 August, inclusively, the island was supplied with RES. The share of hydroelectric power plant was 25–30%, but, for example, on 29 July, this rose to as much as 90%. The next RES periods without diesel were 5–13 August 2018, and 3–6 September 2018. An interesting case occurred during the lack of wind energy supply on 28–29 March 2018. The windless period began just after midnight on 27 March 2018, and lasted for 36 h. The improvement took place only in the afternoon of 29 March. In the period of windlessness, the task of securing the system with energy was successfully taken over by the hydroelectric power plant, which worked from 1:00 a.m. on 28 March, until 8:00 a.m. on 29 March, completely alone, without the support of diesel. After the start of the wind farm, part of the energy coming from this area was assigned to the current needs of the island, and some to the pump station; therefore, the diesel generators were also included in the work to obtain full power. As stated in Reference [43], the necessity of a greater participation of the diesel generator in the operation of the system resulted from the deliberate reduction of wind farm capacity. The currently operating wind park with a capacity of 5 × 2.3 MW was adapted to the planned upper reservoir with a larger capacity. In the opinion of an expert, the wind capacity was intentionally reduced by the operator to 60% by turning off the turbines to ensure stable network operation. Reference [55] presented a graph concerning the share of renewable energy and diesel in energy production in one of the tests carried out in June 2016. The graph shows periodic shutdown of wind turbines (e.g., on 7 June, for 14 h, as well as on 23 June), or deliberate reduction of production capacity to about 7 MW, and in extreme cases, even to 5 MW. This caused the consumption of the reserve, and hence, the need to fill the tank for several days using wind energy, and the author of these considerations to conclude the need to eliminate the hydro component from the system. Whatever the motivations and prerequisites of the activities described in Reference [43], as a result of these research tests, a significant integration of both RES sources was achieved. Further considerations in this chapter confirm the groundlessness of the inference from Reference [43]. The analysis of the operation of the hydropower plant in the following months confirms its effectiveness, although it did not always work as spectacularly as in the case shown in Figure 10. Both sources show integration and complement each other, while increasing the hydro activity and the longer elimination of the diesel generator. Power supply of the island was secured by both the wind energy and the potential energy of water. Energies 2018, 11, 2812 13 of 20 Energies 2018, 11, x FOR PEER REVIEW 13 of 20

Energies 2018, 11, x FOR PEER REVIEW 13 of 20 Figure 10. Operation of a hydroelectric plant in a windless period on 28–29 March 2018. Own study Figure 10. Operation of a hydroelectric plant in a windless period on 28–29 March 2018. Own study based on data from Red Eléctrica de España. Monitoring REE (Red Eléctrica de España) was carried out based on data from Red Eléctrica de España. Monitoring REE (Red Eléctrica de España) was carried at 10-min intervals [58]. For the purpose of this work, the graphical relationship is shown in half-hourly out at 10‐min intervals [58]. For the purpose of this work, the graphical relationship is shown in intervals. Signs: (1) water power, and (2) water in the bottom tank (required wind to be pumped into half‐hourly intervals. Signs: (1) water power, and (2) water in the bottom tank (required wind to be the upper tank). pumped into the upper tank). Figure 11 presents the average monthly generation of energy from renewable sources and diesel in theFigure period 11 from presents 27 June the 2015 average to the monthly end of March generation 2018 [55 of,58 energy,59]. from renewable sources and dieselAt in present, the period the from island 27 hasJune the 2015 financial to the end support of March from 2018 the [55,58,59]. government in Madrid. The cost of energyAt generationpresent, the on island the island has ofthe El financial Hierro is support almost 3.5 from times the higher government than in continental in Madrid. Spain. The cost In this of energy generation on the island of El Hierro is almost 3.5 times higher than in continental Spain. In situation, which is undoubtedly difficult for the local community, the reduction in the prices of oil in thisthe yearsituation, 2015 turnedwhichFigure is out undoubtedly10. to Operation be particularly of a hydroelectric difficult advantageous plant for in athe windless local period [ 44community, on]. 28–29 March 2018. the Own reduction study in the prices of oil in the year 2015 basedturned on data out from to Red be Eléctrica particularly de España. Monitoring advantageous REE (Red Eléctrica [44]. de España) was carried In the followingout years, at 10‐min the intervals share [58]. ofFor RES the purpose in the of this energy work, the balance graphical increasedrelationship is shown significantly; in nevertheless, the systemIn the onfollowing the islandhalf‐hourly years, of intervals. El Hierrothe Signs: share (1) required water ofpower, RES further and (2)in water diagnosis,the in the energy bottom decisions, tank balance (required wind and increased to modernizationbe significantly; works. pumped into the upper tank). nevertheless,The presented the system research on andthe island monitoring of El resultsHierro allowedrequired us further to expect diagnosis, savings decisions, related to and the modernizationreduction of the works. dieselFigure share11 presents (before the average the monthly implementation generation of energy of the from system renewable of sources even and 40,000 barrels per diesel in the period from 27 June 2015 to the end of March 2018 [55,58,59]. year), ensuring fullAt self-sufficiency present, the island has on the the financial RES basis, support andfrom abovethe government all, the in Madrid. preservation The cost of of the valuable El Hierro biosphereenergy reserve generation thanks on the to island the of reduction El Hierro is almost of CO 3.5 timesemissions. higher than in continental Spain. In this situation, which is undoubtedly difficult for the local 2community, the reduction in the prices of The problemoil in was the year the 2015 water turned out reservoirs, to be particularly whose advantageous location [44]. was inappropriate, and this fact was previously ignored.In In the municipal following years, locations the share (here: of RES Valverde, in the energy the capitalbalance increased city of thesignificantly; island), it is prohibited nevertheless, the system on the island of El Hierro required further diagnosis, decisions, and to build water reservoirsmodernization of works. considerable sizes.

(a) (a) Figure 11. Cont.

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(b)

Figure 11. The share of individual sources in energy generation (a) from 27 June 2015, to the end of December 2016, (b) from 1 January 2017, to the end of June 2018, based on the own elaboration of the Red Eléctrica de España data.

The presented research and monitoring results(b) allowed us to expect savings related to the reduction of the diesel share (before the implementation of the system of even 40,000 barrels per Figure 11. The shareFigure 11. of The individual share of individual sources sources in in energy energy generation generation (a) from ( 27a) June from 2015, 27 to Junethe end 2015, of to the end of year), ensuringDecember full 2016,self‐ (sufficiencyb) from 1 January on 2017,the RESto the basis,end of June and 2018, above based all, on the own preservation elaboration of of the the valuable DecemberEl Hierro 2016, biosphereRed (b )Eléctrica from reserve de 1 JanuaryEspaña thanks data. 2017, to the to reduction the end of CO June2 emissions. 2018, based on the own elaboration of the Red EléctricaThe deproblem España was data. the water reservoirs, whose location was inappropriate, and this fact was previously Theignored. presented In municipalresearch and locations monitoring (here: results Valverde, allowed us theto expectcapital savings city ofrelated the toisland), the it is reduction of the diesel share (before the implementation of the system of even 40,000 barrels per prohibited to build water reservoirs of considerable sizes. 6. Possibilities ofyear), Improvement ensuring full self‐sufficiency of El Hierro on the RES RES basis, and above all, the preservation of the valuable El Hierro biosphere reserve thanks to the reduction of CO2 emissions. El Hierro6. Possibilities is characterizedThe problemof Improvement was by the good water of El solarreservoirs, Hierro exposure RESwhose location conditions. was inappropriate, The number and this offact solar was hours during a previously ignored. In municipal locations (here: Valverde, the capital city of the island), it is month rangesEl between Hierro is 140characterized h (January) by good and solar 234 exposure h (August), conditions. which The gives number 2339 of solar h in hours total during during a the entire prohibited to build water reservoirs of considerable sizes. year (an averagemonth ranges figure between over 30140 years) h (January) (RES and data). 234 h An(August), average which daily gives radiation 2339 h in total energy during exceeds the entire 6 kWh/m2. 2 Figureyear 12 (an illustrates6. average Possibilities figure exemplary of overImprovement 30 years) results of (RES El Hierro ofdata). power RES An average density daily measurements radiation energy exceeds for the 6 kWh/m solar radiation. on Figure 12 illustrates exemplary results of power density measurements for the solar radiation El Hierro performedEl Hierro by the is characterized author on by 25good July. solar exposure conditions. The number of solar hours during a on El Hierromonth performedranges between by 140 the h author(January) on and 25 234 July. h (August), which gives 2339 h in total during the entire year (an average figure over 30 years) (RES data). An average daily radiation energy exceeds 6 kWh/m2. Figure 12 illustrates exemplary results of power density measurements for the solar radiation on El Hierro performed by the author on 25 July.

Energies 2018, 11, x FOR PEER REVIEW 15 of 20 (a) (b) (a) (b)

Figure 12.FigureMeasurements 12. Measurements results results of the of powerthe power density density of of solar solar radiation carried carried out outin El in Hierro El Hierro on 25 on 25 July, July, as functions of daytime and spatial orientation of the receiver (the angle to the ground and as functions of daytime and spatial orientation of the receiver (the angle to the ground and geographic geographic direction): (a) 9 a.m., (b) 10.45 a.m., (c) 12.30 p.m., and (d), 2.15 p.m., based on the own direction):research. (a) 9 a.m., (b) 10.45 a.m., (c) 12.30 p.m., and (d), 2.15 p.m., based on the own research.

The tests were performed for various seasons of the day and different spatial orientations of the receiver. Momentary values ranging between as much as 1200 and 1450 W/m2 were obtained. This speaks well for the use of the solar energy in the system. The results of the same measurements conducted by the author on Gran Canaria are similar. They were published in Reference [4].

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7. Summary The summary contains general conclusions and suggestions of the author. 1. In isolated locations, the share of energy from renewable resources in the overall energy balance may be limited by the requirements regarding the minimum conventional generator load, system stability, as well as the passive power and voltage control. 2. The hybrid system based on wind energy was introduced on El Hierro. It was supplemented using an energy storage within the pumped hydro storage. The solution did not ensure the assumed 100% energy self-sufficiency. In principle (per annum) the wind energy covered the demand of the inhabitants. However, there were fluctuations in its generation, including even windless periods (7–10 days) [4]. They were the result of the location of the island within the zone of impact of trade winds. Their speed (3.4–13.8 m/s) guaranteed very good working conditions for wind turbines. Their force of impact was the greatest in February and August. In October, the unstable impact of sirocco was observed (silence or very strong wind) [60]. As is the case with the majority of islands, El Hierro is not connected with the continental grid; therefore, it is necessary to use a diesel generator [4]. The plans stipulate the connection by means of an underwater cable (by the year 2050) and cooperation with regard to the energy balance between all islands of the archipelago [8]. The diversification of RES within a large area will allow the limitation of the stochastic nature of the impact of climatic changes on the operation of the system through the reciprocal compensation of profits and losses. 3. The problems with the achievement of energy self-sufficiency, which have been raised, are to a certain extent the result of mistakes and changes in the project, introduced already during the construction of the facility, in particular, the lack of the integration of the water reservoir capacities and the production capacities of the wind park, as well as the resulting necessity of the planned reduction in the capacity of the wind park to ensure the stability of the grid. The upper reservoir in the crater seemed exceptionally advantageous. If, however, the interference with the rock substrate aimed at its strengthening and protection against leakage turned out to be impossible (except waterproofing), other possibilities of increasing the effectiveness of the investment must be found. 4. Reference [43] specifies two proposals of very radical changes. The possibility of providing an additional capacity of the hydro reservoir was considered. Such a solution requires significant investment outlays and cannot be physically implemented under the El Hierro conditions. The second proposal refers to the total elimination of the hydroelectric plant from the system. In such a situation, the energy would come from the wind farm at the full operation of five turbines, and during the periods of shortage or fluctuations of wind, from the diesel generation. Leaving aside the issue of feasibility, none of the presented options seems to be satisfactory to ensure the fully reliability and effective operation of the RES hybrid system. The design and implementation of the system lasted a long time and required particularly high financial outlays. The facility of this importance must not function in an ineffective manner (maximum average annual share of RES without hydro-accumulation was 30%). On the basis of detailed monitoring of the functioning of the system [58], as well as the situation presented in Figure 10, the suggestions of the expert from Reference [43] regarding the necessity of elimination of the hydroelectric power plant proved unjustified. The analysis of the operation of the hydroelectric plant in the following months confirmed its usefulness because it contributed to the power supply of the system, although it did not always work as spectacularly as on 28 and 29 March 2018. In cooperation with the wind farm, its share was often at the level of 25–30% RES, and sometimes even 90%. Energies 2018, 11, 2812 16 of 20

5. To sum up, the results of the monitoring of energy sources on El Hierro and their share in the satisfaction of the island’s energy demand, Figure 11 shows the continuous improvement of the GdV project [55]. The original priority objective, which was the share of RES at the level of 100%, has not been accomplished yet. Studies and tests show that the wind park functions in a proper manner. The applied system, particularly the hydro-installation, requires further tests, the accurate monitoring and the possible modification. The process of integration of the system components is long-term. 6. As stated in Reference [8], El Hierro is an integral part of the Canary Islands’ energy plan for powering the archipelago exclusively from RES. This effect will be achieved in 2050, thanks to the introduction of energy connections between the islands. According to the authors of Reference [18], the hybrid energy systems based on the wind energy have an expected life of 65 years. The operational data of wind turbines guarantees 20 years; therefore, their prior modernization and replacement will be necessary. 7. Owing to the output from the renewable energy sources on the island of El Hierro, the emission of greenhouse gases was reduced on an annual basis, i.e., nitrogen oxides by 100 tonnes, carbon dioxide by 18,700 tonnes, and sulphur dioxide by 400 tonnes per year. The suggestions of the author of this article point to several aspects of the case regarding the increase of the energy storage capacity on El Hierro (1–4) and to supplement the RES system with PV installations (5). 1. The storage of energy becomes necessary because of the fact that “supplies” from RES are neither stable nor synchronised with the demand for the energy. As well as the growing use of renewable sources in the generation of energy, the challenge is to find a reliable solution for its storage. In order to minimize the risk of power supply interferences, the storage of energy from RES should be implemented on two levels (development of the grid and improvement of the energy quality) [15]. The problem specifically refers to isolated sites (maintenance of the stable operation of the grid). Despite the great technological progress in the storage of energy, there are still many issues related to the applications in such locations. Possible selection of additional energy storage should be preceded by the detailed analysis, including economic aspects. 2. At present, pumped hydroelectric storages (PHS), characterized by high efficiency and reliability, are used on a large scale. In the majority of cases, it is recommended to introduce this technology to applications with long-lasting mass storage. On a global scale, the installed power in the PHS accumulation systems reaches almost 200 GW. PHS on El Hierro, if dimensioned properly, is particularly effective in the case of the long-lasting storage. In modern solutions of this type, there is an operable generator, which can also be used as an electric motor to power pumps (reduction in the costs of infrastructure), achieving 80% of the energy conversion efficiency. Then, the full power can be obtained even within 10 s during operation and during a maximum of one minute of shut-down. In the case under consideration, water is available. The cost of construction of a hydro-accumulator was lower in view of the formed upper reservoir [55]. 3. On the other hand, in the case of sudden power loss, storage can stabilize voltage and frequency until the start of diesel generators. Such an accumulator can also be used to capture the excess energy from renewable sources and use it during the periods of high demand, which translates into short-term storage. For this purpose, lithium-ion batteries or lead-acid batteries are used. In not a long time, other modern technologies will become more and more widespread such as flow batteries with zinc bromide and water hybrid batteries [14]. They are characterized by low costs and the controllable capacity. In the case of the short-lasting and high demand for power, the FESS (flywheel energy storage system) is the best solution. Its response time is very short and its use in RES applications is suitable for balancing the network frequency. It also mitigates the effects of wind oscillation. For instance, on the islands of Flores and Graciosa, it ensures the share of RES in the energy balance at the level of even 75% per year. In systems based on PV, FESS can be integrated with batteries in order to improve the efficiency of the system and extend the service life of the accumulator [61–63]. Energies 2018, 11, 2812 17 of 20

4. At present, fast development of electro-mobility is observed [27,59,64,65]. The “vehicle to grid” trends (the system which enables the bi-directional electricity ﬂow between an electric vehicle and the grid) can also be implemented on El Hierro, where local authorities prepare the replacement of 6400 cars with electric vehicles, as well as 35 charging stations [60]. They can be used as energy storages [65]. In this case, the possibility of the quick response is particularly important; this technology complements well the long-term hydro storage. The batteries in the cars will collect energy and release it into the grid for the purpose of better balancing of the supply and demand. They will be charged at night and during the time of increased windiness. In Europe, studies have been conducted with regard to the possibility of using electric vehicles as energy storages in isolated energy systems. The authors of Reference [27] reported that the share of transport in the total energy demand in São Miguel in the Azores archipelago was 40%. 5. The suggestions of the author also indicate the possibility of complementing the system with the photovoltaic installation to supply the selected facilities, e.g., the pump system of the PHS. The validity of this concept is conﬁrmed by the results of measurements of the solar radiation power density, performed by the author of the present study (Figure 12). On El Hierro, there are plans to utilize the energy of the sun, but in principle, they refer to collectors [60]. An example of the current effective use of the PV conversion on El Hierro is the lighthouse—Faro de Orchilla. The installation consists of 46 Si modules with a unit power of 75 Wp and the 3700 Ah battery. Even the installation of such a low power, generating 5400 kWh, allows for eliminating 6.6 tons of CO2 per year from the environment [66]. The inhabitants of El Hierro also provide their houses with PV applications [67].

Funding: This research received no external funding. Conﬂicts of Interest: The author declares no conﬂict of interest.

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