Economic feasibility analysis of a solar energy and solid oxide fuelcell-based cogeneration system in Malaysia

R. K. Akikur1,4 • R. Saidur2 • K. R. Ullah1 • S. A. Hajimolana3 •

H. W. Ping1 • M. A. Hussain3

Received: 11 July 2015 / Accepted: 5 October 2015

� Springer-Verlag Berlin Heidelberg 2015

Abstract The current study presents a concept of a

cogeneration system integrated with solar energy and solid

oxide fuel cell technology to supply electrical and thermal

energy in Malaysia. To appraise the performance, the

system is analysed with two case studies considering three

modes of operation. For the case-1, typical per day average

electricity and hot water demand for a single family have

been considered to be 10.3 kWh and 235 l, respectively.

For the case 2, electricity and hot water demand are con-

sidered for the 100 family members. Energy cost, payback

period, future economic feasibility and the environmental

impact of the system are analysed for both cases using an

analytical approach. The overall system along with indi-

vidual component efficiency has been evaluated, and the

maximum efficiency of the overall system is found to be

48.64 % at the fuel cell operation mode. In the present

study, the proposed system shows 42.4 % cost effective-

ness at higher load. Energy costs for case-1 and case-2 have

been found to be approximately $0.158 and $0.091 kWh-1,

respectively, at present. Energy costs are expected to be

$0.112 and $0.045 kWh-1 for the case-1 and case-2,

respectively, considering future (i.e. for the year 2020)

component cost.

Keywords Cogeneration � Solid oxide fuel cell � Solarenergy � Economic analysis � Efficiency � Malaysia

List of symbols

a Anode

Ac Area of the receiver cover (m2)

Ar Area of the receiver (m2)

Bg Flow permeability

c Cathode

Cp Specific heat (kJ kg-1 K-1)

da Anode thickness (lm)

dc Cathode thickness (lm)

D Diameter (m)

Deff Effective diffusion coefficient

E0 Standard potential

F Faraday’s constant (C mol)

h Specific enthalpy (kJ kg-1)

hc,ca Convection heat coefficient (kW m-2 K-1)

hr,ca Radiation heat coefficient (kW m-2 K-1

I Current (A)

J Current density (A m-2)

Jo,i Exchange current density (A m-2)

L Electrolyte thickness (lm)

Lc Collector’s length (m)

Nus Nusselt number_N Flow rate (kg s-1)

P Pressure (bar)

P0 Partial pressure (bar)

Q Heat rate (kW)

R Universal gas constant (J mol-1 K-1)

& R. Saidur

saidur@kfupm.edu.sa; saidur912@yahoo.com

1 UM Power Energy Dedicated Advanced Centre

(UMPEDAC), Level 4, Wisma R&D UM, University of

Malaya, 59990 Kuala Lumpur, Malaysia

2 Centre of Research Excellence in Renewable Energy (CoRE-

RE), King Fahd University of Petroleum and Minerals

(KFUPM), Dhahran 31261, Saudi Arabia

3 Department of Chemical Engineering, Faculty of

Engineering, University of Malaya, 50603 Kuala Lumpur,

Malaysia

4 Solar Energy Technologies, School of Computing,

Engineering and Mathematics, Western Sydney University,

Penrith South, NSW 2751, Australia

123

Clean Techn Environ Policy

DOI 10.1007/s10098-015-1050-6

Rs Series resistance

S Solar radiation (W m-2)

T Temperature (�C or K)

V Voltage (V)

w Collector width (m)_W Power (kW)

Greek letters

r Stefan–Boltzmann constant (kW m-2 K-4)

q Density (kg m-3)

l Dynamic viscosity of oxygen

ri Irreversibility loss

a Temperature coefficient

b Temperature coefficient

g Efficiency

Acronyms

HEX Heat exchanger

mp Maximum power

OC Open-circuit voltage

PTSC Parabolic trough solar collectors

ref Reference

RSOFC Reversible solid oxide fuel cell

SOSE Solid oxide steam electrolyser

SOFC Solid oxide fuel cell

SC Short circuit

Introduction

The power generation sector of Malaysia has rapidly grown

along with the industrial and manufacturing sectors. Elec-

tricity generation in Malaysia mainly depends on fossil fuel

and nuclear power. With the current usage rate, it is esti-

mated that oil and gas reserve will be exhausted by 2030.

As a result, the government has devoted a great deal of

attention to the renewable-based sustainable energy as an

alternative power source. Due to its geographical disposi-

tion, hydroelectric and solar energy have higher potential

in Malaysia. Because of the average daily solar irradiance

of 5.5 kW m-2, solar energy has been used as a stand-

alone or in hybrid systems to electrify the nation, while

reducing the use of fossil fuel (Hossain et al. 2015; Shezan

et al. 2015; Solangi et al. 2011).

Over the recent years, many studies have been con-

ducted on renewable-based systems and policies to tackle

the future energy demand and global warming (Chen and

Hong 2015; Cucchiella and D’Adamo 2015; Cucchiella

et al. 2015; Duic 2015; Ingwersen et al. 2014; Mohammad

Rozali et al. 2015; Vance et al. 2015). Although solar

energy and fuel cell have been getting substantial attention

to improve the applicability, only very few studies have

been conducted concerning the integration of solar energy

and reversible solid oxide fuel cells (RSOFC) in a cogen-

eration system. A novel cogeneration system has recently

been developed by the present authors integrating solar

energy and SOFC in order to supply thermal and electrical

energy (Akikur et al. 2014). Besides, many studies on

system design and model-based fuel cell technology have

also been presented in the literature (Becker et al. 2012;

Chen and Ni 2014; Lamas et al. 2013; Naimaster and Sleiti

2013; Tanaka et al. 2014; Xu et al. 2012). Summary of

some of those studies has been provided as follows:

Chen and Ni (2014) presented a cogeneration/trigen-

eration system based on SOFC in Hong Kong for load

supply in a hotel. An economic analysis of the system was

also conducted. The system was designed for supplying

1000 kW electrical power. Those authors reported that the

system could also provide 630 kW of cooling and

191.03 kW of water heating loads utilizing 1936 kW of

input fuel. They reported overall efficiency of 84.02 % for

the cogeneration system. Moreover, they stated that the

system’s payback period would be 5 years if the gov-

ernment provides 50 % subsidy for the total system’s cost.

Tanaka et al. (2014) proposed a SOFC-based cogeneration

system for an electric vehicle’s charging facility. A mul-

tifamily apartment’s electrical and thermal loads were

considered for the proposed system’s performance analy-

sis. A 16 kW of SOFC was considered based on required

energy demand. The system supplied thermal energy of

minimum 4 kW to maximum 12 kW. It also found that

the proposed system’s overall efficiency reached approx-

imately 77 %, and throughout the year, the primary

energy saving rate exceeded by 30 %. Naimaster and

Sleiti (2013) presented a medium-level economical

SOFC-based combined heat and power (CHP) system for

an office building in three different locations in the United

States. The SOFC of 175 kW was used and found up to

14 % less annual utility cost compared to the baseline

high-voltage AC system. In addition, the said system

reduced up to 62 % CO2 emissions compared with the

conventional system. They also predicted that the pro-

posed system would be more cost competitive compared

with the conventional system in near future when the cost

of SOFC becomes reduced. Lamas et al. (2013) proposed

a residential cogeneration system and analysed different

operating combinations (i.e. H2, natural gas and conven-

tional grid system) of fuel fed to the SOFC. For the

system analysis, 0.7 kW of SOFC, 0.20 m3 of hot water

tank and 43.2 kW of auxiliary water boiler were consid-

ered. It was found that the proposed system reduced the

primary energy consumptions by 23.9, 25.2 and 28.6 % in

the summer, shoulder and winter seasons, respectively,

compared to the conventional system. Moreover, the

system covered 99.4 % of residential energy requirements

using only hydrogen and natural gas as a fuel. They also

R. K. Akikur et al.

123

revealed that if the hydrogen could be produced from

renewable sources, about 42.3 % of primary energy

reduction would be possible compared to the natural gas-

fuelled SOFC system. Becker et al. (2012) carried out a

study on 1 MW of SOFC in a polygeneration system for

combined production of heat, power and hydrogen. The

SOFC was used for the cogeneration system, and then

hydrogen was separated for further application using a gas

stream. The overall efficiency of the system was 85.2 %,

where the electrical efficiency of the SOFC was 48.8 %.

Xu et al. (2012) developed a conceptual design and a

mathematical of a natural gas-fuelled cogeneration sys-

tem. The SOFC was designed for generating 1 kW of

energy, and it was found that the system can supply

1.005 kW of electrical power and 0.521 kW of thermal

energy with the electrical and combined efficiencies of

52.1 and 79.2 %, respectively.

Moreover, the United States and the members of the

European Union have started applying fuel cell-based

system successfully for residential applications. In Asia,

over the last decade, Japan has installed many residential

fuel cell systems (Mahlia and Chan 2011). However, new

renewable-based system analysis in a specific geographical

condition is needed while considering solar energy and

SOFC system to make it practically more feasible.

A cogeneration system was presented by the present

authors in previous study (Akikur et al. 2014), where it was

focused on the system modelling and development. Costs

of renewable energy system and SOFC vary geographically

due to climatic conditions and local electricity tariff.

Consequently, it is essential to carry out a study in terms of

economic as well as environmental impact analysis of the

system under a particular weather condition. In addition, an

uncertainty analysis of the system to increase the stability

of the system was carried out. However, the hybrid SOFC

and solar PV-based cogeneration system has not been

implemented in Malaysia and many other parts of the

world to produce the thermal and electrical energy. Hence,

the focuses of this article are to present the performance

analysis of a cogeneration system considering the solar

radiation data and typical household energy demands in

Malaysia. An economic as well as environmental feasi-

bility study to illustrate the auspiciousness of solar energy

and SOFC coupling in a cogeneration system was also

carried out.

Methodology

Conceptual design considerations and survey data

The average solar radiation data for Kuala Lumpur in 2009

are presented in Table 1. The maximum average radiation

was found in April, May and June, and the lowest was in

November and December.

The residential electrical energy consumption depends

on the number of family members or house dimensions.

The average expenditure per month for a small family or a

small house is considered approximately $19.88 (1

USD = 3.27 MYR), for a medium house $33.64 and for a

bungalow $107 (Mahlia and Chan 2011). The case study of

the proposed cogeneration system has been carried out

considering a typical house with six occupants and 100

similar family members in Malaysia. On average, about

4387 kWh of electrical energy is needed per year for a

family, and the family has to pay $367 per year according

to the electricity tariff of the Malaysian government

(Mahlia and Chan 2011). The hourly average electrical

energy demand is illustrated in Table 2, where the survey

data were taken from the literature (Mahlia and Chan

2011). On the other hand, the average hot water demand for

the same size family is considered 20,520 l month-1

(20.52 m3). The hot water temperature depends on the

weather, air, water receiver and ground temperature. The

ground temperature and the average hourly hot water

consumed for a typical household in Malaysia are pre-

sented in Table 3 and Fig. 1, respectively.

Cogeneration system model

The main energy sources of the proposed cogeneration

system comprised a parabolic trough solar collector

(PTSC), solar photovoltaic (PV) and reversible SOFC

(RSOFC) as shown in Fig. 2. The energy input of the solar

energy-based cogeneration system varies with the time and

weather. As a consequence, for a continuous operation of a

solar-based system, another auxiliary system is required. In

this study, the hydrogen is produced and stored using solar

energy for steam electrolysis during the day time to ensure

a continuous power supply at night. The operating modes

of the system considering H2 storage, RSOFC and hybrid

solar energy are described next.

System description

The system can be operated in three modes. (1) The solar–

solid oxide fuel cell (SOFC) mode or solar–SOFC mode,

which is for lower solar radiation time when the solar PV

and SOFC are used for electrical and thermal load supply;

(2) The solar–solid oxide steam electrolyser (SOSE) mode

or solar–SOSE mode, which is for higher solar radiation

time when PV is used for power supply to the electrical

load and to the steam electrolyser to generate hydrogen

(H2); and (3) The SOFC mode, which is for the power and

heat generation mode of RSOFC using the storage H2 at

night. Figure 3 shows the operational diagram of the

Economic feasibility analysis of a solar energy and solid oxide fuel cell-based…

123

cogeneration system, which is validated by the Ref. (Aki-

kur et al. 2014) and the system is described below

according to the operation mode.

Solar–SOSE mode

Water is supplied from the storage tank to the PTSC, where

the water absorbs heat energy provided by the PTSC and

then steam is heated by the heat exchanger-1 (HEX-1)

before being fed into the RSOFC. If the steam is heated to

700 �C or above, then it enters the cathode of the RSOFC,

or it passes through the preheater-1. In this mode, the

RSOFC works for steam electrolysis. The solar PV pro-

vides the required electricity to electrolyse the steam and

produce hydrogen and oxygen. The solar PV also provides

the electricity for electrical load in this mode. The pro-

duced H2 with unreacted steam and O2 pass through the

HEX-1 and release heat for the steam. Finally, heat ener-

gies (60–100 �C) are extracted from the H2 and H2O for the

heat load when it passes through HEX-3, which then finally

enter the hydrogen and water tanks, respectively.

SOFC mode

A SOFC system provides electricity for the load using the

storage hydrogen as a fuel during night and until sunrise.

Hydrogen from the tank is preheated by the preheater-2

initially, which then flows towards the anode of the SOFC.

Heat energy is provided by the SOFC to heat up the input

H2 at operating temperature. Air is provided to the cathode

through the preheater to raise the temperature. The pro-

duced electricity reaches the load, and steam passes

through the HEX-2 and releases the heat which is absorbed

by the input H2.

Solar–SOFC mode

This mode is operated after the sunrise, from early hours of

the day through a few hours before the sunset. The solar

energy collected by the PV modules is used for the load

supply, and the collectors are used for thermal energy

storage. An additional power for the load is delivered by

the SOFC. The operation of the SOFC has been described

Table 1 Hourly average solar radiation data in W m-2 of Malaysia for the year in 2009

Hour Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

1 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0

2 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0

3 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0

4 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0

5 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0

6 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.1 0.0 0.0

7 10.5 11.5 22.8 37.0 32.4 31.7 17.9 26.6 34.0 42.9 42.2 27.0

8 124.3 121.4 166.0 213.1 178.8 159.9 113.4 166.1 178.5 170.8 199.4 157.2

9 315.1 292.3 348.0 431.4 379.2 334.8 277.2 339.3 335.6 343.8 361.2 353.5

10 516.2 452.8 528.7 597.2 546.5 469.3 432.0 467.7 496.6 546.0 517.4 513.9

11 654.7 652.4 614.0 681.8 657.7 593.5 562.6 583.3 573.0 664.1 564.4 609.7

12 745.8 740.8 655.1 716.6 702.7 698.3 634.1 637.7 666.0 713.1 550.5 637.4

13 695.3 677.1 647.6 646.4 685.5 711.4 653.6 662.9 676.8 704.4 518.1 605.8

14 633.8 571.1 613.1 572.0 665.1 673.7 670.6 627.2 644.0 647.5 431.9 456.8

15 452.6 510.4 439.7 472.1 585.0 537.0 555.1 590.7 536.9 522.8 365.5 389.6

16 346.4 381.9 322.2 370.6 436.3 422.7 439.7 416.1 385.1 337.9 213.1 285.1

17 245.0 239.8 231.7 236.9 266.5 250.7 254.9 243.6 219.3 184.9 102.6 153.6

18 81.6 80.8 91.6 77.9 84.1 74.7 89.4 82.2 60.3 47.4 24.9 39.9

19 2.8 3.2 3.5 1.9 1.3 2.0 4.0 3.4 0.3 0.0 0.0 0.0

20 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0

21 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0

22 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0

23 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0

24 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0

Monthly total 4824.01 4735.42 4684.05 5054.91 5221.24 4959.81 4704.75 4846.86 4806.11 4925.63 3891.02 4229.39

R. K. Akikur et al.

123

in the SOFC mode section. For the thermal load, PTSC

provides heat energy in this mode of operation, and the

heat is stored in the thermal storage tank.

Analytical description

An analytical description of hydrogen production and

power generation in both modes with the major

components of the system is presented in the following

(Akikur et al. 2014):

Hydrogen production

The total energy demand (DH) for the RSOFC in SOSE

mode can be expressed by Eq. (1).

DH ¼ DG þ TDS ð1Þ

where, TDS is the thermal energy in J mol-1 H2, and DG is

the electrical energy demand (free Gibson energy change),

and the electrical energy demand decreases with the

increasing thermal energy, but the total energy demand

does not change significantly.

The hydrogen production mainly depends on the exter-

nal DC current supply to the electrolyser. Hence, the total

electrical energy to the RSOFC in the hydrogen-production

mode is defined by the Eq. (2).

_WSOSE ¼ VSOSE ISOSE ð2Þ

where VSOSE is the output potential of RSOFC, and ISOSE is

the current density delivered by DC sources.

The total current delivered by the PV can be evaluated

by solving Eq. (3) and the Equations given in Table 4.

Table 2 Daily electrical energy

demands in kWh in a year

excluding water heating in

Malaysia (Mahlia and Chan

2011)

Hour Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

1 0.507 0.478 0.502 0.519 0.506 0.470 0.475 0.478 0.499 0.478 0.480 0.472

2 0.524 0.491 0.400 0.531 0.480 0.511 0.480 0.486 0.511 0.491 0.492 0.485

3 0.524 0.495 0.518 0.535 0.522 0.400 0.492 0.495 0.515 0.495 0.496 0.489

4 0.524 0.495 0.518 0.535 0.522 0.400 0.492 0.495 0.515 0.495 0.496 0.489

5 0.526 0.497 0.505 0.537 0.400 0.476 0.497 0.492 0.517 0.497 0.498 0.491

6 0.519 0.491 0.400 0.531 0.480 0.511 0.480 0.486 0.511 0.491 0.492 0.485

7 0.503 0.400 0.498 0.515 0.502 0.453 0.471 0.474 0.495 0.400 0.476 0.468

8 0.395 0.369 0.394 0.410 0.397 0.347 0.369 0.369 0.389 0.369 0.369 0.360

9 0.387 0.361 0.360 0.402 0.389 0.338 0.355 0.354 0.361 0.361 0.361 0.352

10 0.354 0.329 0.354 0.370 0.357 0.306 0.320 0.320 0.348 0.329 0.329 0.318

11 0.395 0.369 0.394 0.410 0.397 0.347 0.369 0.369 0.389 0.369 0.369 0.360

12 0.412 0.386 0.412 0.386 0.412 0.386 0.385 0.379 0.405 0.385 0.386 0.377

13 0.428 0.402 0.426 0.402 0.393 0.379 0.396 0.396 0.422 0.401 0.402 0.393

14 0.428 0.402 0.426 0.402 0.393 0.379 0.396 0.396 0.422 0.401 0.402 0.393

15 0.453 0.426 0.453 0.426 0.453 0.400 0.421 0.426 0.446 0.426 0.427 0.418

16 0.462 0.400 0.458 0.474 0.462 0.412 0.434 0.429 0.435 0.400 0.435 0.426

17 0.453 0.426 0.453 0.426 0.453 0.400 0.421 0.426 0.446 0.426 0.427 0.418

18 0.449 0.422 0.446 0.422 0.450 0.422 0.417 0.416 0.420 0.422 0.423 0.414

19 0.424 0.398 0.420 0.398 0.425 0.375 0.392 0.392 0.418 0.397 0.398 0.389

20 0.395 0.369 0.394 0.410 0.397 0.347 0.369 0.369 0.389 0.369 0.369 0.360

21 0.404 0.377 0.402 0.418 0.405 0.355 0.372 0.371 0.397 0.377 0.378 0.368

22 0.424 0.398 0.420 0.398 0.425 0.375 0.392 0.392 0.418 0.397 0.398 0.389

23 0.445 0.418 0.442 0.418 0.446 0.396 0.413 0.412 0.438 0.418 0.418 0.410

24 0.449 0.422 0.446 0.422 0.450 0.422 0.417 0.416 0.420 0.422 0.423 0.414

Table 3 Monthly average ground temperature in Malaysia

Month Ground temperature (�C)

January 26.1

February 27.0

March 27.2

April 27.1

May 27.0

June 26.5

July 26.1

August 26.3

September 26.7

October 26.9

November 26.6

December 26.0

Economic feasibility analysis of a solar energy and solid oxide fuel cell-based…

123

I ¼ ISC 1� C1 expV � DV

C2VOC

� �� 1

� �� �þ DI ð3Þ

In the hydrogen production mode, the output potential

VSOSE is the summation of the Nernst potential (E) and the

over potentials (given in Table 4) (Ni et al. 2007a).

VSOSE ¼ E þ gSOSEconc; i þ gohmic þ gact;i; i ¼ a; c ð4Þ

The outlet flow of H2 and O2 depend on the cell current

density (J) and can be calculated by Eq. (5).

_NH2;out ¼J

2F¼ _NH2O;utilized ð5Þ

_NO2;out ¼J

4Fð6Þ

The inlet water steam flow at the RSOFC is a known

parameter. Therefore, the outlet flow rate of H2O can be

determined using Eq. (7).

_NH2O;out ¼ _NH2O;in �J

2Fð7Þ

The heat energy supplied to the electrolyser for the H2O

steam electrolysis depends on the heat generation by the

irreversibility losses (Ni et al. 2007a). The over potentials

of SOSE responsible for direct generation of the heat can

be obtained using Eq. (8).

ri ¼ 2F gSOSEconc;i þ gohmic þ gact;i�

ð8Þ

when, ri � TDS, the external heat is not needed for the

water splitting reaction, thus Qheat;SOSE ¼ 0.

If, ri � TDS, the external heat is needed and the heat

input can be determined using Eq. (9).

Qheat;SOSE ¼ TDS � ri½ � _NH2O;utilized ð9Þ

The required heat input for the steam electrolysis is

stabilized at constant temperature by the heater. Since

steam from the PTSC varies with the solar radiation, the

heat exchanger-1 and the heaters are used to heat up the

steam at desired temperature.

The amount of heat energy provided by the PTSC is

determined by solving the Eq. (10) with the help of the

Equations given in Table 4.

_Qu ¼ Aap FR Sr;ar � Ar

Aap

� �UL Tr;i � T0

� �� �ð10Þ

Hydrogen storage The conventional tank under a pres-

sure of 30 bar can be a cost-effective way to store the

produced hydrogen. Electrolysers can produce pressure

without any additional hydrogen compressor. Hence, the

hydrogen produced at 30 bar from the solid oxide elec-

trolyser can be stored in a conventional hydrogen tank

(Kalinci et al. 2015; Zoulias and Lymberopoulos 2007).

Power generation

The output power in power generation mode can be

expressed using Eq. (11)

_WSOFC ¼ VSOFCISOFC ð11Þ

where ISOFC is the produced current which is related to the

amount of utilized hydrogen can be expressed by Eq. (12)

0

5

10

15

20

25

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

Ave

rage

hou

rly

use,

Litr

e Time

Fig. 1 Average hourly hot

water usage in a typical

household in Malaysia

Fig. 2 General concept of the proposed cogeneration system

R. K. Akikur et al.

123

ISOFC ¼ AJSOFC ¼ Að2 _NH2;utilizedFÞ ð12Þ

where, A (m2) is the cell’s active area.

The fuel utilization ratio can be calculated by using

Eq. (13) (Colpan 2009)

Uf ¼_NH2;utilized

_NH2;inlet

ð13Þ

where, the oxygen utilization is the half of hydrogen uti-

lization _NO2;utilized ¼ _NH2;utilized

� �2

The output voltage of a fuel cell depends on the polar-

ization losses and can be expressed using Eq. (14) (Ni et al.

2006, 2007b)

VSOFC ¼ E � gSOFCconc;i � gohmic � gact;i ð14Þ

where, the Nernst potential, Ohmic, activation and the

concentration overpotentials can be determined using

Equations given in Table 4.

From the Steady Flow Energy Equation, energy balance

Equation can be expressed by Eqs. (15) or (16). (Gardner

1997)

QinþWin¼QoutþWoutþDH ð15Þ

or

Qout � Qin ¼ DG � DHf c�DHref ð16Þ

where, DG and DHfc are the Gibbs energy and enthalpy of

fuel cell reaction, respectively (Gardner 1997).

The total heat output and the heat gain are reduced by

heat losses from the external preheater, fuel cell stack and

losses up to the heat exchanger. The usable heat output and

heat gain are then further reduced by the effectiveness of

the heat exchanger. Net usable heat gain from a complete

fuel cell system at SOFC mode can be evaluated by sub-

tracting the heat output from heat exchanger and the

external preheating heat input using Eq. (17)

Qusable;net ¼ Qfc;net þ QH2cr � Qloss

� �ehcx � Qep ð17Þ

where, Qfc;net, QH2cr and Qep are the net heat gain within fuel

cell stack, heat from combustion of recirculated hydrogen

and external preheating heat input, respectively. ehcx is the

heat exchanger effectiveness, Qloss is the heat loss by the

surrounding. If the system is well isolated then, Qloss ¼ 0.

The net heat gain within fuel cell stack can be expressed

by Eq. (18).

Qfc;net ¼ Qfcr þ Qrvl � Qarr ð18Þ

where, Qfcr, Qrvl and Qarr are the heat generated from fuel

cell reaction, the heat recovery from voltage loss and the

heat absorbed by reforming reaction, respectively. For the

hydrogen fuel as an input, no reformation is needed, thus

for this study Qarr ¼ 0.

System cost analysis

Energy cost

The economic analysis of the whole system has been car-

ried out to focus on the estimation of the unit cost ($/kWh)

of the produced energy. The annual total cost can be

Fig. 3 Operational diagram of

a solar- and SOFC-based

cogeneration system (Akikur

et al. 2014)

Economic feasibility analysis of a solar energy and solid oxide fuel cell-based…

123

calculated by the sum of investment cost as well as the

operation and maintenance cost (Ca&m) using Eq. (19)

(Akikur et al. 2014).

Cat ¼ Cai þ Co&om ð19Þ

The annual investment cost, Cai can be calculated from

the total purchasing cost, Cpc disregarding the individual

component replacement cost during its lifespan, n using

Eq. (20).

Table 4 Equations used to evaluate the parameters and analyse the proposed cogeneration system

Current delivered by the PV

Constant 1 C1 ¼ 1� Imp

ISC

� exp � Vmp

C2VOC

�

Constant 2C2 ¼

Vmp=VOC�1

ln 1�Imp=ISCð ÞChange of current DI ¼ a S

Sref

� DT þ S

Sref� 1

� ISC

Change of voltage DV ¼ �bDT � RSDI

Output voltage of SOSE

Nernst potential

E ¼ E0 þ RT2F

lnP0H2

P0O2

� 1=2

P0H2O

264

375

Ohmic overpotential gohmic ¼ JL/

Activation overpotential gact;i ¼ RTFsinh�1 J

2Jo;i

�

Concentration overpotential

gSOSEconc;a ¼ RT4F

ln

ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiP0O2

� 2

þ JRTlda=2FBgð Þr

P0O2

0BB@

1CCA

gSOSEconc;c ¼ RT2F

ln1þJRTdc=2FD

effH2O

P0H2

1�JRTdc=2FDeffH2O

P0H2O

� �

Heat energy of PTSC output

Aperture area Aap ¼ w � Dc;o

� �Lc

Heat removal factor FR ¼ _mrCpr

ArUL1� exp � ArULF1

_mrCpr

� �

Receiver’s absorbed radiation Sr;ar ¼ S grOverall heat loss coefficient between the ambient and the receiver

UL ¼ Ar

hc;caþhr;cað ÞAc

þ 1hr;cr

� ��1

Concentration overpotential of fuel cell operation mode

Concentration overpotential

gSOFCconc;a ¼ � RT2F

ln1� RT=2Fð Þ Jda=Deff

H2P0H2

�

1þ RT=2Fð Þ Jda=DeffH2

P0H2O

� 24

35

gSOFCconc;c ¼ � RT4F

lnp0=dO2ð Þ� p0=dO2ð Þ�P0

O2

� exp RT=4Fð Þ JdO2 dc

.Deff

O2p0

� h iP0O2

24

35

Overall and individual efficienciesof the system’s components

Efficiency of SOSE gSOSE ¼ LHVH2_NH2 ;out

_WSOSEþQheat;SOSEþQheat;H2O

Efficiency of PTSC gPTSC ¼ FR g0 � ULTi�Ta

GBC

� h i

Efficiency of PV gPVmax ¼ Pm

S�Ac

Overall efficiency of solar–SOSE mode gsolarþSOSEsys ¼ WPV

out;loadþ _NH2 ;outLHVH2

WPVinput

þPPTSCinput

þQheat;SOSE

Electrical efficiency of SOFC gSOFCel ¼ WSOFC;net

_NH2 ;inletLHVH2

Thermal efficiency of SOFC gSOFCheat ¼ Qusable;net

H2;consumptionLHVH2

Combined overall efficiency gSOFCOverall ¼ gSOFCel þ gSOFCheat

Overall efficiency of solar–SOFC mode gsolarþSOFCsys ¼ WPV

out;loadþWSOFC

elþWSOFC

heatþQwater

heat

WPVinput

þPPTSCinput

þ _NH2 ;inletLHVH2

R. K. Akikur et al.

123

Cai ¼ Cpc CRF ð20Þ

where, capital recovery factor (CRF) can be determined

using Eq. (21).

CRF ¼ i 1þ ið Þn

1þ ið Þn�1ð21Þ

where, i is the annual interest rate (%).

The unit cost of energy, Cu ($/kWh) can be calculated

using Eq. (22).

Cu ¼Cat

Eec

ð22Þ

where, Eec is the annual net usable electrical energy pro-

duction from the system which is the sum of electrical

energy provided by the PV and the fuel cell.

Payback period

The viability of any system can be evaluated by analysing

the payback period method. This is a period of time that

taken to be equal or cross the total investment cost of the

system by saving the annual energy cost of the conven-

tional system. The payback period can be determined by

the Eq. (23).

PB ¼ Total investment cost

Annual total cost savingð23Þ

In this study, the total investment cost includes the

capital, replacement and operating and maintenance costs,

respectively.

Efficiency calculation

The efficiency of the system can be calculated by solving

the Equations presented in Table 4. The efficiency of the

individual components can also be determined by using

those equations according to the operation mode.

Result and discussion

The cogeneration system has been designed based on the

Malaysian weather conditions as shown in Fig. 4. It has to

be noted that the fuel cell provides the energy demands of

13 h (i.e. first 7 h and last 6 h in a day). The solar PV can

provide the load demand during 9 a.m. to 5 p.m. without

any energy shortage. Solar PV works with fuel cell in

parallel for the remaining hours of the day when the solar–

PV cannot meet the total energy demand alone. The hourly

average solar radiation data as well as the load demand has

been considered to determine the system parameters and

analyse the performance. The analytical approach has been

used to determine the optimal system parameters like solar

PV, collector, fuel cell size etc. and found the right com-

bination of parameters that can provide the demand without

energy shortage at low cost.

Case studies

Two case studies have been conducted considering two

different load demands in this section. The values of sys-

tem parameters have been determined using the data given

in Table 5 and solving the equations in Sect. 2. Analysis

was carried out with the basic assumptions given as follows

(Akikur et al. 2014):

(1) Mass flow of the input fuel gas and all the reacting

products of fuel cell are stable.

(2) Incoming fuel and air have uniformly been dis-

tributed to each individual cell in the stack at SOFC

mode.

(3) The air supplied to the cathode is composed of

21 % oxygen and 79 % nitrogen.

(4) Temperatures of both the anode outlet gas and

cathode outlet gas are equal to the operating

temperature of the cell stack at both SOSE and

SOFC mode of operations. The current and voltage

of every cell unit are the same.

(5) Pressure at the anode and the cathode of the SOFC

is considered constant and equal.

(6) Radiation heat transfer between gas channels and

solid structure is negligible.

(7) Contact resistances are negligible.

(8) Pressure change at SOFC is negligible.

(9) Liquid H2O is fed to the PTSC in a reference

environment condition, i.e. 298.15 K and 1 atm.

(10) Heat losses inside the pipe are negligible.

Fig. 4 Yearly average solar radiation in Malaysia and the operation

mode of the system

Economic feasibility analysis of a solar energy and solid oxide fuel cell-based…

123

The system for a single family: case 1

The cogeneration system has been designed to meet the

energy needs of a single family. The optimal system has

been designed considering the average hourly electrical

and hot water demand for a family, given in Table 2 and

Fig. 1 respectively. The typical per day average electricity

and hot water demands are 10.3 kWh and 235 l approxi-

mately (Mahlia and Chan 2011).

The calculated optimal values for the system component

to meet the energy requirements are shown in Table 6. The

fuel cells stack of 1.3 kW with current density (J) and

active area (A) of a single cell of 1200 A m-2 and 0.01 m2

have been considered for providing the energy demand and

hydrogen production. The maximum energy demand is

considered to be 0.537 kW per hour. If the operating

voltage of fuel cell stack is considered 24 V, total 33 cells

are required in series and two cells are in parallel to meet

the power demand. The operating voltage of a single cell is

0.73 volt at 850 �C which is calculated using Eq. (14). At

constant pressure of 1 bar with 80 % fuel utilization, the

hydrogen and oxygen requirements for the system are

calculated using Eqs. (12) and (13).

H2 fuel is preheated before entering the fuel cell stack

through the HEX-2. The produced steam from the chemical

reaction and unused H2 passes through the HEX-2. It has to

be noted that the input fuel absorbs the heat and raises the

temperature. Then approximately 23.4 l of hot water per

day at desired temperature can be harnessed by HEX-3

when 5 9 10-3 kg s-1 water at room temperature passes

through the HEX. For the operation, the sufficient area of a

HEX is found about 0.1 m2 which is calculated by NTU

method given in Akikur et al. (2014). A DC/AC inverter of

0.6 kW is considered for the electric load supply from the

fuel cell. On the other hand, a DC/DC converter of 1 kW

with MPPT facility is considered for interfacing between

PV and electrolyser at H2 production mode.

To produce sufficient amount of H2 as to ensure the H2

requirement during SOFC mode of operation, the optimal

solar PV system has been designed in Solar–SOSE mode.

According to weather conditions, the solar–PV of 2 kW

can provide the energy requirements in the day time and

the energy needed for sufficient hydrogen production. The

monthly average power generation of PV and the power

demand from PV in order to meet the electrical load and

the hydrogen production rate are presented in Table 7. To

ensure the power generation at night, 154.89 kg of

hydrogen is required in a year, whereas the designed sys-

tem can produce approximately 164.39 kg of hydrogen. It

also has to be noted that in November and December

hydrogen production rates are lower than the requirements.

However, excessive production in other months can tackle

the shortage in other months. The maximum hydrogen

production has found to be 15.77 kg in the month of May.

Hence, 20 kg of hydrogen storage tank would be enough

for the designed system. The PV can generate

3342.31 kWh of power in a year, where 1603.94 kWh for

electric load demand and rest of 1901.72 kWh used for

hydrogen production. However, there are still some power

shortages from the solar PV in some months at the early

day and the afternoon for insufficient solar radiation.

During the hydrogen production period, the PTSC pro-

vides the initial heat energy. For that operation, a collector

of 3-m length (Lc) and 1.5-m (w) width is considered for

Table 5 Values of input

parameters in the present CHP

model

Parameter Value

Solar thermal subsystem

Stefane Boltzmann constant (r) 5.67 9 10-8

Collector outer diameter Dc,o (m) 0.09

Solid oxide fuel cell subsystem

Pressure [P (bar)] 1

The thickness of anode [da (lm)] 500

The thickness of cathode [dc (lm)] 50

Electrolyte thickness [L (lm)] 50

Solar photovoltaic subsystem

Temp. coefficient of open-circuit voltage at reference solar irradiance (V/C) 0.248

Temp. coefficient of short-circuit current at reference solar irradiance (A/C) 0.0054

Reference solar radiation [Sref (W m-2)] 1000

Voltage at maximum power point [Vmp (V)] 50

Current at maximum power point [Imp (A)] 5

Open-circuit voltage [Voc (V)] 62

Short-circuit current [Isc (A)] 5.4

R. K. Akikur et al.

123

calculating the total area and the water steam temperature

using the Eq. (10). The area has been found to be 4.23 m2

for the case-1. Then the temperature of steam rises in HEX-

1 during the steady-state operation, and then steam flows

into the electrolyser. Moreover, the required area of the

HEX is determined considering the overall heat-transfer

coefficient of 0.05 kW m-2 K-1, and it is found that

0.5 m2 HEX would be appropriate for the operation. A

furnace is considered as a preheater to maintain the oper-

ating temperature of electrolyser. In this study, it operates

only at start-up period; otherwise, the steam reaches the

required temperature when it passes through the HEX-1. In

this mode of operation, approximately 32.4 l of hot water

per day can be drawn from the heater HEX-3 by passing

water at the flow rate of 0.001 kg s-1 at normal tempera-

ture (25 �C) through the HEX.

In solar–SOFC mode of operation, the power from

SOFC depends on the power delivered by the PV.

According to Malaysian weather conditions, the system

needs to operate few hours in solar–SOFC mode to meet

the demand because the solar radiation is not sufficient to

fulfil the demand. Moreover, from September to December,

the system needs to operate in this mode for three hours.

The power management between solar–PV and SOFC in a

year is shown in Fig. 5.

A total of 60 l of hot water at the temperatures in the

range of 55–60 �C per day can be collected from the HEX-

3 whereas the total requirement is 235 l day-1. Hence, to

meet the thermal load requirements, an additional solar

collector can be added. From the calculation, it is found

that 1.41 m2 (1-m length and 1.5-m width) collector can

provide 198 l day-1 hot water at the temperature range of

47–68 �C at the water flow rate of 0.0045 kg s-1 through

the collector.

The system for 100 single families: case 2

In this section, the cogeneration system has been analysed

considering load demand for 100 single families in a dis-

tribution system as presented in Table 2 and Fig. 1.

According to the demand and weather conditions, optimal

values of the cogeneration systems parameters are deter-

mined and illustrated in Table 8 similar to case-1. The

values of solar–PV and fuel cell have been chosen to meet

the total energy demand. The other components such as

heat exchanger, inverter and converter have also been

designed accordingly. The daily average energy demand is

10.3 MWh with the maximum per hour load 53.7 kW.

A SOFC of 130 kW is considered with the current density

and the active area of a single cell being 1200 A m-2 and

0.01 m2, respectively. If the individual cell operates at

0.73 V, totally 33 cells are required in series and approx-

imately 209 cells in parallel intended to operate at 24 V to

provide 60 kW electrical load.

Table 6 The system components value to meet the energy demands for case-1

Components PV Solar collector Fuel cell stack HEX 1 HEX 2 HEX 3 DC/AC inverter DC/DC converter

Specifications 2 kW 4.23 m2 1.3 kW 0.5 m2 0.1 m2 0.01 m2 0.6 kW 1 kW

Table 7 Monthly total value of different parameters to meet the demand for Case-1

Month Total power

from PV (kWh)

Power remain for

H2 production (kWh)

H2 production

(kg)

H2 needed for

SOFC (kg)

Jan 289.33 161.43 14.72 13.88

Feb 265.40 153.83 13.23 12.04

Mar 279.73 150.32 12.93 13.03

Apr 292.34 165.69 14.25 13.06

May 312.80 183.32 15.77 13.22

Jun 286.94 174.19 14.98 11.80

Jul 281.31 162.14 13.94 12.88

Aug 289.66 167.72 14.42 12.73

Sep 277.61 155.90 13.41 13.05

Oct 293.83 176.30 15.16 12.98

Nov 221.91 112.70 9.69 13.12

Dec 251.36 138.17 11.88 13.11

Total 3342.21 1901.72 164.39 154.89

Economic feasibility analysis of a solar energy and solid oxide fuel cell-based…

123

The solar collectors with the aperture area of 68.2 m2,

with the length and width being 20 and 3.5 m, respectively,

have been considered to provide the thermal energy for the

water during solar radiation time. The solar–PV of 200 kW

is considered for H2 production and electric load supply.

Monthly power provided for the H2 production after ful-

filling the electrical load demand, the H2 production at

solar radiation period and the H2 requirement at off-sun

period are calculated and shown in Table 9. The size of

DC/DC converter is taken according to the maximum

power generation of PV. Figure 6 shows the electrical load

supply management in Solar–SOFC mode of operation.

To meet the hot water load, the HEX-3 is used, and

approximately 3500 and 3200 kg day-1 of hot water at

54–63 �C can be harvested by the solar–SOSE and SOFC

modes of operation, respectively. The amount (i.e.

23,500 l day-1) of hot water from HEX-3 is not sufficient

to fulfil the entire demand. Hence, the collector of 15-m

length and 2.5-m width is considered in order to supply the

additional hot water demand.

Efficiency calculation

The system efficiency has been evaluated considering the

typical single-house load demand. The individual compo-

nents efficiency is calculated using the equations given in

Table 4. Summary of important parameters for efficiency

calculations for all the modes of operation is illustrated in

Table 10. The efficiency of the SOFC at heat and power

generation modes is determined considering the average

electrical load of 0.47 kWh in a year. The average H2 flow

rate of 8.40 9 10-6 kg s-1 is needed as input to meet the

demand. The SOFC can generate approximately 0.41 kW

of thermal energy, and a certain portion of it is used in

HEX-2. As a consequence, the remaining 0.32 kW of net

thermal energy can be used for the heat load. In this case,

the electrical, thermal and the overall efficiencies of SOFC

are found to be 45.22, 38.76 and 83.98 % (using LHV of

H2), respectively. However, the overall system efficiency is

found to be lower than the SOFC efficiency because of a

small amount of thermal energy being used for water

heating at *60 �C) for household application in Malaysia.

The efficiency at higher solar radiation period or Solar–

SOSE mode has been evaluated considering the average

solar radiation of 516 W m-2. The solar PV of 250 W with

the area of 1.73 m2 is considered for this study. Total 2 kW

of solar–PV (8 pieces) is selected to meet the electrical

energy demand and the steam electrolysis. At 516 W m-2

of radiation, a total of 1.01 kW of electric power can be

supplied by the PV, where approximately 0.345 kW of

power is needed for electric load and the remaining

0.655 kW is used for H2 production. Hence, the efficiency

of solar PV is found about 14.24 %.

The efficiency of electrolyser varies with the solar

radiation. At higher radiation, it operates at higher effi-

ciency. The efficiency at 516 W m-2 radiations is found to

Fig. 5 Electrical power management at Solar–SOFC mode of operation for the case-1

Table 8 The system components’ values to meet the energy demands for the case-2

Components PV Solar collector Fuel cell stack HEX 1 HEX 2 HEX 3 DC/AC inverter DC/DC converter

Specifications 200 kW 68.2 m2 130 kW 9.0 m2 0.9 m2 3 m2 60 kW 150 kW

R. K. Akikur et al.

123

be more than 100 % which varies with the solar radiation.

The electrical power from solar PV of 0.65 kW is used for

steam electrolysis. The heat energy of steam is 0.22 kW

provided by the PTSC, and the heat energy provided by

HEX-2 which is approximately 0.96 kW [calculated using

Eq. (8, 9)] is considered as input to calculate the efficiency

of the SOSE. When the H2 production rate is

1.56 9 10-5 kg s-1 at 516 W m-2 with the LHV of

249.2 kJ mol-1, the efficiency of SOSE reached up to

105.09 %. Furthermore, the overall system efficiency at

solar–SOSE mode is calculated, where the input powers of

PV and PTSC are determined by multiplying the total

surface area and the solar radiation on it (516 W m-2), and

it is found to be approximately 26 %.

At Solar–SOFC mode of operation, energy demand is

provided by the PV and SOFC. The PV acts as a primary

energy source at this time, and the remaining energy

requirement is provided by SOFC. According to the

Malaysian weather conditions, the average solar radiation

in a year in solar–SOFC mode is 122.5 W m-2, when the

average powers supplied by PV and SOFC are 0.215 and

0.201 kW, respectively, to meet the electric energy

demand. The efficiency of solar PV and the electrical

efficiency of SOFC are found to be 12.74 and 44.98 %,

respectively. The electrical efficiency of SOFC is slightly

lower than that of the SOFC mode because of the capacity

factor of SOFC. At full-load operation, the SOFC shows

higher efficiency. The overall system efficiency in this

mode of operation is found to be 24.56 %.

Economic and environmental impact analysis

An economic analysis has been conducted in this study

considering the parametric values given in Table 11. In

Table 9 Monthly total parameter values to meet the demands for the case-2

Month Power from PV

(MWh)

Power remain for

H2 production (MWh)

H2 production

(kg)

H2 needed for SOFC

(kg)

Jan 28.93 16.14 1472.45 1388.08

Feb 26.54 15.38 1322.93 1204.04

Mar 27.97 15.03 1292.70 1302.51

Apr 29.23 16.57 1424.92 1306.33

May 31.28 18.33 1576.54 1321.57

Jun 28.69 17.42 1498.05 1179.99

Jul 28.13 16.21 1394.36 1288.46

Aug 28.97 16.77 1442.40 1272.63

Sep 27.76 15.59 1340.73 1305.06

Oct 29.38 17.63 1516.21 1297.73

Nov 22.19 11.27 969.24 1312.29

Dec 25.14 13.82 1188.30 1310.64

Total 334.22 190.17 16,438.82 15,489.34

Fig. 6 Electrical power management at Solar–SOFC mode of operation for the case-2

Economic feasibility analysis of a solar energy and solid oxide fuel cell-based…

123

order to evaluate the cost of energy, Eqs. (19) to (23) have

been used.

The SOFC and the solar–PV are usually the most

expensive of the systems due to the photovoltaic module of

operation which is costly. The unit price of these compo-

nents ranges from 0.54$/Wp up to 3.35$/Wp depending on

the manufacturer, performance and warranty. In this anal-

ysis, an average cost of solar–PV is considered to be 1.34$/

Wp (Desideri and Campana 2014). The cost of a PTSC

with the supporting structure, reflecting mirror, receiver,

tracking system and foundation is assumed as 368.5$/m2.

The operation and maintenance (O&M) cost has been

considered as 5 % of the investment cost (IC) of PTSC,

which covers the water cost that is used to extract the heat

energy from the PTSC. The additional PTSC intended to

meet the thermal energy demand is also considered for the

energy cost calculation.

The SOFC cost has been considered as 1000$/kW

according to the US DOE SECA program (Zink et al. 2007)

and 4 % of investment cost (IC) of SOFC as the O&M cost.

The cost of preheater is covered by the O&M cost of SOFC,

which is used in both at H2 production and power generation

modes. The preheater in both SOFC and Solar–SOSEmodes

is used only at the start up time of fuel cell and electrolyser.

Otherwise, it has no activity since theHEX-1 andHEX-2 can

provide the required heat for the operation at the full mode

operation. The high-temperature HEX has been used in this

study is costlier than the lower temperature HEX. The entire

individual component’s controlling cost has been included in

the O&M cost of the component.

The cogeneration system’s total costs for the case-1 and

case-2 are given in Table 12, where the capital cost is the

initial investment of the system components at the

installation time. The replacement cost of individual

components depends on the components’ life time. For

instance, the SOFC’s operational lifetime is approximately

5 years. To determine the replacement cost, 10 % discount

rate has been considered on every replacement.

Environmental impact

The electricity generated from the photovoltaic system

utilizing solar energy is one of the best sources of green

Table 10 The calculated values of various efficiencies considering three modes of operation

At SOFC mode

Avg. electrical load 0.47 kW Electrical efficiency of SOFC 45.40 %

Avg. input H2 flow rate 8.37 9 10-6 kg s-1 Overall efficiency of SOFC 84.15 %

Thermal efficiency of SOFC 38.76 % Overall system efficiency 48.64 %

At solar-SOFC mode At solar-SOSE mode

Avg. power delivered by the PV for load supply 0.215 kW Total power provided by the PV 1.01 kW

Avg. power delivered by the SOFC for load supply 0.201 kW Power delivered by the PV for electric load 0.354 kW

H2 supply to the stack 3.6 9 10-6 kg s-1 The power remain for steam electrolysis 0.65 kW

Net heat gain within fuel cell stack 0.18 kW H2 production rate 1.56 9 10-5 kg s-1

Net usable heat gain from complete fuel cell system 0.14 kW Net energy delivered by PTSC 0.22 kW

Electrical efficiency of SOFC 44.98 % Avg. temperature gain of water from PTSC 300 �CThermal efficiency of SOFC 38.76 % Efficiency of PV 14.24 %

Combined efficiency of SOFC 83.74 % Efficiency of SOSE 105.09 %

Efficiency of PV 12.74 % Efficiency of PTSC 60 %

Overall system efficiency 24.59 % System overall efficiency 26 %

Table 11 The assumptions for economic analysis (Akikur et al.

2014; Zink et al. 2007)

Parameter Value Units

Fuel cell 1000 $/kW

O&M cost for fuel cell 4 % IC of SOFC

Solar PVa 1.34 $/W

O&M cost for solar PV 0 % IC

PTSC systema 368.5 $/m2

O&M cost for solar thermal 5 % IC of PTSC system

Low temperature HEX 536 $/m2

Medium temperature HEX 1072 $/m2

High temperature HEX 5360 $/m2

Converter/inverter 57.14 $/kW

Air flow system 2 % IC of SOFC

SOFC module lifetime 5 Years

Solar PV module lifetime 25 Years

Solar PTSC lifetime 25 Years

Plant lifetime 20 Years

Annual interest rate 5 %

Carbon price 0 $/ton CO2

R. K. Akikur et al.

123

energy. The greenhouse gas emission, i.e. CO2 during the

operation of a PV system is zero. On the other hand, the

SOFC-based system emits little amount of CO2 based on

the utilized fuel. For instance, in this proposed system, the

SOFC produces electricity utilizing H2 fuel, where H2

reacts with oxygen and produces clean water. Hence, it

could be stated that the proposed system would be a zero

CO2 emission energy generation system. The study pre-

sented by Ngan and Tan (2012) has been used to compare

the proposed system with other off-grid power generation

system used in Malaysia. Ngan and Tan (2012) considered

different power generation systems with stand-alone diesel,

hybrid PV–diesel without and with battery, hybrid wind–

diesel without and with battery and, hybrid PV–wind–

diesel without and with battery and compared the CO2

emissions between those systems. The annual CO2 emis-

sion reductions achieved based on the electric loads con-

sidered in our system have been calculated and compared

with the system presented by Ngan and Tan (2012) and are

presented in Table 13.

Feasibility analysis

Economic feasibility is one of the most important aspects

of any power generation system that depends on the total

investment cost and the return on investment costs during

the project lifetime.

The proposed cogeneration system’s payback period and

energy cost are mainly affected by the cost of solar–PV and

SOFC. However, variations of the energy costs of the two

cases result from the costs of the solar collectors, HEXs,

and the O&M. The cost increments for the SOFC and PV

are linear with the capacity, but the costs of solar collector

and the HEX increase based on the area required in which

increment is not linear with the requirement. The economic

feasibility of the proposed system considering the present

and future costs of solar–PV and SOFC is determined and

given in Table 14. After analysing the cogeneration system

in Malaysian weather conditions, the system for the case-1

appears to be less efficient than the case-2. The payback

period of the system for case-1 crosses the projection time

(20 years) considering the solar–PV and SOFC costs at

present to 2017. However, in 2020, when the costs of

solar–PV and SOFC are considered as 0.5$/W and 400$/

kW, respectively, the payback period is found to be

17.50 years. On the other hand, the system in the case-2 is

highly feasible. At present, the energy cost and the payback

period of the system in case-2 are not too high compared to

the 2017’s and 2020’s projected results.

Feasibility analyses of a few SOFC-based cogeneration

systems are given in Table 15 based on the literature sur-

vey and discussed to evaluate the proposed system’s pos-

sibility as a future energy solution.

Chen and Ni (2014) presented a cogeneration/trigener-

ation system based on a load demand of a Hotel in Hong

Kong. The system consisted of 5 units of 200 kW SOFC

energy server which provided 8.76 GWh of energy annu-

ally and a cogeneration/trigeneration with four chillers.

Moreover, they disclosed that if the government provides

50 % subsidy of the total system cost, the payback periods

would be just a little more than 10 and 5.7 years for

cogeneration and trigeneration system, respectively.

Table 12 Total costs of the

system in projection time

periods for case-1 and 2

Component Capital ($) Replacement cost ($) O&M ($/year) Total ($)

Case-1

Fuel cell 600.00 1620.00 24.00 2724.00

Solar–PV 2680.00 – – 2680.00

Solar collector 2078.34 – 103.92 4260.60

Inverter 34.28 92.57 – 126.85

Converter 85.71 231.417 – 317.127

Heat exchangers 643.20 – – 643.20

Air flow system 54.48 – – 54.48

Total cost 6181.37 1943.98 127.92 10,811.61

Case-2

Fuel cell 60,000.00 162,000.00 2400.00 272,400.00

Solar–PV 268,000.00 – – 268,000.00

Solar collector 38,452.98 – 1922.65 78,828.60

Inverter 3428.40 9256.68 – 12,685.08

Converter 8571.00 23,141.70 – 31,712.70

Heat exchangers 10,612.80 – – 10,612.80

Air flow system 5448.00 – – 5448.00

Total cost 394,513.18 194,398.38 4322.65 679,687.18

Economic feasibility analysis of a solar energy and solid oxide fuel cell-based…

123

Vialetto and Rokni (2015) studied a SOFC and heat

pump-based cogeneration systems focusing on electrical

and heat load demands of a resort located in a northern

European climate (Denmark). The system was simulated

considering different operating strategies to unveil the

lucrative solution for the selected location. Two strategies

were considered: continuous operation (CO), where the

electricity generation of the system is constant for a certain

period, and the other one is an equivalent electrical load

following (ELF), where the electricity production is equal

to the demand. The simulation results illustrated that the

CO strategy needs 1 kW of SOFC and the ELF strategy

needs 2 kW of SOFC where the payback periods for the

CO and ELF strategy are 16 and 15 years, respectively.

Mahlia and Chan (2011) presented a cogeneration sys-

tem using a SOFC in Malaysia for electrical load of

10.3 kW day-1 and thermal load of 1.85 kW day-1,

respectively. The study reported the proposed system’s

payback period over the projected life (20 years) of the

system for lower load applications.

Al-Qattan et al. (2014) presented a cogeneration system

to provide cooling for 805 residential villas, four schools,

two community shopping centres and four houses of wor-

ship in Kuwait. A SOFC of 18 MW generated electrical

power to operate chillers, and the exhaust energy and heat

from the SOFC were used to run gas turbines and

absorption chillers. The system was designed to meet the

cooling demand of the district, and to feed extra electrical

power to the grid during periods of lower demand. From

the analysis, they revealed that the energy cost of the SOFC

system is $0.0192 kWh-1 for 96 MW cooling load

demand.

Uncertainty of power generation and supply

The system operation depends on the availability of solar

radiation which fluctuates over time. Although the H2 fuel

is lucrative for the large-energy storage system, this storage

system would not be able to maintain the system stability.

To maintain the stability and reliable load supply, an

auxiliary power supply is needed, and the battery storage is

a good candidate for this purpose. The operation strategy

would be modified for stable operation as follows:

• The battery storage could be used instead of SOFC in

solar–SOFC mode which is able to save more H2 and

that would be used when solar radiation is unavailable

for a day.

• In high impulsive day of solar radiation, the load supply

would be considered from SOFC. With regard to H2

fuel, if we consider battery as a backup supply in solar–

SOFC mode; approximately 20 kg of H2 is saved in a

year for the case-1 which is sufficient to cover the load

for few days. The capacity of 0.8 kWh of battery with

50 % maximum depth of discharge (DODmax) is

sufficient to supply the load at solar–SOFC mode.

A flow chart of the system operation is essential to

understand the operation as well as the system stability

which is illustrated in Fig. 7. A battery storage system is

included in the proposed system where it is charged when

the solar radiation is below 500 W m-2 and the solar

radiation fluctuates highly. Otherwise, the solar radiation is

utilized for the hydrogen generation. Although the

Table 14 Economic feasibility study of the proposed system

Present 2017 2020

Case-1

PV ($/W) 1.34 0.7 0.5

SOFC ($/kW) 1000 700 400

Energy cost ($/kWh) 0.158 0.126 0.112

Payback (years) 30.63 24.64 21.15

Case-2

PV ($/W) 1.34 0.7 0.5

SOFC ($/kW) 1000 700 400

Energy cost ($/kWh) 0.091 0.059 0.045

Payback (years) 19.26 13.27 9.77

Table 13 CO2 emission reduction achieved in the present study compared to the system presented in Ref (Ngan and Tan 2012)

Energy generation system Ngan and Tan et al. CO2 emission reduction by the proposed system

Case-1 Case-2

kg year-1 kg kWh-1 kg year-1 kg year-1

Stand-alone diesel system 351,844.0 1.134 102,339.0 1.0 9 107

Hybrid PV/diesel system without battery storage 323,696.5–302,585.8 1.043–0.975 94,151.9 9.4 9 106

Hybrid PV/diesel system with battery storage 246,290.8 0.794 88,011.6 8.8 9 106

Hybrid wind/diesel system without battery 350,788.5–344,455.3 1.131–1.110 71,637.3 7.2 9 106

Hybrid wind/diesel system with battery 344,807.1–309,622.7 1.112–0.998 102,032.0 1.0 9 1007

Hybrid PV/wind/diesel system without battery 323,696.5–299,067.4 1.043–0.964 100,189.9 1.0 9 107

Hybrid PV/wind/diesel system with battery 230,457.8 0.743 100,292.2 1.0 9 107

R. K. Akikur et al.

123

involvement of battery storage uplifts the energy cost, it

ensures the stability of the system operation. The energy

cost for the case-1 has been recalculated considering the

battery storage system, and it has increased from $0.158 to

$0.160 kWh-1 where the battery related expenses has been

adopted from ref. (Shezan et al. 2015)

Conclusion

The study on solar energy and fuel cell (SOFC)-based

cogeneration system indicates that it can be considered one of

the promising energy systems in the residential sector,

especially for higher energy demand. The findings of the case

studies of the system can be concluded as follows: The

combined heat and power efficiencies for SOFC, solar–

SOSE, and solar–SOFC modes are found to be 84.15, 26 and

24.59 %, respectively. Only electrical efficiency for those

modes of operation are found to be 45.40, 14.24 and 24.59 %,

respectively. The system is found to be 42.4 %more feasible

for the case-2 than case-1 with respect to present energy cost.

The costs of energy for the case-1 and case-2 are estimated to

be $0.158 and $0.091 kWh-1, respectively. Payback periods

are calculated as 30.63 and 19.26 years, respectively. In

future (2020), the system is expected to be 59.8 % more

feasible in cogeneration application for higher load demand

Table 15 Feasibility analysis of the present work with the SOFC-based system presented in the literature

Author (year) System Annual load demand (GWh) Payback period (years) Energy cost ($/kWh)

Chen and Ni (2014) Cogeneration/trigeneration 8.76 10/5.7 –

Vialetto and Rokni (2015) Cogeneration – 16 (CO)

15 (ELF)

–

Mahlia and Chan (2011) Cogeneration 3.76 (electrical)

0.68 (thermal)

[20 –

Al-Qattan et al. (2014) Cogeneration 35.04 (cooling) – 0.0192

Present work (2015) Cogeneration 3.76 (electrical)

0.68 (thermal)

[20 0.158

Present work (2015) Cogeneration 376 (electrical)

68 (thermal)

19.26 0.091

Solar radiation?

Yes

No

SOFC work as Hydrogen

production mode

SOFC work as power

generation mode

T of steamIf T 700°C

No

Preheater Yes

PTSC

eLoad

H2 Flow from Storage tank

T of H2

If T 700°C

Preheater

No

Yes

No

Yes

Heat Load

Start

P=Ppv-Pload

PV If Ppv Pload

H2O Flow from Storage tank

Battery

Fig. 7 Operational flow

chart of the proposed

cogeneration system

considering auxiliary load

supply

Economic feasibility analysis of a solar energy and solid oxide fuel cell-based…

123

than for lower load.While the costs of solar PV andSOFC are

$500 and $400 kW-1, respectively, the energy cost and

payback periods for the Case-1 are expected to be

$0.112 kWh-1 and 21.15 years, respectively. The proposed

cogeneration system is further analysed considering the

backup power system to increase the load supply reliability.

RSOFC is still in development phase along with its longer

starting period. Therefore, a backup supply is crucial to avoid

the powermismanagement. The energy cost for the case-1 has

been found to be $0.160 kWh-1 approximately considering

the battery storage system.

From the system analysis, following issues need to be

addressed in future to make solar energy and fuel cell-

based cogeneration system lucrative and practically

feasible:

• The system is analysed under Malaysian weather

conditions in this study, but larger study is required

considering different weather locations. Since the size

of solar PV or collector is directly related to the solar

radiation, energy cost may vary with the location.

• The cost of solar energy as well as SOFC-based power

generation is still higher compared to the fossil fuel-

based system. Hence, incentive in the form of subsidy

from the government is needed.

Acknowledgments The authors would like to gratefully acknowl-

edge the financial support from the University of Malaya under the

High Impact Research MoE Grant UM.C/625/1/HIR/MoE/ENG/22

from the Ministry of Education Malaysia to consummate this

research. The authors also cordially acknowledge the grants UMRG

RP006G-13ICT and ERGS 53-02-03-1100.

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