The Low Temperature Analysis of the Used PV Modules During On-Site Generation in Thailand
This study involved the on-site working characteristic of the multicrystalline silicon (mc-Si) and monocrystalline (c-Si) photovoltaic (PV) modules during operates in the hot humid area. The objective of this study was to find out the crucial temperature which is a thermal boundary for the open circuit voltage (Voc) out put from the PV modules. The output voltages from the PV modules, which various with the climate parameters, were evaluated at the Department of Physics, Faculty of Science, Mahasarakham University. During the on-site investigation, the modules temperatures were assigned at 55, 65 and 75°C, respectively. The data was carried out and analyzed for finding out the crucial temperature of PV modules. Present results show that the Voc of both PV modules were dramatically decreased during the modules temperature is higher than 65°C. In addition, using of both c-Si and mc-Si PV modules at 55-65°C results the Voc output of the PV module in 22-25% decrease from the standard value at the standard test conditions. The study concluded that, both PV modules have no significant differences when operates the modules temperature at lower than 65°C. To keep the module temperature during generation in this location lower than 65°C is benefit for the voltage stability and thermal productivity by PV modules.
In this study, the crucial temperature of PV modules which effect to the dramatically
decrease of voltage during operation in Thailand has been investigated. The
crucial temperature of the PV module is the modules temperature value
which provides the benefit for both of the electricity generation side and the
thermal energy generation side. This study was to study the crucial temperature
which expected to useful for the proper design of the photovoltaic/thermal (PV/T)
module. The c-Si and mc-Si PV module have been used in the study due to these
types of the module are the majority installed in Thailand (Green,
2004; Kirtikara, 1997; Chokmaviroj
et al., 2006; Waewsak et al., 2007)
whereas, these modules have gained problems while operation at the high temperature
(Minemoto et al., 2007). Then these types of
PV module have been used in the study. With the fact that to all amount of solar
energy can not convert to electricity (Tripanagnostopoulos
et al., 2002) and the rest of energy is often found in term of heat
dissipated in PV module and rise up the module temperature. This effect reduces
the modules efficiency (Skoplaki et al., 2008;
Liu and Hao, 2001; Radziemska, 2003)
and provides long-term degradation of PV modules (Katz et
al., 2001; Schoen et al., 2000;
Meyer and van Dyk, 2004; Del Cueto and von Roedern,
The present commercial solar cell converts solar energy into electricity with
a relatively low efficiency, less than 20%. Which mean that, more than 80% of
the absorbed energy is dumped to the surroundings again after electric energy
conversion (Huang et al., 2001). The cell efficiency
is known to decrease due to non-uniform temperatures across the cell. The rise
up of the cell temperature decreases the cell efficiency. The cell at the highest
temperature will limit the efficiency of the whole string. There are several
instances of the study about effect of the temperature which influences on dropping
of voltage and module efficiency which describes as follows:
Andreev et al. (1997) found that the photocurrent
increases with the temperature at 0.1% °C-1 due to the decreasing
of the gap of the solar cell and that the open circuit voltage decreases at
-2 mV°C-1 between 20 and 100°C due to a reduction of the
gap but also due to an increasing of the saturation current. These two effects
lead to a decrease for the maximum available power equal to 0.35% °C-1.
And more recently, this influence has been estimated between -0.3 and -0.5%
°C-1 (Krauter et al., 1999; Emery
et al., 1996; King and Eckert, 1996).
For the module scale, Del Cueto (1996) studied the
performances of several photovoltaic modules using various technologies: crystalline
silicon (c-Si), multicrystalline silicon (mc-Si), Cadmium Telluride (CdTe) and
Copper Indium Diselenide (CIS). The study noted that for all c-Si, mc-Si and
CIS modules, the changes in efficiency due to temperature dependence appear
to be in the range of absolute 1-2% over a temperature change span of 30°C.
Moreover, Minemoto et al. (2007) have been studied
the electrical characteristics of the amorphous silicon (a-Si) and mc-Si in
the unsteady climate condition, 0-600 W m-2 and 0-100°C. And
the study found that the output energy of mc-Si module is sensitive to module
temperature but not to spectrum distribution.
Fukushige et al. (2009) had been study the effects
of the module temperature and irradiance on PV modules outdoors. The study was
found that the performance ratio of the c-Si PV module decreases with increase
in the module temperature. In contrast, the PR of a-Si strongly affected not
only the temperature history but also the difference of irradiation.
The recently studies mentioned above was investigated a characteristics of cells and modules during the solar cell temperature increased. Moreover, the previous studies above have less information of the crucial temperature of PV modules, which provided benefit on the electricity generation and the thermal energy generation.
The present study on the crucial temperature of PV modules was worked at the Department of Physics, Faculty of Science, Mahasarakham University. Mahasarakham Province is the area in the Northeastern, which is the hottest area in Thailand. The modules temperature, the electrical parameters and the weather conditions, e.g., ambient temperature and solar radiation have been measured and analyzed. Finally, the crucial temperature of the PV module is carried out.
MATERIALS AND METHODS
Site of the experiment: The experiment of the PV module was conducted
on October 2008 at the Department of Physics, Faculty of Science, Mahasarakham
University. The experiment was in the area of Mahasarakham University (16°14
N and longitude 103°15 E) and the geometrical location is 150 m above
the sea level. The humidity of the E-san region is dry for long periods during
the winter (November to February) and summer months (March to June). The maximum
temperature was found in a range 44-45°C (Khedari et
al., 2002). The mean temperature and relative humidity in winter and
summer are 20°C, 50% of the Relative humidity (Rh) and 35°C, 60% Rh,
respectively. The rainy season occurs from July to October. The mean temperature
and relative humidity are 29°C and 70% Rh, respectively. The maximum sky
quantities, global and diffuse radiation on a horizontal plane and global illuminance
on a horizontal plane are 1243.6, 683.2 W m-2 and 155 klux, respectively.
Annual means of those skies quantities are 446, 161.7 W m-2 and
59 klux, respectively. The area can be described as countryside (Pattanasethanon
et al., 2007).
Measurement of the PV modules
PV modules: The PV modules, i.e., c-Si PV module and mc-Si PV module, were used in the study. Figure 1a shows the c-Si PV module, which is a product from the BP solar company. The power output from the module is 50 Wp. In case of the mc-Si module (Fig. 1b), it had been produced by the RWE company, with the output at 50 Wp as well. Dimension of both PV modules are 0.45x0.98 m. The electrical characteristics of the c-Si and mc-Si PV modules from manufacturers are shows in Table 1. The electrical information in the table are the output power, the output current, the output voltage and the short circuit current, which the values are 50 W, 3.9 A, 17.4 V and 3.27 A for the c-Si module and 50 W, 2.9 A, 17.2 V and 3.2 A for the mc-Si module, respectively.
Measurement methods: In the experiment, the climate parameters at the
study site were observed. The Global solar irradiation on the plane of PV module
had been measured every 15 min by the Kipp and Zonen pyranometor (solarimeter)-CM11.
||(a) c-Si PV module and (b) mc-Si PV module
||Specification of PV modules
||Typical diagram of the measurement system
The ambient temperature surround the test area was measured for every 15 min
using the DaqPro data logger (model 5500). In case of the PV modules; the Voc
and the module temperature were recorded for every 15 min by data logger as
well. Figure 2 shows typical concept of the measurement system
in this study. The thermocouple type K was used for measuring temperatures.
Six temperature sensors were placed at the bottom of the PV modules. Then, the
measured voltage signals from temperature sensors and pyranometor were recorded
by the DaqPro data logger and stores to the PC via the USB communication cable.
The DaqLab software inside the PC was used for process and control the data
The study was focused on the module temperature due to it cause strong effect
on the reduction of voltage from PV module. The module temperature during the
noon in Thailand could be found in range 50-70°C (Waewsak
et al., 2007; Chokmaviroj et al., 2006;
Sasitharanuwat et al., 2007). Thus, the measurement
was started with the constant module temperature at 55, 65 and 75°C for
the 1st, 2nd and the 3rd day of the experiment, respectively. During the measurement,
the PV modules were laid on the North-South position, which the plane was focused
to the South. The inclination of the module is 16° same as the local latitude.
The module temperature test method is trying to control temperature to be uniformity
throughout the module and varying the solar irradiation. Via this method, the
temperature test panel (Fig. 3) were used to control the PV
module temperature. The PV module was placed inside the temperature test panel
which contained the electrical heater.
||Typical cross section of the temperature test panel for PV
And the six temperature sensors were placed at the bottom of the PV module.
The heater was tuned on during the test, except if the module temperature reached
the design value. In the experiment, the voltage signal form the temperature
sensor would be over limited when the module temperature reached to the design
value. Consequently, the electrical heater would be turned off by the temperature
controller. The electrical heater would be turn on again when the PV module
temperatures lower than the set point value.
The solar irradiation data, the ambient temperature data and the PV parameters
were measured on 21-23 October 2008. These parameters were recoded for every
15 min, from 6:00 am to 6:00 pm. The results were analyzed for the in?uencing
of the temperature on the drop of voltage of both PV modules.
The data obtained from the experiment were measurement has been analyzed by
focus the instantaneous reduction of the output voltage from PV modules.
||Solar irradiation data from the measurement
||The average module temperature and the open circuit voltage
during heat up the module
Then, the Voc during operation at 55, 65 and 75°C were compared
to find out the crucial temperature. The solar irradiation data on 21-23 October
2008, are shown in Fig. 4., the solar irradiation data shows
that, the maximum irradiation in this location (11:00 am to 01:00 pm) is 800
W m-2. The solar irradiation average is 400 W m-2, by
this value, it fits for PV to generate electricity in this area.
Temperature of PV module: The test of the PV module at different temperature
during the day was done in order to know the relevant characteristics of the
module temperature and the Voc during the operation. The c-Si PV
module was heated from 25°C during the morning and reached to 80°C during
the noon and cool down again from the noon to the evening. Table
2 shows the results from the study via this procedure, which the module
temperature and the Voc in each time during the day were plotted
inside (Fig. 5). The information in graph shows that, during
the solar irradiation is increased from the morning to the noon, it causes the
module temperature increased as well.
||Actual data of the C-Si PV module during the heat up procedure
Meanwhile, the Voc of the module
is reduced. The Voc of the PV module is started to decrease at 8:00 am during
the module temperature is reached 55°C. The Voc is continuously
reduced during the module temperature raise from 50°C up to 80°C (from
8:00 am to 1:00 pm). However, the most interesting point is during the module
temperature are between 55 to 75°C in the morning (the circle in Fig.
5). The module temperature beside this point is influenced on the instantaneous
reduction of the open circuit voltage from PV module. The deep discussion of
the module temperature in this range, which influence on the drop of the open
circuit voltage from PV module has been done, in order to find out the crucial
temperature in this range.
Drop of the open circuit voltage: The study deeply on the module temperature
in the range of 55-75°C has been done in order to know the crucial temperature
which extreamly influence on the reduction of PV modules. During the experiment
days, the module temperature was assigned at 55, 65 and 75°C for the 1st,
2nd and 3rd day, respectively. The Voc of PV modules is measured
every 15 min from 6 am to 6 pm. The measurement results of c-Si and mc-Si PV
modules are shown in Fig. 6a and b, which
the actual results are in Table 3 and 4.
The slope analysis was used to define the crucial temperature that influence on the instantaneous reduction of the voltage from the PV module. Table 5 shows that the slope of the c-Si and mc-Si were less significant different during the module temperature is at 55-65°C. During the modules temperature was on 65-75°C, the negative slope was higher than it found in the temperature range of 55-65°C, which means that a drops of the Voc of both module in this temperature range rise faster than in the range of 55-65°C. Moreover, the slope of mc-Si growth faster than c-Si in this temperature range, which mean that the open circuit voltage in mc-Si module is dropped faster than it found in the c-Si module during operate at 65-75°C.
The results from the experiment in Fig. 6 shows that the
Voc generated by the c-Si and mc-Si PV module were similar during
operates at 55 and 65°C. However, for the modules temperature is 75°C,
The study was found that the voltage output from the mc-Si PV module is lower
than the c-Si PV module. The module was heated up to 55, 65 and 75°C, the
Voc from both of the c-Si and mc-Si decreased. The reduction of the
Voc of both modules is show in Fig. 7a and b.
Compare the voc at the standard test condition (STC): The crucial temperature
of PV module was studied on the percentage of the open circuit voltage reduction
in each temperature ranges by do comparison with the test at STC (irradiance
of 1,000 W m-2, solar spectrum of am 1.5 and module temperature at
25°C), which were provided by the manufacturers.
||Actual data of Voc compare to the solar irradiation
of the c-Si PV module during operation in each temperature value
||Open circuit voltage of (a) c-Si PV module and (b) mc-Si PV
module and compare to the solar irradiation
||Actual data of Voc compare to the solar irradiation
of the mc-Si PV module during operation in each temperature value
||Slop of the PV modules in each temperature ranges
The comparison of the open circuit voltage shown in Fig. 8.
||Open circuit voltage of (a) c-Si PV module and (b) mc-Si PV
||Percent drop of Voc from a test at STC
This method was assigned the temperature which its caused the drop of
the Voc at 25% less than the Voc at STC, to be the crucial
temperature. From the results, the crucial temperature, which mainly influences
on the drop of the open circuit from c-Si and mc-Si PV module during operation
in this area exceed 25% of the value at STC, is the temperature at 65°C
(Fig. 8). The study recommend that in using of the c-Si and
mc-Si PV module in this location, especially in summer, should be avoid the
module temperature exceed 65°C.
The study of the crucial temperature of PV modules during the on-site operation
in the North-Eastern part of Thailand was done to evaluate the temperature value,
which it has a strong influences on the reduction of voltage from the PV modules.
The crucial temperature obtained from the study can be effectively used to design
the PV/T module. The PV/T module could be cool down the solar cell temperature
to be lower than the crucial value, by removing heat and using in the other
heating process. The c-Si and mc-Si PV module were used in this study due to
the major types of PV in Thailand. In present study, the measurement of the
output voltage from c-Si PV module during the module temperature is heated up
from 20 to 80°C had been done for subsequencing to the voltage profile of
the PV modules. This results shows that the open circuit voltage of the PV module
is begin to reduce during the module temperature raise from 50 to 80°C.
However, summer in Thailand the module temperature could be found at 50-70°C.
The crucial temperature of PV module is observed at 55, 65 and 75°C. The
investigation of the c-Si and the mc-Si PV module has been done by assigned
the module temperature at 55, 65 and 75°C for threeexperiment days; 21,
22 and 23 Oct 2008, respectively. The results shows that during the c-Si and
mc-Si module are operated at 55-65°C, the open circuit voltage from the
c-Si module and mc-Si module has no significantly difference. The Voc
from both PV modules operated at 65-75°C are dropped faster than at 55-65°C.
Moreover, the Voc of the mc-Si PV module at 65-75°C was reduced
faster than in the c-Si module, which was related to the characteristic of silicon
PV modules reported by Evans and Floschuetz (1977) and
Skoplaki and Palyvos (2009). Using the slope analysis
methods, we concluded that, in using of the mc-Si module in the North-Eastern
part of Thailand, the module temperature should not be exceeded 65°C. The
module temperature at 65°C is the critical temperature for providing the
Voc stability of the PV module in this area. According to Malik
and Damit (2003) which has been noted that the efficiency degradation of
the solar cell is due to the high cells operating temperature at 60-64°C.
Present results suggest that the module temperature at 65°C is considered
the most effective to many kinds of drying activities, e.g., peeled longan,
litchi fruit, rambutan, banana, straw mushroom and the other edible plants in
this area (Janjai et al., 2008, 2009;
Tansakul and Lumyong, 2008; Chanwitheesuk
et al., 2005; Paull et al., 1995;
Breymayer et al., 1993; Jiang
et al., 2002). With the methods, the crucial temperature will be
used to prospering design and construction the PV/T module, for producing both
of the electricity and the heat for the low temperature drying process in Thailand
and also in the temperate countries.
In the present studies, the experiment of the PV modules during the on site generation in Thailand has been demonstrated that, while the c-Si and mc-Si PV modules are heated up by the solar irradiation, the Voc have been reduced to 25% around on noon lower than the value at the STC. Base on this value, the crucial temperature of PV modules has been found at 65°C, which the crucial temperature provides the benefits on both of the electricity generation and the thermal energy generation by PV modules. This crucial temperature is appropriated for some of the food drying processs temperature in Thailand. Moreover, the crucial temperature of PV modules will be applied for the proper design and construction of the PV/T module, to produce heat and electricity at the low temperature in Thailand and temperate countries.
This study was funded by the Division of Support and Development Research, Mahasarakham University and the Thailand Research Fund.
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