16th International Power Electronics and Motion Control Conference and Exposition
Antalya, Turkey 21-24 Sept 2014
Modeling of Photovoltaic Solar Array under Different levels of partial shadow Conditions Ali Mahmood Humada1, 2, Fahmi B. Samsuri1, Mojgan Hojabria1, Mortaza B. Mohamed1, Mohd Herwan Bin Sulaiman1 1
Faculty of Electrical & Electronics Engineering, University Malaysia Pahang, Pekan, Malaysia 2 Electricity Production Directorate of Salahaldeen Ministry of Electricity, Salahaldeen, Iraq e-mail:
[email protected] Abstract—Different methods of configuration have been formulated regarding photovoltaic solar power by employing several techniques. This has been done because of the varying conditions so that the loss of power can be minimized. The main factor which decreases energy output of the photovoltaic PV solar systems is partial shadowing. The way the energy output of partially shadowed arrays varies with the system configuration used, has been studied extensively. A huge degree of disorder still exists, particularly with respect to the best modularity grade for these systems. There are two distinct sub-divisions in the systems implemented in the reconfiguration mechanism: reconfigurable solar arrays, and a switching matrix to do a reconfiguration. Using different methods, the proportions of shadowing obstructions were noted to allow for calculation of the likely shadowing losses. The outcomes of this paper on modeling and monitoring are used to evaluate the photovoltaic system with respect to shadowing losses with different levels and their reliance on the system configuration are selected. It has been found that power loss because of varying conditions is majorly due to the decrease in radiance occurring on the photovoltaic array and can be avoided through selecting the suitable configuration and connection. The simulation results show that the output characteristics of the simulator presented better results with that proposed model. Keywords-component; photovoltaic; configuration; shadowing losses; partial shadowing
I. INTRODUCTION Recently, the solar PV system attracted a great deal of attention with the tendency of electrical energy deregulation and climate conservation. Also, it is promoted in many countries and is considered to be a strategic objective for governments. Nevertheless, the yield concentration of the solar energy is less than planned due to the fact that the output of the PVs is influenced by an insolation condition and temperature changes. In the PV plants mounted in urban areas, affected by several parameters leads to the shadow effect such as clouds, booms, trees, neighbor’s buildings, antenna, or even dust, etc. The modifications of effect these parameters are accomplished by several methods to continue to operate under non-uniforms conditions and presented in [1]. This is accomplished by
Taha Hamad Dakheel3, 4 3
Faculty of Electronics & communications Engineering, Cankaya University Ankara, Turkey 4 Baiji, Electricity Production Directorate of Salahaldeen Ministry of Electricity, Salahaldeen, Iraq
avoiding a large drop which can happen in the yielded energy. A fast and accurate model of PV system under non-uniform conditions are needed to recover the affected system, to achieve a profitable analysis of the PV connections, to appraise the impact of the PV system on the reliability of a transmission and distribution system [2]. Many studies carried out to do the modeling and simulating a PV array and presented in literature, e.g. [3–10]. Most of these studies do not consider the effect of shadowing conditions and claim changing [6, 7], others depend on very complex methodologies [3, 8] or depend on linearization process for reducing the computational affliction [9, 10]. All these studies indicate that as the shadow level reduced, the yielded energy gained more. For instance, Ref [11] shows that when arrays are cleaned, there can be a reduction in 8 – 10% of the power losses. A study was also carried out in Italy using a 1-MWp PV system, which showed that there is 6.9% power losses at plants constructed on sandy soil, while plants constructed on the comparatively compact soil show a power loss of 1.1% [11]. A study has been carried out for examining the tilt angle so that optimal energy can be preserved. As per the recommendations, the annual optimal level of energy capture should have a tilt angle which is within 10 of the latitude. However, an insignificant difference was observed in the annual performance of solar cells using different tilt angles in an experiment carried out in Germany which shows the shading of partial PV arrays, that leads to multiple peaks causing local peaks which will decrease the efficiency of PV systems to a large extent if chosen. The ‘I-V’ properties of solar cells are examined in [12]. Amongst the studies pertaining to system level research is the one carried out by [13] which suggests a modular DC/DC converter mechanism, the purpose of which is to decrease the number of DC/DC components which monitor the maximum power point (MPP) employed by the stand-alone systems. According to this mechanism, all PV modules need to function simultaneously; however, this may not be possible for installations of a greater scale. A reconfiguration pertaining to the cell level has been studied in [13], so that the shadowing impact can be managed
,((( PEMC 2014
461
16th International Power Electronics and Motion Control Conference and Exposition
and the output power can be improved by including outer reconfigurable cells. To enhance the power system, dissimilar cells are coordinated through reconfiguration in a study carried out by [14]. This paper presents a model of PV ¿elds that permits simulating different level of partial shadow conditions by selecting an aggregated connection for each shadow level alone. It is based on the use of grouping shadow levels [11], which has been effectively used in order to examine the P-V and I-V characteristic of PV system under that partial shadow condition. This paper is organized as follows: Section 2 presents the general model of the PV cell and modules. Section 3 shows the details of the proposed model and puts in evidence its features. The results of some application example and the discussion of those results for a PV array under different level of partial shadow conditions is presented in section 5, and Section 5 is devoted to conclusions. II. MODEL OF PV MODULE The commonly assumed model is a single diode model, which is presented in Fig. 1 directly employed for a single photovoltaic cell, and generally used in last studies in purpose of modeling photovoltaic cells [15-17]. Whenever the current source denotes the direction Àow of electron that is generated by photons (incident beam) on the surface of semiconductor, also the non-linear action for the p-n junction is modeled through a diode in parallel mode. Then, the leakage current losses are symbolized by the resistor in parallel with the diode further to the resistance of the associated junction is modeled with the series resistor. Through applying Kirchhoff laws, we can get the following: V V I I L A.(exp( D ) 1) D (1) B Rsh where V and I are the voltage and current for one cell individually, IL is the current generated from the irradiated PV (PV current) while A represents the inverse saturation current of the diode, then Rs and Rsh are the parallel and series resistances respectively, lastly B and VD represented by the following equations: B VD
T q V I .R s
ncell .k .
(2) (3)
Where k is the Boltzmann constant, q is the electron charge, and T is the cell temperature in Kelvin degrees. In the ncell is the ideality factor of the P-N junction, while ncell is the ideality factor of the P-N junction. A PV module may be made of numbers of strings cells connected in parallel, each one of them with Ns seriesconnected cells. The values of A, B, Rs and Rsh can be calculated from the data sheet information of a PV panel and temperature measurement as shown in [16,18], while IL is calculated from irradiance and temperature measurements.
PEMC 2014
Antalya, Turkey 21-24 Sept 2014
Fig. 1 PV cell model Typical PV modules are made of one string of Ns seriesconnected cells and each cell has the same characteristic with the whole module in the case of normal condition. While in case attending mismatch condition the PV module behavior will present different result from before (normal condition) and will show different Performances for the cells in the same module. III. MODELING OF PV ARRAY UNDER MULTI LEVEL OF SHADOW CONDITION One of the most complicated issues the researcher faced before is how to model the PV array under shading conditions and especially for the large PV system. A special classification and configuration is used in this paper and presented in Fig. 2, which depend mainly on the model in Fig. 1. The configuration described in Fig. 2 is formed in groups with numerous strings of the PV modules that received the same level of irradiation. Several modules receive the same graduated of insulation level collected on a string, and such strings connected together and are called a group. Different groups having several shading levels connected together in parallel to form a PV system as presented in Fig. 2 IV.
RESULTS OF SIMULATION
The proposed simulation has been accompanied by considering Malaysian Solar Resources PV panels, characterized by 72 series connected cells. A string with 7 PV modules connected in series, and with the blocking diode has been simulated. Firstly, a measuring of different levels of radiation values carried out in this study to insure effect of partial shading on whole system (different level of radiation applied, 1000, 800, 600, 400, and then 200 w/m2) at the same time and for all modules at a time and this test present in Fig 3 and 4. It is very clear that current generated increases with increasing solar irradiance and maximum output power also increases. On the other hand, the voltage is staying almost constant and it is not varying much. Similarly with increase in cell radiation the output power from the PV modules is also increasing as increasing radiation values with the same temperature values, whereas the open circuit voltage Voc nearly constant with very little increasing
462
16th International Power Electronics and Motion Control Conference and Exposition
as radiation increased. Thus, these results confirm the nonlinear nature of PV module and then ensure the dependency of module P-V and I-V characteristic behavior to introduce and ensure the validity of the proposed method. In this case, the number of strings is 200 ones. The modules have been considered subjected to different levels of insolation and temperature. Furthermore, their irradiation level has been considered very different and put in three levels,
Antalya, Turkey 21-24 Sept 2014
specifically G1= 1000 W/m2, G2 = 500 W/m2, and G3 = 200 W/m2. These affected modules are separated in four groups, each group has strings within the same number of affected modules and same graduated level of radiance. The whole simulation has been accomplished in Matlab environment and employed to calculate the P–V and I–V characteristics of the PV array subjected to multi-level of
Fig. 2 presents a reconfigurable PV array system for a different level of partial shadowing conditions employed in groups for each mismatch level.
Fig. 3 presents the P-V characteristic curve with different levels of irradiation values (1000, 800, 600, 400, 200).
Fig. 3 presents the I-V characteristic curve with different level of irradiation values (1000, 800, 600, 400, 200).
shadow condition. The results of P–V and I–V characteristics are reported in Figs. 5 and 6. They put in evidence the effect of the modules that receives the lower irradiance level in terms of string current drop at high voltage value mismatching conditions of the PV strings, exhibits multi maxima at multi different voltage levels,
with that one occurring at about 125 V being characterized by a consistently lower value of the power with respect to the other ones and the one occurring at about 108V being characterized by a consistently upper value of the power. If similar strings have identical insolation patterns are connected in parallel to form a group, the current output is
PEMC 2014
463
16th International Power Electronics and Motion Control Conference and Exposition
Antalya, Turkey 21-24 Sept 2014
multiplied, but there is no change in the output voltage. Fig. 6 shows the characteristics of these groups.
Fig. 7 presents the P-V characteristic for the total PV array system. Fig. 5 presents the P-V characteristic for the four groups strings. To obtain the overall resultant characteristics of all these groups (i.e., of the entire array), a common voltage is considered; while the current output of each of these groups is added to obtain the resultant current. The resultant characteristics of the PV array are shown in Fig. 7. Fig. 7 and 8 explain the number of peak power from the PV array for the whole system under different level of partial shadow conditions which is dependent on the con¿guration itself, in which the shape of connection between modules are carried out. Lastly, it demonstrated in the study output that the existence of these multiple peaks depends mainly on the shaded pattern, the configuration and the number of groups employed.
Fig. 8 presents the I-V characteristic for the total PV array system. V. CONCLUSION It is possible to counter the issues mentioned above by conducting further research and by utilizing appropriate and up to date components. There can be substantial improvements in the overall working of the array and its accuracy through the application of flexible configuration that has more accurate output results. To assess the processes being implemented, both modeling and simulation is being used. The overall compatibility between the different levels, shading cases a proposed configuration can be enhanced through grouping each shading level alone.
Fig. 6 presents the I-V characteristic for the four groups strings.
ACKNOWLEDGEMENTS The authors would like to acknowledgements Universiti Malaysia Pahang for financially supporting. REFERENCES [1]
PEMC 2014
A. Woyte, J. Nijs, R. Belmans, Partial shadowing of photovoltaic arrays with different system con¿gurations: literature review and ¿eld test results, Solar Energy 74 (3) (2003) 217–233.
464
16th International Power Electronics and Motion Control Conference and Exposition
[2]
[3] [4] [5] [6]
[7] [8]
[9] [10]
A.S. Bouhouras, A.G. Marinopoulos, D.P. Labridis, P.S. Dokopoulos, Installation of PV systems in Greece – reliability improvement in the transmission and distribution system, Electric Power Systems Research 80 (5) (2010)547–555. G. Petrone, G. Spagnuolo, M. Vitelli, Analytical model of mismatched photovoltaic ¿elds by means of Lambert W-function, Solar Energy Materials and Solar Cells 91 (18) (2007) 1652–1657. G. Petrone, C. Ramos-Paja, Modeling of photovoltaic ¿elds in mismatched conditions for energy yield evaluations, Electric Power Systems Research 81 (4) (2011) 1003–1013. H. Patel, V. Agarwal, MATLAB-based modeling to study the effects of partial shading on PV array characteristics, IEEE Transactions on Energy Conversion 23 (1) (2008) 302–310. H. Tsai, C. Tu, Development of generalized photovoltaic model using MAT-LAB/SIMULINK, in: Proceedings of the World Congress on Engineering and Computer Science 2008, 2008, pp. 1–6. M. Villalva, J. Gazoli, E. Filho, Comprehensive approach to modeling and simulation of photovoltaic arrays, IEEE Transactions on Power Electronics 24 (5) (2009) 1198–1208. D. Chan, J. Phang, Analytical methods for the extraction of solar-cell single- and double-diode model parameters from I–V characteristics, IEEE Transactions on Electronic Devices 34 (2) (1987) 286–293. K.-H. Chao, S.-H. Ho, M.-H. Wang, Modeling and fault diagnosis of a photovoltaic system, Electric Power Systems Research 78 (1) (2008) 97–105. A.R. Di Fazio, M. Russo, Photovoltaic generator modelling to improve numerical robustness of EMT simulation, Electric Power Systems Research 83 (1) (2012) 136–143.
PEMC 2014
[11] [12]
[13]
[14] [15]
[16] [17] [18]
Antalya, Turkey 21-24 Sept 2014
A. Massi Pavan, A. Mellit, and D. De Pieri, "The effect of soiling on energy production for large-scale photovoltaic plants," Solar energy, vol. 85, pp. 1128-1136, 2011. G. Bopp, H. Gabler, K. Preiser, D. U. Sauer, and H. Schmidt, "Energy storage in photovoltaic standǦalone energy supply systems," Progress in photovoltaics: Research and applications, vol. 6, pp. 271-291, 1998. M. Alahmad, M. A. Chaaban, J. Shi, and J. Neal, "An adaptive utility interactive photovoltaic system based on a flexible switch matrix to optimize performance in real-time," Solar Energy, vol. 86, pp. 951-963, 2012. C. Chang, "Solar cell array having lattice or matrix structure and method of arranging solar cells and panels," ed: Google Patents, 2003. R. Faranda, S. Leva, V. Maugeri, MPPT techniques for PV systems: energetic and cost comparison, in: in: 2008 IEEE Power and Energy Society General Meeting – Conversion and Delivery of Electrical Energy in the 21st Century, 2008, pp. 1–6. M. Villalva, J. Gazoli, E. Filho, Comprehensive approach to modeling and simulation of photovoltaic arrays, IEEE Transactions on Power Electronics 24 (5) (2009) 1198–1208. W. Desoto, S. Klein, W. Beckman, Improvement and validation of a model for photovoltaic array performance, Solar Energy 80 (1) (2006) 78–88. R. Ramabadran, Matlab based modelling and performance study of series connected SPVA under partial shaded conditions, Journal of Sustainable Development 2 (3) (2009) 85–94.
465
