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33 (2008) 2871 – 2879
Available at www.sciencedirect.com
journal homepage: www.elsevier.com/locate/he
Energy cost analysis of a solar-hydrogen hybrid energy
system for stand-alone applications
Jérémy Lagorsea,, Marcelo G. Simõesb, Abdellatif Miraouia, Philippe Costergc
a
GESC, UTBM, Rue Thierry Mieg, 90000 Belfort, France
Power Electronics Laboratory, Department of Engineering, CSM, Golden, CO 80401, USA
c
Total, 2 place de la Coupole, La Défense 6, 92078 Paris La Défense Cedex, France
b
art i cle info
ab st rac t
Article history:
Three configurations of fuel cell and photovoltaic hybrid systems were evaluated in this
Received 2 January 2008
paper based on economic constraints. In order to estimate the energy cost of each
Received in revised form
configuration, sources were sized with an analytical approach. An energy based modelling
21 March 2008
has been developed with Matlab/Simulink to observe evolution of the system during the
Accepted 21 March 2008
period of one year. The simulation results were used for optimizing the configuration costs
Available online 20 May 2008
in order to obtain the most cost effective system. An appropriate system sizing based on
Keywords:
Fuel cells
Photovoltaic power systems
Solar energy
1.
the proposed optimization solution, showed that a system composed with a photovoltaic
generator, a fuel cell, an electrolizer and a battery can deliver energy in a stand-alone
installation with an acceptable cost.
& 2008 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights
Introduction
In order to produce electricity for a domestic stand-alone
system, the classical solution associating photovoltaic (PV)
cells and batteries presents limits when required to feed a
system throughout one year cycle. Indeed, the battery and the
solar generator have to be over-sized to respond to the critical
periods when the solar insolation delivers a very small
amount of energy. Currently, most of the systems avoid
over-sizing by adding a diesel generator which supplies the
load during critical periods [1]. A possible solution consists in
adding a proton exchange membrane fuel cell (PEM FC) [2].
This kind of fuel cell (FC) has the advantage to produce
electricity without greenhouse emissions when the fuel is
hydrogen. However, when the fuel is methane, for example,
CO2 emissions are produced. Therefore, we consider only
hydrogen as fuel in this study. Fig. 1(a)–(c) show the three
configurations considered in this paper.
reserved.
The configuration in Fig. 1(a) consists of a PV generator, a
battery and a FC fed by hydrogen (H2 ) from an external source
to supply the system during critical periods (i.e. winter in
north hemisphere). A second configuration is shown in Fig.
1(b) that does not use batteries to store energy but only an
electrolizer supplied by PV producing H2 from water by
electrolysis. The water is collected from the rain; and the H2
produced is then stored in a tank and feeds the FC [3,4]. The
last configuration shown in Fig. 1(c) mixes the storage system
of the two previous configurations using both a battery and an
electrolizer to store the energy [5].
In this paper, a methodology to design each configuration
analytically is proposed. The simulation modelling approach
is presented in the next section. The results are discussed and
an optimization based on a cost function is introduced. For
final sizing of each system the energy cost (kWh cost) is
evaluated to discuss and to compare the economic feasibility
of each of those systems.
Corresponding author.
E-mail address: jeremy.lagorse@utbm.fr (J. Lagorse).
0360-3199/$ - see front matter & 2008 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.
doi:10.1016/j.ijhydene.2008.03.054
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Load Power (W)
100
H2
PEM
FC
80
60
40
20
0
0
Electrical
Converter
Load
2
4
6
8
10 12 14
Time (hours)
16
18
20
22
24
Fig. 2 – Load profile on a 24 h period.
Daily average insulation on 1 m2 (Wh)
PV
BAT
H2
Electrolyzer
PEM
FC
Electrical
Converter
6000
5000
4000
3000
2000
1000
0
Load
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Fig. 3 – Daily average insolation on the Odeillo site.
PV
North Africa, like for instance Morocco. Two consumption
peaks are represented in the morning and in the evening. The
night consumption corresponds to devices in sleep mode.
H2
Electrolyzer
PEM
FC
Electrical
Converter
2.1.2.
Load
PV
BAT
Fig. 1 – Configurations layouts. (a) Configuration 1: PV,
battery, FC is fed by an external hydrogen tank; (b)
configuration 2: PV, FC, electrolizer and hydrogen tank and
(c) configuration 3: PV, battery, FC, electrolizer and hydrogen
tank.
2.
7000
System sizing
2.1.
Sizing hypothesis
2.1.1.
Consumption estimation
The first step to size the sources and the other devices is to
evaluate the load profile. The chosen profile is presented in
Fig. 2; the load average power is 50 W which represents an
annual energy consumption of 438 kWh. This consumption
evolution is based on a domestic consumption in countries of
Solar power availability
Obviously, the solar power is linked to the weather conditions, and hence is unpredictable, especially on the insolation
received on a specified area. Based on a real case near
‘‘Perpignan’’ (French Pyrenees), the solar radiation data come
from the year 1999, which appears as a typical year. Indeed,
the radiation data among the seasons belong to the average
values of the site. On this site, the total annual solar energy
received on 1 m2 is about 1.6 MWh. Assuming that a PV
generator with polycrystalline technology presents an efficiency of 10%, 160 kWh are annually obtained using 1 m2 PV
array. The solar radiation data are sampled every 6 min, Fig. 3
shows the variation of daily average insolation over the year
[6]. Because of Sun–Earth geometry, the variations decrease
near the equatorial regions, and increase towards the polar
regions [7].
2.1.3.
Technology choice
In order to obtain a precise energy cost, the technologies of
each device have to be understood. For the FC, a PEM (proton
exchange membrane) cell is considered. This kind of FC
operates with hydrogen as fuel under normal temperature
conditions (from 30 to 200 1C and can work with a pressure of
1 atm. Moreover, this technology becomes commercialized
with stack electrical efficiency about 40%.
The chosen battery is a regular lead-acid battery.
This technology has a good efficiency, low cost and low
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self-discharge (less than 5% per month). The main drawback
for this battery is its weight, but in a stationary system, that is
not important.
The polycrystalline PV cells are currently the best choice in
terms of quality and price. They present an efficiency lower
than the monocrystalline technology (respectively, about
10–13% compared to 15–22%) but they are cheaper. That is
why this technology is commonly used in most of PV
systems.
The last element considered is the electrolizer. At this
moment, two technologies working under normal temperature are available: alkaline and PEM. PEM is a new technology
and is twice as expensive as alkaline technology (30 h=W
against 15 h=W [8]). Furthermore, alkaline technology has
been used for a long time in industry and its lifetime reaches
about 20 years.
2.1.4.
Element sizing
The last step of the sizing is to find the power or capacity of
each device. It depends on the considered configuration.
Several solutions are available and an optimization is needed.
The following section details a first approach, without using
optimization but only the analytical relations.
33 (2008) 2871 – 2879
2873
often activated. On the contrary when the battery capacity is
bigger, the FC is less activated and so, few hydrogen is
consumed. Over a certain battery capacity, the hydrogen
consumption remains quite constant. This is because the PV
power is constant and so, even if the battery is larger, it will
not be fully charged and the autonomy is not improved. Then,
to decrease the hydrogen consumption, the PV and the
battery has to be enlarged. This problem of optimization is
presented in Section 3.3.
Fig. 4 shows that the hydrogen consumption does not
change much when the battery capacity is over 2 kWh. Below
this limit, the capacity decrease involves a sharp hydrogen
consumption increase. So a battery of 2.4 kWh is chosen,
which represents 2 days of autonomy for the system. With
such battery capacity, the yearly hydrogen consumption is
less than 70 m3 (normal) (normal cubic meter with normal
conditions: pressure of 1013.25 hPa and temperature of 0 1C).
Using hydrogen compressed at 200 bar, a 350 L tank is
sufficient to stock the hydrogen during one year.
Finally, the PV surface can be easily calculated assuming
that solar generator delivers the whole energy consumed.
SPV ¼
Econsumed on 1 year
438
2:75 m2
¼
Eproduced on 1 year with 1 m2 160
(1)
This surface represents a 275 W peak PV panel.
2.2.
First sizing
2.2.1.
First configuration
2.2.2.
First, for the configuration number 1 as in Fig. 1(a), the FC
power is fixed. FC net power can be equal to the load average
power (50 W). The load surplus is generated by another device
(PV if available or battery). Considering that the FC auxiliary
systems need about 20% of the net power (for cooling and air
pressurization), it is necessary to use a 60 W FC gross power.
Then, the hydrogen consumption and the battery capacity
have to be fixed. These two variables are linked but there is no
analytical relation between them. Thanks to an estimation
given by a simulation model which is detailed in the next
section, the evolution of hydrogen volume consumed according to battery capacity can be observed. The simulation model
is run with several battery capacities and the corresponding
hydrogen consumption is plotted in Fig. 4. With a low battery
capacity, the hydrogen consumption is high because the FC is
Second configuration
As in the first configuration, FC power has to be determined
first. In this configuration shown in Fig. 1(b), the FC must be
able to supply the load all by itself. So, the FC net power is
100 W (load maximum power) and considering auxiliary
systems consuming 20% of this power, the gross power is
120 W.
Then, it is necessary to estimate the hydrogen tank
capacity. In an initial approach, it is considered that the
hydrogen energy storage system (electrolizer, compressor,
tank and FC) has 100% efficiency. Based on this assumption
and through simulation results, the evolution of stored
energy during a year (8760 h) can be observed in Fig. 5.
The stored energy ranges between 0 and about 80 kWh, so
on this initial approach, the tank has to store this difference
of energy. It is a seasonal storage system: energy produced
during summer period is consumed during winter periods.
80
Stored Energy (kWh)
H2 Volume (m3)
150
100
50
60
40
20
0
12
0
1000 2000 3000 4000 5000 6000 7000 8000 9000
Time (hours)
Fig. 4 – Volume of consumed hydrogen per year against
battery capacity for a fixed photovoltaic power.
Fig. 5 – Amount of stored energy during one year. It is
assumed that a certain energy quantity is present at the
beginning of the year coming from the previous year.
0
0
2
4
6
8
Battery Capacity (kWh)
10
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Table 1 – First sizing results
Device
1st configuration
2nd configuration
3rd configuration (determined by optimization)
2:75 m2
2.4 kWh
60 W
Optimization needed
80 m3 (normal)
13 m2
–
120 W
–
60 m3 (normal)
–
60 m3 (normal)
1.3 kW
Optimization needed
PV
Battery capacity
FC
H2 consumption
H2 storage volume
Electrolizer power
But, taking into account the FC efficiency, around 40%, it
becomes
EH2 ¼
MAXðEstored Þ MINðEstored Þ 8020
¼ 200 kWh
¼
ZFC
0:4
(2)
Considering the hydrogen higher heating value (142 MJ/kg
or 39.4 kWh/kg), the amount of energy to store on chemical
form represents a volume of about 60 m3 (normal). Such an
amount of hydrogen must be reduced using a compressor and
an electrolizer working under pressure. A pressure of 200 bar
would enable to store the hydrogen in a 300 L tank. It should
be noticed that this quantity of hydrogen is not the quantity
consumed, but the quantity to be stored. That is why this
value is less than the one presented in the first configuration.
To size the PV power, it is necessary to evaluate the part of
energy directly consumed from PV ðPart directly from PV Þ and
the part consumed from the energy storage system
ðPartfrom storage Þ. An estimation, confirmed later with the
simulation model, considers that 30% of energy consumed
comes directly from the PV with an efficiency of 100%
neglecting the electrical conversion components efficiency.
The remaining 70% comes from the hydrogen storage. The
hydrogen storage efficiency can be estimated using the
following relation:
ZH2
storage
¼ Zelectrolizer ZFC ¼ 0:4 0:4 ¼ 16%
(3)
The compression efficiency is neglected in comparison to
others efficiencies. Indeed, the compression efficiency is
about 95% [11]. The quantity of energy to produce in one
year can be expressed by Eq. (4).
!
Partdirectly from PV Partfrom storage
þ
Eproduced ¼ Econsumed 1
ZH2 storage
0:3 0:7
þ
2048 kWh
(4)
Eproduced ¼ 438 1
0:16
To produce such an energy amount, a PV array of 12:8 m2 is
required, which represents about 1.3 kWh.
The last element to define is the electrolizer. In this
approach, the electrolizer power is equal to the PV maximum
power to convert all the surplus of PV power in hydrogen.
Hence the electrolizer power is about 1.3 kW.
2.2.3.
Third configuration
The third configuration showed in Fig. 1(c), based on the two
previous configurations, consists of several elements: PV, FC,
electrolizer and battery. It is impossible to size each element
analytically because the characteristics of the different
Optimization needed
60 W
Optimization needed
Optimization needed
devices are linked together. For example, the battery capacity
should increase if the electrolizer power or PV power
decreases. Therefore, this sizing comes from a computer
optimization based on the simulation model further presented. Only FC power is sized like in the first configuration:
its net power is equal to the load average power.
2.3.
First sizing overview
Table 1 presents the results of the first sizing method for the
three configurations, to compare them easily.
3.
System cost optimization
3.1.
Simulation model
The goal of this model is to observe the system on the energy
point of view. Three models have been developed using
Matlab/Simulink, one for each configuration. As the model of
the third configuration is the most complete one, combining
other two configurations, only this model is described in the
paper (Fig. 6).
3.1.1.
PV model
The insolation data (expressed in W=m2 ) is required to
compute the produced PV power using only a constant coefficient depending on PV surface ðSPV Þ and efficiency
ðZPV Þ [9].
PPV ¼ Insolation ZPV SPV
3.1.2.
(5)
Battery model
The battery input power can be positive or negative depending on the charge or discharge mode of operation. The battery
power is obtained from Eq. (6).
PBAT ¼ PPV þ PFC PLOAD
(6)
The state of charge (SOC) is deduced from the battery power
and efficiency:
Z
SOCBAT ¼ ðPBAT CHARGING ZBAT
PBAT
DISCHARGING Þ dt
(7)
When the battery SOC is lower than a threshold value the FC
is activated. On the contrary, when SOC is higher to a
threshold value, FC is stopped and the electrolizer starts up:
the battery power given in Eq. (6) becomes the electrolizer
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Fig. 6 – Third configuration model: storage with hydrogen and lead acid-battery, photovoltaic source and load are also
present.
power (see Eq. (8)).
PELEC ¼ PPV PLOAD
3.1.3.
(8)
Electrolizer model
The electrolizer is simply considered as a constant gain
corresponding to the electrolizer efficiency and an integrator
to determine the amount of produced hydrogen. The amount
of hydrogen consumed by the FC is also determined. The
difference between both gives the amount of available stored
hydrogen, following Eq. (9).
Z
SOCELEC ¼ ðPELECTROLIZER ZELECTROLIZER Þ dt
Z PFC
dt
(9)
ZFC
3.1.4.
FC model
This model permits to calculate hydrogen consumption
according to the delivered power. Indeed FC efficiency ðZFC Þ,
appearing in Eq. (9), is not constant. The difficulty is to
consider that the FC efficiency only depends on the power
delivered. The ratio of energy consumed in hydrogen form
and the electrical energy produced is called global efficiency
ðZglobal Þ. As shown in Eq. (10), it can be expressed as function
of other efficiencies.
Zglobal ¼ Ztotal Zmatter Zsystem
(10)
where Zsystem takes into account the auxiliary consumptions.
Eq. (11) defines it as the ratio between the net and the gross
power:
Zsystem ¼
Pnet
Pgross
(11)
Efficiency Zmatter takes into account the hydrogen losses. In
fact, all the fuel is not consumed and the efficiency depends
on the FC hydrogen supply mode. The case considered here is
the closed mode where the matter efficiency is estimated
between 2% and 5% due to frequents purges of hydrogen
circuit.
Efficiency Ztotal is the ratio between the real voltage ðVðjÞ Þ and
the theoretical voltage ðEfictive Þ if the system would transform
the entire chemical energy (contained in hydrogen) in
electrical energy.
Ztotal ¼
VðjÞ
ZF
Efictive
(12)
Efficiency ZF is called faradic efficiency and is assumed to be
100%. Eq. (13) links FC voltage V with the current density j
[10,11].
VðjÞ ¼ E0 DVact DVohm DVconc
(13)
In Eq. (13), E0 represents the open cell voltage, DVact
represents the activation overpotential, DVohm represents
the ohmic overpotential and DVconc represents the concentration overpotential. It can also be expressed as in Eq. (14) with
the detailed expression of the overpotentials (DV’s).
j
VðjÞ ¼ E0 Aac ln
rj m expðn jÞ
(14)
b
In this empirical equation, Aac represents the Tafel slope, b
the activation coefficient, r the ohmic resistance coefficient, m
and n are the concentration coefficients. Considering a
Ballard Mark V FC where the parameters are given in
Table 2, the gross power and voltage FC against current
density is plotted (Fig. 7) [12].
A maximal power working point ðPMAX Þ of 622 wm=cm2
exists for a current density of 1012 mA=cm2 . An operational
point over this value is not of any interest, because it would
increase losses for a lower power. Considering unitary gross
power ðPUnitary Þ defined in Eq. (15), a correspondence between
voltage and gross power is obtained. Then the total efficiency
and the gross power can also be linked (Fig. 8).
PUnitary ¼
VðjÞ j
PMAX
(15)
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Table 2 – Ballard Mark V fuel cell parameters
Parameter
Finally, based on Eqs. (11) and (15), it is possible to obtain a
relation between global efficiency and the unitary gross
power.
The FC model developed with Simulink is shown Fig. 9. The
signal ‘‘Start FC’’ controls the FC start and stop.
Value
Unit
b
2:89 102
0.04
mA=cm2
r
2:114 104
m
1:4 105
Aac
n
8 10
V
A=cm2
V
When the FC does not work because the battery SOC is high
enough (see Fig. 10(a)) and the solar power is too weak, the
load is supplied by the battery. When the solar power rises
during the day, load is directly supplied by PV and battery is in
charging mode. When the battery SOC reaches its nominal
value, battery charging is stopped and electrolizer is activated
(see Fig. 10(b)).
When the FC is working (see Fig. 11), it supplies the load up
to 50 W. Over this value, either PV supplies the additional load
or the battery supplies it when solar radiation does not exist.
During the day, the PV charges the battery and when battery
reaches its nominal SOC, the FC is stopped.
Many other energy management techniques could be
implemented but a simple energy approach has been
preferred to support the economic stand-point.
700
Voltage
600
Power
1
500
0.8
400
0.6
300
0.4
200
0.2
100
0
0
0.2
0.4
0.6
0.8
1
Current density (A/cm2)
1.2
0
1.4
3.3.
Fig. 7 – Fuel cell voltage and power evolutions against
current density.
Global efficiency (%)
Total efficiency
1
0.6
0.4
0.2
0
0.2
0.4
0.6
0.8
Unitary Gross Power
Cost optimization
A cost optimization is realizable based on the third and the
first configuration but not for the second one. Indeed, the
0.8
0
Simulation results and discussions
cm =mA
Gross Power (mW)
Cell Voltage (V)
3.2.
2
3
1.4
1.2
33 (2008) 2871 – 2879
60
50
40
30
20
10
0
1
0
0.2
0.4
0.6
0.8
Unitary Gross Power
1
Fig. 8 – Fuel cell efficiencies against unitary gross power. (a) Total efficiency against unitary gross power and (b) global
efficiency against unitary gross power.
3
Gross Power
1
Start FC
2
Power
+
+
-KAdd
++
5
H2 Power
Multiply Unitary Gross Power Efficiency
0-->1
Divide
1
s
Integrator
1/10
1
H2 Energy
in Wh
Tenth of Hour
Saturation
Add1
-CPaux
-K4
Net Power
6
Auxiliary Power
Fig. 9 – Simulink FC model.
Wh->m3
2
H2 Quantity in m3
at 15°C
15 C and 1atm
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Table 3 – Costs of the elements
600
PV
Bat
500
Device
Poly-crystalline PV
Power (W)
400
Lead-acid battery
Alkaline electrolizer
PEM fuel cell
Hydrogen
300
200
Value
Unit
Lifetime
5
h=Wpeak
20 years
90
15
8
0.39
h=kWh
h=W
h=W
5 years
20 years
5000 h
–
h=m3 (normal)
100
0
-100
0
4
8
12
16
Time (hours)
20
24
2700
500
Ebat
Pbat
Pelec
2600
2500
300
Energy (Wh)
Power (W)
400
2400
200
2300
100
2200
0
2100
-100
2000
0
4
8
12
16
Time (Hours)
20
24
Fig. 10 – Powers and energies evolutions during 24 h when
FC does not work. (a) PV and BAT powers and (b) battery
and electrolizer powers and stored energy in the battery.
This hypothesis is verified for low-power systems. Table 3
details the unitary cost of the elements [8].
The hydrogen cost applies only for the first configuration
and this cost takes into account the production from a large
plant by electrolysis and the transportation. The details of the
hydrogen cost are available in [13].
Based on those unitary costs, the system total cost is
defined, but the amount of consumed hydrogen remains to be
determined. This information comes directly from the
simulation. The simulation model is run for several combinations of PV power and battery capacity and the hydrogen
consumption and the FC working rate is obtained. After that,
these results are used to calculate the total cost of the system,
assuming the system lifetime is 20 years (equal to the PV
lifetime). Fig. 12 shows the optimal combination of PV power
and battery capacity.
In the configuration 1, the minimum system cost is
obtained for the following combination of PV power and
battery capacity:
PPV ¼ 540 W;
CapBAT ¼ 2 kWh
This leads to a cost of 4544h for 20 years of operation.
300
PV
Bat
FC
250
Power (W)
200
150
4.
Comparison of configurations
4.1.
Configurations costs
100
50
0
-50
-100
0
4
8
12
16
20
24
Time (hours)
Fig. 11 – Powers evolution during 24 h when FC works.
second configuration is fully determined with the first sizing
presented in Section 2.2.2 and, consequently, it does not need
an optimization.
The function to optimize is the system cost. The system
cost function is defined as a sum of PV cost, battery cost,
hydrogen cost and FC cost.
Csystem ¼ CPV þ CBAT þ CH2 þ CFC
(16)
The PV cost is proportional to the PV power (or PV surface)
and the battery cost is proportional to the battery capacity.
With the optimization of configurations 1 and 3, the costs are
estimated and presented in Table 4. The kWh price based on a
20 years lifetime is also presented (see Eq. (17)). The kWh
price can be compared to the average price proposed by EDF
(Electricity of France, French company producing electricity)
which is about 0:12 h=kWh, without taking into account the
price of distribution extension in case of isolated site.
PkWh ¼
Csystem
R
20 years Pload
(17)
The second configuration is 10 times more costly than the
other systems because it uses only the hydrogen storage
system. Indeed, the efficiency of the hydrogen storage system
is very low and therefore the PV has to be larger to produce
more energy. Furthermore, the FC has also to be more
powerful to supply the maximum load power. Consequently,
based on the current cost of FCs and the efficiency of a
hydrogen storage system, a configuration relying only on a
hydrogen storage system is much more expensive than a
solution implying a battery.
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Total Cost (€)
12000
10000
8000
6000
4000
7000
2
4
2)
6000
5000
4000
Battery
3000
Capacit
y (Wh)
2000
6
1000
e
fac
(m
ur
Vs
P
Fig. 12 – Cost optimization of the first configuration.
Table 4 – Configuration cost during 20 years working
Configuration 1
Configuration 2
Configuration 3
Cost ðhÞ
kWh price
ðh=kWhÞ
Global
configuration
efficiency (%)
4544
43,300
5646
0.519
4:943
0.645
About 50
22:4
About 50
The global configuration efficiency ðZGlobal Configuration Þ is the
ratio between the energy consumed by the load ðEConsumed Þ
and the energy produced by the PV ðEfrom PV Þ plus the energy
consumed under hydrogen form ðEfrom H2 Þ as expressed in
Eq. (18) (Efrom H2 applies only for the first configuration). The
global configuration efficiency allows to estimate the waste of
energy between the production and the consumption. This
waste is due to the FC efficiency and the battery efficiency.
Consequently, it should be remarked that the global configuration efficiency can be higher than the FC efficiency.
ZGlobal
4.2.
Configuration
¼
EConsumed
Efrom PV þ Efrom
(18)
H2
Best configuration choice
Regarding the cost, the configuration 2 is not currently
feasible. However, according to the DOE, the target cost for
FC in 2015 is about 0:03 h=W [14,15]. Furthermore, the
improvements for FC should also concern the electrolizer. In
this way, the cost of the second configuration could be less
than 0:5 h=kWh and so, the configuration 2 remains a
promising solution for the future.
The two other configurations are feasible in term of cost;
the cost is about 5 times higher than the tariffs of EDF.
However, configuration 3 proposes a completely stand-alone
solution, producing hydrogen on site. On the other hand it is
more expensive and configuration 1 could be preferred.
Configuration 1 is a real alternative to the classical system
coupling PV, battery and diesel generator.
5.
Conclusion
This paper developed the economic study of three different
systems associating photovoltaic sources and fuel cells. Three
major ways to gather two sources have been covered: battery
storage, hydrogen storage and the use of both. A dimensioning procedure for the systems has been presented. In order to
check the validity of this procedure, a simulation model has
been made for each configuration. The simulation, based on a
realistic photovoltaic production over one year, has allowed to
observe the energy flow. The models and results of the
dimensioning have been used to find the optimal sizing of the
configurations. An optimal sizing of each configuration
allowed to fairly compare the three possibilities of mixing
the two sources of energy. It was concluded that the solution
relying on the only use of hydrogen storage is currently not
feasible. However, this solution could be preferred in near
future when electrolizers and fuel cells become more affordable. The two other configurations are similar on the cost
point of view. The choice among them mainly relies on the
use of the system. If the system’s site can be reached to bring
hydrogen, the configuration relying on battery storage and
fuel cell supplied by an external tank is the best. For a fullyautonomous system, the configuration featuring both hydrogen and battery storage is preferred.
Acknowledgment
The authors thank Total to have originated this project and
for their interest on this work.
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