- Email: [email protected]
Effects of operational conditions on the energy efficiency of photovoltaic modules operating in Malaysia
Accepted Manuscript Effects of Operational Conditions on the Energy Efficiency of Photovoltaic Modules Operating in Malaysia
Mohammad Mafizur Rahman, Md Hasanuzzaman, Nasrudin Abd Rahim PII:
S0959-6526(16)32084-4
DOI:
10.1016/j.jclepro.2016.12.029
Reference:
JCLP 8604
To appear in:
Journal of Cleaner Production
Received Date:
09 April 2016
Revised Date:
06 December 2016
Accepted Date:
07 December 2016
Please cite this article as: Mohammad Mafizur Rahman, Md Hasanuzzaman, Nasrudin Abd Rahim, Effects of Operational Conditions on the Energy Efficiency of Photovoltaic Modules Operating in Malaysia, Journal of Cleaner Production (2016), doi: 10.1016/j.jclepro.2016.12.029
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
ACCEPTED MANUSCRIPT
Highlights
A photovoltaic (PV) system is experimentally investigated under Malaysian climate.
The factors affecting the performance of this system are discussed.
Solar cell performance is enhanced by optimizing the operating parameters.
Output power decreases by 0.22% as cell temperature increases by 1 °C.
A cooling system improves efficiency by 15.72% under peak operating conditions.
ACCEPTED MANUSCRIPT
RESULTANT WORD COUNT: 5733 Effects of Operational Conditions on the Energy Efficiency of Photovoltaic Modules Operating in Malaysia Mohammad Mafizur Rahman, Md Hasanuzzaman, Nasrudin Abd Rahim UM Power Energy Dedicated Advanced Centre (UMPEDAC) Level-4, Wisma R&D, University of Malaya, 59990 Kuala Lumpur, Malaysia. Abstract Photovoltaic (PV) modules convert a small portion of solar radiation into electrical energy and convert the rest into heat. As a result, the temperature of these modules is increased and their electrical efficiency is degraded. In this study, the effects of various operating parameters, such as solar cell temperature, irradiation intensity, mass flow rate of cooling water, humidity, and dust, on the output performance of a PV module are investigated under outdoor operating conditions. A finned tube is placed at the bottom of the PV module for cooling. Results show that the electrical efficiency of the module decreases by 5.82% as solar cell temperature increases by 26.10 °C. The electrical efficiency also decreases by approximately 0.22% as the temperature of the PV module increases by 1 °C. As irradiation intensity increases by 100 W/m2, the solar cell temperature increases by 3.82 °C and the output power increases by 3.14 W, but the efficiency decreases by 0.85%. In summary, solar cell temperature, solar irradiation intensity, mass flow rate of cooling fluids, humidity, and dust significantly affect the performance of PV modules. Keywords: Energy, Solar energy, Photovoltaic, Module, Cooling system. Nomenclature Ac Cross sectional area of fin (m2) Asc Area of solar cell (m2)
Corresponding author: Email: [email protected] / [email protected] (Attn: Dr. Md. Hasanuzzaman)
1
ACCEPTED MANUSCRIPT Eab Total energy absorbed by top surface of module (W) Eb
Total energy transfer by conduction and convection from top surface to bottom surface (W)
Ectop Total energy loss from top surface to bottom surface at ambient temperature by convection process (W) Ee
Electrical energy produced by module (W)
G
Incident irradiation (W/m2)
Imax Maximum current (A) Isc
Short-circuit current (A)
k
Thermal conductivity (W/(mK))
p
Perimeter of fin (m)
Pmax Maximum power (W) psc Packing factor of solar module RH Relative humidity (%) t
Thickness (m)
Ta Ambient temperature (°C) Tb Temperature of tedlar back surface (°C) Tsc Top surface temperature of solar module (°C) Usca Overall heat transfer coefficient through glass cover from top surface of module to ambient (W/(m2K)) Ut Overall heat transfer coefficient from top surface of module to tedlar back surface (W/(m2K)) Vmax Maximum voltage (V) Voc, Open-circuit voltage (V) W
Width of solar module 2
ACCEPTED MANUSCRIPT x
Length of solar module
Greek letter τg Transmissivity of glass ρ
Density (kg/m3)
αsc Absorptivity of solar module ηsc Electrical efficiency of solar module αt Absorptivity of tedlar back sheet
1 Introduction Conventional power generation threatens the environment and impedes environmental sustainability. In modern power generation, greenhouse gases emitted by fossil fuels are considered a global concern that should be addressed effectively (Hasanuzzaman et al., 2011, 2015). To enhance globalization, researchers focus on the development of sustainable energy systems. Renewable energy systems are clean and sustainable potential resources, and the application of these systems have expanded worldwide (Singh, 2013 and Borges Neto et al., 2010). For instance, photovoltaic (PV) technology is an ecofriendly, sustainable, and effective innovation in advanced global development (Hosenuzzaman et al., 2015 and Ahmed et al., 2013). Solar electricity is generated from 15% to 20% of the total incident irradiation, and the remaining proportion is converted into heat and solar cell temperature is increased (Teo et al., 2012 and Jie et al., 2007). As solar cell temperature increases by 1 °C, the output power is reduced by 0.48% under standard test conditions and by 0.52% under outdoor conditions at 500 W/m2 irradiation (Park et al., 2010). At 1000 W/m2 irradiation, the electrical efficiency decreases by 0.06% as solar cell temperature increases by 1 °C (Rahman et al., 2015). The application of a thin-film water flow to the upper surface of a PV module during peak operating hours can lead to an 18.7 °C decrease 3
ACCEPTED MANUSCRIPT in solar cell temperature and a 33% increase in cell efficiency (Hosseini et al., 2011). Thus, effective cooling is necessary to reduce the temperature of solar cells and increase the output efficiency of PV systems. Dubey et al. (2009) found that the glass-to-glass PV module efficiency increases from 9.75% to 10.41% when an air duct is placed at the back of the module. Saad and Masud (2009) increased the PV efficiency by 15% via a water-trickling system on the upper surface of the PV module. Teo et al. (2012) increased the PV efficiency from 8%–9% to 12%– 14% by applying an air flow through a parallel duct attached to the back of a polycrystalline solar module. Bahaidarah et al. (2013) increased the electrical efficiency of a PV module by 9% with 20% solar cell temperature reduction via an effective water-cooling system at the back of a monocrystalline PV module. Chandrasekar et al. (2013) experimentally reduced the solar cell temperature of a PV module by 30% and respectively increased its output power and electrical efficiency by 6.5 W and 1.4% by using a cotton-wick structure with a cooling system consisting of Al2O3/water, CuO/water nanofluid, and water. Sheyda et al. (2013) experimentally increased the module output power by 38% by passing a two-phase flow regime through a microchannel attached to the bottom of a PV module. Ceylan et al. (2014) enhanced the efficiency of a PV module from 10% to 13% by employing a temperature-controlled cooling water flow through a spiral tube heat exchanger system attached to the bottom of the module. Alami (2014) reduced the temperature of a module by using a thin-film water flow through a synthetic clay layer attached to the bottom of the PV module. As a result, the output power and output voltage of the PV module are increased by 19.1% and 19.4%, respectively. The electrical efficiency of the PV module is improved by approximately 8.2%, 9.01%, and 9.75% when it is cooled with water, 1 wt% silica– water, and 3 wt% silica–water nanofluid, respectively, compared with the results of a PV module without cooling systems (Sardarabadi et al., 2014).
4
ACCEPTED MANUSCRIPT Our research investigates the effects of various operating parameters, such as solar cell temperature, irradiation intensity, cooling, humidity, and dust, on the output power and efficiency of a PV module under outdoor operating conditions. 2 Research methodology 2.1 Experimental setup The experimental setup was established on the solar park at Level 3, Wisma R&D, University of Malaya (UM) in Malaysia to investigate the effects of various parameters on the performance of a PV module. The experimental setup mainly consisted of a PV module, a heat exchanger device, a centrifugal pump, and a cooling radiator. A monocrystalline solar module (SY-90M, Shaiyang, Hebei, China) was also used in the experiment. Table 1 summarizes the specifications of the solar module under standard conditions. Table 1 SY-90M monocrystalline module specifications A monocrystalline PV is generally manufactured with layers of different materials: (1) glass top cover, (2) anti-reflective coating, (3) monocrystalline silicon layer, (4) ethylene–vinyl acetate layer, (5) metal back sheet, and (6) Tedlar polyvinyl fluoride layer. The layers are entrenched in a metallic frame (Jones and Underwood, 2001). The properties of the PV layers are listed in Table 2. Table 2 Properties of PV layers A rectangular heat exchanger device composed of a copper tube with a diameter of 22 mm was used to cool the PV module (Figure 1). Figure 1 PV module heat exchanger device The length and width of the heat exchanger device were 950 and 420 mm, respectively. This device consisted of seven parallel circular copper tubes. A semicircular finned plane sheet at the top of each parallel tube was used to secure the device to the back of the solar module and to facilitate 5
ACCEPTED MANUSCRIPT the smooth flow of heat transfer. The fins increased the heat transfer rate from the bottom. Figure 2 shows an image of the experimental setup. Figure 2 Experimental setup A small centrifugal pump (Pentax CP45) was used to circulate water through the heat exchanger tube. The pump capacity was 5–35 L/min, the discharging head was 9–35 m, and the operating power consumption was 0.5 kW. A 1.3 kg/cm2 cooling radiator was used to cool the heated water. Table 3 summarizes the design parameters of the experimental setup. Table 3 Design parameters of experimental setup 2.2 Experimental instrumentation A digital data taker (DT80) was used to measure temperature and irradiation intensity. A maximum power point tracker (MPPT) was utilized to determine and control the output current and output voltage, specifically, Isc, Voc, Imax, Vmax, and Pmax, of the module. A flow meter (LZB-10B) was employed to identify the water discharge and velocity with a measurement range of 16–180 L/h. Two PTFE-exposed welded-tip K-type thermocouples were used to measure the top and bottom surface temperatures of the module. Two additional thermocouples of the same type were utilized to determine the inlet and outlet temperatures of the heat-exchanger device. An ideal data logger was employed to collect temperature data. The temperature measurement range of the data logger was −75 °C to 250 °C. A pyranometer (LI-COR PY82186) was used to measure the solar irradiation intensity. The irradiation measurement range of the pyranometer was 0 W/m2 to 1280 W/m2, its spectral range was 300 nm to 1100 nm, and its operating temperature range was −40 °C to 75 °C. The pyranometer was accurately calibrated prior to use. A humidity sensor (HU1030NA) was utilized to determine the ambient humidity at a range of 20% to 90% RH.
6
ACCEPTED MANUSCRIPT 2.3 Experimental test conditions and data acquisition Data in the presence or absence of cooling conditions were collected on sunny days from January 2015 to March 2015. During the study, the solar park area of the UM Power Energy Dedicated Advanced Center was completely shaded by buildings after 12:40
PM.
The data were collected
from 09:00 AM to 12:40 PM. In this period, solar irradiation intensity varied approximately from 300 W/m2 to 1000 W/m2. Ambient temperature varied approximately from 29 °C to 35 °C. The data used in the analysis were collected under similar meteorological conditions on different days. The efficiency of the solar module was observed as solar irradiation intensity and cell temperature increased. Various mass flow rates (30, 60, 90, and 180 L/h) of the cooling water through the heat exchanger of the PV module were adopted; the effects of irradiation intensity on solar cell temperature and output performance were examined under cooling conditions. The data from the inlet and outlet thermocouples of the heat-exchanger device, the top and bottom surface thermocouples of the module, and the pyranometer were regularly collected by using the data taker at 10 min intervals throughout the experiment. 2.4 Mathematical formulation 2.4.1 Heat transfer from the top surface of the module The total energy absorbed by the top surface of the module can be expressed as follows (Tiwari et al., 2006, Dubey and Tiwari, 2008, Dubey and Tay, 2013): E ab g sc p sc GWx
(1)
The energy lost by convection at the top surface of the module is determined using the following equation: E ctop U sca Tsc Ta Wx
(2)
The amount of energy transferred to the bottom surface of the module is obtained by using Eq. (3): 7
ACCEPTED MANUSCRIPT E b U t Tsc Tb Wx
(3)
The total amount of energy converted into electrical energy is represented by the following:
E e sc p sc GWx
(4)
The energy balance equation for the top surface is expressed as follows: E ab E ctop Eb E e
(5)
The solar cell temperature is calculated using Eq. (6):
Tsc
pscG g sc sc (U scaTa U tTb )
(6)
U scaU t
2.4.2 Heat transfer through a fin The heat transfer from a surface to its surroundings has been described by Newton’s law of cooling (Cengel, 2006):
Q conv hair As (Ts T )
(7)
The heat transfer through a fin is calculated according to Fourier’s law of heat conduction:
Qadiabatic ,tip hair pkAc (Tb T ) tanh ml
(8)
where
m
hair p kAc
(9)
If convection heat transfer is considered from the fin tip, the fin length should be corrected by the following equation: Lc L
t Ac . The corrected length of a rectangular fin is Lc L , and the 2 p
corrected length of a cylindrical fin is Lc L
D . 4
The maximum heat transfer through a fin with infinite conductivity is expressed as follows: Q fin , max hair Afin (Tb Ta )
(10) 8
ACCEPTED MANUSCRIPT The fin efficiency can be described as Eq. (11):
fin
Q fin
(11)
Q fin ,max
However, Q fin finQ fin , max fin hair Afin (Tb Ta ) .
(12)
The efficiency of a very long fin is determined as follows:
longfin
Q fin Q fin , max
hair pkAc (Tb Ta ) 1 kAc 1 hair Afin (Tb Ta ) L hair p ml
(13)
The efficiency of an adiabatic tip is calculated as follows:
adiabatic ,tip
Q fin Q fin , max
hair pkAc (Tb Ta ) tanh ml 1 kAc tanh ml hair Afin (Tb Ta ) L hair p ml
(14)
The total heat-transfer rate from the finned surface is the summation of the heat transfer from the finned surface and the heat transfer from the unfinned surface: Qtotal , fin Qunfin Q fin hair Aunfin (Tb Ta ) fin hair Afin (Tb Ta )
(15)
Table 4 Heat-transfer parameters of the system (Dubey and Tay, 2013) 3 Results and discussion 3.1 Effect of temperature on PV module performance The output power of a PV module depends on various factors, such as solar irradiation intensity, ambient temperature, humidity, and wind velocity. Under outdoor operating conditions, the solar irradiation intensity continuously fluctuates. Figure 3 Time versus irradiation intensity curve In Figure 3, the data used for the analysis were collected under similar irradiation intensities on different days. An average irradiation value was considered with respect to time throughout the entire analysis. As solar irradiation intensity increased, solar cell temperature and output power
9
ACCEPTED MANUSCRIPT increased. The solar module efficiency was directly related to the solar cell temperature (Figure 4). Figure 4 Solar cell temperature versus efficiency curve In the initial state and in the absence of cooling conditions (Figure 4), the efficiency of the module was 13.29%, and the solar cell temperature was 33.82 °C. Under peak operating conditions, the module efficiency decreased to 7.46%, whereas the solar cell temperature increased to 59.92 °C. The total electrical efficiency decreased by 5.82%, which was 43.83% of the initial efficiency. The solar cell temperature increased by 26.10 °C. In the absence of cooling and outdoor operating conditions, the electrical efficiency decreased by 0.22% as the solar cell temperature increased by 1 °C. In Figures 5 and 6, the temperatures at different layers, namely, top glass surface, bottom surface, and solar cell, of the solar module increased as the duration was prolonged in the absence and presence of cooling conditions as the irradiation intensity increased with duration. Figure 5 Temperatures at different layers of the solar module (without cooling) In the current investigation, the solar cell temperatures under outdoor operating conditions without cooling were 33.82 °C and 59.92 °C in the initial and peak periods, respectively. Chandrasekar et al. (2013) found that the solar cell temperatures in the absence of cooling conditions in the Bharathidasan Institute of Technology (BIT) campus at Anna University, Tiruchirappalli, India are approximately 37 °C at 600 W/m2 irradiation and approximately 65 °C at 1300 W/m2 irradiation in the initial and peak operating periods, respectively; the experiment was run in April 2012 at the maximum ambient temperature of 37 °C prevailing at that time. Bahaidarah et al. (2013) conducted an experiment at King Fahd University of Petroleum and Minerals (KFUPM) in Dhahran, Saudi Arabia in February 2012 when the maximum ambient temperature was 21 °C and recorded a solar cell temperatures of 25 °C at 240 W/m2 irradiation and 44 °C at 979 W/m2 10
ACCEPTED MANUSCRIPT irradiation in the absence of cooling conditions. The solar cell temperatures in the present investigation are consistent with the results obtained by Chandrasekar et al. (2013) but are different from those obtained by Bahaidarah et al. (2013). These differences were attributed to the incident irradiation and ambient temperature variations. Figure 6 Temperatures at different layers of the solar module (with cooling) In the current investigation, the solar cell temperatures with water cooling were 31.09 °C and 49.64 °C in the initial and peak operating periods, respectively. Chandrasekar et al. (2013) conducted a study in the BIT campus in April 2012 when the maximum ambient temperature was 37 °C and found that the temperatures of a cooled solar cell were approximately 40 °C at 600 W/m2 irradiation and 50 °C at 1300 W/m2 irradiation under initial and peak operating conditions, respectively. Bahaidarah et al. (2013) also performed a study at KFUPM in February 2012 when the maximum ambient temperature was 21 °C and observed that the temperatures of a cooled solar cell were 22 °C at 240 W/m2 irradiation and 35 °C at 979 W/m2 irradiation. Hence, the temperatures of the cooled solar cell in the present investigation are consistent with the results obtained by Chandrasekar et al. (2013) but are different from those observed by Bahaidarah et al. (2013). These deviations were ascribed to the differences in solar irradiation intensity, wind velocity, ambient temperature, and cooling capacities of the coolant and heat-exchanger device. Therefore, different operating cell temperatures were obtained in our study and those in previous studies (Chandrasekar et al., 2013; Bahaidarah et al., 2013). In a PV module, 15% to 20% of solar radiation is converted into electricity, and the remaining proportion is converted into heat (Teo et al., 2012). In the solar cell layer of a PV module, some portions of heat energy can be transferred to the environment through convection, whereas other portions can be transferred to the Tedlar bottom surface. Some portions of solar radiation are directly absorbed by the Tedlar back surface because of the packing factor, which is responsible 11
ACCEPTED MANUSCRIPT for the additional heat generation at the bottom surface (Dubey and Tay, 2013). The top glass surface transmits 96% of the incident irradiation to the solar cell surface. Moreover, the overall heat transfer coefficient through the glass covering the top surface of the module to the environment Usca is 7.14 W/(m2K). The overall heat transfer coefficient of the Tedlar back surface sheet to the outside environment is 5.81 W/(m2K). Thus, the heat transferred from the bottom surface to the environment is lower than the heat transferred from the glass cover to the environment. Consequently, the Tedlar bottom surface temperature is higher than the top glass surface temperature (Dubey and Tay, 2013, Dubey and Tiwari, 2008). Eq. (6) shows that solar cell temperature is directly related to the Tedlar bottom surface temperature, ambient temperature, and incident irradiation. In Table 2, the specific heat capacity of the monocrystalline solar cell layer of a PV module is much higher than that of the Tedlar bottom layer, that is, the solar cell layers rapidly absorb more heat. Thus, the temperature of solar cells is higher than those of the top glass surface and the Tedlar bottom surface. 3.2 Effect of irradiation intensity on PV module performance The effects of irradiation intensity on the PV module cell temperature, output power, and efficiency were also investigated under outdoor operating conditions with and without cooling. Figure 7 Irradiation intensity versus solar cell temperature curve In Figure 7, the solar cell temperature increases as irradiation intensity increases. Without cooling, the solar cell temperature was 33.82 °C in the initial period, and this temperature subsequently increased to 59.92 °C during the peak operation. The solar cell temperature increased by 26.10 °C when the irradiation intensity increased by 683 W/m2. The solar cell temperature increased by 3.82 °C as irradiation intensity increased by 100 W/m2 without cooling conditions. Under water-cooling conditions and in the initial period of the investigation, the solar cell temperature was 31.09 °C, which increased to 49.65 °C in the peak operating period. The solar cell temperature increased by 12
ACCEPTED MANUSCRIPT 18.56 °C when the irradiation intensity increased by 683 W/m2. With cooling, the solar cell temperature increased by 2.72 °C as irradiation intensity increased by 100 W/m2. Teo et al. (2012) conducted an experiment on the rooftop of the EA building at the National University of Singapore in September 2009 and found that irradiation intensity ranged from 280 W/m2 to 1200 W/m2 without cooling, and the module operating temperature ranged from 47 °C to 65 °C. By comparison, irradiation intensity ranged from 550 W/m2 to 1050 W/m2 with cooling, and the operating temperature of the module ranged from 41 °C to 48 °C. The solar cell temperature increased by 1.8 °C and 1.4 °C as irradiation intensity increased by 100 W/m2 in the absence and presence of an air cooling system, respectively. Bahaidarah et al. (2013) conducted an experiment at KFUPM in February 2012 when the maximum ambient temperature was 21 °C and found that the irradiation intensity ranged from 240 W/m2 to 979 W/m2. In the absence of cooling conditions, the operating temperature of the module ranged from 25 °C to 44 °C. Under cooling conditions, the operating temperature of the module ranged from 21 °C to 35 °C. The solar cell temperature increased by 2.6 °C and 1.9 °C as irradiation intensity increased by 100 W/m2 without and with a water-cooling system, respectively. Chandrasekar et al. (2013) performed an experiment in the BIT campus in April 2012 when the maximum ambient temperature was 21 °C and observed that the operating irradiation ranged from 600 W/m2 to 1300 W/m2. Without cooling, the module-operating temperature ranged from 37 °C to 65 °C. With cooling, the module-operating temperature range was 40 °C to 50 °C. The solar cell temperature increased by 4 °C and 1.4 °C as irradiation intensity increased by 100 W/m2 without and with a water-cooling system, respectively. Table 5 Comparison of irradiation intensities and cell temperatures obtained from different investigations
13
ACCEPTED MANUSCRIPT Our results were similar to those of Chandrasekar et al. (2013) and Bahaidarah et al. (2013) but were different from those of Teo et al. (2012) because of variations in incident solar irradiation levels, module-operating temperatures, coolant effectiveness degrees, wind velocities, and ambient temperatures. Figure 8 Irradiation intensity versus output power curve Figure 8 shows that the output power of the PV module increased as irradiation intensity increased. The initial incident irradiation was approximately 312 W/m2 and the output power was 27.12 W in the absence of cooling conditions. During the peak operation, the incident irradiation level was approximately 995 W/m2, and the output power was 48.59 W. The output power increased by 21.47 W with an approximately 683 W/m2 increase in the irradiation intensity. In the absence of cooling conditions, the output power increased by 3.14 W as irradiation intensity increased by 100 W/m2. Under water-cooling conditions, the initial incident irradiation level was approximately 312 W/m2 and the output power was 29.72 W. During the peak operation, the incident irradiation level was approximately 995 W/m2 and the output power was 56.23 W. The output power increased by 26.51 W with an approximately 683 W/m2 increase in the irradiation intensity. Under cooling conditions, the output power increased by 3.88 W as irradiation intensity increased by 100 W/m2. Figure 9 Irradiation intensity versus efficiency curve In Figure 9, the electrical efficiency of the PV module decreased as irradiation intensity increased. Without cooling, the initial incident irradiation level was approximately 312 W/m2 and the electrical efficiency of the module was 13.29%. During peak operation, the incident irradiation level was approximately 995 W/m2 and the electrical efficiency of the module was 7.46%. The electrical efficiency of the module decreased by 5.82% as irradiation intensity increased by 683 W/m2. Without cooling, the electrical efficiency of the module decreased by 0.85% as irradiation intensity increased by 100 W/m2. With water cooling, the initial incident irradiation level was 14
ACCEPTED MANUSCRIPT approximately 312 W/m2 and the electrical efficiency of the module was 14.56%. During peak operation, the incident irradiation level was approximately 995 W/m2 and the electrical efficiency of the module was 8.64%. The electrical efficiency of the module decreased by 5.92% as irradiation intensity increased by 683 W/m2. With cooling, the electrical efficiency of the module decreased by 0.87% as irradiation intensity increased by 100 W/m2. 3.3 Effect of cooling on PV module performance The flow rate of the cooling water was set at 90 L/h to investigate the cooling effect on PV module performance. Figure 4 shows that the module with a water-cooling system exhibited an efficiency of 14.56% and a solar cell temperature of 31.09 °C in the initial state. Under peak operating conditions, the module efficiency decreased to 8.64%, whereas the solar cell temperature increased to 49.65 °C. The total electrical efficiency decreased by 5.92%, which was 40.68% of the initial efficiency. By contrast, the solar cell temperature increased by 18.56 °C. Under water cooling and outdoor operating conditions, the electrical efficiency decreased by 0.32% as solar cell temperature increased by 1 °C. The effect of the flow rate of cooling water on the PV module performance was also investigated. Figure 10 Solar cell temperatures at different flow rates Figure 10 illustrates that the solar cell temperature decreased as the flow rate increased with various irradiation intensities. Thus, the solar module efficiency increased as the flow rate of cooling water increased. However, the solar cell temperature slightly decreased as the flow rate of cooling water increased. Figure 11 Flow rate versus solar cell temperature curve Figure 12 Flow rate versus efficiency curve Figures 11 and 12 correspondingly reveal the decrease in solar cell temperature and the increase in PV module efficiency at different flow rates under peak operating conditions. These patterns 15
ACCEPTED MANUSCRIPT changed linearly up to a 90 L/h flow rate of cooling water. Solar cell temperature slightly decreased as the flow rate increased and exceeded 90 L/h. Hence, 90 L/h is the most suitable flow rate to enhance the efficiency of the PV module. Figure 4 also indicates that the efficiency of the PV module is enhanced by using a water-cooling system. As shown in Figure 4, the solar cell temperature decreased by 10.28 °C when the water-cooling system was used. During peak operating conditions, a water flow rate of 90 L/h increased the output power by 7.64 W and the electrical efficiency by 1.17%. Under cooling and outdoor operating conditions, in which the cell temperature was 17.16% lower, the module output power or efficiency was 15.72% higher than that in the absence of cooling conditions. Chandrasekar et al. (2013) reduced the solar cell temperature by 20 °C and increased the output power by 6.5 W and electrical efficiency by 1.4% under outdoor operating conditions. Bahaidarah et al. (2013) also decreased the solar cell temperature by 20% and increased the electrical efficiency by approximately 9% via a back surface water-cooling system. Table 6 Comparison of performance improvements by cooling systems employed in different studies Thus, the performance of the cooling system used in the current study was better than those employed by Chandrasekar et al. (2013) and Bahaidarah et al. (2013). 3.4 Heat transfer through heat-exchanger fins The fins attached to the half-round copper sheet of the heat-exchanger device also increased the cooling rate of the PV module (Figure 13). Figure 13 Heat transfer through the fins of the rectangular half-round copper sheet with cooling
16
ACCEPTED MANUSCRIPT Figure 13 illustrates the heat transferred from the fin surface attached to the rectangular half-round copper sheet at the back surface of the module. With water cooling, the system with a fin surface can remove 5 W more heat than that without a fin surface. Therefore, the effective water-cooling method used in this study decreased the temperature at the bottom surface and the temperature of the solar cell. At the bottom surface, heat was also directly lost to ambient air by convection. Heat was also transferred to ambient air from the fins attached to the rectangular half-round copper sheet of the heat exchanger. Heat was also transferred to the flowing water from the back surface. 3.5 Effect of dust on PV module performance The effect of dust on the performance of the PV module was also investigated for 2 consecutive days under outdoor operating conditions with similar irradiation levels. Dust (0.01 g/cm2) was applied to the top surface of the PV module, and the output power and efficiency of the module were observed. Figure 14 Effect of dust on solar cell output power under outdoor operating conditions Figure 15 Effect of dust on solar cell efficiency under outdoor operating conditions Figures 14 and 15 respectively show that the output power of the PV module reached 48.89 W and its electrical efficiency was 7.51% in the peak operating period under outdoor conditions. With dust on the top surface of the PV module, the output power decreased to 40.14 W and the electrical efficiency was 6.16% in the peak operating period. Thus, the output power and efficiency decreased by 8.75 W and 1.34%, respectively. The performance of the module with dust on its surface was 17.90% lower than that of the module without dust. 4 Conclusion The operating parameters affecting the performance of the PV module are described as follows:
17
ACCEPTED MANUSCRIPT As the solar cell temperature increases by 26.10 °C, the electrical efficiency of the module decreases by 5.82%, that is, electrical efficiency decreases by 0.22% as temperature increases by 1 °C. The solar cell temperature increases by 26.10 °C when the irradiation intensity increases by 683 W/m2, that is, temperature increases by 3.82 °C as irradiation intensity increases by 100 W/m2. As irradiation intensity increases by 683W/m2 under outdoor operating conditions, output power increases by 21.47 W, that is, output power increases by 3.14 W as irradiation intensity increases by 100 W/m2. As the flow rate of cooling water increases, the temperature of solar cells decreases and the efficiency of the PV module increases. A low cooling water flow rate is economical and effective for the cooling of PV modules. Cooling water is passed through a heat exchanger at the back of the PV module. Under peak operating conditions and at a flow rate of 90 L/h, the solar cell temperature decreases by 10.28 °C. As the temperature of the PV module decreases, its output power and electrical efficiency increase by 7.64 W and 1.17%, respectively. Under peak outdoor operating conditions, the output performance is increased by 15.72% when a water cooling system is used. With 0.01 g/cm2 of dust on the solar module surface, the output power and efficiency of the solar module decrease by 8.75 W and 1.34%, respectively. This finding is 17.90% lower than the output generated by the module without dust. Therefore, temperature, irradiation intensity, and dust can decrease the energy efficiency of PV modules. Water cooling systems can effectively reduce the solar cell temperature and consequently increase the energy efficiency of PV modules. In a large power plant, water cooling system can save a considerable amount of power. 18
ACCEPTED MANUSCRIPT Acknowledgments The authors are grateful for the financial support provided by the University of Malaya Research Grant (UMRG) scheme (Project no. RP016A-15SUS).
References Ahmed, F., Al Amin, A.Q., Hasanuzzaman, M., Saidur, R., 2013. Alternative energy resources in Bangladesh and future prospect. Renew. Sust. Energ. Rev. 25, 698-707. Alami, A.H., 2014. Effects of evaporative cooling on efficiency of photovoltaic modules. Energy Conv. Manag. 77, 668-679. Armstrong, S., Hurley, W.G., 2010. A thermal model for photovoltaic panels under varying atmospheric conditions. Appl. Therm. Eng. 30, 1488-1495. Bahaidarah, H., Subhan, A., Gandhidasan, P., Rehman, S., 2013. Performance evaluation of a PV (photovoltaic) module by back surface water cooling for hot climatic conditions. Energy, 59, 445-453. Borges
Neto,
M.R.,
Carvalho,
P.C.M.,
Carioca,
J.O.B.,
Canafístula,
F.J.F.,
2010.
Biogas/photovoltaic hybrid power system for decentralized energy supply of rural areas. Energy Policy. 38, 4497-4506. Cengel, Y.A., 2006. Heat and Mass Transfer: A practical Approach. Third ed. Mc Graw Hill, Singapore. Ceylan, I., Gürel, A.E., Demircan, H., Aksu, B., 2014. Cooling of a photovoltaic module with temperature controlled solar collector. Energy Build. 72, 96-101. Chandrasekar, M., Suresh, S., Senthilkumar, T., Karthikeyan, M.G., 2013. Passive cooling of standalone flat PV module with cotton wick structures. Energy Conv. Manag. 71, 43-50. Dubey, S., Sandhu, G.S., Tiwari, G.N., 2009. Analytical expression for electrical efficiency of PV/T hybrid air collector. Appl. Energy. 86, 697-705. 19
ACCEPTED MANUSCRIPT Dubey, S., Tay, A.A.O., 2013. Testing of two different types of photovoltaic–thermal (PVT) modules with heat flow pattern under tropical climatic conditions. Energy Sustain Dev. 17, 112. Dubey, S., Tiwari, G.N., 2008. Thermal modeling of a combined system of photovoltaic thermal (PV/T) solar water heater. Sol. Energy. 82, 602-612. Hasanuzzaman, M., Al Amin, A.Q., Khanam. S., Hosenuzzaman, M., 2015. Photovoltaic power generation and its economic and environmental future in Bangladesh. J. Renew. Sustain. Energy. 7, 013108. Hasanuzzaman, M., Rahim, N.A., Saidur, R., Kazi, S.N., 2011. Energy savings and emissions reductions for rewinding and replacement of industrial motor. Energy. 36, 233-240. Hatch, J.E, 1984. Aluminum. Properties and Physical Metallurgy, Second ed. Aluminum Association Inc. and ASM International, Ohio. Hosenuzzaman, M., Rahim, N.A., Selvaraj, J., Hasanuzzaman, M., Malek, A.B.M.A., Nahar, A., 2015. Global prospects, progress, policies, and environmental impact of solar photovoltaic power generation. Renew. Sust. Energ. Rev. 41, 284-297. Hosseini, R., Hosseini, N., Khorasanizadeh, H., 2011. An experimental study of combining a photovoltaic system with a heating system. World Renewable Energy Congress 2011, 8-13 May 2011, Linköping, Sweden, 2993-3000 Jie, J., Jian-Ping, L., Tin-Tai, C., Wei, H., Gang, P., 2007. A sensitivity study of a hybrid photovoltaic/thermal water-heating system with natural circulation. Appl. Energy. 84, 222– 237. Jones, A.D., Underwood, C.P., 2001. A thermal model for photovoltaic systems. Pergamon. 70, 349–359.
20
ACCEPTED MANUSCRIPT Jooss, W., 2002. Multicrystalline and back contact buried contact silicon solar cells. PhD dissertation, Universitat Konstanz Fachbereich Physik. Lai, J., Perazzo, T., Shi, Z., Majumdar, A., 1997. Optimisation and performance of high resolution micro-optomechanical thermal sensors. Sensors and Actuators. 58, 113-119. Lu, Z.H., Yao, Q., 2007. Energy analysis of Si solar cell modules based on an optical model for arbitrary layers. Sol. Energy. 81, 636-647. Notton, G., Cristofari, C., Mattei, M., Poggi, P., 2005. Modelling of a double-glass photovoltaic module usingfinite differences. Appl. Therm. Eng. 25, 2854-2877. Park, K.E., Kang, G.H., Kim, H.I., Yu, G.J., Kim, J.T., 2010. Analysis of thermal and electrical performance of semi-transparent photovoltaic (PV) module. Energy. 35, 2681-2687. Phylipsen, G.J.M., Alsema, E.A., 1995. Environmental Life-Cycle Assessment of Multicrystalline Silicon Solar Cell Modules. Report No. 95057. Netherlands Agency for Energy and the Environment. Rahman, M.M., Hasanuzzaman, M., Rahim, N.A., 2015. Effects of various parameters on PVmodule power and efficiency. Energy Conv. Manag. 103, 348-358. Saad, O., Masud, B., 2009. Improving photovoltaic module efficiency using water cooling. Heat Transf. Eng. 30, 499 - 505. Sardarabadi, M., Passandideh-Fard, M., Heris, S.Z., 2014. Experimental investigation of the effects of silica/water nanofluid on PV/T (photovoltaic thermal units). Energy. 66, 264-272. Singh, G.K., 2013. Solar power generation by PV (photovoltaic) technology: A review. Energy. 53, 1-13. Teo, H.G., Lee, P.S., Hawlader, M.N.A., 2012. An active cooling system for photovoltaic modules. Appl. Energy. 90, 309-315.
21
ACCEPTED MANUSCRIPT Tiwari, A., Sodha, M.S., Chandra, A., Joshi, J.C., 2006. Performance evaluation of photovoltaic thermal solar air collector for composite climate of India. Sol. Energy Mater. Sol. Cell. 90, 175–189. Valeh-e-Sheyda, P., Rahimi, M., Karimi, E., Asadi, M., 2013. Application of two-phase flow for cooling of hybrid microchannel PV cells: A comparative study. Energy Conv. Manag. 69, 122130.
22
ACCEPTED MANUSCRIPT
Figure Captions
Figure 1 PV module heat exchanger device Figure 2 Experimental setup Figure 3 Time versus irradiation intensity curve Figure 4 Solar cell temperature versus efficiency curve Figure 5 Temperatures at different layers of the solar module (without cooling) Figure 6 Temperatures at different layers of the solar module (with cooling) Figure 7 Irradiation intensity versus solar cell temperature curve Figure 8 Irradiation intensity versus output power curve Figure 9 Irradiation intensity versus efficiency curve Figure 10 Solar cell temperatures at different flow rates Figure 11 Flow rate versus solar cell temperature curve Figure 12 Flow rate versus efficiency curve Figure 13 Heat transfer through the fins of the rectangular half-round copper sheet with cooling Figure 14 Effect of dust on solar cell output power under outdoor operating conditions Figure 15 Effect of dust on solar cell efficiency under outdoor operating conditions
ACCEPTED MANUSCRIPT
Figure 1 PV module heat exchanger device
ACCEPTED MANUSCRIPT
(1) (2)
(4)
(3)
(5) (7)
(6)
(8) (10)
(9) (11)
Note: (1) Monitor, (2) Datataker, (3) MPPT, (4) Radiator, (5) Water tank, (6) Pump, (7) Flow meter, (8) Pyranometer, (9) Water inlet, (10) Water outlet and (11) PV module
Figure 2 Experimental setup
ACCEPTED MANUSCRIPT
1280.00
15.01.2015 16.01.2015 19.01.2015
1080.00
20.01.2015 21.01.2015
Irradiation (W/m2)
23.01.2015 12.03.2015
880.00
13.03.2015 Average
680.00
480.00
280.00 8:52
9:21
9:50
10:19 Time
10:47
11:16
11:45
Figure 3 Time vs irradiation intensity curve
12:14
12:43
13:12
ACCEPTED MANUSCRIPT
Efficiency (%)
16 14 12 10 Without cooling
8
With cooling
6 30
35 40 45 Solar cell temperature (°C)
50
Figure 4 Solar cell temperature vs efficiency curve
55
60
ACCEPTED MANUSCRIPT
Temperature (°C)
60 55 50 45 40 Top surface temperature
35
Bottom surface temperature Solar cell temperature
30 25 8:52
9:21
9:50
10:19
10:47
11:16
11:45
12:14
12:43
Time
Figure 5 Temperatures at different layers of the solar module (without cooling)
ACCEPTED MANUSCRIPT
50
Temperature (°C)
Top surface temperature
45
Bottom surface temperature Solar cell temperature
40
35
30
25 8:52
9:21
9:50
10:19
10:47
11:16
11:45
12:14
12:43
Time
Figure 6 Temperatures at different layers of the solar module (with cooling)
Solar cell temperature (°C)
ACCEPTED MANUSCRIPT
60 Without cooling
With cooling
55 50 45 40 35 30 25 300
400
500
600
700
800
900
Irradiation (W/m2)
Figure 7 Irradiation intensity vs solar cell temperature curve
1000
Output Power (W)
ACCEPTED MANUSCRIPT
60 55 50 45 40 35
Without cooling
With cooling
30 25 300
400
500
600
700
800
Irradiation (W/m2)
Figure 8 Irradiation intensity vs output power curve
900
1000
ACCEPTED MANUSCRIPT
Efficiency (%)
16 14 12 10 Without cooling
With cooling
8 6 300
400
500
600
700
800
Irradiation (W/m2)
Figure 9 Irradiation intensity vs efficiency curve
900
1000
Solar cell temperature (°C)
ACCEPTED MANUSCRIPT
Solar cell temperature at different flow rate
58
At 30 L/h At 60 L/h At 90 L/h At 180 L/h
53 48 43 38 33 28 300
400
500
600 700 Irradiation (W/m2)
800
900
Figure 10 Solar cell temperatures at different flow rates
1000
Solar cell temperature (°C)
ACCEPTED MANUSCRIPT
54 52 50 48 46 0
20
40
60
80 100 120 Flow rate (L/h)
140
160
Figure 11 Flow rate vs solar cell temperature curve
180
200
ACCEPTED MANUSCRIPT
Efficiency (%)
8.8
8.6
8.4
8.2 20
40
60
80
100 120 Flow rate (L/h)
140
Figure 12 Flow rate vs efficiency curve
160
180
200
ACCEPTED MANUSCRIPT
Heat transfer (W)
8
Heat transfer from fin to ambient
6
heat transfer without fin
4
2
0 300
400
500
600
700
800
900
1000
Irradiation (W/m2)
Figure 13 Heat transfer through the fins of the rectangular half-round copper sheet, with cooling
ACCEPTED MANUSCRIPT
Output Power (W)
50 46 42 38 34 30 Without Dust
26
With dust
22 18 300
400
500
600
700
800
900
1000
Irradiation (W/m2)
Figure 14 Effect of dust on solar cell output power under outdoor operating conditions
ACCEPTED MANUSCRIPT
13
Efficiency (%)
12 11 10 9 8 7
Without Dust
6
With dust
5 300
400
500 600 Irradiation (W/m2)
700
800
900
1000
Figure 15 Effect of dust on solar cell efficiency under outdoor operating conditions
Table 1 SY-90M mono-crystalline module specifications Place of Origin Brand name Model number Material Size (mm) Number of cells Max. power Voc (V) Isc (A) Vmp (V) Imp (A) Mass (kg) Size of cell (mm)
Hebei, China (Mainland) SHAIYANG SY-90M Monocrystalline silicon 1200×545×35 4×9 90 W 22.03 5.30 18.36 4.90 7.0 125 ×125
Table 2 Properties of PV layers Layers
Thickness t (m)
Thermal conductivity k (W/(mK))
Density ρ (kg/m3)
Specific heat capacity (J/(kgK))
Glass
0.003 (Armstrong and Hutley , 2010)
1.8 (Notton et al., 2005)
3000 (Jones and Underwood, 2001)
500 (Jones and Underwood, 2001)
Anti-reflection coating (ARC)
100×10-9 (Jooss, 2002)
32 ( Lai et al., 1997)
2400 ( Lai et al., 1997)
691 ( Lai et al., 1997)
Mono-crystalline cell
225×10-6 (Armstrong and Hutley , 2010)
148 (Lu and Yao, 2007)
2330 (Jones and Underwood, 2001)
677 (Jones and Underwood, 2001)
Ethylene vinyl 500×10-6 (Lu and Yao, acetate (EVA) 2007)
0.35 (Lu and Yao, 2007)
960 (Armstrong and Hutley , 2010)
2090 (Armstrong and Hutley , 2010)
Rear contact
10×10-6 (Phylipsen and Alsema, 19950
237 (Hatch 1984)
2700 (Hatch 1984)
900 (Hatch 1984)
Tedlar
0.0001 (Lu and Yao, 2007)
0.2 (Lu and Yao, 2007)
1200 (Jones and Underwood, 2001)
1250 (Jones and Underwood, 2001)
Table 3 Design parameters of experimental setup Parameters Incident irradiation, G (W/m2) Area of solar cell, Asc (m2) Ambient temperature, Ta (°C) Area of the inside rectangular half round, Ah (m2) Total area of the plate attached to the bottom surface of the module, Asheet (m2) Unfinned area of the two sides of the rectangular half round, Aunfin (m2) Fin area of the two sides of the rectangular half round, Afin (m2) Cross sectional area of the fin, Ac (m2) Perimeter of the fin, p (m) Fin characteristics parameter (m) Corrected length for the rectangular fin, Lc (m) Mass flow rate of fluid, mf (L/h)
Value 300 -1000 0.654 27 0.2176 0.252 0.0144 0.0864 0.0018 1.804 3.88902 0.006 30-180
Table 4 Heat transfer parameters of the system Parameters Transmissivity of glass, τg Absorptivity of the solar module, αsc Packing factor of the solar module, psc Overall heat transfer coefficient through the glass cover from the top surface of the module to the ambient, Usca (W/(m2K))
Value 0.96 0.9 0.8 7.14
Overall heat transfer coefficient of the top surface of module to the tedlar back surface, Ut (W/(m2K))
150
Thermal conductivity of the copper fin, k (W/(m2K)) Specific heat of water, Cf (J/(kgK))
385 4200
Table 5 Comparison of irradiation intensities and cell temperatures obtained from different investigations Authors, year, time and location Experiment Location
Teo et al. (2012), September 2009, EA Without building, National University of cooling Singapore. Latitude 1° 17′ N, With longitude 103° 46′ E cooling
Irradiation (W/m2)
Operating temperature Maximum Cell Comparison with (°C) ambient temperature present investigation temperatur increment At starting At peak At starting At peak e (°C) per 100 period period period period W/m2 irradiation 280
1200
47
65
1.8
550
1050
41
48
1.4
Bahaidarah et al. (2013), February, 2012, KFUPM, Dhahran, Saudi Arabia. Latitude 26°18'N, longitude 50°08'E
Without cooling
240
979
25
44
21
2.6
With cooling
240
979
21
35
21
1.9
Chandrasekar et al. (2013), April, 2013, Anna University, BIT campus, Tiruchirappalli, India. Latitude 10°39′N, longitude 78°44′E
Without cooling
600
1300
37
65
37
4
With cooling
600
1300
40
50
37
1.4
In the current investigation (2015)
Without cooling
312
995
34
60
35
3.82
With cooling
312
995
31
50
35
2.71
Differs from the present investigation owing to different operating conditions Agrees with the present investigation
Agrees with the present investigation
Table 6 Comparison of performance improvements by cooling systems employed in different studies Authors, year, time and location
Irradiation
Operating temperature Maximu Cell Performance (°C) m temperature improvement (W/m2) ambient reduction by applying At At peak At starting At peak temperatu applying cooling (%) starting period period period re (°C) cooling (°C) period
Experiment Location
Bahaidarah et al. (2013), February, 2012, KFUPM, Dhahran, Saudi Arabia. Latitude 26°18'N, longitude 50°08'E Chandrasekar et al. (2013), April, 2013, Anna University, BIT campus, Tiruchirappalli, India. . Latitude 10°39′N, longitude 78°44′E In the current investigation, (2015)
Without cooling
240
979
25
44
21
With cooling
240
979
21
35
21
Without cooling
600
1300
37
65
37
With cooling
600
1300
40
50
37
Without cooling
312
995
34
60
35
With cooling
312
995
31
50
35
15
9
20
16
10
16
Mohammad Mafizur Rahman, Md Hasanuzzaman, Nasrudin Abd Rahim PII:
S0959-6526(16)32084-4
DOI:
10.1016/j.jclepro.2016.12.029
Reference:
JCLP 8604
To appear in:
Journal of Cleaner Production
Received Date:
09 April 2016
Revised Date:
06 December 2016
Accepted Date:
07 December 2016
Please cite this article as: Mohammad Mafizur Rahman, Md Hasanuzzaman, Nasrudin Abd Rahim, Effects of Operational Conditions on the Energy Efficiency of Photovoltaic Modules Operating in Malaysia, Journal of Cleaner Production (2016), doi: 10.1016/j.jclepro.2016.12.029
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
ACCEPTED MANUSCRIPT
Highlights
A photovoltaic (PV) system is experimentally investigated under Malaysian climate.
The factors affecting the performance of this system are discussed.
Solar cell performance is enhanced by optimizing the operating parameters.
Output power decreases by 0.22% as cell temperature increases by 1 °C.
A cooling system improves efficiency by 15.72% under peak operating conditions.
ACCEPTED MANUSCRIPT
RESULTANT WORD COUNT: 5733 Effects of Operational Conditions on the Energy Efficiency of Photovoltaic Modules Operating in Malaysia Mohammad Mafizur Rahman, Md Hasanuzzaman, Nasrudin Abd Rahim UM Power Energy Dedicated Advanced Centre (UMPEDAC) Level-4, Wisma R&D, University of Malaya, 59990 Kuala Lumpur, Malaysia. Abstract Photovoltaic (PV) modules convert a small portion of solar radiation into electrical energy and convert the rest into heat. As a result, the temperature of these modules is increased and their electrical efficiency is degraded. In this study, the effects of various operating parameters, such as solar cell temperature, irradiation intensity, mass flow rate of cooling water, humidity, and dust, on the output performance of a PV module are investigated under outdoor operating conditions. A finned tube is placed at the bottom of the PV module for cooling. Results show that the electrical efficiency of the module decreases by 5.82% as solar cell temperature increases by 26.10 °C. The electrical efficiency also decreases by approximately 0.22% as the temperature of the PV module increases by 1 °C. As irradiation intensity increases by 100 W/m2, the solar cell temperature increases by 3.82 °C and the output power increases by 3.14 W, but the efficiency decreases by 0.85%. In summary, solar cell temperature, solar irradiation intensity, mass flow rate of cooling fluids, humidity, and dust significantly affect the performance of PV modules. Keywords: Energy, Solar energy, Photovoltaic, Module, Cooling system. Nomenclature Ac Cross sectional area of fin (m2) Asc Area of solar cell (m2)
Corresponding author: Email: [email protected] / [email protected] (Attn: Dr. Md. Hasanuzzaman)
1
ACCEPTED MANUSCRIPT Eab Total energy absorbed by top surface of module (W) Eb
Total energy transfer by conduction and convection from top surface to bottom surface (W)
Ectop Total energy loss from top surface to bottom surface at ambient temperature by convection process (W) Ee
Electrical energy produced by module (W)
G
Incident irradiation (W/m2)
Imax Maximum current (A) Isc
Short-circuit current (A)
k
Thermal conductivity (W/(mK))
p
Perimeter of fin (m)
Pmax Maximum power (W) psc Packing factor of solar module RH Relative humidity (%) t
Thickness (m)
Ta Ambient temperature (°C) Tb Temperature of tedlar back surface (°C) Tsc Top surface temperature of solar module (°C) Usca Overall heat transfer coefficient through glass cover from top surface of module to ambient (W/(m2K)) Ut Overall heat transfer coefficient from top surface of module to tedlar back surface (W/(m2K)) Vmax Maximum voltage (V) Voc, Open-circuit voltage (V) W
Width of solar module 2
ACCEPTED MANUSCRIPT x
Length of solar module
Greek letter τg Transmissivity of glass ρ
Density (kg/m3)
αsc Absorptivity of solar module ηsc Electrical efficiency of solar module αt Absorptivity of tedlar back sheet
1 Introduction Conventional power generation threatens the environment and impedes environmental sustainability. In modern power generation, greenhouse gases emitted by fossil fuels are considered a global concern that should be addressed effectively (Hasanuzzaman et al., 2011, 2015). To enhance globalization, researchers focus on the development of sustainable energy systems. Renewable energy systems are clean and sustainable potential resources, and the application of these systems have expanded worldwide (Singh, 2013 and Borges Neto et al., 2010). For instance, photovoltaic (PV) technology is an ecofriendly, sustainable, and effective innovation in advanced global development (Hosenuzzaman et al., 2015 and Ahmed et al., 2013). Solar electricity is generated from 15% to 20% of the total incident irradiation, and the remaining proportion is converted into heat and solar cell temperature is increased (Teo et al., 2012 and Jie et al., 2007). As solar cell temperature increases by 1 °C, the output power is reduced by 0.48% under standard test conditions and by 0.52% under outdoor conditions at 500 W/m2 irradiation (Park et al., 2010). At 1000 W/m2 irradiation, the electrical efficiency decreases by 0.06% as solar cell temperature increases by 1 °C (Rahman et al., 2015). The application of a thin-film water flow to the upper surface of a PV module during peak operating hours can lead to an 18.7 °C decrease 3
ACCEPTED MANUSCRIPT in solar cell temperature and a 33% increase in cell efficiency (Hosseini et al., 2011). Thus, effective cooling is necessary to reduce the temperature of solar cells and increase the output efficiency of PV systems. Dubey et al. (2009) found that the glass-to-glass PV module efficiency increases from 9.75% to 10.41% when an air duct is placed at the back of the module. Saad and Masud (2009) increased the PV efficiency by 15% via a water-trickling system on the upper surface of the PV module. Teo et al. (2012) increased the PV efficiency from 8%–9% to 12%– 14% by applying an air flow through a parallel duct attached to the back of a polycrystalline solar module. Bahaidarah et al. (2013) increased the electrical efficiency of a PV module by 9% with 20% solar cell temperature reduction via an effective water-cooling system at the back of a monocrystalline PV module. Chandrasekar et al. (2013) experimentally reduced the solar cell temperature of a PV module by 30% and respectively increased its output power and electrical efficiency by 6.5 W and 1.4% by using a cotton-wick structure with a cooling system consisting of Al2O3/water, CuO/water nanofluid, and water. Sheyda et al. (2013) experimentally increased the module output power by 38% by passing a two-phase flow regime through a microchannel attached to the bottom of a PV module. Ceylan et al. (2014) enhanced the efficiency of a PV module from 10% to 13% by employing a temperature-controlled cooling water flow through a spiral tube heat exchanger system attached to the bottom of the module. Alami (2014) reduced the temperature of a module by using a thin-film water flow through a synthetic clay layer attached to the bottom of the PV module. As a result, the output power and output voltage of the PV module are increased by 19.1% and 19.4%, respectively. The electrical efficiency of the PV module is improved by approximately 8.2%, 9.01%, and 9.75% when it is cooled with water, 1 wt% silica– water, and 3 wt% silica–water nanofluid, respectively, compared with the results of a PV module without cooling systems (Sardarabadi et al., 2014).
4
ACCEPTED MANUSCRIPT Our research investigates the effects of various operating parameters, such as solar cell temperature, irradiation intensity, cooling, humidity, and dust, on the output power and efficiency of a PV module under outdoor operating conditions. 2 Research methodology 2.1 Experimental setup The experimental setup was established on the solar park at Level 3, Wisma R&D, University of Malaya (UM) in Malaysia to investigate the effects of various parameters on the performance of a PV module. The experimental setup mainly consisted of a PV module, a heat exchanger device, a centrifugal pump, and a cooling radiator. A monocrystalline solar module (SY-90M, Shaiyang, Hebei, China) was also used in the experiment. Table 1 summarizes the specifications of the solar module under standard conditions. Table 1 SY-90M monocrystalline module specifications A monocrystalline PV is generally manufactured with layers of different materials: (1) glass top cover, (2) anti-reflective coating, (3) monocrystalline silicon layer, (4) ethylene–vinyl acetate layer, (5) metal back sheet, and (6) Tedlar polyvinyl fluoride layer. The layers are entrenched in a metallic frame (Jones and Underwood, 2001). The properties of the PV layers are listed in Table 2. Table 2 Properties of PV layers A rectangular heat exchanger device composed of a copper tube with a diameter of 22 mm was used to cool the PV module (Figure 1). Figure 1 PV module heat exchanger device The length and width of the heat exchanger device were 950 and 420 mm, respectively. This device consisted of seven parallel circular copper tubes. A semicircular finned plane sheet at the top of each parallel tube was used to secure the device to the back of the solar module and to facilitate 5
ACCEPTED MANUSCRIPT the smooth flow of heat transfer. The fins increased the heat transfer rate from the bottom. Figure 2 shows an image of the experimental setup. Figure 2 Experimental setup A small centrifugal pump (Pentax CP45) was used to circulate water through the heat exchanger tube. The pump capacity was 5–35 L/min, the discharging head was 9–35 m, and the operating power consumption was 0.5 kW. A 1.3 kg/cm2 cooling radiator was used to cool the heated water. Table 3 summarizes the design parameters of the experimental setup. Table 3 Design parameters of experimental setup 2.2 Experimental instrumentation A digital data taker (DT80) was used to measure temperature and irradiation intensity. A maximum power point tracker (MPPT) was utilized to determine and control the output current and output voltage, specifically, Isc, Voc, Imax, Vmax, and Pmax, of the module. A flow meter (LZB-10B) was employed to identify the water discharge and velocity with a measurement range of 16–180 L/h. Two PTFE-exposed welded-tip K-type thermocouples were used to measure the top and bottom surface temperatures of the module. Two additional thermocouples of the same type were utilized to determine the inlet and outlet temperatures of the heat-exchanger device. An ideal data logger was employed to collect temperature data. The temperature measurement range of the data logger was −75 °C to 250 °C. A pyranometer (LI-COR PY82186) was used to measure the solar irradiation intensity. The irradiation measurement range of the pyranometer was 0 W/m2 to 1280 W/m2, its spectral range was 300 nm to 1100 nm, and its operating temperature range was −40 °C to 75 °C. The pyranometer was accurately calibrated prior to use. A humidity sensor (HU1030NA) was utilized to determine the ambient humidity at a range of 20% to 90% RH.
6
ACCEPTED MANUSCRIPT 2.3 Experimental test conditions and data acquisition Data in the presence or absence of cooling conditions were collected on sunny days from January 2015 to March 2015. During the study, the solar park area of the UM Power Energy Dedicated Advanced Center was completely shaded by buildings after 12:40
PM.
The data were collected
from 09:00 AM to 12:40 PM. In this period, solar irradiation intensity varied approximately from 300 W/m2 to 1000 W/m2. Ambient temperature varied approximately from 29 °C to 35 °C. The data used in the analysis were collected under similar meteorological conditions on different days. The efficiency of the solar module was observed as solar irradiation intensity and cell temperature increased. Various mass flow rates (30, 60, 90, and 180 L/h) of the cooling water through the heat exchanger of the PV module were adopted; the effects of irradiation intensity on solar cell temperature and output performance were examined under cooling conditions. The data from the inlet and outlet thermocouples of the heat-exchanger device, the top and bottom surface thermocouples of the module, and the pyranometer were regularly collected by using the data taker at 10 min intervals throughout the experiment. 2.4 Mathematical formulation 2.4.1 Heat transfer from the top surface of the module The total energy absorbed by the top surface of the module can be expressed as follows (Tiwari et al., 2006, Dubey and Tiwari, 2008, Dubey and Tay, 2013): E ab g sc p sc GWx
(1)
The energy lost by convection at the top surface of the module is determined using the following equation: E ctop U sca Tsc Ta Wx
(2)
The amount of energy transferred to the bottom surface of the module is obtained by using Eq. (3): 7
ACCEPTED MANUSCRIPT E b U t Tsc Tb Wx
(3)
The total amount of energy converted into electrical energy is represented by the following:
E e sc p sc GWx
(4)
The energy balance equation for the top surface is expressed as follows: E ab E ctop Eb E e
(5)
The solar cell temperature is calculated using Eq. (6):
Tsc
pscG g sc sc (U scaTa U tTb )
(6)
U scaU t
2.4.2 Heat transfer through a fin The heat transfer from a surface to its surroundings has been described by Newton’s law of cooling (Cengel, 2006):
Q conv hair As (Ts T )
(7)
The heat transfer through a fin is calculated according to Fourier’s law of heat conduction:
Qadiabatic ,tip hair pkAc (Tb T ) tanh ml
(8)
where
m
hair p kAc
(9)
If convection heat transfer is considered from the fin tip, the fin length should be corrected by the following equation: Lc L
t Ac . The corrected length of a rectangular fin is Lc L , and the 2 p
corrected length of a cylindrical fin is Lc L
D . 4
The maximum heat transfer through a fin with infinite conductivity is expressed as follows: Q fin , max hair Afin (Tb Ta )
(10) 8
ACCEPTED MANUSCRIPT The fin efficiency can be described as Eq. (11):
fin
Q fin
(11)
Q fin ,max
However, Q fin finQ fin , max fin hair Afin (Tb Ta ) .
(12)
The efficiency of a very long fin is determined as follows:
longfin
Q fin Q fin , max
hair pkAc (Tb Ta ) 1 kAc 1 hair Afin (Tb Ta ) L hair p ml
(13)
The efficiency of an adiabatic tip is calculated as follows:
adiabatic ,tip
Q fin Q fin , max
hair pkAc (Tb Ta ) tanh ml 1 kAc tanh ml hair Afin (Tb Ta ) L hair p ml
(14)
The total heat-transfer rate from the finned surface is the summation of the heat transfer from the finned surface and the heat transfer from the unfinned surface: Qtotal , fin Qunfin Q fin hair Aunfin (Tb Ta ) fin hair Afin (Tb Ta )
(15)
Table 4 Heat-transfer parameters of the system (Dubey and Tay, 2013) 3 Results and discussion 3.1 Effect of temperature on PV module performance The output power of a PV module depends on various factors, such as solar irradiation intensity, ambient temperature, humidity, and wind velocity. Under outdoor operating conditions, the solar irradiation intensity continuously fluctuates. Figure 3 Time versus irradiation intensity curve In Figure 3, the data used for the analysis were collected under similar irradiation intensities on different days. An average irradiation value was considered with respect to time throughout the entire analysis. As solar irradiation intensity increased, solar cell temperature and output power
9
ACCEPTED MANUSCRIPT increased. The solar module efficiency was directly related to the solar cell temperature (Figure 4). Figure 4 Solar cell temperature versus efficiency curve In the initial state and in the absence of cooling conditions (Figure 4), the efficiency of the module was 13.29%, and the solar cell temperature was 33.82 °C. Under peak operating conditions, the module efficiency decreased to 7.46%, whereas the solar cell temperature increased to 59.92 °C. The total electrical efficiency decreased by 5.82%, which was 43.83% of the initial efficiency. The solar cell temperature increased by 26.10 °C. In the absence of cooling and outdoor operating conditions, the electrical efficiency decreased by 0.22% as the solar cell temperature increased by 1 °C. In Figures 5 and 6, the temperatures at different layers, namely, top glass surface, bottom surface, and solar cell, of the solar module increased as the duration was prolonged in the absence and presence of cooling conditions as the irradiation intensity increased with duration. Figure 5 Temperatures at different layers of the solar module (without cooling) In the current investigation, the solar cell temperatures under outdoor operating conditions without cooling were 33.82 °C and 59.92 °C in the initial and peak periods, respectively. Chandrasekar et al. (2013) found that the solar cell temperatures in the absence of cooling conditions in the Bharathidasan Institute of Technology (BIT) campus at Anna University, Tiruchirappalli, India are approximately 37 °C at 600 W/m2 irradiation and approximately 65 °C at 1300 W/m2 irradiation in the initial and peak operating periods, respectively; the experiment was run in April 2012 at the maximum ambient temperature of 37 °C prevailing at that time. Bahaidarah et al. (2013) conducted an experiment at King Fahd University of Petroleum and Minerals (KFUPM) in Dhahran, Saudi Arabia in February 2012 when the maximum ambient temperature was 21 °C and recorded a solar cell temperatures of 25 °C at 240 W/m2 irradiation and 44 °C at 979 W/m2 10
ACCEPTED MANUSCRIPT irradiation in the absence of cooling conditions. The solar cell temperatures in the present investigation are consistent with the results obtained by Chandrasekar et al. (2013) but are different from those obtained by Bahaidarah et al. (2013). These differences were attributed to the incident irradiation and ambient temperature variations. Figure 6 Temperatures at different layers of the solar module (with cooling) In the current investigation, the solar cell temperatures with water cooling were 31.09 °C and 49.64 °C in the initial and peak operating periods, respectively. Chandrasekar et al. (2013) conducted a study in the BIT campus in April 2012 when the maximum ambient temperature was 37 °C and found that the temperatures of a cooled solar cell were approximately 40 °C at 600 W/m2 irradiation and 50 °C at 1300 W/m2 irradiation under initial and peak operating conditions, respectively. Bahaidarah et al. (2013) also performed a study at KFUPM in February 2012 when the maximum ambient temperature was 21 °C and observed that the temperatures of a cooled solar cell were 22 °C at 240 W/m2 irradiation and 35 °C at 979 W/m2 irradiation. Hence, the temperatures of the cooled solar cell in the present investigation are consistent with the results obtained by Chandrasekar et al. (2013) but are different from those observed by Bahaidarah et al. (2013). These deviations were ascribed to the differences in solar irradiation intensity, wind velocity, ambient temperature, and cooling capacities of the coolant and heat-exchanger device. Therefore, different operating cell temperatures were obtained in our study and those in previous studies (Chandrasekar et al., 2013; Bahaidarah et al., 2013). In a PV module, 15% to 20% of solar radiation is converted into electricity, and the remaining proportion is converted into heat (Teo et al., 2012). In the solar cell layer of a PV module, some portions of heat energy can be transferred to the environment through convection, whereas other portions can be transferred to the Tedlar bottom surface. Some portions of solar radiation are directly absorbed by the Tedlar back surface because of the packing factor, which is responsible 11
ACCEPTED MANUSCRIPT for the additional heat generation at the bottom surface (Dubey and Tay, 2013). The top glass surface transmits 96% of the incident irradiation to the solar cell surface. Moreover, the overall heat transfer coefficient through the glass covering the top surface of the module to the environment Usca is 7.14 W/(m2K). The overall heat transfer coefficient of the Tedlar back surface sheet to the outside environment is 5.81 W/(m2K). Thus, the heat transferred from the bottom surface to the environment is lower than the heat transferred from the glass cover to the environment. Consequently, the Tedlar bottom surface temperature is higher than the top glass surface temperature (Dubey and Tay, 2013, Dubey and Tiwari, 2008). Eq. (6) shows that solar cell temperature is directly related to the Tedlar bottom surface temperature, ambient temperature, and incident irradiation. In Table 2, the specific heat capacity of the monocrystalline solar cell layer of a PV module is much higher than that of the Tedlar bottom layer, that is, the solar cell layers rapidly absorb more heat. Thus, the temperature of solar cells is higher than those of the top glass surface and the Tedlar bottom surface. 3.2 Effect of irradiation intensity on PV module performance The effects of irradiation intensity on the PV module cell temperature, output power, and efficiency were also investigated under outdoor operating conditions with and without cooling. Figure 7 Irradiation intensity versus solar cell temperature curve In Figure 7, the solar cell temperature increases as irradiation intensity increases. Without cooling, the solar cell temperature was 33.82 °C in the initial period, and this temperature subsequently increased to 59.92 °C during the peak operation. The solar cell temperature increased by 26.10 °C when the irradiation intensity increased by 683 W/m2. The solar cell temperature increased by 3.82 °C as irradiation intensity increased by 100 W/m2 without cooling conditions. Under water-cooling conditions and in the initial period of the investigation, the solar cell temperature was 31.09 °C, which increased to 49.65 °C in the peak operating period. The solar cell temperature increased by 12
ACCEPTED MANUSCRIPT 18.56 °C when the irradiation intensity increased by 683 W/m2. With cooling, the solar cell temperature increased by 2.72 °C as irradiation intensity increased by 100 W/m2. Teo et al. (2012) conducted an experiment on the rooftop of the EA building at the National University of Singapore in September 2009 and found that irradiation intensity ranged from 280 W/m2 to 1200 W/m2 without cooling, and the module operating temperature ranged from 47 °C to 65 °C. By comparison, irradiation intensity ranged from 550 W/m2 to 1050 W/m2 with cooling, and the operating temperature of the module ranged from 41 °C to 48 °C. The solar cell temperature increased by 1.8 °C and 1.4 °C as irradiation intensity increased by 100 W/m2 in the absence and presence of an air cooling system, respectively. Bahaidarah et al. (2013) conducted an experiment at KFUPM in February 2012 when the maximum ambient temperature was 21 °C and found that the irradiation intensity ranged from 240 W/m2 to 979 W/m2. In the absence of cooling conditions, the operating temperature of the module ranged from 25 °C to 44 °C. Under cooling conditions, the operating temperature of the module ranged from 21 °C to 35 °C. The solar cell temperature increased by 2.6 °C and 1.9 °C as irradiation intensity increased by 100 W/m2 without and with a water-cooling system, respectively. Chandrasekar et al. (2013) performed an experiment in the BIT campus in April 2012 when the maximum ambient temperature was 21 °C and observed that the operating irradiation ranged from 600 W/m2 to 1300 W/m2. Without cooling, the module-operating temperature ranged from 37 °C to 65 °C. With cooling, the module-operating temperature range was 40 °C to 50 °C. The solar cell temperature increased by 4 °C and 1.4 °C as irradiation intensity increased by 100 W/m2 without and with a water-cooling system, respectively. Table 5 Comparison of irradiation intensities and cell temperatures obtained from different investigations
13
ACCEPTED MANUSCRIPT Our results were similar to those of Chandrasekar et al. (2013) and Bahaidarah et al. (2013) but were different from those of Teo et al. (2012) because of variations in incident solar irradiation levels, module-operating temperatures, coolant effectiveness degrees, wind velocities, and ambient temperatures. Figure 8 Irradiation intensity versus output power curve Figure 8 shows that the output power of the PV module increased as irradiation intensity increased. The initial incident irradiation was approximately 312 W/m2 and the output power was 27.12 W in the absence of cooling conditions. During the peak operation, the incident irradiation level was approximately 995 W/m2, and the output power was 48.59 W. The output power increased by 21.47 W with an approximately 683 W/m2 increase in the irradiation intensity. In the absence of cooling conditions, the output power increased by 3.14 W as irradiation intensity increased by 100 W/m2. Under water-cooling conditions, the initial incident irradiation level was approximately 312 W/m2 and the output power was 29.72 W. During the peak operation, the incident irradiation level was approximately 995 W/m2 and the output power was 56.23 W. The output power increased by 26.51 W with an approximately 683 W/m2 increase in the irradiation intensity. Under cooling conditions, the output power increased by 3.88 W as irradiation intensity increased by 100 W/m2. Figure 9 Irradiation intensity versus efficiency curve In Figure 9, the electrical efficiency of the PV module decreased as irradiation intensity increased. Without cooling, the initial incident irradiation level was approximately 312 W/m2 and the electrical efficiency of the module was 13.29%. During peak operation, the incident irradiation level was approximately 995 W/m2 and the electrical efficiency of the module was 7.46%. The electrical efficiency of the module decreased by 5.82% as irradiation intensity increased by 683 W/m2. Without cooling, the electrical efficiency of the module decreased by 0.85% as irradiation intensity increased by 100 W/m2. With water cooling, the initial incident irradiation level was 14
ACCEPTED MANUSCRIPT approximately 312 W/m2 and the electrical efficiency of the module was 14.56%. During peak operation, the incident irradiation level was approximately 995 W/m2 and the electrical efficiency of the module was 8.64%. The electrical efficiency of the module decreased by 5.92% as irradiation intensity increased by 683 W/m2. With cooling, the electrical efficiency of the module decreased by 0.87% as irradiation intensity increased by 100 W/m2. 3.3 Effect of cooling on PV module performance The flow rate of the cooling water was set at 90 L/h to investigate the cooling effect on PV module performance. Figure 4 shows that the module with a water-cooling system exhibited an efficiency of 14.56% and a solar cell temperature of 31.09 °C in the initial state. Under peak operating conditions, the module efficiency decreased to 8.64%, whereas the solar cell temperature increased to 49.65 °C. The total electrical efficiency decreased by 5.92%, which was 40.68% of the initial efficiency. By contrast, the solar cell temperature increased by 18.56 °C. Under water cooling and outdoor operating conditions, the electrical efficiency decreased by 0.32% as solar cell temperature increased by 1 °C. The effect of the flow rate of cooling water on the PV module performance was also investigated. Figure 10 Solar cell temperatures at different flow rates Figure 10 illustrates that the solar cell temperature decreased as the flow rate increased with various irradiation intensities. Thus, the solar module efficiency increased as the flow rate of cooling water increased. However, the solar cell temperature slightly decreased as the flow rate of cooling water increased. Figure 11 Flow rate versus solar cell temperature curve Figure 12 Flow rate versus efficiency curve Figures 11 and 12 correspondingly reveal the decrease in solar cell temperature and the increase in PV module efficiency at different flow rates under peak operating conditions. These patterns 15
ACCEPTED MANUSCRIPT changed linearly up to a 90 L/h flow rate of cooling water. Solar cell temperature slightly decreased as the flow rate increased and exceeded 90 L/h. Hence, 90 L/h is the most suitable flow rate to enhance the efficiency of the PV module. Figure 4 also indicates that the efficiency of the PV module is enhanced by using a water-cooling system. As shown in Figure 4, the solar cell temperature decreased by 10.28 °C when the water-cooling system was used. During peak operating conditions, a water flow rate of 90 L/h increased the output power by 7.64 W and the electrical efficiency by 1.17%. Under cooling and outdoor operating conditions, in which the cell temperature was 17.16% lower, the module output power or efficiency was 15.72% higher than that in the absence of cooling conditions. Chandrasekar et al. (2013) reduced the solar cell temperature by 20 °C and increased the output power by 6.5 W and electrical efficiency by 1.4% under outdoor operating conditions. Bahaidarah et al. (2013) also decreased the solar cell temperature by 20% and increased the electrical efficiency by approximately 9% via a back surface water-cooling system. Table 6 Comparison of performance improvements by cooling systems employed in different studies Thus, the performance of the cooling system used in the current study was better than those employed by Chandrasekar et al. (2013) and Bahaidarah et al. (2013). 3.4 Heat transfer through heat-exchanger fins The fins attached to the half-round copper sheet of the heat-exchanger device also increased the cooling rate of the PV module (Figure 13). Figure 13 Heat transfer through the fins of the rectangular half-round copper sheet with cooling
16
ACCEPTED MANUSCRIPT Figure 13 illustrates the heat transferred from the fin surface attached to the rectangular half-round copper sheet at the back surface of the module. With water cooling, the system with a fin surface can remove 5 W more heat than that without a fin surface. Therefore, the effective water-cooling method used in this study decreased the temperature at the bottom surface and the temperature of the solar cell. At the bottom surface, heat was also directly lost to ambient air by convection. Heat was also transferred to ambient air from the fins attached to the rectangular half-round copper sheet of the heat exchanger. Heat was also transferred to the flowing water from the back surface. 3.5 Effect of dust on PV module performance The effect of dust on the performance of the PV module was also investigated for 2 consecutive days under outdoor operating conditions with similar irradiation levels. Dust (0.01 g/cm2) was applied to the top surface of the PV module, and the output power and efficiency of the module were observed. Figure 14 Effect of dust on solar cell output power under outdoor operating conditions Figure 15 Effect of dust on solar cell efficiency under outdoor operating conditions Figures 14 and 15 respectively show that the output power of the PV module reached 48.89 W and its electrical efficiency was 7.51% in the peak operating period under outdoor conditions. With dust on the top surface of the PV module, the output power decreased to 40.14 W and the electrical efficiency was 6.16% in the peak operating period. Thus, the output power and efficiency decreased by 8.75 W and 1.34%, respectively. The performance of the module with dust on its surface was 17.90% lower than that of the module without dust. 4 Conclusion The operating parameters affecting the performance of the PV module are described as follows:
17
ACCEPTED MANUSCRIPT As the solar cell temperature increases by 26.10 °C, the electrical efficiency of the module decreases by 5.82%, that is, electrical efficiency decreases by 0.22% as temperature increases by 1 °C. The solar cell temperature increases by 26.10 °C when the irradiation intensity increases by 683 W/m2, that is, temperature increases by 3.82 °C as irradiation intensity increases by 100 W/m2. As irradiation intensity increases by 683W/m2 under outdoor operating conditions, output power increases by 21.47 W, that is, output power increases by 3.14 W as irradiation intensity increases by 100 W/m2. As the flow rate of cooling water increases, the temperature of solar cells decreases and the efficiency of the PV module increases. A low cooling water flow rate is economical and effective for the cooling of PV modules. Cooling water is passed through a heat exchanger at the back of the PV module. Under peak operating conditions and at a flow rate of 90 L/h, the solar cell temperature decreases by 10.28 °C. As the temperature of the PV module decreases, its output power and electrical efficiency increase by 7.64 W and 1.17%, respectively. Under peak outdoor operating conditions, the output performance is increased by 15.72% when a water cooling system is used. With 0.01 g/cm2 of dust on the solar module surface, the output power and efficiency of the solar module decrease by 8.75 W and 1.34%, respectively. This finding is 17.90% lower than the output generated by the module without dust. Therefore, temperature, irradiation intensity, and dust can decrease the energy efficiency of PV modules. Water cooling systems can effectively reduce the solar cell temperature and consequently increase the energy efficiency of PV modules. In a large power plant, water cooling system can save a considerable amount of power. 18
ACCEPTED MANUSCRIPT Acknowledgments The authors are grateful for the financial support provided by the University of Malaya Research Grant (UMRG) scheme (Project no. RP016A-15SUS).
References Ahmed, F., Al Amin, A.Q., Hasanuzzaman, M., Saidur, R., 2013. Alternative energy resources in Bangladesh and future prospect. Renew. Sust. Energ. Rev. 25, 698-707. Alami, A.H., 2014. Effects of evaporative cooling on efficiency of photovoltaic modules. Energy Conv. Manag. 77, 668-679. Armstrong, S., Hurley, W.G., 2010. A thermal model for photovoltaic panels under varying atmospheric conditions. Appl. Therm. Eng. 30, 1488-1495. Bahaidarah, H., Subhan, A., Gandhidasan, P., Rehman, S., 2013. Performance evaluation of a PV (photovoltaic) module by back surface water cooling for hot climatic conditions. Energy, 59, 445-453. Borges
Neto,
M.R.,
Carvalho,
P.C.M.,
Carioca,
J.O.B.,
Canafístula,
F.J.F.,
2010.
Biogas/photovoltaic hybrid power system for decentralized energy supply of rural areas. Energy Policy. 38, 4497-4506. Cengel, Y.A., 2006. Heat and Mass Transfer: A practical Approach. Third ed. Mc Graw Hill, Singapore. Ceylan, I., Gürel, A.E., Demircan, H., Aksu, B., 2014. Cooling of a photovoltaic module with temperature controlled solar collector. Energy Build. 72, 96-101. Chandrasekar, M., Suresh, S., Senthilkumar, T., Karthikeyan, M.G., 2013. Passive cooling of standalone flat PV module with cotton wick structures. Energy Conv. Manag. 71, 43-50. Dubey, S., Sandhu, G.S., Tiwari, G.N., 2009. Analytical expression for electrical efficiency of PV/T hybrid air collector. Appl. Energy. 86, 697-705. 19
ACCEPTED MANUSCRIPT Dubey, S., Tay, A.A.O., 2013. Testing of two different types of photovoltaic–thermal (PVT) modules with heat flow pattern under tropical climatic conditions. Energy Sustain Dev. 17, 112. Dubey, S., Tiwari, G.N., 2008. Thermal modeling of a combined system of photovoltaic thermal (PV/T) solar water heater. Sol. Energy. 82, 602-612. Hasanuzzaman, M., Al Amin, A.Q., Khanam. S., Hosenuzzaman, M., 2015. Photovoltaic power generation and its economic and environmental future in Bangladesh. J. Renew. Sustain. Energy. 7, 013108. Hasanuzzaman, M., Rahim, N.A., Saidur, R., Kazi, S.N., 2011. Energy savings and emissions reductions for rewinding and replacement of industrial motor. Energy. 36, 233-240. Hatch, J.E, 1984. Aluminum. Properties and Physical Metallurgy, Second ed. Aluminum Association Inc. and ASM International, Ohio. Hosenuzzaman, M., Rahim, N.A., Selvaraj, J., Hasanuzzaman, M., Malek, A.B.M.A., Nahar, A., 2015. Global prospects, progress, policies, and environmental impact of solar photovoltaic power generation. Renew. Sust. Energ. Rev. 41, 284-297. Hosseini, R., Hosseini, N., Khorasanizadeh, H., 2011. An experimental study of combining a photovoltaic system with a heating system. World Renewable Energy Congress 2011, 8-13 May 2011, Linköping, Sweden, 2993-3000 Jie, J., Jian-Ping, L., Tin-Tai, C., Wei, H., Gang, P., 2007. A sensitivity study of a hybrid photovoltaic/thermal water-heating system with natural circulation. Appl. Energy. 84, 222– 237. Jones, A.D., Underwood, C.P., 2001. A thermal model for photovoltaic systems. Pergamon. 70, 349–359.
20
ACCEPTED MANUSCRIPT Jooss, W., 2002. Multicrystalline and back contact buried contact silicon solar cells. PhD dissertation, Universitat Konstanz Fachbereich Physik. Lai, J., Perazzo, T., Shi, Z., Majumdar, A., 1997. Optimisation and performance of high resolution micro-optomechanical thermal sensors. Sensors and Actuators. 58, 113-119. Lu, Z.H., Yao, Q., 2007. Energy analysis of Si solar cell modules based on an optical model for arbitrary layers. Sol. Energy. 81, 636-647. Notton, G., Cristofari, C., Mattei, M., Poggi, P., 2005. Modelling of a double-glass photovoltaic module usingfinite differences. Appl. Therm. Eng. 25, 2854-2877. Park, K.E., Kang, G.H., Kim, H.I., Yu, G.J., Kim, J.T., 2010. Analysis of thermal and electrical performance of semi-transparent photovoltaic (PV) module. Energy. 35, 2681-2687. Phylipsen, G.J.M., Alsema, E.A., 1995. Environmental Life-Cycle Assessment of Multicrystalline Silicon Solar Cell Modules. Report No. 95057. Netherlands Agency for Energy and the Environment. Rahman, M.M., Hasanuzzaman, M., Rahim, N.A., 2015. Effects of various parameters on PVmodule power and efficiency. Energy Conv. Manag. 103, 348-358. Saad, O., Masud, B., 2009. Improving photovoltaic module efficiency using water cooling. Heat Transf. Eng. 30, 499 - 505. Sardarabadi, M., Passandideh-Fard, M., Heris, S.Z., 2014. Experimental investigation of the effects of silica/water nanofluid on PV/T (photovoltaic thermal units). Energy. 66, 264-272. Singh, G.K., 2013. Solar power generation by PV (photovoltaic) technology: A review. Energy. 53, 1-13. Teo, H.G., Lee, P.S., Hawlader, M.N.A., 2012. An active cooling system for photovoltaic modules. Appl. Energy. 90, 309-315.
21
ACCEPTED MANUSCRIPT Tiwari, A., Sodha, M.S., Chandra, A., Joshi, J.C., 2006. Performance evaluation of photovoltaic thermal solar air collector for composite climate of India. Sol. Energy Mater. Sol. Cell. 90, 175–189. Valeh-e-Sheyda, P., Rahimi, M., Karimi, E., Asadi, M., 2013. Application of two-phase flow for cooling of hybrid microchannel PV cells: A comparative study. Energy Conv. Manag. 69, 122130.
22
ACCEPTED MANUSCRIPT
Figure Captions
Figure 1 PV module heat exchanger device Figure 2 Experimental setup Figure 3 Time versus irradiation intensity curve Figure 4 Solar cell temperature versus efficiency curve Figure 5 Temperatures at different layers of the solar module (without cooling) Figure 6 Temperatures at different layers of the solar module (with cooling) Figure 7 Irradiation intensity versus solar cell temperature curve Figure 8 Irradiation intensity versus output power curve Figure 9 Irradiation intensity versus efficiency curve Figure 10 Solar cell temperatures at different flow rates Figure 11 Flow rate versus solar cell temperature curve Figure 12 Flow rate versus efficiency curve Figure 13 Heat transfer through the fins of the rectangular half-round copper sheet with cooling Figure 14 Effect of dust on solar cell output power under outdoor operating conditions Figure 15 Effect of dust on solar cell efficiency under outdoor operating conditions
ACCEPTED MANUSCRIPT
Figure 1 PV module heat exchanger device
ACCEPTED MANUSCRIPT
(1) (2)
(4)
(3)
(5) (7)
(6)
(8) (10)
(9) (11)
Note: (1) Monitor, (2) Datataker, (3) MPPT, (4) Radiator, (5) Water tank, (6) Pump, (7) Flow meter, (8) Pyranometer, (9) Water inlet, (10) Water outlet and (11) PV module
Figure 2 Experimental setup
ACCEPTED MANUSCRIPT
1280.00
15.01.2015 16.01.2015 19.01.2015
1080.00
20.01.2015 21.01.2015
Irradiation (W/m2)
23.01.2015 12.03.2015
880.00
13.03.2015 Average
680.00
480.00
280.00 8:52
9:21
9:50
10:19 Time
10:47
11:16
11:45
Figure 3 Time vs irradiation intensity curve
12:14
12:43
13:12
ACCEPTED MANUSCRIPT
Efficiency (%)
16 14 12 10 Without cooling
8
With cooling
6 30
35 40 45 Solar cell temperature (°C)
50
Figure 4 Solar cell temperature vs efficiency curve
55
60
ACCEPTED MANUSCRIPT
Temperature (°C)
60 55 50 45 40 Top surface temperature
35
Bottom surface temperature Solar cell temperature
30 25 8:52
9:21
9:50
10:19
10:47
11:16
11:45
12:14
12:43
Time
Figure 5 Temperatures at different layers of the solar module (without cooling)
ACCEPTED MANUSCRIPT
50
Temperature (°C)
Top surface temperature
45
Bottom surface temperature Solar cell temperature
40
35
30
25 8:52
9:21
9:50
10:19
10:47
11:16
11:45
12:14
12:43
Time
Figure 6 Temperatures at different layers of the solar module (with cooling)
Solar cell temperature (°C)
ACCEPTED MANUSCRIPT
60 Without cooling
With cooling
55 50 45 40 35 30 25 300
400
500
600
700
800
900
Irradiation (W/m2)
Figure 7 Irradiation intensity vs solar cell temperature curve
1000
Output Power (W)
ACCEPTED MANUSCRIPT
60 55 50 45 40 35
Without cooling
With cooling
30 25 300
400
500
600
700
800
Irradiation (W/m2)
Figure 8 Irradiation intensity vs output power curve
900
1000
ACCEPTED MANUSCRIPT
Efficiency (%)
16 14 12 10 Without cooling
With cooling
8 6 300
400
500
600
700
800
Irradiation (W/m2)
Figure 9 Irradiation intensity vs efficiency curve
900
1000
Solar cell temperature (°C)
ACCEPTED MANUSCRIPT
Solar cell temperature at different flow rate
58
At 30 L/h At 60 L/h At 90 L/h At 180 L/h
53 48 43 38 33 28 300
400
500
600 700 Irradiation (W/m2)
800
900
Figure 10 Solar cell temperatures at different flow rates
1000
Solar cell temperature (°C)
ACCEPTED MANUSCRIPT
54 52 50 48 46 0
20
40
60
80 100 120 Flow rate (L/h)
140
160
Figure 11 Flow rate vs solar cell temperature curve
180
200
ACCEPTED MANUSCRIPT
Efficiency (%)
8.8
8.6
8.4
8.2 20
40
60
80
100 120 Flow rate (L/h)
140
Figure 12 Flow rate vs efficiency curve
160
180
200
ACCEPTED MANUSCRIPT
Heat transfer (W)
8
Heat transfer from fin to ambient
6
heat transfer without fin
4
2
0 300
400
500
600
700
800
900
1000
Irradiation (W/m2)
Figure 13 Heat transfer through the fins of the rectangular half-round copper sheet, with cooling
ACCEPTED MANUSCRIPT
Output Power (W)
50 46 42 38 34 30 Without Dust
26
With dust
22 18 300
400
500
600
700
800
900
1000
Irradiation (W/m2)
Figure 14 Effect of dust on solar cell output power under outdoor operating conditions
ACCEPTED MANUSCRIPT
13
Efficiency (%)
12 11 10 9 8 7
Without Dust
6
With dust
5 300
400
500 600 Irradiation (W/m2)
700
800
900
1000
Figure 15 Effect of dust on solar cell efficiency under outdoor operating conditions
Table 1 SY-90M mono-crystalline module specifications Place of Origin Brand name Model number Material Size (mm) Number of cells Max. power Voc (V) Isc (A) Vmp (V) Imp (A) Mass (kg) Size of cell (mm)
Hebei, China (Mainland) SHAIYANG SY-90M Monocrystalline silicon 1200×545×35 4×9 90 W 22.03 5.30 18.36 4.90 7.0 125 ×125
Table 2 Properties of PV layers Layers
Thickness t (m)
Thermal conductivity k (W/(mK))
Density ρ (kg/m3)
Specific heat capacity (J/(kgK))
Glass
0.003 (Armstrong and Hutley , 2010)
1.8 (Notton et al., 2005)
3000 (Jones and Underwood, 2001)
500 (Jones and Underwood, 2001)
Anti-reflection coating (ARC)
100×10-9 (Jooss, 2002)
32 ( Lai et al., 1997)
2400 ( Lai et al., 1997)
691 ( Lai et al., 1997)
Mono-crystalline cell
225×10-6 (Armstrong and Hutley , 2010)
148 (Lu and Yao, 2007)
2330 (Jones and Underwood, 2001)
677 (Jones and Underwood, 2001)
Ethylene vinyl 500×10-6 (Lu and Yao, acetate (EVA) 2007)
0.35 (Lu and Yao, 2007)
960 (Armstrong and Hutley , 2010)
2090 (Armstrong and Hutley , 2010)
Rear contact
10×10-6 (Phylipsen and Alsema, 19950
237 (Hatch 1984)
2700 (Hatch 1984)
900 (Hatch 1984)
Tedlar
0.0001 (Lu and Yao, 2007)
0.2 (Lu and Yao, 2007)
1200 (Jones and Underwood, 2001)
1250 (Jones and Underwood, 2001)
Table 3 Design parameters of experimental setup Parameters Incident irradiation, G (W/m2) Area of solar cell, Asc (m2) Ambient temperature, Ta (°C) Area of the inside rectangular half round, Ah (m2) Total area of the plate attached to the bottom surface of the module, Asheet (m2) Unfinned area of the two sides of the rectangular half round, Aunfin (m2) Fin area of the two sides of the rectangular half round, Afin (m2) Cross sectional area of the fin, Ac (m2) Perimeter of the fin, p (m) Fin characteristics parameter (m) Corrected length for the rectangular fin, Lc (m) Mass flow rate of fluid, mf (L/h)
Value 300 -1000 0.654 27 0.2176 0.252 0.0144 0.0864 0.0018 1.804 3.88902 0.006 30-180
Table 4 Heat transfer parameters of the system Parameters Transmissivity of glass, τg Absorptivity of the solar module, αsc Packing factor of the solar module, psc Overall heat transfer coefficient through the glass cover from the top surface of the module to the ambient, Usca (W/(m2K))
Value 0.96 0.9 0.8 7.14
Overall heat transfer coefficient of the top surface of module to the tedlar back surface, Ut (W/(m2K))
150
Thermal conductivity of the copper fin, k (W/(m2K)) Specific heat of water, Cf (J/(kgK))
385 4200
Table 5 Comparison of irradiation intensities and cell temperatures obtained from different investigations Authors, year, time and location Experiment Location
Teo et al. (2012), September 2009, EA Without building, National University of cooling Singapore. Latitude 1° 17′ N, With longitude 103° 46′ E cooling
Irradiation (W/m2)
Operating temperature Maximum Cell Comparison with (°C) ambient temperature present investigation temperatur increment At starting At peak At starting At peak e (°C) per 100 period period period period W/m2 irradiation 280
1200
47
65
1.8
550
1050
41
48
1.4
Bahaidarah et al. (2013), February, 2012, KFUPM, Dhahran, Saudi Arabia. Latitude 26°18'N, longitude 50°08'E
Without cooling
240
979
25
44
21
2.6
With cooling
240
979
21
35
21
1.9
Chandrasekar et al. (2013), April, 2013, Anna University, BIT campus, Tiruchirappalli, India. Latitude 10°39′N, longitude 78°44′E
Without cooling
600
1300
37
65
37
4
With cooling
600
1300
40
50
37
1.4
In the current investigation (2015)
Without cooling
312
995
34
60
35
3.82
With cooling
312
995
31
50
35
2.71
Differs from the present investigation owing to different operating conditions Agrees with the present investigation
Agrees with the present investigation
Table 6 Comparison of performance improvements by cooling systems employed in different studies Authors, year, time and location
Irradiation
Operating temperature Maximu Cell Performance (°C) m temperature improvement (W/m2) ambient reduction by applying At At peak At starting At peak temperatu applying cooling (%) starting period period period re (°C) cooling (°C) period
Experiment Location
Bahaidarah et al. (2013), February, 2012, KFUPM, Dhahran, Saudi Arabia. Latitude 26°18'N, longitude 50°08'E Chandrasekar et al. (2013), April, 2013, Anna University, BIT campus, Tiruchirappalli, India. . Latitude 10°39′N, longitude 78°44′E In the current investigation, (2015)
Without cooling
240
979
25
44
21
With cooling
240
979
21
35
21
Without cooling
600
1300
37
65
37
With cooling
600
1300
40
50
37
Without cooling
312
995
34
60
35
With cooling
312
995
31
50
35
15
9
20
16
10
16