International Journal of Application or Innovation in Engineering & Management (IJAIEM)
Web Site: www.ijaiem.org Email: editor@ijaiem.org
Volume 3, Issue 3, March 2014
ISSN 2319 - 4847
Low power photovoltaic system with lead acid
battery for 5V regulated voltage – electronic
circuits
A. El Abbassi1, A. El Amrani2, M. El Amraoui3 and C. Messaoudi4
1
Laboratory of Physical Instrumentation and Measurements, Dept. of Physics, FST, B.P. 509,
Boutalamine, Errachidia, University My Ismail, Morocco.
2
LPSMS, Dept. of Physics, FST, B.P. 509, Boutalamine, Errachidia, University My Ismail, Morocco.
3
LASMAR, Dept. of Physics, FS, Meknes, University My Ismail, Morocco.
4
OTEA, Dept. of Physics, FST, B.P. 509, Boutalamine, Errachidia, University My Ismail, Morocco.
ABSTRACT
The present work concern the study of monocrystalline silicon based photovoltaic (PV) module as input unit for alone low power
PV system. The PV module is associated with simple controlling circuit for the lead acid battery as storage unit and the voltage
regulator 5V DC as output unit of the PV system. Such PV system may be used as a power supplier for some electronics devices;
portable phones and small computers, luminous traffic sign and displays, programmable components and microcontrollers,
timers, embedded systems (GSM, PIC, FPGA cards…). Indeed, the aim of our investigation resides in the conception and
realization of reliable low cost portable photovoltaic system. A number of measurements have been performed, and the reliability
of the PV system has been investigated. At first, an indoor study of the photovoltaic module has been investigated; the
measurements showed that the short circuit current increases linearly with the light radiation, in particular at low light
intensities. In addition, in order to regulate a voltage value of 4 to 5V DC when the system is connected to the output load
resistance, the resistance value should be higher than 100 . Thus, the input voltage must be at least of 1 to 3V larger than the
regulated voltage of 4 to 5V DC.
Keywords: photovoltaic systems, battery, microcontroller, DC regulator, voltage, PV module.
1. INTRODUCTION
A photovoltaic PV module is a device which is able to convert solar energy into electric energy. Many techniques and
algorithms [1]‒[3] are used in order to obtain optimal conditions [4], [5]. Because the current-voltage I-V and powervoltage P-V characteristics may change from one module to another, a control should be associated to the module. In this
paper a low power photovoltaic systems with lead-acid battery for 5V regulated voltage for low power electronic circuits
is proposed. The mainly function of a battery (i.e. lead acid) in photovoltaic systems is to provide power when the
generating sourced is unavailable. The most commonly used batteries for PV systems have been lead-acid batteries.
Commercial batteries most suited for stand-alone power supplies have been those intended for stationary or float service.
These are designed for applications [6] such as serving as emergency power sources in uninterruptible power supplies. In
this use, the lead acid battery may be kept fully charged during the day throughout the diode, but immediately takes up
load demand when the PV source fails. More recently, this type of batteries has been developed to meet the specific
requirements of low power PV systems. Thus, the features based photovoltaic systems are of high reliability and low
maintenance costs [7]. Moreover, the battery maintenance is one of the major maintenance requirements of stand-alone
photovoltaic system [8]. In addition, such PV systems may concern the portable electronic devices: portable phones,
portable computer, panel displays, microprocessors and microcontroller and FPGA cards associated with low voltage (i.e.
5V) [9].
2. EXPERIMENTAL DETAILS
The PV source used for our study concerns two PV modules (model: OY350-HELIOS); each module is based on 20
silicon crystalline cells, which each 10 PV cells is connected between in series and in parallel with the 10 PV cells one
(Fig. 1). The surface of the module is 14cmx8cm. A Philips Lampe (PAR 38 EC FLOOD 30°, 230V 120W 6A) has been
chosen as the simulator light irradiation for the indoor current-voltage PV module measurements. A lux meter and power
meter (105lux=103W/m2) has been used for measuring the irradiance. A lead battery (HT640, HUITONG BATTERY
CO., LTD) with a nominal voltage of 6V and nominal capacity of 4Ah (i.e. the battery is normally rated 10-h discharge
rate) was chosen for our study on battery performances. For the all voltage-current I-V measurements, a digital compact
ammeter and voltmeter have been used. Thus, a potentiometer as a rheostat (or variable resistor) has been used for the I-V
measurements. A thermometer HD8601P (100 platinum RTD range: -50°C to +199°C) was used for the temperature
measurements. All the tests were carried out at room temperature and in open air.
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Volume 3, Issue 3, March 2014
ISSN 2319 - 4847
Figure 1: PV module shown 10 cells connected between in series and in parallel with the 10 PV cells one.
Our original proposed photovoltaic system is based on a photovoltaic module of voltage between 0V and12V (and
maximum current of 350mA), a lead acid battery of 6V and 4Ah, a circuit for the battery charging protection and the
output regulation voltage (Fig. 2). The battery is charged throughout different diodes; D1, D2 and D3. The output unit of
the PV system is supplied via the regulating circuit throw diode D1. When the PV voltage becomes inferior to the battery
voltage, the PV module is decoupled to the rest of system and the battery voltage is applied to the regulating circuit
throughout D4.
Connected for full input voltage
D1
VI
VO
VDD =5V
u1 7805
GND
PV 0-12VDC
D2
C2
C1
C3
C4
D3
R1
D4
Battery
6V 4Ah
Figure 2: Schema of the conceived low power PV system.
3. PHOTO-ELECTRICAL PV MODULE CHARACTERISTICS
The current voltage I- V characteristics of the studied PV module with different light intensities is shown in Fig. 3. We
noticed that the current increase with light intensity; it passes from about 8mA at intensity value of 3000lux up to 88mA
at 25000lux; as know the current depend mainly on the incident optical power [10]. In addition, the power increases with
light intensities (between 62lux and 25000lux) as a result of current increases (Fig. 4). The maximum power is achieved
at light intensity of 25000lux, which corresponds to the power value of 350mW. Similar behavior has been reported in
others work [11]. Thus, tracking of the maximum power point (MPP) of photovoltaic system is usually an essential part of
PV systems. Indeed, PV generation systems have two major problems; the electrical conversion efficiency and the electric
power generated by PV module that change continuously with weather conditions [12]‒[16]. The MPP tracking (MPPT)
technique is largely used in several researcher works with depth details [17]‒[20].
100
90
25000Lux
Current (mA)
80
10000Lux
70
6500Lux
60
5000Lux
3000Lux
50
1000Lux
40
500Lux
30
62Lux
20
10
0
0
1
2
3
4
5
6
Voltage (mA)
Figure 3: Current versus voltage characteristics for different light intensities.
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400
25000Lux
350
10000Lux
6500Lux
300
Power (mW)
5000Lux
3000Lux
250
1000Lux
200
500Lux
62Lux
150
100
50
0
0
1
2
3
4
5
6
Voltage (V)
Figure 4: Power versus voltage characteristics for different light intensities.
4. VARIABLE RESISTANCE EFFECT AT THE BATTERY LEVEL
The main function of the regulator circuit is to charge the battery and protect it from the overcharging as well as the deep
discharging that could damage the battery. Our particular regulator circuit is presented in Fig. 5; the input condenser (i.e.
capacitor) value of 100µF, is generally used in order to avoid the oscillation of the integrated circuit based regulation. The
output condenser allows reducing the short possible oscillations. In addition, the integrated circuit based regulation
delivers a tension between the output terminal (VO) and the intermediate terminal (GND). The condenser with lower
capacity value of 100nF (i.e. C2 and C3) was used generally to stabilize the regulated voltage by attenuating the possible
impulse parasites. Indeed, the u1 7805 is used in order to regulate the output voltage at about 5V with filtering out the DC
power noise.
Connecting for full input voltage
I input
D1
VI
V input
V output
VO
u1 7805
GND
D2
C1
C2
C3
C4
D3
R1
D4
Regulator
circuit control
Battery circuit
control
R
Figure 5: PV system circuit with variable resistance at the battery level.
4.1 Regulated voltage measurements versus input voltages and resistances at the battery level
A blocking diode is generally inserted between the battery and the photovoltaic module in order to prevent the battery
losing charge trough the module at night. As known, the delivered voltage is regulated (i.e. Vreg) for the input voltage
(VI) at least is 2 to 3 V larger than the value of Vreg. In order to show this behavior, we represent in fig. 6 the regulated
voltage versus the input voltage for different resistance values. We noticed for the different values of resistance and in
order to regulate 5V that the input voltage is approximately 8V, which is about 3V larger than the regulated voltage.
Below the threshold regulation voltage, a linear regime is observed. Thus, for the input voltage less than 4V, no
regulation of the voltage has been observed. For R1 with low value, the threshold input voltage is about 7,85V with input
current of about 27,17mA for a radiation of 6500lux. For R3 with higher value, the threshold input voltage is about 8,14V
that correspond to an input current of about 8,4mA for a radiation of 1000lux. In this study the relation between the input
voltage and the output voltage is given by (Fig. 6):
Vinput  Voutput  3V
(1)
We noticed, from this particular value of 8V, that the regulated voltage is obtained independently on the resistances
value. The regulated value is about 5V, which is adapted to the indoor and outdoor low power applications [21], [22].
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Regulating voltage (V)
5
4
3
R1 =10 
R1
R2 =100 
R2
2
R3 =1 k
R3
1
0
0
2
4
6
8
10
12
Input voltage (V)
Figure 6: Output regulated voltage versus input voltages for different resistance values at the battery level.
We present the simultaneously influence of the resistance at the battery level as well as the light intensities on the voltage
regulation performances, as shown in Fig. 7. For light intensity higher than 5000lux, the output voltage is immediately
regulated, which remain independent on the resistance. Moreover, for light intensity lower than 3000lux, the regulated
voltage value of 5V is only possible for high resistance value of about 1k; high resistance may correspond to the
deterioration of battery in practice [23], [24]. This behavior shows that the regulation is not inevitably influenced by the
battery aging.
Regulated voltage (V)
6
5
4
3
1000 lux
Série1
Série3
3000 lux
2
5000 lux
Série2
6500 lux
Série4
1
0
0
200
400
600
800
1000
1200
Battery resistance load ()
Figure 7: Regulated voltage versus battery resistance load.
4.2 Input voltage and regulated voltage measurements versus light intensities
The input voltage of the PV module depends on the resistances value as well as the light intensities. For a high resistance
value (i.e. 1k), the input voltage values are achieved quickly compared to 10 or 100 (Fig. 8). For light intensity
values less than 5000lux, the regulated voltage is mainly dependant on the resistance values (Fig. 9). Thus, for a
resistance value of 1k, the regulated voltage is abruptly achieved than rather for 100 or 10 one. However for light
intensities higher than 5000lux, the regulated voltage remains independent on the resistance value.
12
Input voltage (V)
10
8
6
R 1 =10 
Série1
Série2
R 2 =100 
4
R 3 =1 k
Série3
2
0
0
5000
10000
15000
20000
25000
30000
Light intensity (Lux)
Figure 8: Input voltage versus light intensity for different resistances at battery level.
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Regulated voltage (V)
6
5
4
R1 =10 
Série1
R2 =100 
Série2
R3 =1 k
Série3
3
2
1
0
0
5000
10000
15000
20000
25000
30000
Light intensity (Lux)
Figure 9: Input voltage versus light intensity for different resistances at battery level.
5. VARIABLE RESISTANCE EFFECT AT THE OUTPUT LEVEL
In order to explain the influence of output resistance values on the voltage regulation performances, a variable resistance
is placed on the output (Fig. 10).
Connecting for full input voltage
I input
D1
VI
V input
VO
V output
u1 7805
GND
D2
R
C2
C1
C3
C4
D3
R1
D4
Regulator
circuit control
Battery circuit
control
Figure 10: PV system circuit with variable output resistance.
5.1 Regulated voltage measurements versus input voltages and output resistances load
As shown previously, the regulated voltage is well obtained for the input voltage exceeded with about 3V (Fig. 11). Thus,
as shown in Fig. 12 (i.e. regulated voltage versus output resistances for different light intensities), the regulated voltage of
5v is only possible for high resistance value (i.e. 1k), which remain independently of the light intensities. This
behaviour it not similar to that already observed previously; the regulated voltage is more sensitive to the output
resistance than the battery level one.
Regulated voltage (V)
6
5
4
R1 =10 
R1
3
R2 =100 
R2
2
R3 =1 k
R3
1
0
2
4
6
8
10
12
Input voltage (V)
Figure 11: Regulated voltage versus input voltage.
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Regulated voltage (V)
6
5
4
3
Série1
1000 lux
3000 lux
Série2
5000 lux
Série3
2
6500 lux
Série4
1
0
0
200
400
600
800
1000
1200
Output resistance load ()
Figure 12: Regulated voltage versus output resistance load for different light intensities.
5.2 Input voltage and regulated voltage measurements versus light intensity
The input voltage is sensitive to the resistances at the output system (Fig. 13). For light intensity higher than 5000lux (i.e.
high photogenerated current), the regulated voltage is achieved only for resistance value of 1k. The interesting
regulated voltage is related to the output resistance value higher than 1k and light intensity upper to 5000lux. However,
for light intensity values lower than 5000lux, the regulated voltage is confirmed mainly dependant on the resistance
values (Fig. 14). Thus, for a resistance value of 1k, the regulated voltage is abruptly achieved than rather for 100 or
10 one. We noticed for low output resistance (less than 100) that no regulation was observed for high light intensity
values; the low output resistance may induce a relatively short-circuit current, and consequently a low voltage drop.
Figure 13: Input voltage versus light intensity for different resistances load.
Regulated voltage (V)
6
5
4
3
R 1 =10 
Série1
2
R2 =100 
Série2
R3 =1 k
Série3
1
0
0
5000
10000
15000
20000
Light intensity (Lux)
25000
30000
Figure 14: Regulated voltage versus light Intensity for different resistances load.
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6. Conclusion
PV module suppliers and major users have developed many low power regulators for power photovoltaic systems. These
regulators can be quite sophisticated, taking into account such effects as the solar radiation variation, the battery voltages
as well as the output consumption. In this work, a simple controlling circuit has been proposed for the low power PV
systems. The procedure design consists of the selecting of required capacity for the battery storage, which can provide a
reserve capacity in order to cover an exceptionally long period without sunshine, and seasonal storage. Thus, we have
developed an original low power photovoltaic system associated with lead-acid battery for 5V regulated voltage for low
power electronic applications. Indeed, various parameters have been investigated and considered in order to obtain a
stable regulated voltage at the output level. We noticed that the regulated voltage depends mainly on the input voltage
light intensity, the resistance at the battery level, and the resistance at the output level. As these parameters influence
generally the global PV system performances, it is difficult to size theoretically the PV system without taking into account
the detailed experimental study as well as have investigated powerfully here, which prove that our conceived and tested
PV system is meaningful and very promising for low power electronic applications. In addition, the outdoor tests for the
proposed PV system have been carried out (that not presented here); we noticed that the output voltage remain regulated
and stable of about 5V during the day, which proves the reliability of such system for the voltage supplying requirement
between 4V and 5V.
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AUTHORS
A. El Abbassi received the B.S. degree in applied sciences from College of Ibn Khaldoun -El jadida,
Morocco in 1988, the M.S. degree in high frequency and telecommunications from Faculty of Sciences
of El Jadida, in 1997, and the Ph.D Transistors MOS: Modeling and characterization from Faculty of
Sciences of El Jadida, in 2002. His research interests are the microelectronics and transmission
systems.
A. El Amrani received the B.S. degree in applied sciences from College of El Mansour Dahbi,
Morocco in 1997, the M.S. degree in Circuit, systems, micro and nano technologies for high frequency
communications and optics from Faculty of Sciences and Technology of Limoges, France, in 2005,
and the Ph.D. in high frequency electronics and optoelectronics from XLIM Research institute of
Physics, MINACOM Department, Limoges, France in 2008. His research interests are the
photoelectronic devices and optoelectronic systems.
M. El Amraoui received the B.S. degree in applied sciences from College of Hassan II Midelt,
Morocco in 1993, the M.S. degree in Materials, from Faculty of Sciences Meknes, Moulay Ismail
University in 2005, and the Ph.D. in Applied Physics to Materials and Archeomaterials from Faculty
of Sciences Meknes, Moulay Ismail University in 2011. His research interests are the Applied
Materials and systems.
C. Messaoudi received the Bachelor of sciences degree from College of Omar Ibn Abdelaziz, Oujda,
Morocco in 1978, the MS degree 1987 in materials science and the Ph.D in 1991, in Material Physics
Laboratory from Faculty of Sciences of Rabat, Morocco. His researchs are focused on optoelectronic
devices and systems.
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