research article open access scenario analysis of a

Wu et al. Sustainable Chemical Processes 2014, 2:5http://www.sustainablechemicalprocesses.com/content/2/1/5

RESEARCH ARTICLE Open Access

Scenario analysis of a bioethanol fueled hybridpower generation systemWei Wu1*, Yuan-Tai Hsu2 and Po Chih Kuo1

Abstract

Background: Regarding most of FC/PV/Battery based hybrid power generation systems, the photovoltaic (PV)power usually dominates the main power supply and the water electrolyzer is used to produce hydrogen. Theenergy efficiencies of these hybrid power generation (HPG) systems are usually low due to the low conversionefficiency of PV cell and the extra power consumption to hydrogen production. To reduce the electricity demandby the PV system and improve the energy efficiency of hydrogen production unit, a scenario-based design of theHPG system is necessary.

Result: This paper proposes an EFC/PV/Battery based hybrid power generation system to meet 24-hour powerdemand. An ethanol-fueled fuel cell (EFC) power generator not only dominates the main power supply, but also acombination of the stand-alone EtOH-to-H2 processor and PEMFC can ensure higher energy efficiency. A PV systemis treated as an auxiliary power generator which can reduce the (bio)ethanol consumption. A backup battery notonly stores excess power from PV or EFC, but also it can precisely satisfy the power demand gap. Finally, scenarioanalysis of the hybrid power generation (HPG) system in regard to the hybrid power dispatch and energy efficiencyis addressed.

Conclusion: An optimized fuel processing unit using ethanol fuel can produce high-purity hydrogen. Thesimulation shows that the stand-alone EtOH-to-H2 processor not only guarantee the high energy efficiency, butalso it can continuously produce hydrogen if the fuel is enough. According to scenarios for the daily operation ofthe HPG system, the EFC power dominates the power supply during the night, the PV system dominates thepower supply during the day and the backup battery aims to instantly compensate the power gap and store theexcess power from PV or EFC. According to the hybrid power dispatch, the distribution of the HPG systemefficiency is specified.

Keywords: Hybrid power system, Scenario analysis, Ethanol-fueled fuel cell system, Energy efficiency

BackgroundRecently the interest in renewable and sustainable powergeneration techniques such as photovoltaic, wind, andfuel cell powered systems has grown. The off-grid hybridpower system is increasingly popular for remote areapower generations, even though the photovoltaic (PV)or wind system is highly dependent on weather conditionsand locations. Muselli et al. [1] developed a stand-alonehybrid power system which was composed of the PVpanels, an electrical generator using fossil fuels, andbattery storage, and Elhadidy [2] studied the feasibility

* Correspondence: [email protected] of Chemical Engineering, National Cheng Kung University,Tainan 70101, TaiwanFull list of author information is available at the end of the article

© 2014 Wu et al.; licensee Chemistry Central LCommons Attribution License (http://creativereproduction in any medium, provided the orDedication waiver (http://creativecommons.orunless otherwise stated.

of using wind/solar/diesel energy conversion systemsto meet the power demand of the specific communityin Saudi Arabia. Notably, a gasoline or diesel engine isusually treated as the backup power generator.The PV system generates electricity during daylight

hours, but the fuel cell system produces electricity as longas hydrogen is supplied. To address the clean powergeneration system, Hwang et al. [3] proposed a solar/fuelcell hybrid power system to meet the daily load demandof a typical family in Taiwan, Uzunoglu et al. [4] inves-tigated dynamic models and simulation of this kind ofhybrid power generation systems with appropriate controlstrategies, and Zervas et al. [5] provided an optimal decisionframework for managing the hybrid energy systems.Similarly, these hybrid systems all involve the water

td. This is an Open Access article distributed under the terms of the Creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, andiginal work is properly credited. The Creative Commons Public Domaing/publicdomain/zero/1.0/) applies to the data made available in this article,

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Wu et al. Sustainable Chemical Processes 2014, 2:5 of 12http://www.sustainablechemicalprocesses.com/content/2/1/5

electrolyzer for producing hydrogen. The electrolyzer issimpler and does not require complex units, but there isno solution to reduce its large electricity consumption.For most of hybrid systems, the PV panel is larger so as tocarry out water electrolysis by using the excess power.Therefore, the overall energy efficiency is quite low [6].The hydrogen fuel cells have been considered the most

promising for automotive application, but the guidelinesfor the hydrogen storage, safer operation and transporta-tion are quite rigorous [7]. The fossil fuel processing unitcould produce the high purity of hydrogen [8,9], but theexternal energy supply and large carbon emissions are notavoided. If biomass can replace fossil fuels as the feedstock,the net-zero greenhouse gas (GHG) emissions of hydrogenproduction systems can be achieved. Liquefied ethanol is apopular feedstock because it is easily made by fermentation,no compressed storage is needed, and lower operatingtemperatures are required for reforming processes [10,11].In this paper, an ethanol fueled HPG system is proposed.

The modeling, optimization and design of the EtOH-to-H2

processor is achieved by using Aspen Plus. The scenarioanalysis of the HPG system in regard to the daily loaddemand of a typical family in Taiwan [3] is investigatedin Matlab. Since the EFC power unit cannot rapidly meetthe load demand due to complicated chemical reactions inthe ethanol reforming process, the lithium-ion battery isconsidered to meet the power gap when the excess powerfrom PEMFC and PV units have been completely storedin the battery in advance. According to prescribed hybridpower dispatch, it is verified that the energy efficiencyof the proposed HPG system is superior to the otherrenewable hybrid energy system.

Hybrid power generation systemThe ethanol-fueled HPG system is shown in Figure 1.Both PV generator and PEMFC stack are treated as powersources. The lithium-ion battery is denoted as an electricity

Figure 1 Hybrid power generation system.

storage/instant supply device. The stand-alone EtOH-to-H2

processor in place of the devices of the hydrogen stor-age tank and water electrolyzer aims to produce highpurity hydrogen. Other devices, including converters/inverters and power management (DC bus), are used tomeet the voltage specification.

EtOH-to-H2 processorThe EtOH-to-H2 processor shown in Figure 2 is consid-ered as a stand-alone hydrogen production system,which is composed of an ethanol steam reforming (ESR)reactor, a low-temperature water-gas-shift (LTWGS) re-actor, the pressure swing adsorption (PSA) unit, and aburner. The simple heat integration is adopted to im-prove the water heat recovery; (i) the waste heat gener-ated from the burner is applied to preheat the mixingfeed flow using a heat exchanger (HEX1) and then meetsthe heat demand of the reforming reactions in the ESRreactor; (ii) the inlet water flow is preheated by a heatexchanger (HEX2) to increase the feed temperature; (iii)the temperature of flue gas discharged from the heatingjacket of the ESR reactor is expected to be low.

ESR reactorAccording to the kinetic experiments for the ethanolsteam reforming reactions over Co3O4-ZnO catalyst atatmospheric pressure and temperature in the 600-800 Krange [12], first the reactions of ESR are shown as:

C2H5OH→CH3CHO þH2 r1ð Þ;ΔH01 ¼ 71 kJmol−1 ð1Þ

C2H5OH→COþ CH4 þH2 r2ð Þ;ΔH02 ¼ 52:9 kJmol−1 ð2Þ

COþH2O↔CO2 þH2 r3ð Þ;ΔH03 ¼ −34:5 kJmol−1 ð3Þ

CH3CHOþ 3H2O→2CO2 þ 5H2 r4ð Þ;ΔH04 ¼ 127:4 kJmol−1

ð4Þ

Figure 2 Stand-alone EtOH-to-H2 processor.


Second, the kinetic models of four reactions (r1, …, r4)are expressed by power-law rate expressions [12]:

r1 ¼ 2:1� 104 exp −70R

1TESR

−1

773

� �� PC2H5OH ð5Þ

r2 ¼ 2:0� 103 exp −130R

1TESR

−1773

� �� PC2H5OH ð6Þ

r3 ¼ 1:9� 104 exp −70R

1TESR

−1

773

� ��

� PCOPH2O−PC2OPH2

exp 4577:8TESR

−4:33� �

0@

1A

ð7Þ

r4 ¼ 2:0� 105 exp −98R

1TESR

−1

773

� �� PCH3CHOP

3H2O

� �

ð8Þ

where TESR is the temperature of the ESR reactor, Pi

(i = C2H5OH, CO, H2O, …) is corresponding partialpressure, and R is the universal gas constant. Moreover,the one-dimensional, pseudo-homogeneous model is builtby the Aspen Plus. The assumptions for the steady-statesimulation of the ESR reactor include gas phase reactions,plug-flow reactor, and no pressure drop. The thermo-dynamic properties of some species are evaluated byusing the Peng-Robinson equation of state. Other parame-ters include the fluid density = 0.02 kmol m-3, catalystweight = 5 kg, and sizes of the reactor with the diameterand length of the reactor D = 0.5 m and L = 1.5 m.

LTWGS reactorTo reduce CO as well as enhance hydrogen yield, theLTWGS reactor could be directly connected to the ESRreactor, where the reaction scheme is:

COþH2O↔Cat CO2 þ 2H2; ΔH o

R ¼ −41:15 kJmol−1

ð9Þ

For a moderately exothermic reaction with Sud-Chemiecommercial available catalysts, we assume that the reactoris adiabatic and the operating temperature is between400 K and 600 K. Moreover, the kinetic model is describedby [13],

rW ¼ 82:2 exp −47400RTWGS

� �PCOPH2O−

PCO2PH2

KWGS

� �

ð10Þ

where TWGS is the temperature of the WGS reactor andKWGS is the equilibrium constant of the WGS reactionshown by

ln KWGSð Þ ¼ 5693:5TWGS

þ 1:077 ln TWGSð Þ þ 5:44� 10−4TWGS

−1:125� 10−7T2WGS−

49170

T2WGS

−13:148

ð11Þ

BurnerRegarding the design of burner, we assume that (i) H2 iscompletely separated by PSA, (ii) all components of theburner are completely burned, and (iii) its Aspen module


is considered as an adiabatic and stoichiometric reactor.The combustion reaction in the burner is shown asfollows:

C2H5OH þ 3O2→2CO2 þ 3H2O;ΔH ob;EtOH ¼ −1279 kJmol−1

ð12ÞCH4 þ 2O2→CO2 þ 2H2O;ΔH o

b;CH4¼ −803:1 kJmol−1 ð13Þ

H2 þ 12O2→H2O;ΔH o

b;H2¼ −242 kJmol−1 ð14Þ

COþ 12O2→CO2;ΔH

ob;CO ¼ −283 kJmol−1 ð15Þ

Sensitivity analysisRegarding the effect of fuel utilization, the ratio of hydrogento ethanol (H2/C2H5OH) is specified by adjusting ethanolflow or water flow in the feed.

I. The profiles of H2/C2H5OH vs. S=Cð ÞjH2O atdifferent TESR,in is depicted in Figure 3(a). It showsthat the maximum hydrogen yield can be achievedby adjusting the water flow at constant ethanol flow.The profiles of H2/C2H5OH vs. (S/C)|EtOH atdifferent TESR,in is depicted in Figure 3(b). Similarly,it shows that the maximum hydrogen yield isobtained by adjusting the ethanol flow at constantwater flow. The corresponding operating ranges arebounded by 2≤ S=Cð ÞjEtOH;H2O≤2:5 and 600K ≤TESR,in ≤ 800K. Notably, the manipulation of ethanolflow can ensure the larger hydrogen yield than thewater flow at the same TESR,in, and the increase ofTESR,in cannot induce the high hydrogen yield.According the heat recovery design, the waste gastemperature at the outlet of heating jacket decreaseswhen the preheated temperature of ESR increases.The low reactor temperature would reduce theconversion of ethanol reforming reactions.

II. According to the sensitivity analysis by adjusting onevariable (S/C)|EtOH, the optimization tool of AspenPlus is employed to determine the optimal operatingconditions, S=Cð ÞjEtOH ¼ 27:2 kgmol=hr

12:7 kgmol=hr = 2.14 atTESR,in =600 K. The steady-state simulation of thesystem at optimal conditions is shown in Figure 4,where the flowrate of hydrogen product can achieve55.62 kgmol/hr, i.e. H2/C2H5OH =4.38 and theethanol conversion can achieve 95%.

PEM fuel cell systemA Ballard 5 kW PEMFC stack system consists of 30 cellsconnected in series to provide output current up to 100A, which is directly connected to an ethanol-to-hydrogenprocessor. The high purity of hydrogen produced fromthe processor is fed to the anode and the excess hydrogen

needs to be recirculated. Referring to an empirical fuel cellstack model by [14,15], the output voltage of a single fuelcell (Vfc) is expressed by

V fc ¼ E −Vact −Vohm ð16Þ

(i) The open circuit cell potential E via the Nernstequation is described by

E ¼ 1:229− 8:5� 10−4 Tfc − 298:15� �þ RTfc

2Fln PH2 PO2ð Þ0:5h i

ð17Þ

(ii) The activation overvoltage Vact is described by afirst-order dynamic with the effects of double layercapacitance charging at the electrode-electrolyteinterfaces

dVact

dt¼ ifc

Cdlþ ifcEact

V actCdlð18Þ

where the activation drop Eact is defined by

Eact ¼ β1 þ β2Tfc þ β3Tfc ln CO2ð Þ þ β4Tfc ln icð Þ ð19Þ

and the parametric coefficients β1,…, β4 are expressed by

β1 ¼ −0:948

β2 ¼ 0:00286þ 0:0002 ln Afc� �þ 4:3� 10−5 ln CH2ð Þ

β3 ¼ 7:6� 10−5

β4 ¼ −1:93� 10−4

ð20Þ

and

CO2 ¼ 1:97� 10−7PO2 exp498Tfc

� �

CH2 ¼ 9:174� 10−7PH2 exp−77Tfc

� � ð21Þ

(iii) The ohmic overvoltage is given by:

Vohm ¼ lmAfc

rMifc ð22Þ

where the membrane resistivity rM is described by

rM ¼181:6 1þ 0:03 ifc

Afc

� �þ 0:062 Tfc

303

� �2 ifcAfc

� �2:5�

11:866−3 ifcAfc

� �h iexp 4:18 Tfc−303

Tfc

� �h ið23Þ

Figure 4 Optimization and simulation of EtOH-to-hydrogen processor.

Figure 3 Fuel utilization ratio of ethanol-to hydrogen processor at different TESR,in by adjusting (a) (S/C)| H2O (b) (S/C)|EtOH.


Table 1 PEMFC Parameters

Parameter Value

Van 0.005 m3

kan 0.065 mol s− 1atm− 1

PBPR 1 atm

Vca 0.01 m3

kca 0.065 mol s− 1atm− 1

F 96485 Cmol-1

Afc 232 cm2

lm 178 × 10− 4 cm

R 8.314 Jmol− 1K− 1

Cdl 0.035 × 232 F

λO2 2


Above of all parameters for modeling the PEMFCsystem have been defined in the nomenclature section.Based on the ideal gas law and the principle of moleconservation, the partial pressures of hydrogen ( pH2

)and oxygen (pO2

) associated with reactant flow rates atthe anode and cathode along with the cell current aremodeled as.

dpH2

dt¼ RTfc

V an_mH2;in − kan pH2

− pH2;in

� �−15Fifc

� ð24Þ

dpO2

dt¼ RTfc

V ca_mO2;in − kca pO2

− pBPR� �

−7:5F

ifc

� ð25Þ

Notably, two pressure regulators with fixed parameters(kan, kca) are added to manipulate the outlet hydrogen

Figure 5 PEMFC power versus current at different Tfc.

flow at the anode and the outlet oxygen flow at thecathode. The above model equations show that the fuelcell performance is affected by current density (ifc), fuel celltemperature (Tfc), hydrogen and oxygen partial pressure.Referring parameter values of the fuel cell model in Table 1,Figure 5 shows that the maximum cell power outputappears when the current is operated around 250A andthe cell temperature is fixed at Tfc = 75°C. Moreover, thevoltage and power of the stack is given by Vstack = 30Vfc;Pfc =VstackifcAfc.Remark 1: To address the feasible manipulation of

the fuel cell stack, two pressure regulators for manipu-lating the outlet flow rates of hydrogen and oxygen atthe anode and cathode, respectively, are required. Inaddition, the oxygen starvation phenomenon should beavoided, i.e., the following inequality for oxygen excessratio (λO2 ),

_mO2;in

8:75ifc=F≥ λO2 ð26Þ

should be satisfied by increasing the inlet flow rate ofoxygen ( _mO2;in) or air flow [15].Remark 2: The stack requires a circulating water sys-

tem to keep the relative humidity of membrane as wellas regulate the stack temperature. It is assumed that thestack system is isothermal, the relative humidity is keptat a desired level, and the hydrogen flow in the inlet offuel cell ( _mH2;in ). In fact, the fuel processing delays, in-cluding reaction time and transportation delay existsuch that the power gap between supply and demand isinevitable.

Table 2 PV Parameters

Symbol Value

T0 298 K

TNOTC 316 K

E0 1000 W m− 2

κ 1.3854 × 10− 23 J K− 1

Eg 1.12 eV

p1 2.96 Am2W− 1

p2 − 8.6 × 10− 4 m2W− 1

p3 0.0037 K− 1

p4 1272.3 AK− 3

Rs 1.29 Ω

Rsh 154.1 Ω


Photovoltaic generatorA photovoltaic (PV) generator is composed of numbers ofsolar cells connected in series and parallel to provide thedesired output terminal voltage and current. Using theKirchoff ’s current law the terminal current Is through thesolar cell is expressed by [3].

Is ¼ Iph − Id − Ish ð27Þ

Figure 6 PV power versus voltage (a) at different Es while Tj = 25°C: (b

(i) The photocurrent Iph is described as

Iph ¼ p1Es 1þ p2 Es−E0ð Þ þ p3 Tj−T 0� � � ð28Þ

(ii) The diode loss current Id is described as

Id ¼ p4T3j exp −

Eg

κTj

� �exp

e0af Nsκ

V s þ RsIsT j

� �−1

�

ð29Þ(iii) The shunt current Ish is shown by

Ish ¼ V s þ RsIsRsh

ð30Þ

where the cell junction temperature Tj is expressed by

Tj ¼ Ta þ Es

800TNCOT−20ð Þ ð31Þ

where P1, P2, and P3 are empirical constants. E0 andT0 are reference solar radiation and reference junctiontemperature, respectively. The P4 is an empirical constant,af is the ideality factor of the PV array, Eg is the gap en-ergy voltage of silicon, κ is Boltzmann’s constant, Vs is

) at different Ta while Es = 350 Wm− 2.


the terminal voltage, Ns and Rs are the number of cells inseries and series resistance, and Rsh is the parallel resist-ance. All the above parameter values for the PV system areshown in Table 2. Figure 6 shows that the maximum poweroutput of the PV system exists at different Ta and Es.

Auxiliary devicesThe auxiliary devices shown in Figure 1 include a lithium-ion battery which is considered as a high-capacity energystorage to compensate the power gap and share the loaddemand and several he boost DC/DC converters are usedto boost the DC voltage of the units of PV, PEMFC andbattery. The dynamic responses of battery are faster thanother units in the hybrid power system, in our approachthe modeling of battery is omitted and the well-definedcharging/discharging mechanism is considered [16,17].The DC/AC pulse-width modulation (PWM) is used tomeet the specification of the household electricity, wherethe dynamics with regard to AC voltage and current wave-form are shown in Figure 7 using the SimPowerSystems™toolbox in Matlab.

Scenario analysisFor the proposed HPG system, the solar irradiance, waterand ethanol are denoted as energy sources. Assumed thatthe weather variation is inevitable and the sources of waterand ethanol are reliable, the HPG system is considered as

Figure 7 DC/AC PWM inverter connected to DC/DC converter.

the optimal power generator since the optimized EFCpower generator according to optimal operating condi-tions in Figures 4 and 5 is specified and the maximumPV power in Figure 6 is achieved by using the maximumpower point tracking (MPPT) controller. Moreover, sce-nario analysis of the daily operation of the HPG systemis addressed as follows.

1. Hybrid power dispatch: Figure 8(a) shows that thePV and PEMFC systems are dispatched to preciselymeet the daily household load demand [3]. In ourdesign, the daily PV power distribution shown inFigure 8(b) is fixed according to prescribed patternsof solar irradiance. A scenario shows that both PVand PEMFC are integrated to instantly cope withthe peak power. Especially, the EFC power shoulddominate the main electricity supply during the dayand night.

2. Power gap compensation: If the EtOH-to-H2 processorcannot produce pure hydrogen immediately due toslow reactions, then the EFC power decay at thismoment. It is caused by the fuel processing delay suchthat the power demand gap (desired Pfc-actual Pfc)shown in Figure 8(b) appears. Assumed that the rapidresponse of Li-ion battery can instantly compensatethe power demand gap and the battery charging fromPV and EFC units is always larger than the battery

Figure 8 The daily operation of HPG system without use of battery: (a) Power profiles from PFC and PPV; (b) Responses of EFC power generator.


discharging, Figure 9(a) and 9(b) show that the HPGsystem can precisely meet the daily load demand. Inthis perfect scenario, the hybrid power dispatchingshown in Figure 9(a) is confirmed where the batterycontribution (green area) aims to compensate thepower demand gap during each time period. Figure 9(b) shows that the battery is recharged by the excesspower from PV and PEMFC during day and night.

Regarding hybrid power dispatching problem, the PVunit (blue bars) provides 34.5% total power, the battery(green bars) is 12.4% and the EFC (red bars) is about53.1%. Notably, the battery is charged from the EFC isabout 56.1% and 43.9% from the PV. It implies that thePV power is used to save 39.9% fuel consumption.

System efficiencyThe efficiency of the power generation system is usuallyaffected by the electric power, mechanical energy andheat. To ignore the effects of mechanical energy andheat, the efficiency of the HPG system is investigatedas follows.

A. Photovoltaic efficiencyAccording to the formulation of solar cell efficiencylimits [18], the PV efficiency is described as

ηmax ¼Pmax

EsAsð32Þ

where ηmax is the maximum efficiency of the PV system,Pmax is the maximum PV power, and As is the surfacearea of the solar panel.B. EFC efficiency

Referring the experimental data for ethanolreforming processes [19,20], the energy efficiency ofEtOH-to-H2 processor is defined as

ηESR ¼ _mH2;inHHVH2

_mEtOH ;inHHVEtOH þ _mH2O;inHHVH2Oð33Þ

and the energy efficiency of fuel cell is described as

ηfc ¼Pfc

_mH2;inHHVH2

ð34Þ

where HHVi represent the high heating value of speciesi. _mEtOH ;in and _mH2O;in represent the inlet flow rate of

Figure 9 HPG system according to daily power demand: (a) Hybrid power dispatch; (b) Recharge power for battery.


ethanol and water, respectively. Moreover, the efficiencyof the EFC is expressed by ηefc = ηesrηfc. Figure 10 showsthat the energy efficiency of the EFC unit is increasingif the load demand increases, but the energy efficiencyof the FC unit without the use of EtOH-to-H2 processordecreases if the load demand is larger than 5 kW. It isverified that the EFC design can ensure higher energyefficiency than the conventional hydrogen fueled fuelcell system.C. According to above efficiency of each unit, the

(overall) system efficiency of HPG system isexpressed as

ηoverall ¼PPV þ Pfc þ Pbattery� �

ηconverterηinverterPPV=ηmax þ Pfc=ηefc þ Pbattery=ηbattery

ð35Þ

where ηbattery, ηconverter and ηinverter are efficiencies ofLi-ion battery, DC/DC converter and DC/AC inverter,respectively. The battery power Pbattery is evaluated byPd − Pefc − PPV where Pd is set as the load. Referringthe initial efficiency of Li-ion battery [21], we assumeηbattery for a new battery. Referring to references [22,23],we assume ηconverter =0.9 and ηinverter = 0.98. Referringthe hybrid power dispatching in Figure 9(a), the hy-brid system efficiency by Eq. (35) is shown in Figure 11.Based on the hybrid power system using parallel andseries connections, the system efficiency is around11% during the day, but it reaches over 60% duringthe night. Obviously, the PV system induces lowersystem efficiency and it can be significantly improvedby using the integrated reformer/fuel cell system andbattery.

Figure 10 Energy efficiencies for EFC and PEMFC.


ConclusionsAn optimized fuel processing unit using ethanol fuel canproduce high-purity hydrogen. The simulation shows thatthe stand-alone EtOH-to-H2 processor not only guaranteehigher energy efficiency, but also it can continuouslyproduce hydrogen if the fuel is enough. According toscenarios for the daily operation of the HPG system, theEFC power dominates the power supply during the night,the PV system dominates the power supply during the dayand the backup battery aims to instantly compensate thepower gap and store the excess power from PV or EFC.According to the hybrid power dispatch, the distributionof the HPG system efficiency is specified.

Nomenclature

af, ideality factorAfc, effective fuel cell area, cm

2

As, surface area of the solar panel, m2

CO2 , oxygen concentration at the cathode/membraneinterface, molm-3

η

Figure 11 HPG system efficiency.

CH2 , hydrogen concentration at the anode/membraneinterface, molm-3

Cdl, Double layer capacitance, FE0, Reference solar radiation, W m− 2

Eg, Gap energy voltage for silicon, eVEs, solar radiation, Wm-2

i, current density, Acm-2

Is, terminal current of PV cell, Akan, kca, flow constant of anode and cathode, mol s− 1atm− 1

lm, Membrane thickness, cmcp, specific heat capacity, J K− 1kg− 1

Pi, partial pressure of i component, atmPBPR, back pressure, atmP, cell power, WTa, ambient temperature, KT0, reference junction temperature, KTNCOT, normal cell operating temperature, KRs, series resistance, ΩRsh, parallel resistance, Ωu, superficial velocity, m s− 1

Vs, terminal voltage of PV cell, V


Competing interestsThe authors declare no competing financial interests.

Authors’ contributionsThe energy efficiency of the ethanol-fueled fuel cell (EFC) is higher than thehydrogen-fueled fuel cell system. With the aid of the stand-alone EtOH-to-H2processor and backup battery. The HPG system efficiency according tohybrid power dispatch is improved. All authors read and approved the finalmanuscript.

AcknowledgmentThe authors would like to thank the National Science Council of the Republicof China for financially supporting this research under Contract No. NSC100-2211-E-006-264.

Author details1Department of Chemical Engineering, National Cheng Kung University,Tainan 70101, Taiwan. 2National Yunlin University of Science and Technology,Douliou, Yunlin 64002, Taiwan.

Received: 27 November 2013 Accepted: 14 February 2014Published: 4 March 2014

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doi:10.1186/2043-7129-2-5Cite this article as: Wu et al.: Scenario analysis of a bioethanol fueledhybrid power generation system. Sustainable Chemical Processes 2014 2:5.

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