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25Статья поступила в редакцию 22.02.10. Ред. рег. № 728
The article has entered in publishing office 22.02.10. Ed. reg. No. 728
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ОПРЕДЕЛЕНИЕ ОСНОВНЫХ ПАРАМЕТРОВ СОЛНЕЧНЫХ БАТАРЕЙ
К. Тепе1, К. Агбенотовосси1, Г. Джетели1, С. Оуро-Джобо1,
К. Напо , Л. Пичон
Лаборатория солнечной энергетики, Кафедра возобновляемых источников энергии UNESCO, Факультет естественных наук Университета Ломе-Того BP 1515, Ломе-Того, тел.: (228) 225 3329, (228) 905 59 76, e-mail: kossi.tepe@yahoo.fr 2Лаборатория металловедения UMR 6630 CNRS, Университет Пуатье, Франция Университет Ломе, Лаборатория солнечной энергетики
Заключение совета рецензентов: 09.03.10 Заключение совета экспертов: 15.03.10 Принято к публикации: 18.03.10
В данной статье представлены результаты работы по исследованию характеристик фотоэлектрических солнечных батарей с использованием устройств фотоспектрального анализа. В этих устройствах при определении основных характеристик фотогальванических элементов используется принцип объединения фотоэлектрического эффекта и фотоспектрального отклика под действием излучения.
Такие исследования фотогальванических элементов позволяют предсказывать основные параметры солнечных батарей. В данной работе результаты, полученные при исследовании свойств фотогальванических элементов, сопоставляются с результатами, полученными при непосредственном исследовании свойств солнечных батарей. Эти результаты согласуются между собой с точностью, удовлетворительной для определения основных параметров, характеризующих солнечные батареи, реализованным фотоспектральным методом, основные результаты использования которого представлены в данной статье.
Ключевые слова: солнечная энергетика, фотогальванические элементы, характеристики солнечных батарей.
DETERMINATION OF BASIC PARAMETERS OF SOLAR PANELS K. Tepe1, K. Agbenotowossi1, G. Djeteli1, S. Ouro-Djobo1, K. Napo1, L. Pichon2
'Laboratoire sur l'Energie Solaire, Chaire Unesco des Énergies Renouvelables, Faculté des Sciences, Université de Lomé-Togo BP 1515, Lomé-Togo, tel.: (228)225 3329, (228) 905 59 76, e-mail: kossi.tepe@yahoo.fr 2Laboratoire de Métallurgie Physique UMR 6630 CNRS, Université de Poitiers - France Université de Lomé, Laboratoire sur l'Energie Solaire
Referred: 09.03.10 Expertise: 15.03.10 Accepted: 18.03.10
This article presents the results of the work of characterization of the photovoltaic solar panels with the use of the photospectral devices of characterization. These devices combine the photoelectric effect and photo-spectral response under illumination for the determination of the fundamental characteristics of photovoltaic cells.
The manipulations performed on the photovoltaic cells permits to predict the basic characteristics parameters of solar panels. Indeed, in this paper the results obtained by characterizing photovoltaic cells are correlated with those obtained with a direct characterization of a panel. The precision obtained is satisfactory for the knowledge of the basic parameters characterising the solar panels with the photo-spectral method realized and whose main work is presented in this article.
Keywords: solar energy, photovoltaic cells, parameters of characterization of the solar panels.
Kossi Tepe
Organization: University of Lomé-Togo, Faculty of Science, Department of Physics, Solar Energy Laboratory.
Education: Master's degree in material science in 1994 at University of Lomé, Post-graduate degree in computer sciences (IT) in 1995. DEA in engineering sciences in 2004, phD student 2005.
Experience: Scientific research project in characterization of solar cells, member of Laboratory of Solar Energy of University of Lomé, Network manager at university of Lomé and lecturer in computer sciences. Responsible of University's network since 2003.
Main range of scientific interests: renewable energy, solar energy, computer sciences and collaborative work.
Publications: 2 papers in international scientific journal.
International Scientific Journal for Alternative Energy and Ecology № 2 (82) 2010
© Scientific Technical Centre «TATA», 2010
K. Agbenotowossi
Organization: University of Lomé-Togo, Faculty of Science, Department of Physics, Solar Energy Laboratory.
Education: Master's degree in material science in 2002 at University of Lomé, DEA in material sciences in 2009.
Experience: Scientific research project in characterization of solar cells, member of Laboratory of Solar Energy of University of Lomé.
Main range of scientific interests: renewable energy, solar energy.
Organization: DPMM - Institut IUT P' - UPR 3346 CNRS - University of Poitiers- ENSMA-Francee, Poitiers, Materials physics Laboratory (PHYMAT).
Education: Master's degree in material science in 1994 at the University of Poitiers, DEA in material science in 1995, phD degree in 1999 at university of Poitiers.
Experience: Lecturer at University of Poitiers, Maitre of conference since 1999, Chief of chemistry Department at IUT of Poitiers 2005-2008, Director of chemistry Department at IUT of Poitiersdes 2002-2005.
Main range of scientific interests: solar energy, optoelectronic thin films and its applications.
Publications: 28 papers in international scientific journal, 13 oral communications and 13 communications by poster.
Luc Pichon
Organization: University of Lomé-Togo, Faculty of Science, Department of Physics, Solar Energy Laboratory.
Education: Master's degree in material science in 1985 at University of Poitiers, DEA in material sciences in 1986, phD degree in 1989, DESS-CAAE (MBA).
Experience: Lecturer at University of Lomé, Maître of conference since 2005, member of Laboratory of Solar Energy of University of Lomé, Director of office de BTS in TOGO since 2001.
Main range of scientific interests: renewable energy, solar energy, infrared spectroscopy, geometrical optic, optoelectronic thin films and its applications.
Publications: 15 papers in international scientific journal.
G. Djeteli
Introduction
Many researches have been conducted on silicon, which is undoubtedly the most widely used material for the manufacture of solar panels [1, 2]. The characterization of these solar panels is necessary in the design of this type of electricity generation based on photovoltaic installations. To have the skills to understand better the issues related to the design, the implementation and maintenance of photovoltaic systems, devices of characterization of photovoltaic cells have been implemented.
In southern countries the solar field seems to be in favour to the installation of solar photovoltaic systems, while northern countries are more advanced in the use of this form of cleaner energy, which is an alternation among renewable energies. The collaboration of two laboratories of Northern countries and Southern countries helped to implement not only devices for characterization of photovoltaic cells in the laboratory but also give a method for validation of laboratory results with real site of presence of sunlight.
This article describes techniques used in the laboratory for characterizing the photovoltaic cells with the determination of their basics parameters and to provide those of corresponding solar panels.
Experimental devices
Experimental setup of characterization under white light
The device set up for white light response (Fig. 1). It consists of:
- a source of white light illuminating the cell under normal impact;
- a power supply controlled through a computer;
- a multimeter measuring the voltage in the boundary of the cell and connected to the RS232 interface of a the computer for data acquirement;
- a multimeter measuring the intensity of current connected also to the RS232 interface of the computer;
- a cell from which the characteristics are determined under illumination;
- a contact temperature sensor of PT100 type;
- a computer which allows to manipulate the experiment devices through a program we conceived and easily used under an operating system like Windows.
Рис. 1. Общая схема для исследования свойств
под действием белого света Fig. 1. White light characterization synoptic circuit
As the solar panels are made up of several cells, the answer of an elementary cell will determine the way the panel will answer under illumination of radiation. It is therefore necessary to consider the response of a photovoltaic cell, when subjected to radiation to better reproduce the spectrum and intensity of the average solar radiation at ground level with the normalization AM1.5 [2]. A photo-sensor put near the solar cell enables to measure the intensity of illumination.
Device for characterization of solar panel
The experimental characterization circuit panel (Fig. 2), consists of:
- a solar panel made at the laboratory on solar energy (LES);
- a multimeter measuring the intensity of current in the circuit;
- a multimeter measuring the voltage in the boundary of solar panel;
- a variable resistor to vary the current in the circuit.
Рис. 3. Вид установки Fig. 3. View of the setting
These devices are used to study the electrical response under illumination of photovoltaic cells and a direct characterization of solar panels. The results obtained on solar cells are correlated with those obtained by direct characterization of the panel in order to analyze the differences when estimating the basic parameters as [2-4]:
- Peak power Ppk or maximum power Pmax: the optimal use of a photo-generator is to operate under load at its maximum voltage and current corresponding to maximum power Pmax, it depends on illumination and the nature of photo-generator. Under the standard conditions of sunlight SCS (1000 Wm-2, 25° C, solar spectrum AM 1.5), this power is called the peak power or peak watt (Wpk);
- The open circuit voltage (voc): voltage measured directly when the photo-generator has no charge placed at its terminals. It is a constant value for a cell varies with technology and illumination;
- The short circuit current (Isc) is the current measured at the terminals of photo-generator by connecting an ohmmeter directly. In this case the generator is put in short-circuit and the current is maximal;
- The shunt resistance (Rsh) is imaginary intrinsic resistance which takes into account the loss of current between positive and negative terminals of photogenerator and which can be deduced from electricity principle in the equivalent circuit;
- The seriesl resistance (Rs): It is a resistance issued from different electric resistance that the current meets on its way (intrinsic resistance of contacts and layers), it can also be deduced from electricity principles in an equivalent circuit;
- The fill factor FF: given by equation (1):
FF = ■
I V
m m
(1)
Рис. 2. Схема для исследования свойств батареи Fig. 2. Panel characterization circuit
The panel is illuminated by a solar light; its intensity is measured with a sensor not shown (Fig. 2). The next view (Fig. 3) presents the setting with the solar panel and measuring devices.
with Im - current at maximumpower; Vm - voltage at maximumpower; Isc - short circuitcurrent; Voc - open-circuit voltage.
It gives the aspect of the characteristic curve and therefore the response of the cell. The more this factor is away from 1 the less cell is ideal; in any case this factor is less than 1.
International Scientific Journal for Alternative Energy and Ecology № 2 (82) 2010
© Scientific Technical Centre «TATA», 2010
Experiments
Preparation of samples cells
The manipulations were realised on:
- Solar panel setup at the Laboratory on Solar Energy (LES), with 32 photovoltaic cells, connected in series and grouped in 4 rows of 8 cells. Each cell has a used area of S = 147.43 cm2;
- Samples of cells identical to those used in the setup of the solar panel and prepared following an appropriate protocol (connectors realised by soldering tin aluminium material). The usable surface of the sample cell is approximately S = 3.7 cm2.
Manipulations
The first manipulation consisted to determinate the current-voltage characteristics of cells by using the device setup for white light characterization. The principe of this experimental device uses the photovoltaic effect [3-5] (Fig. 1). The data response collected at the boundary of the solar cells is sent to a database for manipulation.
The use of this database permitted to draw the current-voltage and power-voltage curves for analysis. These results are then correlated with those obtained by other teams by direct characterization of the photovoltaic solar panel.
Results and Analysis
Experiment on samples cells
The measures focused on two sets of cells used in the setting of the panel. The samples cells are called 1 and 2.The response curves (Fig. 4 and Fig. 5) are shown below.
Рис. 4. Кривые зависимости тока и мощности от напряжения при напряжении источника света 20 В Fig. 4. Curves of current-voltage and power-voltage characteristics under light voltage of 20 V
The power curves are deduced from the data response I and V of the cells with the power formula P = IU. These response curves (Fig. 4 and 5), allowed us to obtain the characteristics parameters of Table 1. The series resistant is obtained by the tangent at the I(V) curve at the point P1(I = 0, V = Voc) and the shunt resistant by the tangent at the same curve at the point P2 (I = Isc, V = 0).
Рис. 5. Кривые зависимости тока и мощности от напряжения при напряжении источника света 25 В Fig. 5. Curves of current-voltage and power-voltage characteristics under light voltage of 25 V
Таблица 1
Электрическая характеристика образца элемента
Table 1
Electrical characteristic of sample cell
Light voltage (V) Rs (П) Rsh (П) P L max (W) FF V * oc (mV) ^cc (mA)
20 1.2 12.5 0.01699 0.475 452.3 -79
25 1.16 10.5 0.0168 0.483 451.53 -77
The results in Table 1 let us making the following observations:
- The maximum power of a sample cell is
Pmax (sample) = 0.017 W;
- its open circuit voltage Voc (sample) = 0.452 V;
- its fill factor is FF (sample) = 0.48;
- The low value of the fill factor shows that the cell used in the setting of the panel is meanly ideal [2, 6];
- These various values increase slightly with the power of illumination used except the open circuit voltage Voc, which decreases according to data collected in papers [2, 6, 7];
- The negative values of current are due to the use of the cell as a receptor when using external generator (Fig. 1). The variation of the voltage of this generator permits to invert the polarity to positives values when this voltage comes down to the cells' one. For the use of the cell as generator, the power-voltage curve has been inverted. The decrease of the shunt resistance and current (Isc) here although the voltage lighting increased from 20 to 25 V can be explained by warming of the cell with recombination of charge carriers.
According to the law of addition of voltage [8], and the proportionality between current density and the illuminated surface, these results allow the following simulations:
I = JS (2)
with J - current density; S - the illuminated surface.
- The open circuit voltage of the panel is Foc (panel) = 32Voc (sample) = 14.464 V
- The fill factor is FF (estimated) = FF (sample), which provides:
- The maximum power of the panel:
Pmax (estimated) _ Pmax (sample) ' 32 S/S = 21.67 • (3)
Experiment on panel This experiment was conducted under a solar flux average of 705.94 Wm-2 and 896.71 Wm-2. The results of measurements of the intensity I and voltage V are sent to a database whose use permit to plot the curves below (Fig. 6 and Fig. 7).
Рис. 6. Характеристические кривые солнечной батареи I = f(V) и P = g(V), Е = 705,94 Wm-2 Fig. 6. Characteristics curves I = f(V) and P = g(V) of solar panel, Е = 705,94 Wm-2
- The open circuit voltage of the panel is around Foc (panel) = 15 V;
- The form factor is FF panel (panel) = 0.50;
- The short current circuit panel is around Icc (panel) = 3 A;
- The maximum power of the panel is around Pmax (panel) = 23 W;
- The open circuit voltage Voc increases slightly with illumination but the time of exposure has heated the solar panel. This can explain the decrease of the value of Voc here with the shunt resistance while the series resistance increases slightly.
Таблица 2
Электрическая характеристика солнечной батареи
Table 2
Electrical characteristic of the solar panel
E (W/m2) (Q) Rsh (Q) P 1 max (W) FF V y co (V) Icc (A)
705.94 1.72 329 22.9848 0.516 15.21 2.93
896.71 2.6 70.5 22.078 0.44 14.73 3.4
Approaching of estimated values to experimental panel measures
The manipulations performed on the panel and a cell allows making some comparisons presented in Table 3. In the first column, we find the experimental results of the panel, the second column represents the experimental values obtained from samples cells used, the third column the expected results of the panel and the last column shows the accuracy between estimated values and the measured values on the panel.
Таблица 3 Сравнение характерных параметров
Table 3
Table of comparison of characteristic parameters
Parameter Solar panel Sample cells Estimated Accuracy
Voltage Voc, V 15 0,452 14,464 4%
Fill factor 0,50 0,48 0,48 4%
Electrical Power, W 23 0,017 21,67 6%
Рис. 7. Характеристические кривые солнечной батареи I = f(V) and P = g(V), Е = 896,71 Wm-2 Fig. 7. Characteristics curves I = f(V) and P = g(V) of solar panel, Е = 896,71 Wm-2
The characteristics parameters of the panel obtained from the experimental curves (Fig. 6 and Fig. 7), are summarized in Table 2.
From the results in Table 2, we can make the following remarks:
This Table 3 shows that the estimated values are not very far from the experimental parameters values obtained from the solar panel. The accuracy of this measure is around 4% allows us to admit that the estimated values seem to be in agreement with the experimental values even if the accuracy on the power panel is about 6%.
Conclusion
The results obtained on the panel and samples cells show that the electrical characteristics such as open circuit voltage Voc, the fill factor (FF) and power panel sizes are predictable from measurements made on the setup of
International Scientific Journal for Alternative Energy and Ecology № 2 (82) 2010
© Scientific Technical Centre «TATA», 2010
characterization. These results confirm that the work on the setup of characterization can provide for any solar panel, the electrical characteristic quantities such as:
- The open circuit voltage Voc;
- The short circuit current Isc;
- The fill factor for assessing the degree of idealistic generator obtained;
- The maximum power of working of the solar panel.
These fundamental quantities are essential to the design and evaluation of the needs of energy leads on use of photovoltaic panels system of production of current.
References
1. Percebois J. L'énergie solaire-perspectives économiques, éditions du centre national de la recherche scientifique. France, 1975.
2. Ricaud A. Photopiles solaires; Presses Polytechniques et Universitaires Romandes. Collection «Cahiers de Chimie». Suisse, 1997.
3. Green M.A. Englewood C. Solar cells: operating principles, technology and system applications. N.J. Prentice-Hall (la bible anglosaxonne des physiciens du solaire). Sydney, 1992.
4. Durisch W., Tille D., Worz A., Plapp W. Characterisation of photovoltaic generators // Applied Energy. 2000. No. 65. P. 273-284.
5. Ali Naci Celik, Nasir Acikgoz. Modelling and experimental verification of the operating current of monocrystalline photovoltaic modules using four-and fiveparameter models // Applied Energy. 2007. No. 84. P. 1-15.
6. Labouret A., Villoz M. Énergie solaire photo-voltaïque. Dunod. France, 2003.
7. Labouret A., Cumunel P., Braum J.-P., Farragi B. Cellules solaires: Les bases de l'énergie photovoltaïque. 3è édition d'ETSF, DUNOD. France, 2001.
8. Braun J.-P., Cumunel P., Farraggi B., Labouret A. Les cellules solaires. Collection ETSF, DUNOD. France, 2001.
3-Я МЕЖДУНАРОДНАЯ ВЫСТАВКА ТЕХНОЛОГИИ СОЛНЕЧНОЙ ЭНЕРГЕТИКИ
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