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Modelization of hybrid systems with hydrogen and renewable energy oriented to electric propulsion in sailboats

Vctor Alfonsn a,*, Andres Suarez a, Angeles Cancela b, Angel Sanchez b, Rocio Maceiras b

a Defense University Center, Escuela Naval Militar, Plaza de Espan~a 2, 36920 Marn, Spainb Chemical Engineering Department, EEI, University of Vigo, 36310 Vigo, Spain

11764inte r n atio nal j ournal of hydr ogen e ner g y 3 9 ( 2014) 11763 e11773

a r t i c l e i n f o

Article history:Received 23 March 2014Received in revised form9 May 2014Accepted 16 May 2014Available online 18 June 2014

Keywords: Sailboat Electric Battery Fuel cell HydrogenElectrolyzer

a b s t r a c t

This paper presents a conceptual model of a hybrid electric sailboat in which energy from electric grid is stored in batteries and energy from renewable energies (eolic, solar and hydro) is stored as hydrogen. The main objective of this model is to study the viability of electrifying traditional sailboats with internal combustion engines into hybrid systems with batteries and fuel cell. The most important advantage of this design is the possibility to reduce up to zero emissions of traditional sailboat. Conversion of renewable energy to hydrogen is performed through an electrolyzer and post conversion to energy is carried out by a fuel cell. The fuel cell with the batteries forms the hybrid system (batteries-fuel cell) for propulsion electrical energy supply. In order to model the boat dynamic and energysystems, modular mathematical models were developed under Matlab-Simulink, using afixed-step solver for the simulation of global model. A simulated logic controller manages the global model. In this paper, many models have been used: some of them are based in literature models and others were developed from experimental data. A control strategy has also been developed to manage energy flows and then it has been embedded to Mat-lab language. The global model permits test the performance of the sailboat.Copyright 2014, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.

Introduction

The increase of energetic and environmental problems has favored the development of alternative energy conversion systems [1]. Transport machines with only internal combus- tion engine (ICE) are being replaced by hybrid systems using two or more power sources [2,3]. Battery systems are the most widely used power sources due to their high efficiency and relatively low cost [4]. On the other hand, fuel cell systems are

a new emerging technology that could solve environmental problems, contribute the accomplishment of Kyoto Protocol and besides it can help to solve the oil dependence [5e7]. Due to similarities between batteries and fuel cell systems, their combined effect promise great results [8].Furthermore, in recent years the implementation of renewable sources as photovoltaic and eolic energy in Hybrid Renewable Energy Systems (HRES) is becoming popular for power generation [9]. The main disadvantage of these type ofrenewable energy sources is their seasonal nature, which

* Corresponding author. Tel.: 34 986 804942.E-mail addresses: valfonsin@cud.uvigo.es, valfonsin@gmail.com (V. Alfonsn). http://dx.doi.org/10.1016/j.ijhydene.2014.05.1040360-3199/Copyright 2014, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.

means great variability over time [10,11]. Generation of hydrogen based on renewable resources using electrolyzers could become the nexus for the implementation of this tech- nology in hybrid systems [12,13].Plus land vehicles [14,15], it is possible to incorporate fuel cell and battery hybrid systems in boats [16]. Hydrogen pro- duction is performed with renewable energy provided by several photovoltaic panels and small eolic generators located in the own boat. Furthermore, if a sailboat is selected, this energy production can be increased during the sail navigation with one or more hydrogenerators.For this type of systems, where many power sources are mixed, mathematical simulation has become in object of study for battery electric vehicles and all kind of hybrid con- figurations and even specific software has been developed [17e19]. However, there is a lack of information about battery electric ship simulations and even less about energy renew- able sources applied in these kinds of vehicles.There is not any information about Energy Management Unit (EMU) strategies in the case of HRES implemented in sailboats. But, it is possible to find a vast amount of informa- tion in many application areas as transportation, distributed generation or portable applications. Some of most important are: direct integration, single converter based or multiple converter based [20].In this paper, a conceptual zero emissions electric sailboat is studied. Renewable energy sources (photovoltaic, eolic and hydrogeneration), energy storage with batteries (in the case of electrical energy provided by the grid) and an electrolyzer-fuel cell system (for renewable energy) are implemented. Subse- quently independent modular models with each energy sys- tem has been developed in Matlab/Simulink and embedded. All of these individual models are managed by a logic controller implemented in Matlab.

Conceptual design

The idea of zero emissions ships is not new, several kinds of ships exist with some of the zero-emission characteristics and even some of them have become commercial. Configurations with batteries, fuel cells or both (hybrid systems) have been developed and applied to catamarans, yachts and boats [21e24]. A conceptual sailboat design with a hybrid battery/ fuel cell energy system has been raised. Battery system is responsible for storing electrical energy from the grid, and whole of fuel cell, electrolyzer and hydrogen canisters are responsible for storing renewable energy.Renewable generation is provided through three sources:wind turbines, photovoltaic panels and hydrogeneration

1. Wind turbines placed to the top of the mast (only one) or placed in the stern (one or two elements are possible), and whose operation relies on wind power and it is operative during the sailboat cruise or even when sailboat remains in port.2. Photovoltaic panels, placed on ship hull, whose operation it is possible during the ship cruise or when ship remains in port, depending on the effective radiation.

3. Renewable energy source is hydrogeneration. One or two marine generators are responsible for electric energy gen- eration during sail navigation, without electric motor operation.

Renewable energy flows to the electrolyzer where is con- verted to hydrogen, and then it is stored in tanks or canisters. Optimal hydrogen storage devices are metal hydride canisters which due to their elevated weight are perfect to be used as boat ballast. When control decides to supply energy to system, fuel cell device converts hydrogen to electrical energy. All implemented devices are part of a conceptual idea for zero emission sailboats, and one possible distribution is depicted in Fig. 1.

Model description

Once a conceptual design for a zero emission sailboat has been established, it is necessary to size the magnitude of each element and even define the number of them that may be needed. A design and analysis powerful tool for this procedure is mathematical simulation with Matlab-Simulink software.

Fig. 1 e Conceptual design of a zero emission sailboat.

11766inte r n atio nal j ournal of hydr ogen e ner g y 3 9 ( 2014) 11763 e11773

In Fig. 2 all existing models and a scheme with their arrangement are shown. All renewable energy sources: photovoltaic, eolic and hydrogeneration are detailed and each individual model system is developed through mathematical equations or experimental data.Furthermore, in this group the system for renewable en- ergy storage composed by electrolyzer, fuel cell, compressor and tank is described. Energy grid storage by batteries is modeled in order to characterize the battery system, for this, it is necessary to take into account the dynamic behavior and the capacity. A propulsion model is explained; in addition to electric motor model a dynamical model to calculate the mechanical energy required is developed. Finally, a possible control to manage and link all systems is shown and subse- quently it is modeled. The connection of all of them allows a global simulation thereby helping to scale the hybrid system with hydrogen and renewable energy.

Renewable energy generation and storage

In this section, energy obtained from wind generator, photo- voltaic panels and marine generators (hydrogenerators) are modeled. The surplus of renewable energy sources power is stored in batteries or H2 tanks based on electrolyzers used to convert the electrical energy to the H2 energy [25].

Photovoltaic generationModeling of photovoltaic module (PV) is usually based in the approximation of non-linear IeV curves obtained with ideal PV circuit model, PV circuit model with series resistance or both series and parallel resistance [26e28]. Model is based only on the manufacturer's data and methodology used to predict the electrical power available from PV sailboat panel is based on the five-parameter photovoltaic model presented by De Soto [29], who uses an equivalent circuit with series and shunt resistances together with a diode in parallel, obtaining IeV relationship for characteristic curve.This model has been modified by Hadj Arab et al. [30] to es- timate the maximum power output in operating conditions [31]:G

where G is the incident irradiance, Pmp is the power output, T is the temperature, Pmp is the maximum power, Gref and Tref are incident irradiance and temperature refer to standard rated conditions (SRC). By multiplying the unitary power for each panel by the number of panels, the power being generated by the panels at each moment is obtained.The main advantage of this model, apart from its reliability, accuracy and simple implementation, is the easiness to obtain valid parameters in wide operation ranges from the data pro- vided by the manufacturer, which in many cases are under standard nominal conditions, usually 1000 W/m2 and 25 C.

Wind generatorFor this model, wind speed data are put into the model block that refers to the wind generator in order to calculate the electrical energy produced by the device from the wind kinetic energy.Each wind turbine has its own characteristic curve that distinguishes it from the others, and defines its behavior for various wind speeds, that is, providing the power generated by the device for each value. The start up speed for the wind generator is low; this means that there is not energy output at very low wind speeds.To determine the output power of wind turbines, a poly- nomial adjustment is used [32], which relates wind speed to output power; this information is generally provided by eolic turbine manufacturers. From manufacturer's data and with Matlab adjustment tool (cftool) a polynomial is obtained. Once this polynomial is obtained, this is implemented as a Matlab function that may be subsequently called with Simulink m-function block during simulation.The wind speed values can be obtained with an anemom- eter placed on a boat or even via meteorological data of marine buoys. In the last case, it would be useful to subtract the for- ward speed of sailboat.

Marine generator (hydrogenerator)This device uses sailing navigation to generate electrical power from a propeller and a small generator [33]. When electric motor is running the device or devices are raised up toPmp G

ref

Pmp;ref 1 g T Tref (1)

avoid the friction of the propeller. Procedure for marine

Fig. 2 e Global model with DC BUS.

generator model is the same than eolic generator model. The polynomial adjustment is performed from manufacturer data which are then implemented to Matlab-Simulink. Commer- cial hydrogeneration devices typically incorporate inside AC/ DC converters and the data provided by the manufacturer usually include converter efficiency [34]. In the case that it isnot possible, efficiency value must be included in model.

Compression takes place in three stages to obtain the maximum amount of hydrogen compressed, which is ach- ieved when the ratio between the output and input pressures for each compressor stage are equal and therefore the energy consumed at each stage is the same. The molar flow of com- pressed hydrogen is expressed as follows:n poly 1

hcomp

Electrolyzer modelIn electrolyzer, electric current passes through a series of electrolytic cells, where there is a water input current. Due to

FH2 ;comp Pet;comp

npoly

hcomp

2 RT6

P2 P1

h poly 3 hpoly 175

(4)the electrolysis provoked by the electric current, water current is split into two separate currents: hydrogen and oxygen.The currentevoltage curve chosen for the electrolyzer is shown in Eq. (4) [35]. The number of active electrolyzers used depends on the input power, when this exceeds maximum nominal power for one electrolyzer, both of them are switched on.

Ie

where npoly is the polytropic coefficient, hcomp is the efficiency of the compression, P1 (bar) and P2 (bar) the input and output pressures, respectively, Pet;comp is the energy used in each stage.The tank is the final element in the model. The tank model is simple, the inflow from the compressor and outflow to the fuel cell of hydrogen are taken into account and this is inte- grated in order to have a real value for the amount of hydrogenVe Ve;0 b ln

Ie;0

Re Ie (2)

stored per year. Thus, using the evolution of the amount ofhydrogen, the tank can be scaled accordingly. The balance forwhere Ve (V) is the voltage of a cell, Ve;0 (V) is the reversible voltage for a cell, b (V 1) is a characteristic coefficient of the electrolyzer, Ie;0 (A) is the exchange current, Re (U) is the Ohmic resistance in the cell and Ie (A) is the current.Electrolyzer only works for values above 15% of its rated power although this value can be changed. A parasitic loss of1% is assumed for each electrolyzer switched on [36].

Compression and storage of hydrogenOnce hydrogen production occurs, high pressure storage will be necessary. For this reason, a model for a compressor must be developed and implemented after electrolysis stage. The compressor buffer is an intermediate tank between the gas outlet from the electrolyzer, which works continually, and the compressor input.The second function has a control system for the tank level, which, once reached a set level, activates an emptying signal to the compressor to evacuate the hydrogen towards the higher capacity tank. The two input variables are the electrolyzer output flow and the flow to the compressor creating a hydrogen balance that, by being integrated, repre- sents the amount of hydrogen:

d N H2 ;buf dt FH2 ;buf ;in FH2 ;buf ;out (3)

2where NH2 ;buf is the number of accumulated moles in the buffer, FH ;buf ;in (mol s 1) the hydrogen flow entering from the

the tank is the following:

d N H2 ; Tank dt FH2 ;in;Tank FH2 ;out;Tank (5)

2where: dNH2 ;Tank is the number of accumulated moles, FH2 ;in;Tank (mol s 1) the hydrogen flow entering from the compressor and FH ;out;Tank (mol s 1) the output towards the fuel cell.

Hydrogen consumption modelThe fuel cell works in the opposite way to the electrolyzer, thus unregulated direct electrical current and water are ob- tained from the combination of hydrogen and oxygen. The input current at the anode will be the hydrogen obtained by of electrolysis, supplied by the pressurized storage tank, whereas the input current at the cathode will be air with approximately 21% oxygen, reacting gas, and nitrogen, which is inert.In this case, a hydrogen consumption model has been constructed rather than a fuel cell electric power model [37]. An equation to model the hydrogen intake as a function of power demanded by the fuel cell (by the motor and the auxiliary systems) can be used.Thus, based on the simple reaction stoichiometry, Fara- day's Constant, fuel cell efficiency and stack potential Vc , the following equation is obtained [17]:

Pelectric

2electrolyzer and FH ;buf;out (mol s 1) the output towards thecompressor. Applying a logical comparison system with

H2usage

2Vc F

(6)memory, a trigger signal can be sent once a particular level is reached and a deactivation signal can be sent if a lower level is reached.When buffer reaches the desired level, the compressor is triggered and compresses the hydrogen at nominal power, to achieve a lower volume of gas and thus a smaller final storage tank. A discontinuous flow model has been chosen, to avoid large hydrogen flows to the compressor that would need a much more powerful compressor.

This equation depends only on the power demanded by the fuel cell Pelectric and stack potential Vc is referred to the lower heating value of hydrogen, as [38]:

h (7)Vcfc 1:25

It yields the hydrogen mass flux H2usage , in moles per sec- ond, which makes possible to know the hydrogen tank level at every moment.

Grid energy storage. Battery model

Main energy source of zero sailboats is provided by grid and electrical energy storage made with batteries while boat is in port. The purpose of battery simulation is to predict the bat- tery dynamic behavior versus energy demand (battery discharge) or energy supply (battery charge). Furthermore, battery capacity is influenced by current that flows through battery. Magnitude of these effects is influenced by the type of battery being used. All these factors are considered in this section about battery model.

Battery dynamic behavior. Open circuit voltageIn this case, dynamic behavior model is performed through a simple battery equivalent circuit (Fig. 3) where it is necessary to know internal resistance and open circuit electric potential (OCV) [17,39]. Assuming that current is flowing out the battery, as is depicted in Fig. 3, basic voltage equation is [40]:

V E IZ (8)

where V is terminal voltage, E is open circuit voltage (OCV), I is current across circuit and Z internal resistance. OCV values change in function of battery state of charge (SoC), and they can be introduced in battery model from a Matlab function. Internal resistance values and OCV plots are obtained from experimental data [41] or are provided from literature [42]. All of them vary depending battery technology used (lead acid, nickelecadmium, lithium, etc).

Battery capacity model. Peukert coefficientBattery capacity is affected by the discharge power magni- tude, generally when discharge is high, the capacity is lower and vice-versa. The power magnitude is affected by battery technology used. This effect is important for electric vehicles due to high and discontinuous discharge currents. To compensate this effect Peukert's equation is implemented [43].Some authors consider this model is non-optimal for vehicle simulation since temperature effect is not being taken into account and correction factor is obtained with constant discharge current [43,44]. But this last factor in a sailboat simulation is not a problem because current under discharge conditions is quite constant and the temperature effect can be considered if necessary [45], moreover the simulation

objective is to obtain a first estimate in order to study viability for a zero emission sailboat.Peukert's equation was originally developed for lead acid batteries, but has since been used for other types [46]. Equa- tion estimates the available capacity using the following equation:

disCp Tdis $Ik (9)

where Cp is theoretical Peukert capacity (A h), Idis is discharge current, Tdis discharge time and k the Peukert's coefficient, which value varies depending of the kind of battery. Peukert's coefficient can be estimated with experimental data or data provided by manufacturer.

Sailboat propulsion

Drive resistance of a vessel over the sea (hydrodynamic resistance) is a complex task, but Delft Series [47] shows good results in the case of sailboats. These series have been developed in Delft Ship Hydrodynamics Laboratory for several different sailboat hulls. This series let to estimate mechanical power demand and with motor efficiency can be obtained electric power to be supplied by batteries and fuel cell system.

Mechanical power. Delft seriesGeometrical coefficients used to define the shape of a boat are: the prismatic coefficient Cp , longitudinal center of buoyancy LCB, ratio between beam of waterline and canoe body draft Bwl =Tc , ratio of length at the waterline and displaced volume Lwl =Vol1=3 and relation between beam of waterline and length at the waterline Lwl =Bwl [47]. If these data are not available the software (Free!Ship Plus) can provide thisinformation.Frictional resistance (RF) is obtained from sum of resistance of hull, keel and rudder from next equation [48]:

F 2 c Fh k Fk r FrR 1 rv2 S C S C S C (10)

where r is density of water, v forward speed of sailboat, S is the wetted area at zero speed and CF is the friction coefficient for dipped parts.Grigson [49] and Katsui et al. [50] proposed methods to predict friction resistance for model-through ship-scale Rey- nolds numbers, by solving the momentum integral equation. The 25th ITTC RC [51] conducted an analytical study on fric- tion lines, starting to analyze the possible recommendationfor a new formula. This correctional line is shown below:

CF

0:00665770:042612$log Re0:56725 (11)log Re 4:3762

And Reynolds number (Re) for dipped parts is determined separately with:

Rnh

V0:7Lwl ; Rn

km

VCk y Rn

cm

VCr (12)m

Fig. 3 e Simple equivalent circuit model composed of four cells.

where m is the kinematic viscosity (saltwater or freshwater)and Lwl the waterline length.To approximate the residual resistance, drive resistance is included and frictional resistance is excluded, therefore wave

Fig. 4 e Flow diagram for logic control.

resistance is included. To obtain mathematic model several sailboats were submitted to tank testing with different Froude numbers:

To obtain mechanical motor power demanded to the electric motor, brake horsepower (BHP), it is necessary to es-timate the propeller open water efficiency (hp ):

VFn pgL

(13)

EHP hp BHP hh ho hm hrr (17)

1 pExperimental data were processed and analyzed with sta- tistical process to obtain a polynomial for Froude number depend on hull geometry [48]:

where: hh is the hull efficiency, h0 is the propeller efficiency, hmmechanical efficiency, hrr relative rotative efficiency.Brake horsepower (BHP) corresponds to the mechanicalpower supplied by diesel generator, in the case of electric Rr

a a C

Bwl Lwl

2 a LCB a a a

Lwl Cp2 a Cp

0Vc rg

3 Tc2

4 V1=3

51wl

3

6 V1=3

sailboat is supplied by electric motor, therefore it is necessaryto know electric motor efficiency that lets to calculate the

2 a7 LCB

a8

Lwl V1=3

a9

Lwl V1=3

(14)

electric power demand.

Electric demand. Motor efficiencyEach Delft coefficient (an) is determined for a Froude number and with Residual resistance and frictional resis- tance. Total boat resistance can be obtained:Rt Rf Rr (15) Effective horsepower (EHP) is calculated with total resis-tance and the sailboat speed:

EHP Rt *V (16)

Motor efficiency can be provided by manufacturer as a single data or a power curve, but it is possible to model this electric motor efficiency from motor losses. Losses are classified in four types and can be estimated as product of corresponding con- stant with angular speed (u) or motor torque (T) [17,52]: Copper conductor losses kc T2 , iron losses ki u, friction and windagelosses ku u3 , constant losses due to electronic control (C).Knowing losses value, mechanical efficiency can be described as:

Fig. 5 e Sailboat global model modeled under environment Simulink.

output power

BHP

systems which are modeled with experimental data or curveshMotor output power

losses BHP

kc T2

ki u

ku u3

(18) C

provided by manufactures include this efficiency and power value should not be modified.These constants take typical values depending of kind ofmotor selected: brushed DC motor or brushless motor. Adding the auxiliary elements power demand, the total electric power demand that the batteries and/or the fuel cell must supply can be obtained.

Energy and management control

Before to link all modeled systems, it is necessary to adapt the output conditions of each of the previously systems to DC BUS voltage conditions, thus a model for electrical conversion can be developed. Once all systems are operating under the same conditions, control can be defined and modeled. In this sec- tion, all of these facts are described.

Electrical conversionShips are normally powered by diesel generators which are the combination of a diesel engine with electrical generator, converting liquid fuel (diesel) in electrical power to feed an electrical motor. When performing a power conversion sys- tem on a boat by a hybrid system with fuel cell and batteries, it may easily be replaced by an electrical converter which transform DC battery electrical energy to adequate form to feed electric motor.A simple model can be developed with electrical converter efficiency (DC/DC or inverter DC/AC) and the motor efficiency. Electrical energy stored is transformed to mechanical power to move the propeller. Converters take efficiency values be- tween 90 and 95% [53]. Inverter DC/AC efficiency value is slightly under DC/DC converter efficiency.Other elements of hybrid power system include indepen- dent converter devices as fuel cell, electrolyzers or photovol- taic panels, and efficiency must be considered. However, other

Control strategy for power managementOnce all models are defined, it is necessary to determine a control strategy. Usually, a fuel cell hybrid system works in parallel, and in this case this structure was selected. Of all kind of existing architectures for parallel configuration, the multiple DC/DC converter based topology was implemented for the power management [54]. This is the most common energy management strategy for Fuel Cell Hybrid Power Sources used in Fuel Cell Hybrid Vehicles, and therefore a good first approximation to implement these systems in ma- rine applications.The first step is to develop a flow chart where strategy can be evaluated. A simple scheme is depicted in Fig. 4. This strategy is subsequently implemented as a Matlab function under m-file extension, which lets to embed logic control in global Simulink model.Control begins with an energy balance parameter, where F is defined as summation of energy generated with energy demanded. If parameter F takes negative values, it means that sailboat operates with energy of fuel cell and/or battery. If state of charge of battery and hydrogen is higher than the minimum, both systems operate in hybrid mode, the fuel cell works with nominal power and the battery supplies the rest of demand (only when it is necessary). Preference of supplying fuel cell energy instead of battery energy is due to hydrogen energy provides from renewable sources whose cost is zero.If hydrogen level is lower than a minimum, the battery supplies whole energy. On the other hand if battery state of charge is lower than minimum, fuel cell system supplies power demand, and if this power demand is upper than nominal fuel cell power, sailboat will operate under safe mode (warning) to come back to port.

Fig. 6 e Effective horsepower (EHP) obtained with Freeship software.

Another significant part of control strategy occurs when renewable energy is upper than demand power. Two cases are possible: In the first case, the boat is connected to grid in port or

Table 1 e Components of battery and fuel cell hybrid system.

ComponentNominal power (W)

Motor: brushless, asynchronous (48 VDC)10,000

Eolic generator (24 VDC)350

Hydrogenerator (24 VDC)1000

Solar monocrystalline panel (24 VDC)560

PEM fuel cell (24 VDC)2400

Electrolyzer (48 VDC)800

LiFePO4 batteries 40 Ah (48 VDC)624

provided to a DC BUS (usually operating at a voltage of approximately 48 V). Every one of these systems has an elec- tric converter, but for eolic generator and hydrogenerator parameterized curves that include this efficiency have been used.Electrolyzer uses excess power from DC BUS to transform energy and water into hydrogen. Hydrogen serves to store energy (free source) and when control decides to supply more energy to DC BUS, fuel cell is responsible for hydrogen reconversion into electrical energy. Battery system is bidi- rectional and it can be charged or discharged when control decides it.Power demanded by electric motor is the main output control. When boat is operating with electric motor, controller decisions are based in this parameter and prioritize this power demand. An electric conversion DC/DC for DC motors or DC/ AC for induction motors is required.Finally when sailboat remains at port, batteries are charged with the electricity network and renewable energy sources are responsible to electrolyze hydrogen.

Fig. 5 shows the sailboat model once implemented underduring sail navigation. When it is connected to grid, the battery

Simulink

environment. All renewable energy sources andwill be charged with this kind of energy and renewable energy(photovoltaic and eolic energy) will electrolyze hydrogen.In the second possible case, the boat is moving but if electric motor is running, renewable energy cannot generate energy to electrolyze hydrogen because all energy is used with electrical motor and auxiliary elements. But if boat is sailing without electric motor, hydrogen generation can take place. Furthermore, hydrogen generator will go into operation increasing renewable energy generation.

Global model

Once controller is defined, the individual models can be con- nected to each other. Energy from renewable sources is

energy provided by a charging station are interpreted as aninput for logic control and the power demanded by electric motor as an energy output. Control evaluates this energy flow and when it is necessary it will supply more energy from battery and fuel cell.

Results

Once sailboat design is performed and individual models are developed, some with theoretical equations and others with experimental data, all of them are linked together with a logic controller that will manage all systems for a predefined strategy with the purpose of obtaining positive results.

Fig. 7 e Power management strategy from a real route simulation of one zero sailboat with Matlab/Simulink.

Fig. 8 e Batteries and hydrogen consumption for a real route simulation of one zero sailboat with Matlab/Simulinkdepicted.

Subsequently, a conceptual sailboat with zero emissions can be simulated for real routes and different weather con- ditions (wind and radiation) in order to test the performance of the sailboat global model. This global model was tested for motor sailboats up to 10 m in length or type A, for areas of ocean navigation and recreational use. The maximum cruising speed recommended for this type of electrical ships is6 knots. For these values of speed, the balance between per- formance and range cannot be guaranteed.Spanish PER normative requires an autonomy of 12 miles with a speed constant value of 6 knots [55]. Effective horse- power (EHP) for a sailboat with 10 m in length and for a cruise of 12 miles was estimated using Free!Ship software in 2086 W. Fig. 6 shows the EHP obtained with this software as function of the sailboat speed. Consequently, and using a propeller open water efficiency of hp 0; 46(provided by Free!Ship) the brakehorsepower (BHP) is 4497 W. Finally, energy required for cruisePER normative (105 min) was estimated in 10 kWh.Nevertheless, in most of the cases, real routes are not under constant speed, and in sailboats electric motor is switched off when wind is enough to propel the boat. The proposed model allows to simulate real routes. An example of one of them is shown in Fig. 7; where a real sailboat simulation originally with ICE which is adapted to a hybrid energy system can be seen. The main characteristics of this system are shown in Table 1. In this simulation, sailboat sails up to 4 h and it travels a total distance of 24 miles for various speed ranges, and consequently, with several values for the power demanded (electric motor and auxiliary energy). Boat sails without motor supply, only with yachting, and it reaches high values of total power demanded for the hybrid system. Total energy consumed was estimated in 11.5 kWh for this travel. Thus, this cruise characteristic is well above PER normative.The power management is responsible of satisfying ener- getic demand with the battery and fuel cell system. The ef- fects of selecting an adequate control strategy are shown in Fig. 7. In addition, the consumption of hydrogen and battery discharge (State of Charge) for this travel can be observed in Fig. 8. The simulation begins with battery charged with grid energy. On the other hand, the initial amount of hydrogen corresponds to the electrolysis of renewable energy (wind and sun) for a week at port. In this case, when battery state of charge reaches 50 per cent of state of charge, fuel cells supply a part of necessary power and it is stored as hydrogen. The last value of battery state of charge is greater than 20%, a typical value of security to keep batteries in a good condition and a safe value to get back at port.

Conclusions

In this paper, a conceptual zero emission sailboat is analyzed. Simulink software was used as a toolbox to convert MCI sail- boats into hybrid sailboats with batteries and fuel cells. The hybrid sailboat is based on an electric boat whose energy source proceed from renewable energies (eolic, solar and marine) and energy available from recharge point, which is provided by electricity network when boat berths at the port. Renewable energy is stored as hydrogen obtained with an electrolyzer and grid energy is directly stored in batteries. Hydrogen can be reconverted in electrical energy through a fuel cell. A logic controller is responsible of managing all stored energy to supply electric motor demand.This model can be used as a toolbox in order to study a possible implementation of zero emission systems in sail- boats. From some manufacturer data, the simulation could be launched, so that, with several simulations the conceptual design of one Zero Sailboat could be optimized in order to apply this knowledge in the manufacture of a real boat, which could verified the normative of different countries.For future work, this global model will allow comparing different commercial sailboats with several profiles of hulls, choosing the optimal number of renewable elements and therefore the battery capacity necessary to obtain the minimal range of the boat.

references

[1] Sorrentino M, Pianese C, Maiorino M. An integrated mathematical tool aimed at developing highly performing and cost-effective fuel cell hybrid vehicles. J Power Sources2013;221:308e17.[2] Li Q, Chen W, Li Y, Liu S, Huang J. Energy management strategy for fuel cell/battery/ultracapacitor hybrid vehicle based on fuzzy logic. Int J Electr Power & Energy Syst2012;43:514e25.[3] Ramos-Paja CA, Romero A, Giral R, Calvente J, Martinez- Salamero L. Mathematical analysis of hybrid topologies efficiency for PEM fuel cell power systems design. Int J Electr Power Energy Syst 2010;32:1049e61.[4] Gerssen-Gondelach SJ, Faaij APC. Performance of batteries for electric vehicles on short and longer term. J Power Sources 2012;212:111e29.[5] Chen P. Configuration of solar-hydrogen mild hybrid fuel cell power systems for electric vehicles. J Power Sources2012;201:243e52.

[6] Anandarajah G, McDowall W, Ekins P. Decarbonising road transport with hydrogen and electricity: long term global technology learning scenarios. Int J Hydrogen Energy2013;38:3419e32.[7] Gonza lez Y, Rodrguez S. A comparative study on the ultrafine particle episodes induced by vehicle exhaust: a crude oil refinery and ship emissions. Atmos Res2013;120e121:43e54.[8] Pollet BG, Staffell I, Shang JL. Current status of hybrid, battery and fuel cell electric vehicles: from electrochemistry to market prospects. Electrochim Acta 2012;84:235e49.[9] Bajpai P, Dash V. Hybrid renewable energy systems for power generation in stand-alone applications: a review. Renew Sustain Energy Rev 2012;16:2926e39.[10] Ringel M. Fostering the use of renewable energies in the European Union: the race between feed-in tariffs and green certificates. Renew Energy 2006;31:1e17.[11] Lloyd B, Subbarao S. Development challenges under the clean development mechanism (CDM)dcan renewable energy initiatives be put in place before peak oil? Energy Policy 2009;37:237e45.[12] Gibson TL, Kelly NA. Optimization of solar powered hydrogen production using photovoltaic electrolysis devices. Int J Hydrogen Energy 2008;33:5931e40.[13] Rodrguez CR, Riso M, Jime nez Yob G, Ottogalli R, Santa Cruz R, Aisa S, et al. Analysis of the potential for hydrogen production in the province of Co rdoba, Argentina, from wind resources. Int J Hydrogen Energy 2010;35:5952e6.[14] Brown D, Alexander M, Brunner D, Advani SG, Prasad AK.Drive-train simulator for a fuel cell hybrid vehicle. J PowerSources 2008;183:275e81.[15] Van Mierlo J, Van den Bossche P, Maggetto G. Models of energy sources for EV and HEV: fuel cells, batteries, ultracapacitors, flywheels and engine-generators. J Power Sources 2004;128:76e89.[16] McConnell VP. Now, voyager? The increasing marine use of fuel cells. Fuel Cells Bull 2010;2010:12e7.[17] Larminie J, Lowry J. Electric vehicle technology explained.Oxford: John Wiley & Sons; 2003.[18] Markel T, Brooker A, Hendricks T, Johnson V, Kelly K, Kramer B, et al. ADVISOR: a systems analysis tool for advanced vehicle modeling. J Power Sources2002;110:255e66.[19] Moore RM, Hauer KH, Friedman D, Cunningham J, Badrinarayanan P, Ramaswamy S, et al. A dynamic simulation tool for hydrogen fuel cell vehicles. J Power Sources 2005;141:272e85.[20] Erdinc O, Uzunoglu M. Recent trends in PEM fuel cell- powered hybrid systems: investigation of application areas, design architectures and energy management approaches. Renew Sustain Energy Rev 2010;14:2874e84.[21] Fonseca N, Farias T, Duarte F, Gonalves G, Pereira A. The HIDROCAT project e an all electric ship with photovoltaic panels and hydrogen fuel cells. World Electr Veh J 2009;3.[22] Zero CO2 yacht sets off on first stage of mediterranean mission. Fuel Cells Bull 2010;2010:5.[23] Nemo H2: Amsterdam's latest canal cruise boat is powered by hydrogen. Hol Shipbuild 2010;59:29e32.[24] Siuru B. Sailing the deep blue gets greener. Diesel Prog NorthAm Ed 2010;76:44e5.[25] Busby RL. Hydrogen and fuel cells: a comprehensive guide.Tulsa: PennWell Corporation; 2005.[26] Garca-Valverde R, Espinosa N, Urbina A. Optimized method for photovoltaic-water electrolyser direct coupling. Int J Hydrogen Energy 2011;36:10574e86.[27] Ishaque K, Salam Z. An improved modeling method to determine the model parameters of photovoltaic (PV)

modules using differential evolution (DE). Sol Energy2011;85:2349e59.[28] Vengatesh RP, Rajan SE. Investigation of cloudless solar radiation with PV module employing MatlabeSimulink. Sol Energy 2011;85:1727e34.[29] De Soto W. Improvement and validation of a model for photovoltaic array performance; 2004.[30] Hadj Arab A, Chenlo F, Benghanem M. Loss-of-load probability of photovoltaic water pumping systems. Sol Energy 2004;76:713e23.[31] Rosell JI, Iba n~ ez M. Modelling power output in photovoltaicmodules for outdoor operating conditions. Energy ConversManag 2006;47:2424e30.[32] Bilodeau A, Agbossou K. Control analysis of renewable energy system with hydrogen storage for residential applications. J Power Sources 2006;162:757e64.[33] Queeney T. Electricity from heavy water. Ocean NavigJanuary/February 2012;12.[34] Watt&Sea. Technical data sheet cruising hydro generator, vol. 2013; 2013.[35] Santarelli M, Call M, Macagno S. Design and analysis of stand-alone hydrogen energy systems with different renewable sources. Int J Hydrogen Energy 2004;29:1571e86.[36] Kelly NA, Gibson TL, Ouwerkerk DB. A solar-powered, high- efficiency hydrogen fueling system using high-pressure electrolysis of water: design and initial results. Int J Hydrogen Energy 2008;33:2747e64.[37] Sanchez A, Cancela A, Urre jola S, Maceiras R, Alfonsn V.Simulation framework to evaluate the range of hydrogen fuel cell vehicles. I RE CH E 2010;2:840.[38] Larminie J, Dicks A. Fuel cell systems explained. Oxford: JohnWiley & Sons Ltd; 2003.[39] Roscher MA, Sauer DU. Dynamic electric behavior and open- circuit-voltage modeling of LiFePO4-based lithium ion secondary batteries. J Power Sources 2011;196:331e6.[40] Bird J. Electrical circuit theory and technology. Oxford: Taylor& Francis; 2007.[41] Abu-Sharkh S, Doerffel D. Rapid test and non-linear model characterisation of solid-state lithium-ion batteries. J Power Sources 2004;130:266e74.[42] Conway BE. In: Kiehne HA, editor. Battery technology handbook. New York: Marcel Dekker; 1989. p. 517 [J Electroanal Chem 328 (1992) 367e368].[43] Peukert W. U ber die Abhanigkeit der Kapazitat von derEntladestromstarke bei, vol. 27; 1897. pp. 287e8.[44] Doerffel D, Sharkh SA. A critical review of using the Peukert equation for determining the remaining capacity of lead-acid and lithium-ion batteries. J Power Sources 2006;155:395e400.[45] Wu G, Lu R, Zhu C, Chan CC. Apply a piece-wise Peukert's equation with temperature correction factor to NiMH battery state of charge estimation. J Asian Electr Veh 2010;8:1419e23.[46] Omar N, Daowd M, van den Bossche P, Hegazy O, Smekens J, Coosemans T, et al. Rechargeable energy storage systems for plug-in hybrid electric vehicles-assessment of electrical characteristics. Energies 2012;5:2952e88.[47] Larsson L, Eliasson RE. Principles of yatch design. 2nd ed.London: Adlard Coles Nautical; 2000.[48] Keuning JA, Sonnenberg UB. Approximation of the hydrodynamic forces on a sailing yatch based on the 'Delft Systematic Yatch Hull Series'. In: The international HISWA simposium on yatch design and yatch construction; 1998. p. 99.[49] Grigson CWB. A planar friction algorithm and its use in analysing hull resistance. RINA 1999;76.[50] Katsui T, Asai H, Himeno Y, Tahara Y. The proposal of a new friction line, fifth Osaka colloquium on advanced CFD applications to ship flow and hull form design; 2005.

[51] Campana EF, Gorski J, Day AH, Huang D, MacFarlane G, Mikkola T, et al. Final report (The Resistance Committee). ITTC Fukuoka 2008;1:1.[52] Auinger H. Determination and designation of the efficiency of electrical machines. Power Eng J 1999;13:15e23.[53] Choi W, Lee C. Photovoltaic panel integrated power conditioning system using a high efficiency step-up DCeDC converter. Renew Energy 2012;41:227e34.

[54] Zhang X, Mi CC, Masrur A, Daniszewski D. Wavelet- transform-based power management of hybrid vehicles with multiple on-board energy sources including fuel cell, battery and ultracapacitor. J Power Sources 2008;185:1533e43.[55] Government of Spain. Boatmaster's Certif (PER)

2014;2014:1.