A Study on the Effect of Shading on a Photovoltaic Module

Transcription

1 New Physics: Sae Mulli, Vol. 68, No. 11, November 2018, pp A Study on the Effect of Shading on a Photovoltaic Module Ankhzaya Baatarbileg Zulmandakh Otgongerel Gae-Myoung Lee Department of Electrical Engineering, Jeju National University, Jeju 63243, Korea (Received 11 September 2018 : revised 25 October 2018 : accepted 30 October 2018) Most solar photovoltaic (PV) modules frequently get shadowed, completely or partially, resulting in a reduction of PV generation. This paper presents and compares the results from simulations and experimental measurements of the power output from a single PV module under various shading conditions. The study was carried out with a 90 W PV module and a 250 W PV module. The shaded area was increased from 0 to 100% for both variable and constant irradiances to analyze the effect of fluctuations in the solar irradiance certain shading conditions. The effect of shading for irradiance levels from 100 to 900 W/m 2 was investigated. Results showed that for every 100 W/m 2 decrease in the solar irradiance level, the power output decreased by 9, 0.7 and 1.5 W at 0, 25 and 50% shading, respectively. For solar irradiance levels higher than 500 W/m 2, the temperature increased by 1.6, 2.7 and 1.1 C at 0, 25 and 50% shading, respectively, for every 100 W/m 2 increase in the irradiance. PACS numbers: H-, mr Keywords: Effect of shading, Photovoltaic module, Shading profiles I. INTRODUCTION Solar energy runs clean converting sun light to energy with no combustion, and no pollution while it processes a much quite [1]. Photovoltaic (PV) production is the effective and the most agreeable solar concentrating technology. The most PV technology is connected to series cells, arrays in the world to increase PV efficiency and production. However, PV production is variability and uncertainty for changing solar irradiance level. It is the main role factor, influencing the conversion of solar energy into electricity in PV technology. Depending on solar irradiance intensity and its distribution, the mismatch losses occurred in PV module and arrays. The main indicator of mismatch losses is shading effect in PV technology for passing clouds and stayed object on PV area. The most PV cells in module or array frequently get shadowed, partially or completely, by neighboring buildings, trees and passing clouds. In fact, partially myounglk@jejunu.ac.kr and completely shading affected to reduction of PV production due to the difference and non-uniform solar irradiance. Only partial shading can reach to performance losses of 10 20% in residential PV installations [2]. These shadowing objects can reduce the sunlight throughput on PV cells and its results lower system efficiency. PV array can be shaded partially two types: static and dynamic [3]. In particular, shadows stay and move over PV cell, module and array. PV cell, module and array get shadows its output decreased by power losses in the shaded cells [4]. To mitigate effect of shading, the researchers approached various methods. In fact, most commonly used method was PV array configuration considering climate changes in certain regions [5 9]. In case of PV module, the mitigation of shading effects is divided active and passive. The passive method was commonly simple and cheaper using with bypass diodes. The active was used power electronic technology in PV module and PV array configurations [3]. Recently, solutions of partially shaded PV array have been developed, which can be organized into firmware and hardware approaches [10,11]. The main advantages of this study was investigated a This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License ( which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

2 1216 New Physics: Sae Mulli, Vol. 68, No. 11, November 2018 Fig. 2. (Color online) Indoor experimental setup (DL SOLAR-B). Fig. 1. (Color online) Shading profiles. (a) right-to-left and (b) bottom-to-top. PV module level. It helps to understand how single-cell and a PV module impacted by shading effects. It can be take into account selection of PV arrays configuration to determine its power loss and efficiency. In this study, a simulation and an experimental study of effects on PV module under various shading conditions are investigated. Three case studies, indoor, outdoor and simulation, adopted with a 90 W and 250 W PV module. Single PV cell and a module shaded from 0% to 100% under constant and variable solar irradiance levels was investigated considering right-to-left and bottom-to-top shading profiles. II. RESEARCH METHODOLOGY Research methodology for investigating the effect of shading on PV module considered three study cases as following. 1. Case study I: Indoor experimental 2. Case study II: Outdoor experimental 3. Case study III: Simulation based on MAT- LAB/SIMULINK All study cases were carried out with two different PV modules (polycrystalline and monocrystalline). Experimental measurements were analyzed by partially shading the PV module considering as different shading profiles. Shading procedure was used the coverage material, it covered a certain area from its edges, and the remaining area was illuminated on a PV cell. There are three types of shading profiles, many studies were used these profiles to investigate shading effect on the PV module [12]. Among these, right-to-left and bottom-to-top profiles are considered for this entire study in shown Fig Case study I: Indoor experimental The experimental measurements for investigating the shading effect on a PV module was located in the Renewable energy laboratory, College of Engineering, Jeju National University (JNU), South Korea. The laboratory has instrumented engineering training kit tools manufactured by De Lorenzo company [13]. A solar energy modular trainer, DL SOLAR-B, was used in indoor experimental. In Fig. 2, the operating principle of the experiment is draws the block diagram. The trainer consists of a sun simulator which comprises four halogen lamps of 300 Watts provides a high intensity of light to the PV module. It is composed by a metallic structure that supports the lamps and the control unit. The measurement unit measured solar irradiance (W/m 2 ), solar panel temperature ( C), current up to 30 V, ± 15 A (two dc ammeters), voltage up to 40V and power up to 300 W and serial connection which is connected to PC software for data acquisition and processing. That experiment was implemented 36-cells polycrystalline PV module (SYM-90P) manufactured by Sunergy company, which have 2 bypass diode connected with 2 columns in the module. The specification data of the module are listed in Table 1. The module incorporates sensors for the irradiance and temperature measurement. In the experimental setup, the light angle was a 90 on the PV module and the tilt angle of the module was constantly.

3 A Study on the Effect of Shading on a Photovoltaic Module Ankhzaya Baatarbileg et al Table 1. Model SYM-90P Polycrystalline module specification at STC. Material polycrystalline silicon Place of origin Italy Model number SYM-90P Number of cells 4 9 Size, mm Efficiency, % 13.5 P MP P, W (maximum power) 90 I SC, A (short circuit current) 5.15 V OC, V (open circuit voltage) I MP P, A (maximum current) 4.9 V MP P, V (maximum voltage) Size of cell, mm Case study II: Outdoor experimental The outdoor experimental setup was located on rooftop of building at JNU campus as shown in Fig. 3(a). The geographical coordinates of the building are latitude N and longitude E. In this experimental, the two PV modules considered and correspond to: 1) the aforementioned trainer, DL SOLAR-B, is possible to use outdoors; 2) 60-cells polycrystalline PV module (JSMM2503) manufactured by JSPV company, which have 3 bypass diodes, dividing the module in three equal sections. A monocrystalline module was experimented using the electrical circuit as shown in Fig. 3(b). The output power of a PV module requires the measurement of voltage and current values at its terminals. So, load which is the variable resistance (R) was connected through ammeter and parallel with voltmeter. The both modules allow manual configuration of the tilt angle. So, we can calculate suitable tilt angle using the coordinates. On October and November, tilt angle is equal to 40 degree more suitable in Jeju island. Also, the modules are facing South as shown in Fig. 3(a). All experiments on two modules were measured at peak sun hours in experimental days on October and November. Solar irradiance levels were W/m 2 and W/m 2 during poly and mono PV module experiments, respectively. 3. Case study III: Simulation based on MAT- LAB/SIMULINK A simulation model with shading effect should be carried out to investigate the operation of a PV module Fig. 3. (Color online) Outdoor experimental setup (monocrystalline module). (a) Setup during experimental and (b) Experimential circuit. Fig. 4. (Color online) Equivalent circuit of single-diode model. under various shading conditions. In case study, PV cell model implemented with MATLAB/SIMULINK (using the Simscape library). The model was built the commonly used equivalent circuit of single-diode PV cell which is suitable for uniform operating conditions as shown in Fig. 4. In simulation study, the aforementioned a monocrystalline PV module was implemented. To configure and control of each cell components, the module was created series connected cells with bypass diodes. Each cell unknown parameters can be easily found using Newton- Raphson method [14]. Table 2 lists the technical specification of the PV module and the configured parameters, constants of the PV model in MATLAB/SIMULINK.

4 1218 New Physics: Sae Mulli, Vol. 68, No. 11, November 2018 Table 2. Validation of JSSM2503 monocrystalline module technical specification at STC. Parameters Module Model P MP P, W (maximum power) I SC, A (short circuit current) V OC, V (open circuit voltage) I MP P, A (maximum current) V MP P, V (maximum voltage) I d, A (saturation current of diode) e-09 I P V, A (light-generated current of solar cell) a (diode ideality) R P, Ω (shunt resistance) R S, Ω (series resistance) In order to test the validity of the model a comparison with technical specification is very useful. Fig. 5(a) shows the mathematical current-voltage (I-V) curves of the monocrystalline PV module plotted with the experimental data at three different temperature conditions. Fig. 5(b) shows the I-V curves at different irradiances. The circular markers in the graphs represent experimental (I, V) points extracted from the datasheet. After the PV module was modelled on the simulation, we had a one question which was How to model a partial shaded PV cell?. We found that solution [8]. Depending on the non-uniform solar irradiance distribution, the cell can be separated into different illuminated areas. If the area of the partial shading is A 1, at certain irradiance is G 1, the light-generated current I P V 1 and dark saturation current I S1 can be expressed in Eq. (1). Where, J P V 1 and J S1 are light-generated current density and saturation current density of solar cell under partial shaded, respectively. A P V 1 = I 1 J P V 1 I S1 = A 1 J S1 (1) If the area under uniform lighting is G 1, the irradiance is G 2, the light-generated current I P V 2 and dark saturation current I S2 can be expressed in Eq. (2). Where J P V 2 and J S2 are light-generated current density and saturation current density of in solar cell under uniform illuminated, respectively. I P V 2 = A 2 J P V 2 I S2 = A 2 J S2 (2) Fig. 5. (Color online) I-V curves at differrent irradiances, 25 C. (a) I-V curves at different temperatures, 1000 W/m 2 and (b) Shading profiles. According to literature [15], the current equation of partial shaded PV cell is given as following: I = A 1 P pv1 A 1 J S1 [exp V + IR S nv t 1] +A 2 J P V 2 A 2 J S2 [exp V + IR S nv t 1] V + IR S R p (3) Where, the A 1 is the partial shading area, J P V 1 is corresponding light-generated current, J S1 is the corresponding dark saturation current. A 2 is the area under uniform lighting conditions, J P V 2 is the corresponding lightgenerated current, J S2 is the corresponding dark saturation current. Simulated model of partial shaded PV cell is set up based on Eq. (3) in MATLAB/SIMULINK. Addition, partial shading simulation has performed to take into account the space between two adjacent cells 2cm and the space between edge cells and edge of the PV module is 3.5 cm in mentioned two modules. Fig. 6 shows

5 A Study on the Effect of Shading on a Photovoltaic Module Ankhzaya Baatarbileg et al Fig. 6. Flowchart of simulation process in matlab. the flowchart of simulation process in matlab. First of all, the primary parameters are initialized by values as shown Table 2. Then it should be select shading profile (bottom-to-top or right-to-left). Depending on the selection of shading profile, the shading step is chosen differently. On the initial stage, the shading area starts from 0. After that, the important step is condition checking, that senses which area was greater than in both PV module area and shading area. It means if the area of PV module was larger than shading area, the shaded parameters will be calculated using Eq. (3). Then, the all parameters put into PV cell and PV module. After the execution, the output parameters, I, V and P, were saved to memory. Then, shading area is added by shading step. These iteration finishes when the shading area becomes to be more than PV module area. Then all outputs can be printed out. III. RESULTS AND DISCUSSION The shading effect on PV module was investigated under right-to-left and bottom-to-top shading profiles. The module surface shaded area was increased by 10%, 25% Fig. 7. (Color online) Power output versus different shading areas under right-to-left and bottom-to-top shading profiles. (a) Indoor and (b) Outdoor. and column at both shading profiles. A polycrystalline 90 W PV module were analyzed at indoor and outdoor studies. At indoor case, the output power and efficiency of the module were experimented both under constant, various irradiance levels and various shading conditions. For a monocrystalline 250 W PV module was measured carried out at outdoor and simulation was implemented. In addition, output power and module efficiency under various shading conditions were measured in outdoor. 1. Effects of PV single-cell shading under different shading different shading profiles The power output of single-cell shading for the polycrystalline PV module were illustrated in Fig. 7. Solar irradiance levels were 980 W/m 2 and 1050 W/m 2 in indoor and outdoor experimental, respectively. Fig. 7(b)

6 1220 New Physics: Sae Mulli, Vol. 68, No. 11, November 2018 Fig. 8. (Color online) Power output versus different shading areas for monocrystalinne PV module. (a) Right-to-left and (b) Bottom-to-top. shows that the power outputs were ± 1.31 W and ± 1.53 W at right-to-left and bottom-to-top shading experimental under no shading, respectively. After reaching 50% shading, the power outputs were dropped to ± 2.25 W and ± 1.12 W in right-to-left and bottom-to-top shading profiles, respectively. In case of 50% shaded single-cell, the string connected with 18 cells not generated and short-circuited by bypass diode. So, only 1/3 of the PV module was produced. All experimental data have uncertain errors. Therefore, the error bars had 95% confidence interval (CI) using standard errors and standard deviation in this study. The errors can be shown the variance (positive and negative) of the experimented data. The range of CI were from ± 0.67 to ± 3.70 in Fig. 7. For example, in case of 25% shaded single-cell, the output powers can be ± 2.88 W and ± 3.63 W at right-to-left profiles in indoor and outdoors, respectively. Also, it can be seen that Fig. 9. (Color online) Power output versus different shading areas under right-to-left shading profile. (a) Indoor and (b) Outdoor. outdoor experiments had larger error than indoor ones, which was caused by environmental impacts. The effects of single-cell shading for the monocrystalline PV module were illustrated in Fig. 8. Solar irradiance levels were 987 W/m 2 and 974 W/m 2 in right-to-left and bottom-to-top shading experimental, respectively. The power outputs under no shading were ± 1.85 W and ± 1.78 W at right-to-left and bottom-to-top shading experimental, respectively in Fig. 8. While it was 75% shading, the power outputs were reached to ± 1.01 W and ± 1.12 W, respectively. The errors in experimental were ranged from ± 0.56 to ± 1.85 in both shading profiles. In simulated results observed that no shading and 100% shaded conditions, difference of power outputs between simulated and experimented were between 7 W and 9 W at both shading profiles. When the single-cell shaded 75%, the string connected with 20 cells not generated and short-circuited by bypass diode. So, only 2/3 of the PV module was produced. The power outputs of

7 A Study on the Effect of Shading on a Photovoltaic Module Ankhzaya Baatarbileg et al Fig. 10. (Color online) Power output versus different shading areas under right-to-left shading profiles. (a) Shading area increased by 10% and (b) Shading area increased by column. the module under single-cell shading was not depending in a critical manner on the shading profile (right-to-left and bottom-to-top), as similar to the poly-crystalline or monocrystalline. 2. Effects of PV module shading under different shading profiles Fig. 9 and Fig. 10 illustrated the power outputs obtained for polycrystalline and monocrystalline PV module under right-to-left shading profile. Shading areas increased by 10 and 25%. From Fig. 9, it may be observed that at shading area increased by 10% and at no shading condition, the power outputs were ± 1.04 W and ± 1.24 W at indoors and outdoors, respectively. After reaching 10% shading, the power outputs were decreased to ± 1.38 W and ± 1.88 W, respectively. Also, it may be noticed that when the shading area reaches at 20% and 70%, the PV power out- Fig. 11. Power output versus different shading areas under bottom-to-top shading profile. (a) Indoor and (b) Outdoor. puts were decreased by 2/3 and dropped to zero, respectively. That number of power output dropped levels was equal to number of PV module used bypass diodes.from Fig. 10(a), it can be seen that when the shading area reaches at 20%, 50% and 90%, the power outputs were decreased to ± 1.31 W, ± 0.25 W and 0, respectively. These results were similar to Fig. 10(b) at shading area reaches to 1column, 3 columns and 5 columns, respectively. The power output decreased steps depended on number of used bypass diodes. The simulations results were converged to experimental results. The module under right-to-left shading profile determined matching results as obtained by shading a singlecell at both modules. Due to series connected cells. So, the power outputs of single-cell, 20% and 25% shading were 21 ± 1.26 W and 43 ± 1.07 W, polycrystalline and monocrystalline module, respectively. Fig. 11, respectively Fig. 12, illustrated the power outputs of polycrystalline, respectively monocrystalline, PV module under bottom-to-top shading profile. The results can be proven that the power outputs hugely affected

8 1222 New Physics: Sae Mulli, Vol. 68, No. 11, November 2018 Fig. 12. Power output versus different shading areas under bottom-to-top shading profile. (a) Shading area increased by 10% and (b) Shading area increased by cell. Fig. 13. Power output and temperatures of PV module under increment irradiance levels. (a) Power output and (b) Temperature. with shading areas. After reaching 10% shading, the PV modules were no power outputs. In case, shading influenced all series connected cells and generated current critically decreased to reach zero. Therefore, the variance of experimental data was ranged from ±1.94 to ±3.97 in no shading experiments. On the other shading cases, the experimental error was not occured. 3. Effects of shading on PV module under variable irradiance levels The effects of PV module shading under increment irradiance levels were illustrated in Fig. 13. At that experimental, solar irradiance were configured from 100 W/m 2 to 900 W/m 2. The results can be shown that the power outputs were continuously decreased at 25 and 50% shading conditions, when the solar irradiances were under 500 W/m 2. Inversely, at solar irradiances over 500 W/m 2, the power outputs were between 18 ± 2.09 W and 20 ± 2.13 W at both shading conditions. Let s discuss about Fig. 13(a), it was shown at 500 W/m 2 irradiance level the power output was ± 0.95 W, while at 25 and 50% shading conditions the power outputs were ± 2.01 W and 17.6 ± 1.97 W under no shading profile, respectively. Fig. 13(b) shows that temperatures were continuously increased with increasing irradiance levels. Irradiance levels were over 500 W/m 2, the temperatures were increased by 1.6 ± 1.09, 2.7 ± 0.82 and 1.1 ± 0.76 C at 0, 25 and 50% shading conditions for every 100 W/m 2, respectively. The effects of PV module shading under decrement irradiance levels were illustrated in Fig. 14. Solar irradiance levels were configured from 900 W/m 2 to 100 W/m 2. Fig. 14(a) shows that when the irradiance levels decreases from 900 to 500 W/m 2, PV module output was decreased by 9 ± 1.09, 0.7 ± 0.74, and 1.5 ± 1.15 W at 0, 25, and 50% shading profiles, respectively. Fig. 14(b) shows that when the irradiance levels decreased to 500 W/m 2, temperatures were decreased within 1 degree at all shading conditions. Compare with Fig. 13(b) and Fig. 14(b), the cell temperatures more

9 A Study on the Effect of Shading on a Photovoltaic Module Ankhzaya Baatarbileg et al Fig. 14. Power output and temperatures of PV module under decrement irradiation levels. (a) Power output and (b) Temperature. Fig. 15. Experimental results in case of PV module rightto-left shading profile. (a) Power loss and (b) Efficiency loss. affected at increment irradiance levels than the decrements. Addition, the cell temperatures of 25% shading condition were higher than other conditions at all solar irradiance levels. 4. Comparison of results in case of PV module under right-to-left shading profile The comparison of results on PV module under rightto-left shading profiles were illustrated in Fig. 15. It can be seen that power loss and efficiency loss is hugely influenced by shading effect. When the shading area increases by 10 percentages, power output loss sharply increased step by step. The amount of these steps were depend on number of connected cells with bypass diodes. Simulated and experimental results were closely converged each other. Difference between indoor and outdoor experimental was between 5 ± 1.05% and 7 ± 0.59% due to the cell temperature. Indoor experimental cell temperature was higher than outdoors. For the results comparison, the modules power outputs were not depending in a critical manner on polycrystalline and monocrystalline. From the Fig. 15, it can be seen that difference of that two PV modules was observed only number of used bypass diodes. The shading area reach to 10, 20 and 70%, the module power losses were reached to 40 ± 1.11, 60 ± 1.15 and 100 ± 1.18% on 90-W PV module (two bypass diodes), respectively. Also, three bypass diodes used PV module (250-W) shaded by over 10, 20, 50 and 90%, the power losses were reached to 20 ± 0.85, 60 ± 1.10, 90 ± 1.25 and 100 ± 1.29%, respectively. IV. CONCLUSION In this study, the shading effect on PV module under different shading profiles and various shading conditions were investigated. The performed three studies provided an investigation of shading effects on PV modules. Results show that produced power was decreased as shading

10 1224 New Physics: Sae Mulli, Vol. 68, No. 11, November 2018 areas varied between 0% and 100%. A single-cell of PV module shaded by over 50 and 75%, the power outputs were reduced by more than 50%, at 90 W and a 250 W PV modules, respectively. At shading right-to-left profile, the power output dropping points were observed that number of points depended on PV module used bypass diodes. At irradiance levels decreased until 500 W/m 2, the power outputs were decreased by 9, 0.7, and 1.5 W at 0, 25, and 50% shading right-to-left profile, respectively. Inversely, at irradiance levels increased over 500 W/m 2, the cell temperatures were increased by 1.6, 2.7 and 1.1 C at 0, 25 and 50% shading right-to-left profile for every 100 W/m 2, respectively. At variable irradiances levels, the cell temperatures of 25% shading condition was higher than the others. Furthermore, design of PV array can be implemented and performed more efficiency connection of maximum power point track (MPPT) and DC-DC converters under effect of shading. The study results can be take into account for connection of PV array and PV system for evaluating the power losses caused by shading profiles influencing PV modules operation. ACKNOWLEDGEMENTS This paper financially supported by the BRAINKO- REA21PLUS (BK21+) project, South Korea; Jeju National University. REFERENCES [1] N. Kannan and D. Vakeesan, Renew. Sust. Energ. Rev. 62, 1092 (2016). [2] A. J. Hanson, C. A. Deline, S. M. MacAlpine, J. T. Stauth and C. R. Sullivan, IEEE J. Photovolt. 4, 1618 (2014). [3] M. A. Al Mamun, M. Hasanuzzaman and J. Selvaraj, IET Renew. Power Gen. 11, 912 (2017). [4] R. Ramaprabha and Dr. B. L. Mathur, Int. J. Recent Tr. Eng. 2, 56 (2009). [5] L. F. Lavado Villa, D. Picault, B. Raison, S. Bacha and A. Labonne, IEEE J. Photovolt. 2, 154 (2012). [6] S. Pareek and R. Dahiya, in Proceedings of Annual IEEE India Conference (INDICON) (New Delhi, India, December 17-20, 2015). [7] S. Silvestre, A. Boronat and A. Chouder, Appl. Energy 86, 1632 (2009). [8] M. Jazayeri, S. Uysal and K. Jazayeri, in Proceedings of IEEE PES T&D Conference and Exposition (Chicago, IL, USA, April 14-17, 2014). [9] S. Vijayalekshmy, G. R. Bindu and S. R. Iyer, in Proceedings of the World Congress on Engineering (July 2-4, 2014, London, U.K.), Vol. I, pp [10] C. Rahmann, V. Vittal, J. Ascui and J. Haas, IEEE Trans. Sustain. Energ. 7, 173 (2016). [11] G. Cipriani, V. Di Dio, N. Madonia, R. Miceli and F. Pellitteri et al., Electrical Drives, Automation and Motion (2014), pp [12] A. Dolara, G. C. Lazaroiu, S. Leva and G. Manzolini, Energy 55, 466 (2013). [13] DELORENZO global company, Available online: tti/ solar-beng-solar-energy-mo DULAR-TRAINER.pdf (accessed Aug. 30, 2018). [14] T. Xiao, L. Zhang and S. Ma, in System Simulation and Scientific Computing, Part II: International Conference, ICSC 2012, Proceedings Part 2 (Shanghai, China, October 27-30, 2012). [15] L. Castaner and S. Silvestre, Modelling Photovoltaic Systems Using PSpice (Wiley, 2002).