Development of a Thermal Visor to Analyze the Influence on Temperature in the Efficiency of a Solar Panel

Transcription

1 1 Development of a Thermal Visor to Analyze the Influence on Temperature in the Efficiency of a Solar Panel A. L. Malta 1, S. F. Bicalho 1, L. P. Carlette 1,R. S. Moreira 1, D. E. Rodrigues 1, H. A.Pereira 1 1 Universidade Federal de Viçosa, Av. P. H. Rolfs,s/nº,Viçosa, Minas Gerais Abstract A solar panel is influenced by its temperature, usually the lower temperature means that the panel will be more efficient. This paper contains a way to show the temperature along the photovoltaic panel as well as using an algorithm to analyze how this temperature has influenced in the generated power. Index Terms PV module, temperature, thermal visor. O I. INTRODUCTION NE of the challenges of development of the modern society is the energy demand. In this context, the Photovoltaic (PV) module is a good alternative to generate electricity. The sun is a clean and abundant energy source and its potential is practically not used, since the most part of the solar irradiance is reflected back after reach the earth s surface. A PV module is made of a set of connected photovoltaic cells that convert the solar irradiance into electricity. Even so, today there are different uses for this technology; from small electronics devices for example calculator battery chargers and big installations and power plants and satellites [1]. The modeling of photovoltaic panels can be considered a multi physical modeling because it considers the temperature at the panel, the radiation incident on it, and its electric power generation. In this domain, it becomes necessary to make the study of each subset, considering their effects in cascade that influence on each other [2], [3]. A method to increase the PV array efficiency is using concentrators to focus the sunlight on the module. But this method generally increases the temperature of the panel what is an undesirable effect because it can reduce the efficiency of the panel and its useful life. An obstacle considering convert solar energy into electricity is the low efficiency of the PV arrays which are highly dependent on temperature and irradiance, generally lower temperatures means more efficiency, as can be seen in the Figure 1. PV curves are generally made for a constant The authors would like to thank FAPEMIG, CAPES and CNPQ by financial support. Amaury Leite Malta, Heverton Augusto Pereira, Denilson Eduardo Rodrigues, Luan Peterle Carlette, Samuel Fonseca Bicalho and Rodrigo Sampaio Moreira are with the Department of Electrical Engineering, Universidade Federal de Viçosa, Viçosa, Brazil ( s: {amaury.malta, heverton.pereira, denilson.rodrigues, luan.carlette, samuel.bicalho, rodrigo.sampaio}@ufv.br. irradiance and temperature as can be seen in Figure 1 (a) and (b). But the temperature is not constant along the panel and this characteristic influence in the generated power. So it is important to find a way to know how temperature varies to study exactly how the panel behaves. PV curves are generally made for a constant irradiance and temperature as can be seen in Figure 1 (a) and (b). But the temperature is not constant along the panel and this characteristic influence in the generated power. So it is important to find a way to know how temperature varies to study exactly how the panel behaves. (a) (b) Figure 1. Effect of incident irradiance (a) and temperature (b) in I x V curves of a solar panel. Figure 2 shows an example of thermal visor application obtained using a thermographic camera. It is possible visualize the points where there are solar cells with high temperature. This situation can influence the efficiency of the panel because the cells are connect in series.

2 2 A thermographic camera uses the infra-red radiation emitted from an object to calculate the temperature on its surface. Despite being a good way to obtain a thermal visor, using this camera to measure the temperature on a solar panel constantly some problems can occur. First of all, the cost of this type of camera is around R$5, while the total price of the elements used in this project is about 2% of this value. Another important point to consider is the installation of the camera. The only way to do not cause shading on the panel is to construct a structure where the camera is always at the needed distance and angle of the panel; moreover, since the camera receives the temperature of the surface of the objects, some interferences between the lens and the back of the panel can be caused by dust or water, for example. Lastly, the intention is to send the data read by the LM-35, and possibly future other components, through the PIC, to a router; and then, every computer that contains the program made in this paper would be able to draw the thermal visor. amplifies the output voltage of the multiplexer to a value between V and 5V, so that the PIC can receive the signal. The LM-35 sensor which temperature will be read by PIC18F455 is chosen according to the logical state of the respective pins 33, 34 and 35. After the signal acquisition, the PIC receives the value in its analogic input (pin number 2) and then sends this signal to an USB output, which is connected to the computer. In order to determinate the temperatures in the unknown points of the module, it was chosen a method of simple interpolation to obtain a light algorithm and even so with a good resolution. This method can be observed by (1), where S represents the temperature of each sensor and D is the distance between the sensor and where the temperature is wanted. Figure 3: Back side of the panel with the sensors Figure 2. Thermal visor example. II. METHODOLOGY It is proposed a system to measure the temperature on the panel s surface and then a figure that contains the collected data is plotted using the software Matlab. The temperature on the panel is measured using LM-35 transistors, which sensibility is 1/ and accuracy is.5 at 25. Both of the 8 sensors are placed strategically on the back side of the panel as can be seen Figure 3 and Figure 4. The transistor converts the temperature on the surface into an electrical signal that will be sent to the multiplexer. The multiplexer used is the 451, which has 8 channels, 8 inputs and 1 output. This multiplexer switches the sensors following the logic state of 3 pin which are controlled by the PIC controller. For example, if the input signal is 11, what is a 3 in binary, the third input signal will be sent to the output in a low resistance path, while the other 2 inputs will be turned off. The signals that come from the multiplexer are sent to an operational amplifier, in this work, the LM 741, which Figure 4: Position of the sensors (red points) in the panel. (1) To validate this method of interpolation one of the sensor was disconsidered on the algorithm and the temperature on the point where it is located was calculated with the interpolation, after that the value calculated and measured by that sensor were compared. Some tests were run to see the effectiveness

3 3 of this method and a maximum error of 8 percent was obtained, considering real values obtained on the time of 16h45m of day Table 1: Errors for the estimation method Read Value ( ) Calculated Value ( ) Error (%) 4,1 37 7,7 41,7 41 1,7 39,1 4 2,3 41,6 41 1,4 39,68 4, ,8 4,2 37 8, 41,7 44 5,5 The multi-physics modeling represents the influence of various phenomena in which a real system is subjected. There is in Matlab 7.1./Simulink, in Simscape library, a multi physical model of a solar cell. In this software it is possible to analyze the behavior of each cell when it is working as an entire module. The equations for this Model are below: = and are the reverse leakage current in each diode that are equal, in this case, and calculated by (3)and (4), where =3, as a default value. = =,, = + 1 = = and 1 are zero in this work, because these parameters are not informed in the datasheets. In it is shown the Multi Physical Model where is possible to analyze the panel behavior considering the parameters of each solar cell. Moreover, it is possible to observe the change in the series and parallel resistances with temperature. So that we can obtain the characteristics curves for the exactly situation and time the data was collected, because it is possible to submit each cell to a different temperature. The results were obtained for a SM-48KSM Kyocera Panel, which parameters are shown in TABLE II. TABLE II. KYOCERA SM-48KSM PARAMETERS FOR 1 W/M² AND 25 ºC. Parameter III. RESULTS Value , / 1.66 / *STC: AM1.5 spectrum The tests were done in December 6, 212 in the city of Viçosa, Brazil. Figure 5 shows the theoretical irradiance curve for Viçosa in this day. Solar Radiation (W/m²) Maximum Solar Radiation Theoretically Captured Static System Track System - 1 axis Track System - 2 axis Time (Hours) Figure 5: Irradiance Curve in Viçosa MG on December, 6, 212. Figure 6 shows the profile of temperature for the data collected at 16h45m of day It is possible to see that one corner is hotter than the rest of the panel. Figure 7 show the V X I curve. And the Figure 8 shows the curve of maximum power point. A zoom on the PxV curve, Figure 9 shows that a whole panel submitted to 4 Celsius degrees behaves different from a panel in a real system which each solar cell is working in a different temperature. In this situation the panels presented a difference of.75% in the maximum power point.

4 X: 2.47 Y: X: 2.55 Y: Power (W) Figure 9: Zoom at the maximum power point for the collected data and a panel submitted to 4 degress. Current (A) Figure 6: Temperature on the panel Voltage (V) Figure 7: VxI curve for the collected data compared with a panel submitted to 4 degrees. 45 IV. CONCLUSION In this paper, a thermal visor was developed. This device helps the development of simulation of solar panels. A multi physical model was used, and a solar panel with 36 cells and 48 W was analyzed. The tests were done in December 6, 212 in the city of Viçosa, Brazil, and the data collected at 16h45m showed a difference between a constant temperature panel and a multi physical model of.75%. Future works will compare experimental results with the simulation results. V. REFERENCES [1] T. HARAKAWA e T. TUJIMOTO, A Proposal of Efficiency Improvement with Solar Power Generation System, 27th Annual Conference of the IEEE Industrial Electronics Society., 21. [2] R. J. Menner, Multi-Physical Modeling and Experimental Verification of Respiratory System, 29. [3] Z. R. Michael Pokorny, Multi-Physical Model of Gunn Diode Power (W) Voltage (V) Figure 8: VxP curve for the collected data compared with a panel submitted to 4 degrees.

5 5 VI. BIOGRAPHIES Amaury Leite Malta was born in Senhora dos Remédios, Brazil, on November26, He is student of Electrical Engineering at Federal University of Viçosa, Viçosa, Brazil. Currently is integrant of GESEP, where develop works about renewable energy system. Denilson Eduardo Rodrigues received the B.S. degree, M.S. degree and Ph.D. in agricultural engineering from the Universidade Federal de Viçosa UFV, Brazil. Today he is with the Department of Electric Engineering, UFV, Brazil. His research interests are machines, motors microcontrollers, data acquisition, microtractors. Samuel Fonseca Bicalho was born in Joao Monlevade, Brazil. He is student of Electrical Viçosa, Brazil. Currently is integrant of GESEP, where develop works about renewable energy systems. Luan Peterle Carlette was born in Cachoeiro de Itapemirim, Brazil. He is student of Electrical Viçosa, Brazil. He works with Power Systems, especially with photovoltaic energy and control applied to converters. Heverton Augusto Pereira M 12 received the B.S. degree in electrical engineering from the Universidade Federal de Viçosa UFV, Brazil, in 27, the M.S. degree in electrical engineering from the Universidade Estadual de Campinas UNICAMP, Brazil, in 29, and currently is Ph.D. student from te Universidade Federal de Minas Gerais UFMG, Belo Horizonte, Brazil. Since 29 he has been with the Department of Electric Engineering, UFV, Brazil. His research interests are wind power, solar energy and power quality. Rodrigo Sampaio Moreira was born in Vitória da Conquista, Brazil. He is student of Electrical Viçosa, Brazil.