sign in sign up
<<
Home , QBlade, Tidal power

sustainability

Article The Potential for Integration of and Tidal in New Zealand

Navid Majdi Nasab 1,*, Jeff Kilby 1 and Leila Bakhtiaryfard 2

1 Electrical and Electronic Engineering Department, School of Engineering, Computing and Mathematical Sciences Auckland University of Technology, Auckland 1010, New Zealand; [email protected] 2 Technology Research Department, &D Centre, Fusheng Industrial Co., Ltd, Taipei 24142, Taiwan; [email protected] * Correspondence: [email protected]

 Received: 29 January 2020; Accepted: 24 February 2020; Published: 28 February 2020 

Abstract: This research focuses on proposing and evaluating an optimized hybrid system of wind and tidal operating as a renewable generating unit in New Zealand. Literature review indicates increasing worldwide investment in offshore in recent years. Offshore energy shows a high potential as an alternative energy generation solution to that of fossil . Using the capacities of wind and tidal power in renewable technologies would be a suitable alternative for fossil fuels and would help prevent their detrimental effects on the environment. It is a cost-effective procedure for the power generation sector to maximize these renewables as a hybrid system. At the design phase, types appropriate to environmental conditions for an area with high wind speed and tidal flow need to be considered. When selecting which turbines should be used, horizontal or vertical axis, number and length of blades, and optimized rotational speed are all important to get maximum capacity from either the wind or tidal energy for the hybrid system. Comprehensive simulation models of the hybrid system are now being set up, using several available commercial packages such as QBlade, Simulink, and RETScreen. Several different parameters will be required for these simulation models to run in order to test performance, capacity and efficiency of the proposed hybrid system. To decide which regions are suitable for the hybrid system, it will be necessary to analyze available wind and records from NIWA, and online databases such as GLOBAL ATLAS. This next phase of research will aim to create optimized scenarios for the hybrid model by considering the effect of wind and speed on performance. After deciding which region and scenarios are suitable, it will also be necessary to evaluate the costs and returns of a hybrid system. This final phase will be performed using the RETScreen simulation model.

Keywords: Siemens SWT 3.6-107 ; AR2000 tidal turbine; Kaipara harbor

1. Introduction

1.1. Outline of Project Objective Sources of energy which are renewable, such as wind and tidal, continue be to be used for solving the world’s massive demand for energy, and for reducing use of its fossil fuels. In the available literature, the effects of configuration parameters on the performance of wind and tidal turbines are investigated separately. However, there is little research on performance if wind and tidal turbines are combined into one hybrid system. The advantages of a hybrid system consisting of a wind and tidal turbines are predictable energy generation, increased energy density of array, and shared transmission/foundation/operation/maintenance costs. The technical challenges are immaturity of tidal technology, increased operational complexity, maintaining system stability, and finding suitable

Sustainability 2020, 12, 1807; doi:10.3390/su12051807 www.mdpi.com/journal/sustainability Sustainability 2020, 12, 1807 2 of 21 Sustainability 2020, 12, 1807 2 of 21 Sustainability 2020, 12, 1807 2 of 21 locations. This paper describes a New Zealand research project which aims to redress this shortage finding suitable locations. This paper describes a New Zealand research project which aims to redress offinding research suitable by carrying locations. out This a detailed paper describes numerical a New study. Zealand A thorough research and project comprehensive which aims numerical to redress this shortage of research by carrying out a detailed numerical study. A thorough and comprehensive simulationthis shortage and of modellingresearch by will carrying be performed out a deta usingiled numerical QBlade, Simulink, study. A andthorough RETScreen. and comprehensive The intended numerical simulation and modelling will be performed using QBlade, Simulink, and RETScreen. The outcomenumerical of simulation the research and is modelling to propose will an optimizedbe performed hybrid using system QBlade, using Simulink, wind and and tidal RETScreen. turbines The for intended outcome of the research is to propose an optimized hybrid system using wind and tidal powerintended generation. outcome of the research is to propose an optimized hybrid system using wind and tidal turbines for power generation. turbines for power generation. 1.2. Review of Offshore Energy Generation 1.2. Review of Offshore Energy Generation 1.2. Review of Offshore Energy Generation Renewable energy is seen as the only solution in order to solve a developing energy crisis [1]. Renewable energy is seen as the only solution in order to solve a developing energy crisis [1]. Two factorsRenewable are the energy key causes. is seen Theas the first only is global solution warming in order attributed to solve to a thedeveloping combustion energy of fossil crisis fuels. [1]. Two factors are the key causes. The first is global warming attributed to the combustion of fossil fuels. FigureTwo factors1 shows are a the rising key trendcauses. since The the first industrial is global warm revolutioning attributed [2]. to the combustion of fossil fuels. Figure 1 shows a rising trend since the industrial revolution [2]. Figure 1 shows a rising trend since the industrial revolution [2].

Figure 1. Effect of CO2 emission from fossil fuels in the last 1000 years [2]. Figure 1. Effect of CO2 emission from fossil fuels in the last 1000 years [2]. Figure 1. Effect of CO2 emission from fossil fuels in the last 1000 years [2]. The second is the increase of energy demand in recent years. Figure2 shows an oil supply–demand gap startingThe second from is 2000 the whichincrease will of becomeenergy verydemand great in by recent 2040 [years.2]. Figure 2 shows an oil supply– demand gap starting from 2000 which will become very great by 2040 [2].

Figure 2. Supply–demand gap of oil by 2040 [2]. Figure 2.2. Supply–demand gap of oil by 2040 [[2].2].

Renewable energy facilities such as hydro began to be built through the 1900s. Between the 1960s Renewable energyenergy facilitiesfacilities suchsuch asas hydrohydro beganbegan toto bebe builtbuilt throughthrough thethe 1900s.1900s. Between the 1960s and 1980s, geothermal schemes, onshore wind turbines, tidal turbines, and solar panel installations and 1980s, geothermalgeothermal schemes, onshore wind turbines,turbines, tidal turbines,turbines, and solarsolar panelpanel installationsinstallations started to appear. started toto appear.appear. The use of offshore wind energy commenced in 1990s. Figure 3 shows its potential [3]. The use of offshore wind energy commenced in 1990s. Figure 3 shows its potential [3]. Sustainability 2020, 12, 1807 3 of 21

Sustainability 2020, 12, 1807 3 of 21 Sustainability 2020, 12, 1807 3 of 21 The use of offshore wind energy commenced in 1990s. Figure3 shows its potential [3].

FigureFigure 3. 3.Comparison Comparison betweenbetween thethe potentialpotential ofof onshoreonshore andand ooffshoreffshore windwind energyenergy inin didifferentfferent water water Figure 3. Comparison between the potential of onshore and offshore wind energy in different water depthsdepths and and European European energy energy demand demand [ 3[3].]. depths and European energy demand [3]. MostMost existingexisting windwind farmsfarms havehave beenbeen builtbuilt onon land (onshore). (onshore). Currently,Currently, mostmost ofof thethe existingexisting Most existing wind farms have been built on land (onshore). Currently, most of the existing installedinstalled o offshoreffshore capacity capacity has has concentrated concentrated within with thein the United United Kingdom Kingdom (UK), (UK), Denmark Denmark (DK) (DK) and theand installed offshore capacity has concentrated within the United Kingdom (UK), Denmark (DK) and Netherlandsthe Netherlands (NL), (NL), as shown as shown in Figure in Figure4[ 4]. 4 The [4]. installedThe installed generation generation capacity capacity in these in these countries countries has the Netherlands (NL), as shown in Figure 4 [4]. The installed generation capacity in these countries beenhas been forecast forecast to increase to increase from from 2008 2008 to 2020; to 2020; in the in UK the from UK from 0.59 to0.59 13 to GW, 13 DKGW, from DK 0.41from to 0.41 1.3 to GW, 1.3 has been forecast to increase from 2008 to 2020; in the UK from 0.59 to 13 GW, DK from 0.41 to 1.3 andGW, NL and from NL 0.25from GW 0.25 to GW 6 GW to 6 [5 GW]. [5]. GW, and NL from 0.25 GW to 6 GW [5].

Figure 4. Installed Offshore (end of 2011) [6]. Figure 4. Installed (end of 2011) [6]. Figure 4. Installed Offshore Wind Power (end of 2011) [6]. The first offshore wind turbine was installed in Sweden in 1991 at Nogersund. One year later in The first offshore wind turbine was installed in Sweden in 1991 at Nogersund. One year later in 1992,The the firstfirst ooffshoreffshore wind turbine was was installed installed in Denmark, in Sweden off inVindeby 1991 at inNogersund. a water depth One of year between later in 2 1992, the first offshore wind farm was installed in Denmark, off Vindeby in a water depth of between to1992, 4 m the using first gravity offshore foundation wind farm at was a distance installed 3 in km Denmark, from shore. off Vindeby Until 2001, in a Denmark, water depth Sweden, of between and 2 to 4 m using gravity foundation at a distance 3 km from shore. Until 2001, Denmark, Sweden, and The2 to Netherlands4 m using gravity used turbinesfoundation rated at ata distance less than 3 1 km MW. from After shore. 2001, Until Denmark 2001, startedDenmark, to develop Sweden, large and The Netherlands used turbines rated at less than 1 MW. After 2001, Denmark started to develop large oTheffshore Netherlands wind farms: used (a) turbines rated at less (2001) than using 1 MW. turbines After 2001, rated Denmark at 2 MW; started (b) Horns to develop Rev I (2002): large offshore wind farms: (a) Middelgrunden (2001) using turbines rated at 2 MW; (b) I (2002): 160offshore MW usingwind turbinesfarms: (a) rated Middelgrunden at 2 MW; and (2001) (c) Nysted using (2003):turbines 166 rated MW at using 2 MW; turbines (b) Horns rated Rev at 2.3I (2002): MW. 160 MW using turbines rated at 2 MW; and (c) Nysted (2003): 166 MW using turbines rated at 2.3 160 MWThe UK,using Germany, turbines and rated Belgium at 2 MW; started and large (c) Nysted offshore (2003): wind projects 166 MW 2003 using onwards turbines and rated since at 2008 2.3 MW. theMW. UK has dominated. Figure5 shows the evolution of the turbine diameter for both onshore and The UK, Germany, and Belgium started large offshore wind projects 2003 onwards and since offshoreThe wind UK, turbines.Germany, O ffandshore Belgium turbine started diameters large and offs generatinghore wind capacities projects have2003 becomeonwards higher and since than 2008 the UK has dominated. Figure 5 shows the evolution of the turbine diameter for both onshore onshore2008 the from UK has this dominated. year. Figure 5 shows the evolution of the turbine diameter for both onshore and offshore wind turbines. Offshore turbine diameters and generating capacities have become and offshore wind turbines. Offshore turbine diameters and generating capacities have become higher than onshore from this year. higher than onshore from this year. Sustainability 2020, 12, 1807 4 of 21 Sustainability 2020, 12, 1807 4 of 21 Sustainability 2020, 12, 1807 4 of 21

Figure 5. Evolution of the Turbine Diameter in onshore and offshore wind turbines [7]. Figure 5. Evolution of the Turbine Diameter in onshore and offshore wind turbines [7]. Figure 5. Evolution of the Turbine Diameter in onshore and offshore wind turbines [7]. The European Wind Energy Association (EWEA) [5] has forecast 2005 prices. Investment in wind The European Wind Energy Association (EWEA) [5] has forecast 2005 prices. Investment in wind energyenergyThe for European both for both onshore onshore Wind and and Energy off shoreoffshore Association should should reach reach (EWEA)€ 23.5€23.5 billion billion [5] has in in 2020 forecast2020 and 2005€25€25 billion billion prices. in in 2030. Investment 2030. Figure Figure in6 showswind6 shows investment investment after after 2023 2023 is projected is projected to to be be stable, stable, atat aroundaround €25€25 billion billion annually; annually; however however an an increasingincreasing share share of investment of investment off offshoreshore [6 [6].].

Figure 6. Annual Wind Energy Investments up to 2030 based on the European Wind Energy Association (EWEA), 2009c. Figure 6.6.Annual Annual Wind Wind Energy Energy Investments Investments up to up 2030 to based 2030 onbased the European on the European Wind Energy Wind Association Energy Tidal turbines are high energy intensity, because they can gain over four times as much energy (EWEA),Association 2009c. (EWEA), 2009c. per m2 of rotor as a wind turbine [2]. The exploitable tidal energy with present technologies is

Tidal turbinesturbines areare high high energy energy intensity, intensity, because because they they can can gain gain over over four four times times as muchas much energy energy per 2 mperof m rotor2 of rotor as a wind as a turbinewind turbine [2]. The [2]. exploitable The exploita tidal energyble tidal with energy present with technologies present technologies is estimated atis Sustainability 2020, 12, 1807 5 of 21

Sustainability 2020, 12, 1807 5 of 21 about 75 GW worldwide. It is estimated that more than 10% of total (6 GW) is in France and estimated at about 75 GW worldwide. It is estimated that more than 10% of total resource (6 GW) is the UK (3.4 GW). Figure7 shows tide at the world level. in France and the UK (3.4 GW). Figure 7 shows tide resources at the world level.

FigureFigure7. 7. GlobalGlobal tidal resources resources [8]. [8 ].

1.3.1.3. Reasons Reasons for for Investigating Investigating a a Hybrid Hybrid System System (Wind(Wind plus Tidal) Tidal) At anyAt any off shoreoffshore tower tower site site there there is is tidaltidal flowflow as well well as as wind wind flow. flow. At At many many sites sites the thetidal tidal flow flow maymay not not be enoughbe enough to to add add much much extra extra generatinggenerating capacity. capacity. Or, Or, in in the the reverse reverse case, case, wind wind flow flow may may not addnot add much much extra extra generating generating capacity. capacity. However,However, at some some sites, sites, tidal tidal flow flow combined combined with with wind wind flow flow willwill enable enable substantial substantial extra extra generating generating capacity. capacity. Presently, Presently, nobody nobody knowsknows wherewhere such sites are are on on the Newthe Zealand New Zealand coast. Orcoast. anywhere Or anywhere else inelse the in world. the worl Justd. Just identifying identifying suitable suitable sites sites will will contribute contribute new knowledgenew knowledge about places about where places therewhere is potentialthere is pote forntial extra for renewable extra renewable energy generation.energy generation. However, whatHowever, is really what novel is aboutreally thenovel new about project the new described project indescribed this paper, in this is paper, that it is investigates that it investigates whether it whether it is possible to boost power output by installing a hybrid system at an offshore energy is possible to boost power output by installing a hybrid system at an offshore energy generation site generation site where until now, solely wind turbines or solely tidal turbines would have been where until now, solely wind turbines or solely tidal turbines would have been installed. The research installed. The research will be very significant if it demonstrates increased power output is technically willfeasible, be very substantial, significant and if it economic. demonstrates If not,increased the research power outcome output will still is technically be significant, feasible, because substantial, it will andestablish economic. the If reason not, the why research a hybrid outcome system willmay still be infeasible be significant, (technical because difficulty it will integrating; establish the extra reason whypower a hybrid output system not mayenough; be infeasibleconstruction (technical cost too di highfficulty), and integrating; will indicate extra what power the obstacles output notare that enough; constructionneed to be costovercome too high), by future and research. will indicate what the obstacles are that need to be overcome by future research. 2. Methods 2. Methods A wind turbine above level and two tidal turbines below can be combined by an electricA wind microgrid turbine when above connecting sea level andto an two onshore tidal supply[9]. turbines belowParameters sea levelfor offshore can be wind combined turbines by an electricissued microgrid on IEA Wind when TCP connecting Task 37-May to an 2019 onshore can be supply used to [ 9model]. Parameters a hybrid system for offshore [10]. Preliminary wind turbines issuedevaluation on IEA of Wind several TCP simula Tasktion 37-May models 2019 for canthis project be used is tounder model way. a hybridThey are: system [10]. Preliminary evaluation of several simulation models for this project is under way. They are: 2.1. Preliminary Evaluation od Models 2.1. Preliminary Evaluation od Models 2.1.1. QBlade 2.1.1. QBladeQBlade is an open-source wind turbine simulator for the design and simulation of vertical or horizontal axis wind turbines. The functionality includes two-dimensional airfoil design and QBlade is an open-source wind turbine simulator for the design and simulation of vertical or analysis, lift and drag polar extrapolation, rotor blade design, and wind turbine performance horizontal axis wind turbines. The functionality includes two-dimensional airfoil design and analysis, simulation. A generator module, pitch and rotational speed controllers, and the simulation of rotor lift and drag polar extrapolation, rotor blade design, and wind turbine performance simulation. A generator module, pitch and rotational speed controllers, and the simulation of rotor characteristics. QBlade consists of major modules (Figure8) embedded in a graphical user interface [11]: Sustainability 2020, 12, 1807 6 of 21 characteristics.Sustainability 2020QBlade, 12, 1807 consists of major modules (Figure 8) embedded in a graphical user interface6 of 21 [11]: Sustainability 2020, 12, 1807 6 of 21 • AirfoilAirfoil design design and andanalysis analysis • • characteristics.Lift and drag QBlade coeffi consistscient polar of major extrapolations modules (Figure to 360 8)◦ embeddedangle in a graphical user interface •Lift and drag coefficient polar extrapolations to 360° angle [11]:Rotor blade design and optimization • • Rotor• Wind bladeAirfoil turbine design design setup and analysis optimization and simulation. • • Wind• turbineLift and dragsetup coefficient and simulation. polar extrapolations to 360° angle • Rotor blade design and optimization • Wind turbine setup and simulation.

FigureFigure 8. Modules 8. Modules in QBlade in QBlade [11]. [11]. 2.1.2. RETScreen 2.1.2. RETScreen Figure 8. Modules in QBlade [11]. RETScreen is a feasibility study tool developed by the Ministry of Natural Resources, Canada, RETScreen2.1.2. RETScreen is a feasibility study tool developed by the Ministry of Natural Resources, Canada, for evaluating different renewable energy technologies at any location in the world (Figure9). for evaluating different renewable energy technologies at any location in the world (Figure 9). The The RETScreenRETScreen PV is modela feasibility covers study off-grid tool developed PV applications by the Ministry and includes of Natural stand-alone, Resources, hybrid Canada, and water RETScreen PV model covers off-grid PV applications and includes stand-alone, hybrid and water pumpingfor evaluating systems. different It has renewable a global energy climate technologi data databasees at any of location more than in the 6000 world ground (Figure stations, 9). The energy pumping systems. It has a global climate data database of more than 6000 ground stations, energy resourceRETScreen maps PV (i.e. model wind covers maps), off-grid hydrology PV applications data, wind and turbineincludes powerstand-alone, curves, hybrid and and links water to NASA’s resourcepumping maps (i.e. systems. wind Itmaps), has a hydrology global climate data, data wind data turbinebase of power more curves, than 6000 and ground links to stations, NASA’s climate database. RETScreen 4 can determine the technical and financial viability of on-grid renewable climateenergy database. RETScreen 4 can determine the technical and financial viability of on-grid energy, energy efficiency and projects including energy modelling, emission modellings, renewable energy, energy efficiency and cogeneration projects including energy modelling, emission financial analysis, and also sensitivity and risk analysis. [12]. modellings, financial analysis, and also sensitivity and risk analysis. [12].

FigureFigure 9. Schematic 9. 9. SchematicSchematic representation representation representation of of RETScreen RETScreen of RETScreen [12]. [12]. 2.1.3.2.1.3. Simulink Simulink 2.1.3. Simulink SimulinkSimulink is is a a blockblock diagram environment environment for for multidomain multidomain simulation simulation and model-based and model-based design. design. Simulink is a block diagram environment for multidomain simulation and model-based design. It supportsIt supports system-level system-level design, simulation, simulation, auto automaticmatic code code generation, generation, and continuous and continuous test and test and It supports system-level design, simulation, automatic code generation, and continuous test and verificationverification of of embedded embedded systems. Simulink Simulink provides provides a graphical a graphical editor, editor, customizable customizable block libraries, block libraries, verificationand solvers of embedded for modelling systems. and simulatingSimulink provides dynamic sya graphicalstems. It is editor,integrated customizable with MATLAB, block enabling libraries, and solvers for modelling and simulating dynamic systems. It is integrated with MATLAB, enabling and solversincorporation for modelling of MATLAB and simulating algorithms intodynamic models sy andstems. export It is of integrated simulation with results MATLAB, to MATLAB enabling for incorporation of MATLAB algorithms into models and export of simulation results to MATLAB for incorporationfurther analysis.of MATLAB There algorithmsare two major into classes models of items and inexport Simulink: of simulation blocks and results lines. Blocks to MATLAB are used for further analysis. There are two major classes of items in Simulink: blocks and lines. Blocks are used to furtherto analysis. generate, There modify, are combine, two major output, classes and displayof items sign inals. Simulink: Lines are blocks used to and transfer lines. signals Blocks from are one used generate, modify, combine, output, and display signals. Lines are used to transfer signals from one to generate,block modify,to another. combine, The blocks output, are defined and display as below. sign als. Lines are used to transfer signals from one block toS-Function: another. Thedisplays blocks the name are defined of any user-defined as below. function, plus the number of input and output block to another. The blocks are defined as below. specifiedS-Function: by the displaysfunction. the name of any user-defined function, plus the number of input and output S-Function: displays the name of any user-defined function, plus the number of input and output specifiedSum: by Add the function.or subtract inputs. specified by the function. Sum: Add or subtract inputs. Sum: Add or subtract inputs. Mechanical Rotational Reference: is to connect mechanical rotational ports that are rigidly affixed to the frame (ground). Sustainability 2020, 12, 1807 7 of 21 Sustainability 2020, 12, 1807 7 of 21 Mechanical Rotational Reference: is to connect mechanical rotational ports that are rigidly affixedIdeal to the torque frame sensor: (ground). a device that converts a variable passing through the sensor into a control signalIdeal proportional torque sensor: to the a torque device with that aconverts specified a coevariablefficient passing of proportionality. through the sensor into a control signalSolver proportional configuration: to the torque defines with solver a specified settings tocoefficient use for simulation. of proportionality. SolverInertia: configuration: represents an defines ideal mechanical solver settings rotational to use inertia. for simulation. Inertia:Gearbox: represents represents anan ideal ideal, mechanical non-planetary, rotational fixed inertia. gear ratio. Gearbox: represents an ideal, non-planetary, fixed gear ratio. 2.2. Sites which are Suitable for Hybrid Wind and Tidal Generation 2.2. Sites which are Suitable for Hybrid Wind and Tidal Generation Previous investigations of the New Zealand coast have identified good sites for wind energy generation,Previous or investigations good sites for of tidal the energy New Zealand generation. coast However, have identified nobody good has preparedsites for wind a list energy of sites generation,which are suitable or good for sites hybrid for tidal generation, energy i.e.,generati installon. a windHowever, turbine nobody plus tidal has turbineprepared at a the list same of sites site whichto increase are suitable for generated, hybrid generation, and link usingi.e., install a microgrid. a wind turbine A short plus list of tidal sites turbine which at may the be same suitable site tofor increase hybrid generationelectricity generated, has been prepared and link using by referring a microgrid. to previous A short investigations. list of sites which may be suitable for hybridWesterly generation wind patterns has been prevail prepared in most by referring parts of New to previous Zealand. investigations. NIWA recording sites summarize everyWesterly hourly measurement,wind patterns illustratingprevail in most patterns parts of of New Zealand. and NIWA calm in recording different places.sites summarize Figure 10 everyshows hourly sites selected measurement, to show illustrating typical wind patterns patterns. of turbulence and calm in different places. Figure 10 shows sites selected to show typical wind patterns.

FigureFigure 10. 10. NIWANIWA recording recording sites, sites, selected selected to sh showow typical wind patterns in 2014 [13]. [13].

For each site selected, scatter charts (Figure 11) show how often and how strongly blow from For each site selected, scatter charts (Figure 11) show how often and how strongly winds blow different directions during 2014. The center of each plot represents calm conditions. Wind strength is from different directions during 2014. The center of each plot represents calm conditions. Wind shown by the distance from the chart center, in 1 meter-per-second steps. The further a tick is from the strength is shown by the distance from the chart center, in 1 meter-per-second steps. The further a tickcalm is center, from the the calm stronger center, the the wind. stronger Wind directionthe wind. is Wind determined direction by is angle determined from the by center. angle Northerly from the center.winds areNortherly at a 12 o’clockwinds are position; at a 12 easterlies o’clock position at 3 o’clock.; easterlies The duration at 3 o’clock. for which The duration wind blows for fromwhich a windparticular blows direction from a atparticular a certain direction strength isat showna certai byn strength periodic timeis shown symbols by periodic in Figure time 11[13 symbols]: in FigureThe 11 sites[13]: in Figure 11 show typical wind speeds and directions on different New Zealand coastlines: * West coast of the South Island (Greymouth site) has strong south-westerlies (from sea), also strong easterlies (from mountains). However, this coast is stormy (frequent big waves), so cost of building and maintaining offshore turbine towers may be too high. Sheltered sites on this coast are the fiords at the south end, e.g., Dusky . However, fiord sides are mountains which cause turbulent changes in wind direction and velocity. Another sheltered site is a big tidal , Whanganui Inlet at the north end near Farewell Spit. Here mountains are not so high, so turbulent wind changes are not so great. * West coast of the North Island (Awakino site) has strong westerlies and moderate south-easterlies. This coast is also stormy, so cost of building and maintaining offshore turbine towers may also be too high here. Sheltered sites on this coast are several large harbors e.g. Manukau. Shores are hilly to flat, so local turbulence may not be a problem when operating wind turbines. * East coast of the North Island. North-east part from North Cape to East Cape is represented by the Auckland site. This coast is dominated by south-westerlies, but also has strong north-easterlies. Sustainability 2020, 12, 1807 8 of 21

Sea bottom is shallow creating opportunity for offshore tower installation in absence of big waves, (except during north-easterly storms, when wave damage might be a risk). Here are many harbors with deep channels, also many tidal . Sustainability 2020, 12, 1807 8 of 21

FigureFigure 11. 11.Wind Wind patterns patterns in in New New Zealand Zealand [13]. [13].

The eastThe part—from sites in Figure East 11 Cape show to typical Cape Kidnappers—iswind speeds and represented directions on by different the Gisborne New Zealand site. Here, winds fromcoastlines: all directions are mostly gentle. So, this coast may be unsuitable for wind turbines (although north-west* winds West blow coast from of the inland South ranges Island towards(Greymouth coast—and site) has strong may be south-westerlies stronger in some (from years, sea), than also the wind rosestrong diagram easterlies indicates). (from mountains). The east part’sHowever, harbors this coast and estuariesis stormy are(frequent few, small, big waves), and shallow. so cost of Thebuilding south-east and maintaining part from offshore Cape Kidnappersturbine towers to may Cook be too high. is Sheltered represented sites byon thethis coast Akitio are and the fiords at the south end, e.g., Dusky Sound. However, fiord sides are mountains which cause Wellington sites. Winds blow from all directions, and especially strong north-westerlies and northerlies turbulent changes in wind direction and velocity. Another sheltered site is a big tidal estuary, blow from inland ranges towards coast. This coast may have potential for installing wind turbines Whanganui Inlet at the north end near Farewell Spit. Here mountains are not so high, so turbulent offshorewind (but changes just close are tonot coast so great. where sea bottom is shallow—Hikurangi Trench farther out is too deep). There are no* harbors, West coast just of a fewthe North estuaries Island (miniscule). (Awakino site) has strong westerlies and moderate south- easterlies. This coast is also stormy, so cost of building and maintaining offshore turbine towers may * Northalso be coast too high of South here. IslandSheltered (Blenheim sites on this site). coas Betweent are several Farewell large Spit harbors and e.g. Cape Manukau. Campbell, Shores dominant are windshilly to are flat, moderate so local turbulence westerlies may and not north-westerlies. be a problem when The operating offshore wind sea turbines. bottom is shallow in the bays (Golden* EastBay, coast Tasman of the North , Island. Cloudy North-east Bay). Marlborough part from North Cape are to narrowEast Cape harbors is represented with deep channels.by the Auckland Additionally, site. Th thereis coast are someis dominated estuaries, by e.g. south-west Collingwood,erlies, Waimea,but also has Nelson, strong and north- Wairau. However,easterlies. becauseSea bottom this is shallow coast does creating not haveopportunity a strong for windoffshore prevailing tower installation from one in direction,absence of itbig may notwaves, be as (except good forduring wind north-easterly energy. storms, when wave damage might be a risk). Here are many harbors with deep channels, also many tidal estuaries. * East coast of South Island (Christchurch and Dunedin sites). Winds from most directions are The east part—from East Cape to Cape Kidnappers—is represented by the Gisborne site. Here, gentle to moderate. Along the Canterbury coast, north-west winds blow from the mountains winds from all directions are mostly gentle. So, this coast may be unsuitable for wind turbines across(although the plainsnorth-west (and winds may blow be stronger from inland in some ranges years, towards than coas thet—and wind may rose be diagramstronger in indicates). some Onyears, the than Otago the coast wind (Dunedin), rose diagram south-west indicates). The winds east have part's greater harbors and estuaries and are strength. few, small, However, and overall,shallow. this coast may not be good for finding suitable sites. * SouthThe coast south-east of South part Island from (BluCapeff Kidnapperssite) has very to Cook strong Strait prevailing is represented westerlies, by the plus Akitio moderate and easterliesWellington and sites. southerlies. Winds blow Off shorefrom seaall bottomdirections, is shallowand especially in Foveaux strong Strait. north-westerlies Here, wave and attack isnortherlies frequent, blow but waves from inland are moderately ranges towards sized. coast. There This iscoast only may one have large potential harbor for (Blu installingff), and wind several Sustainability 2020, 12, 1807 9 of 21

large shallow estuaries (Mataura, Oreti, Aparima). The south coast of Stewart Island is stormier, with very large waves. It has two large harbors (Paterson and Pegasus).

This review of information about wind speeds and directions on the New Zealand coastline shows that the west coast of the North Island, the south-east coast of the North Island, and the south coast of the South Island are coasts with great potential to generate electricity from wind energy. Bathymetric maps of depth to , also gives information about the storminess of these coasts, suggest that the cost of constructing and maintaining towers in harbors or estuaries may be much less than cost of installation offshore in open water. Open-water tidal circulation around the New Zealand coast is anti-clockwise. It is the reason why when on the west coast are high, tides on the east coast are low. It also creates strong reverse-direction tidal currents in open water where the two coasts meet, i.e., North Cape to Cape Maria van Diemen, Cook Strait, Foveaux Strait, and the South Cape of Stewart Island [14]. Close to shore, where open-water tidal circulation moves across shallow sea bed and enters bays, harbors or estuaries, normal reversals of tidal current are observed twice a day, i.e., incoming and outgoing tides [15]. Huckerby and Johnson (2008) modelled tidal flow around the New Zealand coasts [16,17]. The national distribution of utilizable open tidal currents is very limited. Only four areas have mean current speeds that exceed 1 m/s (Figure 12). Two (north of Cape Reinga and south of Stewart Island) are exposed to severe storms and a third (Cook Strait) is deep water (most parts are too deep to attach towers to seabed) and are also prone to undersea earthquakes. The fourth (Foveaux Strait and adjacent estuaries) is shallow water (seabed 10 to 40 meters below sea level), so easier and cheaper to installSustainability turbines. 2020, 12, 1807 10 of 21

Figure 12. Depth-averagedDepth-averaged tidal current speeds for mean spring flowsflows (in mm/second)./second). Hicks and Hume (1996) determined tidal volumes and current velocities in harbors on the northern Hicks and Hume (1996) determined tidal volumes and current velocities in harbors on the coast of the North Island by (Table1)[ 18]. Their investigation shows that the largest are Kaipara, northern coast of the North Island by (Table 1) [18]. Their investigation shows that the largest are Manukau, Hokianga, Rangaunu, and Whangarei Harbors, respectively. Tidal flows of Kaipara Harbor Kaipara, Manukau, Hokianga, Rangaunu, and Whangarei Harbors, respectively. Tidal flows of are the greatest, exchanging at each spring flood or ebb movement a tidal prism of ~1990 million cubic Kaipara Harbor are the greatest, exchanging at each spring or ebb movement a tidal prism of meters at average current of 1.12 m/s. Bellve, Austin, and [19] cite Hicks and Hume’s data in a ~1,990 million cubic meters at average current of 1.12 m/s. Bellve, Austin, and Woods [19] cite Hicks report identifying the Kaipara harbor as most suitable for tidal energy generation. Crest Energy, based and Hume’s data in a report identifying the Kaipara harbor as most suitable for tidal energy on this evaluation, proposes installing 200 marine turbines in the Kaipara Harbor to generate ~1.2 MW generation. Crest Energy, based on this evaluation, proposes installing 200 marine turbines in the peak with expected power capacity of 1.750 GWh per annum. The Crest Energy proposal is on hold. Kaipara Harbor to generate ~1.2 MW peak with expected power capacity of 1.750 GWh per annum. Intellectual property (designs, models, economic analyses) and development rights are now held by The Crest Energy proposal is on hold. Intellectual property (designs, models, economic analyses) and another company; Todd Energy. development rights are now held by another company; Todd Energy.

Table 1. Characteristics of tidal inlets in North Island [18].

Mean Spring Mean Spring Throat Throat Area Throat Depth Inlet Tidal Prism 106 Tide Range (m) Width@MT (m) @ MT (m2) (mean) @ MT (m2) m3) Hokianga 2.77 228 1090 13000 11.9 Kaipara 2.68 1990 5600 82000 14.6 Katikati 1.6 95.8 380 4680 12.3 Kawhia 2.9 121 600 11000 18.3 Mangawhai 1.8 6.55 216 500 2.31 Manukau 3.38 918 1900 46000 24.2 Ngunguru 1.71 3.83 109 310 2.84 Ohiwa 1.6 28.1 308 1880 6.10 Parengarenga 2.13 73.0 500 7000 14.00 Raglan 2.8 46.0 640 3600 5.63 Rangaunu 2.0 134 1012 6490 6.41 Tairua 1.6 5.02 130 430 3.31 Tauranga 1.6 131 480 6260 13.0 Whananaki 1.8 1.46 79 130 1.60 Whangarei 2.1 155 790 14600 18.5 Whangateau 2.2 10.5 174 660 3.79 Whitianga 1.6 12.6 240 1300 5.42 Sustainability 2020, 12, 1807 10 of 21

Table 1. Characteristics of tidal inlets in North Island [18].

Mean Spring Mean Spring Throat Throat Throat Depth Inlet Tide Range Tidal Prism Width@MT Area @ (mean) @ MT (m) 106 m3) (m) MT (m2) (m2) Hokianga 2.77 228 1090 13,000 11.9 Kaipara 2.68 1990 5600 82,000 14.6 Katikati 1.6 95.8 380 4680 12.3 Kawhia 2.9 121 600 11,000 18.3 Mangawhai 1.8 6.55 216 500 2.31 Manukau 3.38 918 1900 46,000 24.2 Ngunguru 1.71 3.83 109 310 2.84 Ohiwa 1.6 28.1 308 1880 6.10 Parengarenga 2.13 73.0 500 7000 14.00 Raglan 2.8 46.0 640 3600 5.63 Rangaunu 2.0 134 1012 6490 6.41 Tairua 1.6 5.02 130 430 3.31 Tauranga 1.6 131 480 6260 13.0 Whananaki 1.8 1.46 79 130 1.60 Whangarei 2.1 155 790 14,600 18.5 Whangateau 2.2 10.5 174 660 3.79 Whitianga 1.6 12.6 240 1300 5.42

Farther south, some older data are available from Heath (1976) [20] which show large open bays have big tidal prisms but weak tidal flows (Table2). Small harbors or estuaries can have strong flows, but their prisms are small. Large harbors with deep narrow entrances combine large tidal prisms with strong tidal flows. Heath’s measurements indicate Aotea, Waimea, Parengarenga, Tauranga, Kawhia, Rangaunu, Raglan, Whangarei, Bluff, Otago, Hokianga, Manukau, Lythelton, Kaipara, Akaroa, and Wellington Harbor could be worth investigating.

Table 2. Physical characteristics of 32 New Zealand inlets [20].

Cross-Sectional Area Entrance (m) Tidal Compartment Inlet Name Low Tide Mid Tide Spring Neap Tides Spring Tides Neap Tides Spring (103 m2) Spring (103 m2) Tides (m) (m) (106 m3) (106 m3) Moutere 0.4 0.9 4.2 2.4 15 9 Avon-Heathcote - - 2.1 1.3 11 6 Aotea 2.2 3.6 2.9 1.7 59 35 Waimea 2.3 5.8 3.4 1.8 58 31 Whanganui Inlet 2.3 3.9 2.9 1.5 42 22 Parengarenga 6.2 7 2.13 1.4 73 48 Nelson 2 2.6 3.4 2.6 30 23 Tauranga 7.3 7.8 1.62 1.24 178 136 Kawhia 8 11 2.9 1.7 121 71 Porirua-Pauatahanui 1.4 1.8 1.6 1.3 22 17 Rangaunu 7.1 8.8 2.0 1.5 134 101 Raglan 2.9 3.6 2.8 1.8 46 29 Whangarei 13 14 2.46 1.74 164 116 Bluff 3.8 4.5 2.2 1.5 97 66 Sustainability 2020, 12, 1807 11 of 21

Table 2. Cont.

Cross-Sectional Area Entrance Tidal Range (m) Tidal Compartment Inlet Name Low Tide Mid Tide Spring Neap Tides Spring Tides Neap Tides Spring (103 m2) Spring (103 m2) Tides (m) (m) (106 m3) (106 m3) Otago 4.7 5.1 1.74 1.28 69 51 Hokianga 11 13 2.77 1.78 228 147 Manukau 42 46 3.38 1.95 918 530 Whangaruru 21 23 2 1.5 28 21 Lyttelton 28 30 1.92 1.64 72 61 Firth of Thames 400 440 3.72 2.68 2580 1860 Kaipara 73 82 2.68 1.52 1990 1130 Whangaroa 4.3 4.7 1.95 1.34 33 23 Akaroa 45 47 1.89 1.52 81 65 Doubtless Bay 642 652 1.9 1.4 346 255 Paterson Inlet 55 59 2.0 1.4 168 120 Tasman bay 2450 2560 3.44 1.8 16,000 8300 Poverty Bay 140 146 1.4 1.2 81 70 Pelorus Sound 117 121 2.37 1.46 660 410 Bay of Islands 1034 1050 1.95 1.46 340 260 Wellington Harbor 38 39 1.01 0.94 88 82 Queen Charlotte Sound 880 890 1.4 0.5 98 35 Hawke Bay 5250 5300 1.34 1.22 3950 3600

Global Wind Atlas data have been used to identify which of these harbor/estuary sites in Tables1 and2 also have good wind runs (expressed as mean annual wind speed). The latitude, longitude, wind run, and tide range of sites, which appear to have potential for hybrid generation, are summarized in Table3.

Table 3. The geographical coordinates and tide range and wind run of New Zealand harbors and estuaries [20,21].

Location Latitude (deg) Longitude (deg) Spring Tides (m) Neap Tides (m) Annual Wind Speed (m/s) Bluff 46.4 N 168.3 E 2.2 1.5 10.7 − ◦ ◦ Whanganui 40.8 N 175.8 E 3.4 2.6 4.3 Inlet − ◦ ◦ Hokianga 35.1 N 173.3 E 2.77 1.78 4.5 − ◦ ◦ Kawhia 37.8 N 175.3 E 2.9 1.7 4.7 − ◦ ◦ Manukau 37.0 N 174.8 E 3.38 1.95 5 − ◦ ◦ Kaipara 36.8 N 174.8 E 2.68 1.52 6.4 − ◦ ◦ Aotea 37.8 N 175.3 E 2.9 1.7 4.7 − ◦ ◦ Parengarenga 34.5 N 172.9 E 2.13 1.4 8.5 − ◦ ◦ Tauranga 37.7 N 176.2 E 1.62 1.24 4.1 − ◦ ◦ Rangaunu 34.9 N 173.3 E 2.0 1.5 4.5 − ◦ ◦ Whangarei 35.7 N 174.3 E 2.46 1.74 6.5 − ◦ ◦ Otago 45.8 N 170.6 E 1.74 1.28 5.9 − ◦ ◦ Lyttelton 43.6 N 172.7 E 1.92 1.62 4.2 − ◦ ◦ Akaroa 43.8 N 173.0 E 1.89 1.52 4.2 − ◦ ◦ Wellington 41.3 N 174.8 E 1.01 0.94 7.3 − ◦ ◦ Firth of Thames 37.0 N 175.4 E 3.72 2.68 5.7 − ◦ ◦

Many sites identified by Heath or Hicks and Hume as having strong tidal flows and large tidal prisms can be ruled out because wind run is not good (Hokianga, Kawhia, Aotea, Tauranga, Lyttelton, Akaroa). Some harbors in Table3 can be ruled out, because they have commercial ports. Here turbine Sustainability 2020, 12, 1807 12 of 21 monopiles will be navigation hazards (except if the deep-water channel extends upstream beyond wharf). Commercial ports ruled out are Whangarei, Waitemata (Auckland), Manukau (Auckland), Tauranga (south entrance), Port Nicholson (Wellington), Lyttelton (Christchurch), Otago (Dunedin), and Bluff (from wharf to entrance). Some estuaries must also be ruled out, because they contain marine reserves, or they are next to national parks etc. (Port Pegasus, Paterson Inlet, Akaroa, parts of Golden Bay, Whanganui Inlet). Here, the Department of Conservation will not allow resource consent. Finally a few estuaries with deep entrance channels have to be ruled out because their shores are inhabited by tangata whenua (Maori) who say that the estuaries are taonga (valuable possessions) for fishing, gathering shellfish etc; or that the shores are wahi tapu (sacred places) which must not be disturbed. Examples are Parengarenga, Whangaroa, Bay of Islands, and Whangaruru. Maybe also Hokianga, Whaingaroa (Raglan), Aotea, and Kawhia.

2.3. Selection of Turbines The turbines proposed for evaluation are Siemens SWT3.6-107-80m for wind above sea level and Atlantis’AR2000 for tide at below sea level. Atlantis and General Electric are working in partnership since September 2018 on the development and performance validation of Atlantis’ AR2000 tidal generation system (Figure 13 and Table4), which is expected to be the world’s largest and most powerful tidal turbine available for sale to commercial developers in the fourth quarter of 2019. The AR2000 will have a 25-year design with quarter-life interventionsSustainability 2020 for, 12, routine 1807 maintenance. 13 of 21

Figure 13. The AR2000 tidal turbine. Figure 13. The AR2000 tidal turbine. Table 4. AR2000 Tidal Turbine Parameters. Table 4. AR2000 Tidal Turbine Parameters. Item Value Item Value Model AR2000 tidal turbine 2 MW Model AR2000 tidal turbine 2 MW Rated power (kW) 2000 Rated power (kW) 2000 RotorRotor diameter diameter (m) (m) 20 20 HeightHeight from from the the seabed seabed (m) (m) 25 25 SweptSwept area area of of rotor rotor (m 2(m) 2) 314314 Cut-inCut-in speed speed (m (m/s)/s) 1 1 Cut-out speed (m/s) 3 Cut-out speed (m/s) 3 Weight (t) 150 Weight (t) 150 Output power for the range until 4.5 m/s for an AR2000 tidal turbine is shown in Figure 14.

Output power for the range until 4.5 m/s for an AR2000 tidal turbine is shown in Figure 14.

Figure 14. Output power of Tidal turbine—(PTidal max for one rotor=2000 kW→PTidal max for two rotors = 4000 kW).

Figure 15 shows a comparable wind turbine is Siemens, SWT-3.6-107 Offshore which is a production of Siemens Wind Power A/S, a manufacturer from Denmark taken over by Renewable Energy in 2017 (Figure 15 and Table 5).

Table 5. SWT-3.6-107 Offshore Wind Turbine Parameters. Sustainability 2020, 12, 1807 13 of 21

Figure 13. The AR2000 tidal turbine.

Table 4. AR2000 Tidal Turbine Parameters.

Item Value Model AR2000 tidal turbine 2 MW Rated power (kW) 2000 Rotor diameter (m) 20 Height from the seabed (m) 25 Swept area of rotor (m2) 314 Cut-in speed (m/s) 1 Sustainability 2020, 12, 1807 Cut-out speed (m/s) 3 13 of 21 Weight (t) 150

Sustainability 2020, 12, 1807 14 of 21

Item Value Model Siemens SWT-3.6-107 Offshore 3.6 MW Rated power (kW) 3600 Rotor diameter (m) 107 Figure 14. Output powerHub heightof Tidal (m) turbine—(P Tidal max for one rotor=2000 80 kW→PTidal max for two rotors = Figure 14. Output power of Tidal turbine—(PTidal max for one rotor = 2000 kW PTidal max for two 4000 kW). Swept area of rotor (m2) 8992 → rotors = 4000 kW). Cut-in-wind-speed (m/s) 4 Figure 15 showsRated a windcomparable speed (m/s)wind turbine is Siemens, 15SWT-3.6-107 Offshore which is a production of Siemens Wind Power A/S, a manufacturer from Denmark taken over by Siemens Figure 15 showsCut-out-wind a comparable speed wind (m/s) turbine is Siemens, 25 SWT-3.6-107 Offshore which is a production Gamesa Renewable Energy in 2017 (Figure 15 and Table 5). of Siemens Wind PowerRotor A/S, Speed a manufacturer (rpm) from Denmark 13 taken over by Siemens Gamesa Renewable Tower Type Steel tube Energy in 2017 (Figure 15 Tableand 5. Table SWT-3.6-1075). Offshore Wind Turbine Parameters. The wind power curve of the SWT-3.6-107 Offshore wind turbine is depicted in Figure 15.

FigureFigure 15. 15.Output Output power of ofWind Wind turbine—(P turbine—(PWind-max = 3600Wind-max kW). = 3600 kW).

2.4. Selecting ComponentsTable for a 5. MicrogridSWT-3.6-107 System Design Offshore Wind Turbine Parameters. SIMULINK will be used to design a microgrid system for hybrid offshore wind and tidal energy generation (Figures 16 andItem Figure 17) and combined model (Figure 18) with Value Siemens SWT-3.6-107 wind turbines and AtlantisModel AR2000 tidal turbines. Siemens SWT-3.6-107 Offshore 3.6 MW Rated power (kW) 3600 Rotor diameter (m) 107 Hub height (m) 80 Swept area of rotor (m2) 8992 Cut-in-wind-speed (m/s) 4 Rated wind speed (m/s) 15 Cut-out-wind speed (m/s) 25

Rotor Speed (rpm) 13 Figure 16. Simulink model of tidal turbine portion. Tower Type Steel tube Sustainability 2020, 12, 1807 14 of 21

Item Value Model Siemens SWT-3.6-107 Offshore 3.6 MW Rated power (kW) 3600 Rotor diameter (m) 107 Hub height (m) 80 Swept area of rotor (m2) 8992 Cut-in-wind-speed (m/s) 4 Rated wind speed (m/s) 15 Cut-out-wind speed (m/s) 25 Rotor Speed (rpm) 13 Tower Type Steel tube The wind power curve of the SWT-3.6-107 Offshore wind turbine is depicted in Figure 15.

Sustainability 2020, 12, 1807 14 of 21

The wind powerFigure curve 15. of Output the SWT-3.6-107 power of Wind Offshore turbine—(P wind turbineWind-max = is3600 depicted kW). in Figure 15.

2.4. Selecting Components for a Microgrid System Design SIMULINK will be used to design a microgrid system for hybrid offshore offshore wind and tidal energy generation (Figures 16 and Figure17) and 17) combined and comb modelined model (Figure (Figure 18) with 18) Siemens with Siemens SWT-3.6-107 SWT-3.6-107 wind turbineswind turbines and Atlantis and Atlantis AR2000 AR2000 tidal turbines. tidal turbines.

Sustainability 2020, 12, 1807 15 of 21 Figure 16. Simulink model of tidal turbine portion.

Sustainability 2020, 12, 1807 15 of 21

FigureFigure 17. 17. SimulinkSimulink model modelof wind turbine of wind portion. turbine portion.

Figure 17. Simulink model of wind turbine portion.

FigureFigure 18. 18. SimulinkSimulink model of model combined of system. combined system.

3. Results and Discussion

3.1. Site Selected for Simulation Table 6 shows just one site which appears to meet project criteria in all respects (Firth of Thomas does not appear in Table 6 because its wind run is inferior to Kaipara).

Table 6. The geographical coordinates, tide range, and wind run of the New Zealand sites which might be used for modelling a microgrid hybrid system [20,21].

Latitude Longitude Spring Tides Neap Tides Annual Wind Location (deg) (deg) (m) (m) Speed(m/s) Kaipara −36.8°N Figure174.8°E 18. Simulink 2.68 model of 1.52combined system. 6.4 The geographical location of this site is shown in Figure 19. 3. Results and Discussion

3.1. Site Selected for Simulation Table 6 shows just one site which appears to meet project criteria in all respects (Firth of Thomas does not appear in Table 6 because its wind run is inferior to Kaipara).

Table 6. The geographical coordinates, tide range, and wind run of the New Zealand sites which might be used for modelling a microgrid hybrid system [20,21].

Latitude Longitude Spring Tides Neap Tides Annual Wind Location (deg) (deg) (m) (m) Speed(m/s) Kaipara −36.8°N 174.8°E 2.68 1.52 6.4 The geographical location of this site is shown in Figure 19. Sustainability 2020, 12, 1807 15 of 21

3. Results and Discussion

3.1. Site Selected for Simulation Table6 shows just one site which appears to meet project criteria in all respects (Firth of Thomas does not appear in Table6 because its wind run is inferior to Kaipara).

Table 6. The geographical coordinates, tide range, and wind run of the New Zealand sites which might be used for modelling a microgrid hybrid system [20,21].

Latitude Longitude Spring Tides Neap Tides Annual Wind Location (deg) (deg) (m) (m) Speed (m/s) Kaipara 36.8 N 174.8 E 2.68 1.52 6.4 − ◦ ◦

SustainabilityThe geographical 2020, 12, 1807 location of this site is shown in Figure 19. 16 of 21

Figure 19. Map showing the location of the site which might be suitable for modelling a microgrid Figure 19. Map showing the location of the site which might be suitable for modelling a microgrid hybrid system. hybrid system. Using Global Wind Atlas (Figure 20a), NIWA tide forecaster (Figure 20b) and RETScreen Using Global Wind Atlas (Figure 20a), NIWA tide forecaster (Figure 20b) and RETScreen (Figure (Figure 20c), the energy resource parameters for Kaipara harbor are as below Figure 20: 20c), the energy resource parameters for Kaipara harbor are as below Figure 20:

(a)

Sustainability 2020, 12, 1807 16 of 21

Figure 19. Map showing the location of the site which might be suitable for modelling a microgrid hybrid system. Sustainability 2020, 12, 1807 16 of 21

(a)

Sustainability 2020, 12, 1807 (b) 17 of 21

(c)

FigureFigure 20. 20.Tide Tide Heights Heights[22] [22] andand Environmental co conditionsnditions [21] [21 of] ofKaipara . Harbour.

3.2. Wind Energy Yield Estimation Coefficients, which affect the wind energy yield, are listed in Table 7. Some examples of RETScreen output for the short-listed sites are given in Tables 8 and Table 9.

Table 7. Wind energy related coefficients used in energy yield estimation.

Wind Energy Related Coefficients Kaipara Harbor Array losses (%) 0 Airfoil soiling and/or icing losses (%) 2 Miscellaneous losses (%) 6 Pressure adjustment coefficient 0.999 Temperature adjustment coefficient 0.997 Wind shear exponent 0.14 Relevant output parameters from the model are summarized in Table 8. The specific energy yield is found to be 1382 for Kaipara harbors. (The model calculates the specific yield (kWh/m2) of the wind energy equipment, which is a common criterion in the wind to evaluate and compare the performance of a wind turbine in conjunction with the wind regime at the site. The specific yield is obtained by dividing the energy produced by a proxy wind turbine by the swept area of the rotor. The specific yield normally ranges from 150 to 1,500 kWh/m2 per turbine where the low end corresponds to a in a mediocre wind regime and the high end, to a larger wind turbine in a good wind regime.) Annual gross energy yield which is the calculated by multiplying pressure and temperature coefficients at unadjusted energy delivered is 13766 MWh/year. [23]. The Unadjusted energy delivered or produced energy at standard conditions of temperature and atmospheric pressure, is found to be 13826 MWh/year.

Table 8. Summary of energy yield and related output from SWT-3.6-107 Offshore wind turbine. Sustainability 2020, 12, 1807 17 of 21

3.2. Wind Energy Yield Estimation Coefficients, which affect the wind energy yield, are listed in Table7. Some examples of RETScreen output for the short-listed sites are given in Tables8 and9.

Table 7. Wind energy related coefficients used in energy yield estimation.

Wind Energy Related Coefficients Kaipara Harbor Array losses (%) 0 Airfoil soiling and/or icing losses (%) 2 Miscellaneous losses (%) 6 Pressure adjustment coefficient 0.999 Temperature adjustment coefficient 0.997 Wind shear exponent 0.14

Table 8. Summary of energy yield and related output from SWT-3.6-107 Offshore wind turbine.

Summary of Energy Yield and Related Output Kaipara Harbor from SWT-3.6-107 Offshore Wind Turbine Annual mean wind speed (m/s) 6.35 Specific yield (kWh/m2) 1382 Gross energy yield (MWh/year) 13,766 Unadjusted energy delivered (MWh/year) 13,826

Table 9. Tidal energy related coefficients used in energy yield estimation.

Wind Energy Related Coefficients Kaipara Harbor Array losses (%) 0 Miscellaneous losses (%) 6 Pressure adjustment coefficient 0.999 Temperature adjustment coefficient 0.98 Energy adjustment coefficient 1.3

Relevant output parameters from the model are summarized in Table8. The specific energy yield is found to be 1382 for Kaipara harbors. (The model calculates the specific yield (kWh/m2) of the wind energy equipment, which is a common criterion in the wind energy industry to evaluate and compare the performance of a wind turbine in conjunction with the wind regime at the site. The specific yield is obtained by dividing the energy produced by a proxy wind turbine by the swept area of the rotor. The specific yield normally ranges from 150 to 1500 kWh/m2 per turbine where the low end corresponds to a small wind turbine in a mediocre wind regime and the high end, to a larger wind turbine in a good wind regime.) Annual gross energy yield which is the calculated by multiplying pressure and temperature coefficients at unadjusted energy delivered is 13,766 MWh/year. [23]. The Unadjusted energy delivered or produced energy at standard conditions of temperature and atmospheric pressure, is found to be 13,826 MWh/year.

3.3. Tidal Energy Yield Tidal energy yield is more difficult to estimate because RETScreen does not have links to a tidal flow atlas, nor an energy yield estimation module for tidal flow. Presently the energy yield obtainable from tidal flow must be estimated in RETScreen by using average tidal flow and making several Sustainability 2020, 12, 1807 18 of 21 assumptions (Table9). Later in the project, the RETScreen model must be refined or an alternative model found, in order to produce more accurate estimates from a complete range of tidal flow velocities and directions at the site. Meanwhile, the extra energy yield which could be obtained from adding a tidal turbine to each wind turbine at Kaipara harbor is estimated to be at least 415 kWh/m2. The extra annual gross energy yield, without losses, is at least 4130 MWh/year. The extra renewable energy deliverable, after losses, is estimated to be at least 3882 MWh/year, as given in Table 10.

Table 10. Summary of energy yield and related output from AR2000 tidal turbine.

Summary of Energy Yield and Related Output Kaipara Harbor from AR2000 Tidal Turbine Annual mean tidal flow (m/s) 1.12 Specific energy yield (kWh/m2) 415 Gross energy yield (MWh/year) 4130 Tidal energy delivered (MWh/year) 3882

3.4. Economic and Environmental Analysis Assumptions used about installation cost (Table 11) and financial parameters (Table 12) indicates the feasibility of hybrid system (Table 13) as an example of RETScreen output. The assumptions are not entirely hypothetical, because they are derived from real wind and tidal turbine installations overseas [23,24]. In the following examples, assumptions generated by RETScreen for adding a tidal turbine to a wind turbine are extra 30%, extra initial cost $10,400/kW, and extra operating/maintenance cost $70/kW-year.

Table 11. Cost of hybrid system development [24].

Cost item Hybrid Amount ($) Percent of Total Cost (%) Feasibility study 372,000 0.6 Development 1,240,000 2.0 Engineering 868,000 1.4 Energy equipment 46,314,000 74.7 Balance of 8,556,000 13.8 Miscellaneous 4,650,000 7.5 Initial costs-total 62,000,000 100

Table 12. Economic input parameters [23].

Items Value Inflation (%) 2 Discount rate (%) 9 Project life (year) 30 Annual operation and maintenance cost ($/year) for each turbine 490,000 Sustainability 2020, 12, 1807 19 of 21

Table 13. Economic feasibility indicators for hybrid system.

Item Kaipara Harbor IRR (internal rate of return)-equity (%) 9.7 IRR-assets (%) 4.3 MIRR (modified internal rate of return)-equity (%) 9.3 MIRR- assets (%) 6.6 Simple payback (year) 13.6 Total annual savings and revenue 5,051,832 Net present value—NPV ($) 3,312,754 Annual life cycle savings ($) 322,451 Benefit–cost (B–C) ratio 1.2 Energy production cost ($/kWh) 0.344

As seen from Table 11, electrical equipment including turbines accounts for 74% of total cost. About 14%, is balance of plant (BOP) cost, i.e., construction. Other cost parameters are summarized in Table 12. Economic analysis demonstrates a hybrid system which, (wind plus tidal) if installed at Kaipara harbor, may return 9.7% on investment over life of the project, and may pay back construction cost after the first 13 years (Table 13). Environmental analysis (Table 14) demonstrates that there would be a benefit of 8533 tons Co2/year greenhouse gas emission reduction (the amount which would be emitted generating an equivalent amount of energy from burning fossil ).

Table 14. Key RETScreen finding for hybrid model.

Key RETScreen Findings for Hybrid Model Kaipara Harbor Electricity exported to grid MWh 18,042 Electricity exported revenue $ 5,051,832

GHG emission reduction (tons CO2/year) 8533

An example of the key RETScreen findings for hybrid (wind plus tidal) energy deliverable at the Kaipara site is given in Table 14.

4. Conclusions Results so far indicate that Kaipara harbor has good potential for energy generation from a hybrid system (wind plus tidal) with good wind energy yield, and additional energy from tidal energy. To complete this research, it will be necessary to obtain realistic installation and operating cost estimates for the proposed NZ site, plus financial parameters appropriate to the NZ . Preliminary findings for Kaipara site indicate:

It is practical to erect a microgrid system for offshore hybrid wind and tidal generation, at the • selected NZ coastal site. The quantities of electricity generated by a hybrid system (compared to solely offshore wind or • solely offshore tidal) at the selected site. Cost of erecting and operating a hybrid wind plus tidal turbine at Kaipara on the NZ coast. • Value of extra electricity generated by a hybrid (compared with either a single wind or a single • tidal turbine) at the same site. There is an economic benefit from the extra electricity generated. • Sustainability 2020, 12, 1807 20 of 21

The economic benefit may be sufficient to warrant constructing a hybrid wind plus tidal system. • Whether there is a sufficient benefit will remain unknown unless more research is carried out. Completion of the research will establish what benefits exist. One or more benefits might be found: Increased generating capacity (at any site). • Or increase in actual power output (at sites where wind frequency and tidal cycle favor • co-generation). Reduced cost of constructing a tower (per unit of electricity generated) if two turbines can be • installed on it. Plus, reduced cost of operating multiple towers (per unit of electricity generated). • Whether a power company could increase its revenue by sale of extra electricity. • Or whether it could increase its market share (by reducing cost of electricity to customers). •

Author Contributions: “Conceptualization, N.M.N., J.K. and L.B.; methodology, N.M.N., J.K. and L.B.; software, N.M.N.; validation, N.M.N., J.K. and L.B..; formal analysis, N.M.N.; investigation, N.M.N.; resources, N.M.N., J.K.; data curation, N.M.N.; writing—original draft preparation, N.M.N., J.K.; writing—review and editing, N.M.N., J.K.; visualization, N.M.N.; supervision, J.K.; project administration, N.M.N.; funding acquisition, No funding. All authors have read and agreed to the published version of the manuscript. Funding: This research received no external funding. Acknowledgments: The authors wish to acknowledge the technical support of Douglas Hicks who edited and proof-read our draft paper. Conflicts of Interest: The authors declare no conflict of interest.

References

1. Kulkarni, S.J. Tidal Energy: A Review. Int. J. Res. 2015, 2, 55–59. 2. Fraenkel, P. : Exploiting Tidal Currents for Large-scale Power Generation. 2007. Available online: https://www.google.com.hk/url?sa=t&rct=j&q=&esrc=s&source=web&cd=13&ved= 2ahUKEwiljd7tnO7nAhVCI6YKHXBtCVwQFjAMegQIBBAB&url=http%3A%2F%2Fwww.iom3 (accessed on 5 December 2019). 3. Esteban, M.D.; Diez, J.J.; López, J.S.; Negro, V. Why offshore wind energy? Renew. Energy 2011, 36, 444–450. [CrossRef] 4. Green, R.; Vasilakos, N. The economics of offshore wind. 2011, 39, 496–502. [CrossRef] 5. A Report by the European Wind Energy Association; Wind Energy Targets for 2020 and 2030. Available online: http://www.ewea.org/fileadmin/files/library/publications/reports/Pure_Power_III.pdf (accessed on 5 December 2019). 6. Kaldellis, J.; Kapsali, M. Shifting towards offshore wind energy—Recent activity and future development. Energy Policy 2013, 53, 136–148. [CrossRef] 7. Peyrard, C. Offshore Wind Turbine Foundations.EDF R&D . LNHE Laboratoire d Hydraulique St Venant. Available online: https://docplayer.net/37756517-Offshore-wind-turbine-foundations-christophe-peyrard-edf-r-d- lnhe-laboratoire-d-hydraulique-st-venant.html (accessed on 5 December 2019). 8. Pinon, G. Tidal energy—Hydrolien. In Proceedings of the CNRS Conference, Nantes, France, 19–20 October 2016. 9. Wang, L.; Lin, C.-Y.; Wu, H.-Y.; Prokhorov, A.V. Stability analysis of a microgrid system with a hybrid offshore wind and ocean energy farm fed to a power grid through an HVDC link. IEEE Trans. Ind. Appl. 2017, 54, 2012–2022. [CrossRef] 10. Bortolotti, P.; Tarres, H.C.; Dykes, K.L.; Merz, K.; Sethuraman, L.; Verelst, D.; Zahle, F. IEA Wind TCP Task 37: Systems Engineering in Wind Energy-WP2. 1 Reference Wind Turbines; National Renewable Energy Lab.: Golden, CO, USA, 2019. 11. Marten, D.; Wendler, J.; Pechlivanoglou, G.; Nayeri, C.N.; Paschereit, C.O. Development and application of a simulation tool for vertical and horizontal axis wind turbines. In ASME Turbo. Expo. 2013: Turbine Technical Conference and Exposition; American Society of Mechanical Engineers: New York, NY, USA, 2013. 12. Sinha, S.; Chandel, S. Review of software tools for hybrid . Renew. Sustain. Energy Rev. 2014, 32, 192–205. [CrossRef] Sustainability 2020, 12, 1807 21 of 21

13. Denee, C.M.A.T. We Are Here An. Atlas of Aotearoa; Massey University Press: Auckland, New Zealand, 2019. 14. Pinkerton, R.M. The Variation with Reynolds Number of Pressure Distribution Over an Airfoil Section; US Government Printing Office: Washington, WA, USA, 1938. 15. Danao, L.A.; Abuan, B.; Howell, R. Design analysis of a horizontal axis tidal turbine. In Proceedings of the 3rd ASIAN Wave and Tidal Conference, Sheffield, UK, 31 August 2016. 16. Huckerby, J.; Johnson, D.; Nobs Line, N.P. New Zealand’s wave and tidal energy resources and their timetable for development. In Proceedings of the International Conference on Ocean, Energy (ICOE), Brest, France, 15–17 October 2008; pp. 15–17. 17. Johnson, D.; McComb, P.; Beamsley, B.; Zyngfogel, R. Resources: Ocean Wave and Tidal Current Resources in New Zealand, Tech. Rep. P0021-01; MetOcean Solutions Ltd.: New Plymouth, New Zealand, 2008. 18. Hicks, D.M.; Hume, T.M. Morphology and size of ebb tidal deltas at natural inlets on open-sea and pocket-bay coasts, North Island, New Zealand. J. Coast. Res. 1996, 12, 47–63. 19. Bellvé, A.R.; Austin, G.; Woods, B.; Power, T. Pathway to Energy Generation from Marine Tidal Currents in New Zealand’s Kaipara Harbour. Available online: http://www.thesustainabilitysociety.org.nz/conference/2007/ papers/BELLVE-Pathway%20to%20Renewable%20Marine%20Energy.pdf (accessed on 5 December 2019). 20. Heath, R. Broad classification of New Zealand inlets with emphasis on residence times. N. Z. J. Mar. Freshw. Res. 1976, 10, 429–444. [CrossRef] 21. Retscreen International, Clean Energy Project Analysis Software. Available online: https://www.nrcan.gc.ca/maps- tools-publications/tools/data-analysis-software-modelling/retscreen/7465 (accessed on 2 December 2019). 22. NIWA Tide Forecaster. Available online: https://tides.niwa.co.nz/ (accessed on 2 December 2019). 23. Koukouvinis, P.K.; Anagnostopoulos, J.S.; Papantonis, D.E. SPH method used for flow predictions at a Turgo impulse turbine: Comparison with fluent. World Acad. Sci. Eng. Technol. 2011, 79, 659–666. 24. Himri, Y.; Rehman, S.; Draoui, B.; Himri, S. Wind power potential assessment for three locations in Algeria. Renew. Sustain. Energy Rev. 2008, 12, 2495–2504. [CrossRef]

© 2020 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).