Temperature Effects on the Electrical Performance of Large Area Multicrystalline Silicon Solar Cells Using the Current Shunt Measuring Technique

Hala Mohamed Abdel Mageed, Ahmed Faheem Zobaa, Mohamed Helmy Abdel Raouf, Abla Hosni Abd El-Rahman, Mohamed Mamdouh Abdel Aziz
DOI: 10.4236/eng.2010.211112                

Abstract

The temperature effects on the electrical performance of a large area multicrystalline silicon solar cell with back-contact technology have been studied in a desert area under ambient conditions using the current shunt measuring technique. Therefore, most of the problems encountered with traditional measuring techniques are avoided. The temperature dependency of the current shunt from 5ºC up to 50ºC has been investigated. Its temperature coefficient proves to be negligible which means that the temperature dependency of the solar cell is completely independent of the current shunt. The solar module installed in a tilted position at the optimum angle of the location, has been tested in two different seasons (winter and summer). The obtained solar cell short circuit current, open circuit voltage and output power are correlated with the measured incident radiation in both seasons and all results are discussed.

Keywords

Large Area Multicrystalline Silicon Solar Cell, Current Shunt Measuring Technique, Temperature Effects, Short Circuit Current, Open Circuit Voltage, Accumulated Power, Incident Radiation

1. Introduction

It is known that photovoltaic devices such as solar cells generate electrical current when photons with sufficient energy penetrate the semiconductor and excite electrons into the conduction band [1]. However, due to the great need for these cells in massive applications, the solar cell industry has grown rapidly in recent years [2]. There is no doubt that due to low production costs and readily abundance multicrystalline silicon (mc-Si) is a very attractive substrate for solar cells [3,4]. Therefore, it is currently the dominant solar cell material for commercial applications [5,6]. Moreover, according to predictions, it will remain an important and dominant material in photovoltaics over the next 10-30 years, owing to its well recognized properties and its established production technology [7,8].

In fact, back-contact solar cells hold significant promise for increased performance in photovoltaics for the near future. They have several advantages over conventional solar cells [9-13]. Furthermore, characteristics of these back-contact solar cells were studied to improve their performance [14,15].

Short circuit current and open circuit voltage are the two major electrical parameters generally used to characterise the solar cells. Typically, these parameters are traditionally measured by digital multimeters (DMMs). However, as the big sizes of solar cells produce high current intensity with low output voltage; some troubles would appear from the usage of multimeters. Although, in a previous study [16], the hall sensor technique was applied in order to overcome these problems this technique also suffered from some limitations and needed a lot of precautions [17].

Nevertheless, due to the actual need of measuring the solar cells’ high output currents in the desert area; the current shunt measuring technique played an essential role in achieving this task. Nowadays, current shunts are used in such applications to measure current by measuring the voltage developed across their known very low resistance [17,18].

In our application, the current shunt is used in the desert area under different ambient temper-atures. The major factor to be considered is the heat generated by the shunt itself, along with the ambient temperature. Therefore, it is essential to study its behaviour under different temperatures.

In this paper, the calibrated (Holt HCS-1) current shunt 20 Ampere range was used to study the temperature effects on the electrical performance of large solar cell with back-contact technology. It was tested under different temperatures ranging from 5ºC to 50ºC in a temperature test chamber to evaluate its temperature coefficient effect on its characteristics. Then, it was applied in the realistic application to get the short circuit current of a mc-Si solar cell of area 21 cm × 21 cm with back contact technology in two different seasons (winter and summer). The cell short circuit current, open circuit voltage and output power were accurately measured and correlated.

2. Tested mc-Si Solar Cell

The tested mc-Si solar cell with back contact technology is shown in Figure 1. It has a large area of 21 cm × 21 cm. The module was installed in a tilted position at the optimum tilt angles for both seasons that were previously investigated [19].

The cell current was collected by the fine finger grid which is led to the back side through 25 holes. On the back side there are 25 soldering pads for each polarity. The outdoor cell electrical performance was studied by measuring both short circuit current and open circuit voltage in the tilted position.

3. (Holt HCS-1) Current Shunt

In order to measure high currents with best accuracy, Kelvin Four-terminal current shunts are commonly used in the metrology community and in the industrial mea-

Figure 1. Tested mc-Si solar cell.

surement applications, specially, in high current low voltage applications [20].

A (Holt HCS-1) current shunt set consists of seven separate calibrated shunt modules having current ranges from 10 milliamps up to 20 Ampere. Each range can be used for 50% up to 130% of its rated current. In this work, the 20 Ampere range current shunt shown in Figure 2 was preferably used to measure the high short circuit current (I_SC) of our tested solar cell.

This shunt resistor has a coaxial design; where, the resistor being a web of wire arranged coaxially about the axis of the shunt. Actually, it is the most cost effective current sensing elements, having compact package profiles, suitable for current measurements. It has as their major design goal adequate power dissipation and minimal resistance changes with temperature (low temperature coefficient of resistance). Eventually, one of the most important features of this current shunt is that it converts the applied current to voltage drop across its terminals in a linear manner [21-24].

3.1. Temperature Effect on the Current Shunt

Temperature testing aims to prove the resistance capability of test specimens to the environmental influences of the temperature combined with the humidity. The (Votsch-VCL) temperature test chambers are ideally suited to the environmental simulation applications. This type of chambers provides an optimum solution where space is limited. In addition, it is visually attractive with large windows, compact, easy handling, suitable for a broad range of applications involving temperature and relative humidity (RH). Besides, it has touch panel and independent adjustable temperature limiter with standard humidity diagram.

The described 20A current shunt was tested at different temperatures of 5ºC, 10ºC, 20ºC, 30ºC, 40ºC, and 50ºC at RH 50%. Its output voltage was recorded by the 8.5 digit DMM (Fluke 8508A) when the current was applied through it from the (Wavetek 9100) calibrator. Both the DMM and the calibrator used in this test were recently calibrated.

Figure 2. (Holt HCS-1) Current shunt 20 ampere range.

Tables 1, 2 and Figure 3 demonstrate the input-output relation of the 20 Ampere current shunt at different temperatures from 5ºC up to 50ºC respectively.

Figure 3 illustrates the experimentally investigated input-output curve of the 20A (HCS-1) current shunt at the temperatures from 5ºC to 50ºC, which clearly shows that its output voltage is linearly proportional to its input current with approximately the same linearity equation at all temperatures. Eventually, the investigated linearity equation that relates the input current to the output voltage is:

Conflicts of Interest

The authors declare no conflicts of interest.

References

[1]	B. G. Prevo, E. W. Hon and O. D. Velev, “Assembly and Cha-racterization of Colloid Based Antireflective Coatings on Mul-ticrystalline Silicon Solar Cells,” Journal of Materials Chemistry, Vol. 17, No. 8, 2007, pp. 791-799.
[2]	B. Sopori, “Silicon Solar-Cell Processing for Minimizing the Influence of Impurities and Defects,” Journal of Electronic Materials, Vol. 31, No. 10, 2002, pp. 972-980.
[3]	L. A. Dobrzański and A. Dryga?a, “Surface Texturing of Multicrystalline Silicon Solar Cells,” Journal of Achievements in Materials and Manufacturing Engineering, Vol. 31, No. 1, November 2008, pp. 77-82.
[4]	A. A. Istratov, T. Buonassisi, R. J. McDonald, A. R. Smith, R. Schindler, J. A. Rand, J. P. Kalejs and E. R. Weber, “Metal Content of Multicrystalline Silicon for Solar Cells and Its Impact on Minority Carrier Diffusion Length,” Journal of Applied Physics, Vol. 94, No. 10, November 2003, pp. 6552-6559.
[5]	L. A. Dobrza?ski, A. Drygta, P. Panek, M. Lipi?ski and P. Ziêba, “Development of the Laser Method of Multicrystalline Silicon Surface Texturization,” Archives of Materials Science and Engineering, Vol. 38, No. 1, July 2009, pp. 5-11.
[6]	P. Panek, M. Lipinski and J. Dutkiewicz, “Tex-turization of Multicrystalline Silicon by Wet Chemical Etching for Silicon Solar Cells,” Journal of Materials Science, Vol. 40, No. 6, 2005, pp. 1459-1463.
[7]	E. Radziemska, “The Effect of Temperature on the Power Drop in Crystalline Silicon Solar Cells,” Renewable Energy, Vol. 28, No. 1, 2003, pp. 1-12.
[8]	M. Lipiski, P. Ziba and A. Kamiski, “Crystalline Silicon Solar Cells, in Foundation of Materials Design,” Re-search Signpost Publishers, Kerala, 2006, pp. 285-308.
[9]	W. Jooss, K. Blaschek, R. Toelle, T. M. Bruton, P. Fath and E. Bucher, “17% Back Contact Buried Contact Solar Cells,” Pro-ceedings of 16th European Photovoltaic Solar Energy Confe-rence, Glasgow, 1-5 May 2000, pp. 1124-1127.
[10]	D. L. Meier, H. P. Dabis, A. Shibata, T. Abe, K. Kinoshita, C. Bishop, S. Mahajan, A. Rohatgi, P. Doshi and M. Finnegan, “Self Doping Contacts and Associated Solar Cell Structures,” Pro-ceedings of the 2nd World Conference on Photovoltaic Solar Energy Conversion, Vienna, 6-10 July 1998, pp. 1491-1494.
[11]	K. Faika, M. Wagner, P. Fath and E. Bucher, “Simplification of EWT (Emitter-Wrap Through) Solar Cell Fabrication Using Al-P-Codiffusion,” Proceedings of the 28th IEEE Photovoltaic Specialists Conference, Anchorage, 15-20 September 2000, pp. 260-263.
[12]	A. Kress, P. Fath, G. Wil-leke and E. Bucher, “Low-Cost Back Contact Silicon Solar Cells Applying the Emitter-Wrap Through (EWT) Concept,” Proceedings of the 2nd World Conference on Photovoltaic Solar Energy Conversion, Vienna, 6-10 July 1998, pp. 1547-1550.
[13]	W. Neu, A. Kress, W. Jooss, P. Fath and E. Bucher, “Low-Cost Multicrystalline Back-Contact Silicon Solar Cells with Screen Printed Metallization,” Solar Energy Materials & Solar Cells, Vol. 74, No. 1, 2002, pp. 139- 146.
[14]	J. H. Bultman, A. W. Weeber, M. W. Brieko, J. Hoonstra, J. A. Dijkstra, A. C. Tip and F. M. Schuurmans, “Pin up Module: A Design for Higher Efficiency, Easy Module Fabrication and Attractive Appearance,” Proceedings of 16th European Photovoltaic Solar Energy Conference, Glasgow, 1-5 May 2000, pp. 1210-1213.
[15]	A. Schonecker, A. Weeber, W. Sinke, C. Zechner, A. Kress and P. Fath, “Attacking Limiting Factors in 10 × 10 cm2 Multicrystalline Silicon, Emitter Wrap-through Solar Cell Design and Processing,” Proceedings of the 2nd World Conference on Photovoltaic Solar Energy Conversion, Vienna, 6-10 July 1998, pp. 1677-1680.
[16]	A. Ghitas and M. Sabry, “Performance of a Large Area Back Contact Silicon Solar Cell in a Desert Zone,” Proceedings of Cairo 11th International Conference on Energy and Environ-ment, Hurghada, 15-18 March 2009.
[17]	H. A. Mageed, A. Zobaa, A. Ghitas, M. Helmy, M. Sabry, A. A. Rahman and M. M. A. Aziz, “Electrical Performance Study of a Large Area Multicrystalline Silicon Solar Cell Using a Current Shunt and a Micropotentiometer,” Engineering, Vol. 2, No. 4, April 2010, pp. 263-269.
[18]	R. G. Jones, P. Clarkson and A. J. Wheaton, “Calibration of AC Current Shunts,” Precision Electromagnetic Measurements Conference Digest, Sydney, 14-19 May 2000, pp. 492-493.
[19]	H. K. Elminir, A. E. Ghitas, F. El-Hussainy, R. Hamid, M. M. Beheary and K. M. Abdel-Moneim, “Optimum Solar Flat-Plate Collector Slope: Case Study for Helwan, Egypt,” Energy Conversion & Management, Vol. 47, No. 5, 2006, pp. 624-637.
[20]	D. E. Destefan and R. S. Stant, “AC and DC Shunts-Can You Believe Their Specs?” Proceedings of the 20th IEEE Instrumentation and Measurement Technology Conference, Vail, Vol. 2, 20-22 May 2003, pp. 1577-1582.
[21]	C. Xiao, L. Zhao, T. Asada, W. G. Odendaal and J. D. van Wyk, “An Overview of Integratable Current Sensor Technologies,” Conference Record of the 38th IEEE Industry Applications Society Annual Meeting, Salt Lake City, Vol. 2, 12-16 October 2003, pp. 1251-1258.
[22]	American Society for Metals International, “Metals Hand- book: Stain-lessStecls.001 Materials and Special Purpose Metals,” 9th Edi-tion, Vol. 3, ASM International, Metals Park, pp. 640-645.
[23]	T. E. Lipe, “Operation and Reference Manual for the NIST Automated AC-DC Calibration Systems and Software,” National Institute of Standards and Technology Special Publication 250-61, National Institute of Standards and Technology, Fort Collins, May 2004.
[24]	K. Lind, T. Sorsdal and H. Slinde, “Design, Modeling, and Verification of High-Performance AC-DC Current Shunts from Inexpensive Components,” IEEE Transactions on Instrumentation Mea-surement, Vol. 57, No. 1, January 2008, pp. 176-181.