Effect of Light intensity and Temperature on Crystalline Silicon Solar Modules Parameters A. El-Shaer 1, M. T. Y. Tadros 2, M. A. Khalifa 3 1 Physics Department, Faculty of Science, Kafr El-Sheikh University, Kafr El-Sheikh, Egypt 2,3 Physics Department, Faculty of Science, Mansoura University, Mansoura, Egypt Abstract It is significant to understand the effect of the light intensity and temperature on output performance of the crystalline solar modules. Therefore, it is possible to evaluate the J-V curves of solar module under various environmental conditions. This paper discuses the effect of light intensity and temperature on performance parameters of mono-crystalline and poly-crystalline silicon solar module. The experiments have been carried out under a solar simulator for various intensity levels in the range 0.2-1.0 Sun and 10 50 o C, respectively. The results of the two modules indicated that light intensity has a dominant effect on current parameters. It is found that photocurrent; short circuit current and maximum current have been increased linearly with increasing light intensity. So, concentrating system may be regarded as a best choice to enhance the power output of solar system. The power density of the mono-crystalline and poly-crystalline silicon solar module increased from 8.96 and 7.72 mw/cm 2 to 46.72 and 40.4 mw/cm 2 for light intensity 0.2 and 1 Sun respectively. On the other hand, it has been observed that module temperature has a dramatic effect on voltage parameters. Open circuit voltage and maximum voltage are decrease with increasing module temperature. So, the maximum power density of the mono-crystalline and poly-crystalline silicon solar module decreased from 43.4 and 48.76/cm 2 to 36.32 and 41.88mW/cm 2 for temperature 10 o C and 50 o C respectively. Keywords Crystalline Silicon Solar Modules, Light Intensity, Module temperature, J-V characteristics I. INTRODUCTION Solar energy is one of the most promising renewable energy since it provides an unlimited, clean and environmentally friendly energy [1]. Sunlight is by far the largest carbon-free energy source on the planet. More energy from sunlight strikes the Earth in 1 hour (4.3 x10 20 J) than all the energy consumed on the planet in a year (4.1 x10 20 J).one of its drawback is that it is considered as a dilute energy since the solar flux is rarely have a value more than 1 KW/m 2 in the very hot regions in the earth [2]. Therefore, to overcome this disadvantage, it is important to use modules from solar cells for the technological applications. The solar energy converts into three forms of energy such as electricity, chemical fuel, and heat energy [3]. The conversion of sunlight to electrical energy occurs by solar modules. Solar module is a collection of a solar cell which is a device that converts the sunlight directly into direct current (DC) of electrical energy by the photovoltaic phenomena. Among various solar module devices, the Si solar module was first developed, and is still the most widely used photovoltaic device, occupying more than 90% of the solar market nowadays [4] because of the advantages of the Si material over any other materials, such as martial stability, high crystal quality, non-toxic and its crystalline form has an almost ideal band gap for solar energy conversion, i.e. Eg=1.11 ev. Therefore, Silicon has dominated most solar module applications for almost 60 years. The solar irradiation and light intensity are changed daily, due to the rotation of the earth around its own axis, which cause the consequence variation of day and night, and seasonally due to the rotation of the earth around the sun in an elliptical orbit [2]. All solar module parameters, including short-circuit current, open-circuit voltage, fill factor, efficiency and impact of series and parallel resistances are changed due to changing the light intensity and temperature. Therefore, it is important to study the effect of the light intensity on the output performance of the solar module. In this work, a detailed experimental investigation of module parameters with light intensity and temperature has been carried out. The steady state current voltage(j V) characteristics of a silicon p n junction module is often described based on one diode model as given in the following equation: J J ph J o q ( V I R V J R Exp ( s ) 1 s (1) nkt R sh Where q is the elementary charge (1.6x10-19 Coulomb), V is the measured module voltage, k is the Boltzmann s constant (1.38x10-23 J/K) and T is the temperature in Kelvin. Eq.(1) consists of different parameters known as, the light generated current density (J ph ), the reverse saturation current density (J o ), the diode ideality factor (n), the series resistance (R s ) and parallel resistance (R sh ). These parameters have a dominant impact on the shape of JV characteristics of the solar module at any given light intensity and module temperature. 311
J (A/ Cm 2 ) The performance of the solar module, characterized by the values of the short circuit current density (J sc ), open circuit voltage ( ), fill factor (FF) and efficiency (η) of the solar module [5] can be determined. The large values of J sc give the maximum power generated by solar module. The open circuit voltage ( ) occurs when there is no current passing through the module, i.e. V (at I=0). Large gives the maximum power generated by solar module and is given by. KT J ph V ln 1 oc (2) q J o Fill factor (FF) is a measure for the quality of the solar module. It is the ratio of maximum power density (P max ) to the theoretical power density (P t ). Large FF means maximum power generated by solar module. The light source unit contains the xenon lamp (150W), power supply for the lamp and all necessary optics to simulate sunlight. Two commercial solar modules are used in this study mono-crystalline silicon and polycrystalline silicon. The module displays under the xenon lamp in the solar simulator. The standardization of the xenon lamp was performed with respect to the solar spectrum before carry out the experiments by using sensor. The temperature unit was used to adjust a constant temperature from 0 to 60 o C for the solar module. Therefore this unit is connected to J-V measurement system to measure the effect of actual light intensity at constant temperature The J V characteristics of the modules were measured with the help of a "KEITHLEY 2400" Source Meter. The experiments were carried out in the light intensity range 0.2-1.0 Sun with temperature was adjusted at 25 o C and temperature from 10 to 50 o C with light intensity 1 Sun. J V FF m m (3) J sc Efficiency (η) is the ratio of the electrical output power (P out ) compared to the solar input power (P in ). Efficiency is related by J sc, and FF, P P out sh oc (4) in FF J Where P in is the power of the incident light, i.e. P in is the product of the incident light irradiance, measured in W/m 2 or in suns (1000 W/m 2 ), at the surface area of the solar module (m 2 ). In real modules power is dissipated through the resistance of the contacts and through leakage currents around the sides of the device. These effects are equivalent electrically to two parasitic resistances in series and in parallel with the equivalent circuit of solar module. For an ideal module, R sh would be infinite and would not provide an alternate path for current to flow, while R s would be zero, resulting in no further voltage drop before the load [6]. Most of silicon solar modules are designed to work under normal sunlight and their performances are evaluated at 25 o C under an air mass (AM) 1.5 and solar irradiation intensity of 1 Sun. II. P in V EXPERIMENTAL WORK In this work; a detailed experimental study of all solar module parameters for commercial mono and poly crystalline silicon under different light intensity and temperature. A solar simulator was used to carry out the experiments under any constant light intensity and temperature. III. RESULTS AND DISCUSSION A. Effect of light intensity on modules parameters The solar simulator has been calibrated and the module temperature has been adjusted to 25 o C via the temperature unit. Under the steady-state conditions, the J V and power-voltage (P-V) characteristics have been obtained for each module with light intensity as shown in Figure (1, 2). A similarity in the characteristics of mono- and polycrystalline silicon solar modules was found. For the two modules, the short circuit current J SC increases with increasing the light intensity and decreases with increasing the module voltage. For intensity 1 Sun, the Jsc is about 33.7 ma/cm 2 and 34.8 ma/cm 2 for the mono- and poly-crystalline modules respectively. At the same above light intensity, the J sc decreases [7] with increasing the voltage V OC up to 2.44 and 2.08 Volt respectively. 0.04 0.03 0.02 0.01 1.0 Sun 0.8 Sun 0.6 Sun 0.4 Sun 0.2 Sun 1.0Sun 0.8Sun 0.6Sun 0.4Sun 0.2Sun 0.00 0.0 0.4 0.8 1.2 1.6 2.0 2.4 2.8 Cell type = mono C-Si 312
P (W/ Cm 2 ) J (A/ Cm 2 ) P (W/ Cm 2 ) 0.04 J sc 0.03 0.02 1.0 Sun 0.8 Sun 0.6 Sun Cell type = poly C-Si 1.0Sun 0.8Sun 0.6Sun 0.4Sun 0.2Sun 0.048 0.040 0.032 0.024 1.0Sun 1.0 Sun 0.8Sun 0.6Sun 0.4Sun 0.8 Sun 0.2Sun 0.6 Sun 0.4 Sun 0.016 0.4 Sun 0.01 0.2 Sun 0.008 0.2 Sun 0.00 0.0 0.4 0.8 1.2 1.6 2.0 2.4 V(volt) Fig. 1: The J-V curves of: Mono C-Si and Poly C-Si for =25 o C at different light intensities. Figure 2 shows that the maximum power density for the two modules increases with increasing the light intensity. The maximum power density of the mono- and the poly-crystalline modules for light intensity=0.2 Sun was only 8.96 mw/cm 2 and 7.72 mw/cm 2, respectively. Increasing the light intensity to be 1 Sun causes the increase of the power by 80% to reach values 46.72 mw/cm 2 and 40.4 mw/cm 2. So, concentrating system may be regarded a better choice to enhance the output power of solar systems [8]. 0.048 0.040 0.032 0.024 0.016 0.008 0.0 0.4 0.8 1.2 1.6 2.0 2.4 V(volt) 1.0 Sun 0.8 Sun 0.6 Sun 0.4 Sun 0.2 Sun 1.0Sun 0.8Sun 0.6Sun 0.4Sun 0.2Sun 0.0 0.4 0.8 1.2 1.6 2.0 2.4 V(volt) Fig. 2: The P-V curves of: Mono C-Si and Poly C-Si for =25 o C at different light intensities. The dependence of the current parameters with light intensity for the two modules is shown in Figure 3(a, c). It can be easily to say that current parameters of silicon solar module are highly dependent on the light intensity level. Although the values of J sc for the mono- and the poly-crystalline modules for light intensity 0.2 Sun were only 6.7 ma/cm 2 and 6.9 ma/cm 2, respectively, their values increases to be 33.7 ma/cm 2 and 34.8 ma/cm 2 for intensity 1 Sun. Current parameters increase linearly with increasing light intensity. A similar result has been theoretically and experimentally verified by numerous works [9-12]. The values of J ph and J sc are very close to each other or even the same for both monoand the poly-crystalline modules. Figure 3(b, d) illustrates the dependence of voltage parameters, for the two modules, on the light intensity. It has been found that voltage parameters of each module demonstrated a small rise with increasing light intensity. The values of for the mono- and the poly-crystalline modules for light intensity = 0.2 Sun was 2.344 V and 1.999 V, respectively. These values were slightly raised to be 2.43V and 2.08 mv for light intensity =1 Sun. It can be noted from the results that light intensity level has a crucial impact on current parameters of solar module rather than the voltage parameters. 313
Effeciency (%), V m (mv) J ph, J sc, J m (ma/cm 2 ) Effeciency (%), V m (mv) J ph, J sc, J m (ma/cm 2 ) 35 30 25 20 15 10 5 0 2480 2400 2320 2240 2160 2080 1920 1840 1760 Iph Im Vm The dependence of parallel resistance with light intensity for each module is shown in Figure 5(b, d). It has been found that the parallel resistance for the two modules decreases with light intensity. This decrease can be explained in terms of a combination of tunneling and trapping of the carriers through the defect states in the space charge region of the device. These defect states either act as recombination centers or traps depending up on the relative capture cross sections of the electrons and holes for the defect [1, 14, 15]. 11.0 10.5 35 30 Iph Im 10.0 25 20 15 9.5 10 5 0 2080 1920 1840 1760 1680 1600 1520 1440 1360 (d) Voc Vm 9.5 9.0 Fig. 3: Light intensity dependency of current and voltage parameters of: Mono C-Si (a, b) and Poly C-Si (c, d) Therefore, concentrating systems such as Fresnel lenses and Booster mirrors can be used to enhance photocurrent, short circuit current and maximum current values of module. The dependence of efficiency on light intensity, for the two modules, is shown in Figure 4. It has been found that the efficiency of each module demonstrated a small increase with light intensity [13]. The fill factor of the mono- and the poly-crystalline modules was 68% and 44%, respectively and kept constant with change of light intensity. Figure 5(a, c) shows the dependence of series resistance with light intensity for the two modules. It has been found that the series resistance, of each module, decreases with increasing light intensity due to the increase in conductivity of the active layer with the increase in the light intensity [1]. 8.5 8.0 Fig. 4: Light intensity dependency of efficiency of: Mono C-Si and Poly C-Si B. Effect of temperature on modules parameters Similarly to the tests carried out for different light intensity levels, at first the calibration of the solar simulator was performed, light intensity has been adjusted to 1.0 Sun. Under the steady-state conditions, J V characteristics as shown in Figure 6, and P-V characteristics as shown in Figure 7 have been obtained for each module at different module temperature. 314
R sh J(A/Cm 2 ) R s I(A/Cm 2 ) R s 10 So, the poly-crystalline silicon solar module is better than mono-crystalline silicon for hot area. 5Rsh 25 20 15 10 9000 8000 7000 6000 5000 4000 3000 1000 0 8 6 4 2 4000 3500 3000 2500 1500 1000 500 (d) 0.035 0.030 0.025 0.020 0.015 0.010 0.005 10 o C 20 o C 30 o C 40 o C 50 o C 0.0 0.4 0.8 1.2 1.6 2.0 2.4 2.8 Cell type = mono c-si 0.06 10 o C 0.05 0.04 0.03 0.02 0.01 0.00 0.0 0.4 0.8 1.2 1.6 2.0 2.4 Cell type = poly C-Si 20 o C 30 o C 40 o C 50 o C Fig. 5: Light intensity dependency of series and parallel resistance of Mono C-Si (a, b) and Poly C-Si (c, d) Figure 7 shows the variation of the maximum power density with module temperature. It has been found that the maximum power density of the two modules decreases with increasing module temperature, where the maximum power density of the mono-crystalline and the poly-crystalline modules for temperature=10 o C was 43.4 mw/cm 2 and 48.76 mw/cm 2, respectively. Increasing the temperature to 50 o C causes the decrease of the power by 25% and 14% to reach values 36.32 mw/cm 2 and 41.88 mw/cm 2 respectively. Fig. 6: The J-V curves for light=1.0 Sun at different temperatures of Mono C-Si and Poly C-Si The dependence of the current parameters with temperature for the two modules is shown in Figure 8(a, c). It can be to say that current parameters of silicon solar module are slightly affected with temperature. Although the value of J sc for the monocrystalline module for temperature=10 o C were 29.4 ma/cm 2, this value decreases to be 29.07 ma/cm 2 for temperature=50 o C. Decrease of J sc by about 1% with increasing module temperature. The value of J sc for the poly-crystalline module for temperature=10 o C were 59.13 ma/cm 2, this value increases to be 59.93 ma/cm 2 for temperature=50 o C. 315
, V m (mv) P(W /Cm 2 ) J sc, J m (ma/cm 2 ), V m (mv) P(W/Cm 2 ) 0.048 0.040 0.032 0.024 10 o C 20 o C 30 o C 40 o C 50 o C J sc, J m (ma/cm 2 ) 30 29 28 27 26 25 24 23 22 21 2600 Im 0.016 2400 2200 Vm 0.008 0.0 0.4 0.8 1.2 1.6 2.0 2.4 2.8 1800 1600 0.048 0.040 0.032 0.024 0.016 10 o C 20 o C 30 o C 40 o C 50 o C 60 58 56 54 52 50 48 46 44 42 40 38 36 2200 1800 (d) Im Vm Voc 0.008 1600 0.0 0.4 0.8 1.2 1.6 2.0 2.4 Fig. 7: The P-V curves for light=1.0sun at different temperatures of Mono C-Si and Poly C-Si Increase of J sc by about 1% with increasing module temperature can be attributed to the band gap Eg decreases. On the other hand, the decrease in J m arises from the dramatic drop in voltage parameters [16]. For any value of module temperature, the difference between J sc and J m of mono-crystalline module has been found to be smaller than that of the poly-crystalline module. This result indicates that the mono-crystalline module is more appropriate for the ideal module definition. 1400 1200 Fig. 8: Module temperature dependency for current and voltage parameters of Mono C-Si (a, b) and Poly C-Si (c, d) Figure 8(b, d) shows the variation of the voltage parameters with temperature. It has been found that voltage parameters of each module decrease with increasing temperature. The values of and V m for the mono-crystalline module decreases from 2.52V and 1.94V at temperature=10 o C to 2.24 V and 1.65V at temperature=50 o C. About 11% and 14.7% decrement in and V m, respectively has been determined. The values of and Vm for the poly-crystalline module decreases from 2.2V and 1.3V at temperature=10 o C to 1.95V and 1.12 mv at temperature=50 o C. 316
R sh R s FF FF Effeciency (%) Effeciency (%) About 11.3% and 14.4% decrement in and V m, respectively has been observed. It can be noted from the results that the temperature has a crucial impact on voltage parameters of solar module rather than the current parameters [17]. The dependence of fill factor with temperature for each module is shown in Figure 9. It has been found that the fill factor of each module also demonstrated a decrease with temperature increases [1]. The dependence of efficiency with temperature for each module is shown in Figure 10. It has been found that the efficiency of each module demonstrated a decrease with temperature [1,18]. 11.0 10.5 10.0 9.5 9.0 8.5 0.70 11.0 10.5 0.69 10.0 0.68 9.5 0.67 9.0 8.5 0.450 0.445 0.440 0.435 Fig. 10: Module temperature dependency for efficiency of: Mono C-Si and Poly C-Si Figure 11(a, c) shows the dependence of series resistance on temperature for the two modules. It has been found that the series resistance of monocrystalline module demonstrated a small increase with temperature increases, while the poly-crystalline module shows a small decrease with temperature. 2.0 1.8 0.430 Fig. 9: Module temperature dependency of fill factor of: Mono C-Si and Poly C-Si 1.6 1.4 1.2 1.0 1500 1000 500 317
R sh R s 7.4 7.2 7.0 6.8 6.6 6.4 6.2 6.0 400 380 360 340 320 300 280 (d) Fig. 11: Module temperature dependency of series and parallel resistance of: Mono C-Si (a, b) and Poly C-Si (c, d) The dependence of parallel resistance with temperature for each module is shown in Figure 11(b, d). It has been found that the parallel resistance of monocrystalline module decrease with temperature. The parallel resistance of poly-crystalline module increase with temperature. This increase can be attributed to the existence of local in-homogeneities leading to nonuniform current flow or to the charge leakage a cross the p-n junction in the module [1]. IV. CONCLUSION Accurate knowledge of solar module performance parameters from the measured J V characteristics is very important for the quality control and the performance assessment of solar system. In this paper, light intensity and temperature dependency of output performance parameters of mono-crystalline silicon and polycrystalline silicon solar modules has been experimentally investigated. The results of the two modules indicated that light intensity has a dominant effect on current parameters. Short circuit current and maximum current are increase linearly with increasing light intensity. So, the maximum power density output increased by 80% with increasing light intensity from 0.2 Sun to 1.0 Sun. On the other hand, it has been observed that module temperature has a dramatic effect on voltage parameters. Open circuit voltage and maximum voltage are decrease with increasing module temperature. So, the maximum output power density decreased by 25% and 14% for the mono-crystalline and poly-crystalline silicon with increasing module temperature from 10 o C to 50 o C. 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