IOSR Journal of Electrical and Electronics Engineering (IOSR-JEEE) e-ISSN: 2278-1676,p-ISSN: 2320-3331, Volume 8, Issue 2 (Nov. - Dec. 2013), PP 07-15 www.iosrjournals.org www.iosrjournals.org 7 | Page Remedyto the Shading Effect on Photovoltaic Cell 1 Ekpenyong, E.E and 2 Anyasi, F.I 1 Department of Electrical/Electronic Engineering, Cross River University of Technology, P.M.B 1123, Calabar. Nigeria. 2 Department of Electrical and Electronics Engineering, Ambrose Alli University, P.M.B 14, Ekpoma, Edo State, Nigeria. Abstract: Use of by-pass diodes for each PV module may mitigate the negative effect from partial shading. However, this method alone may still face severe energy efficiency degradation caused by the energy loss due to parasitic effects in the EES elements under variable incoming power from the PV modules. Hence, this paper proposes methods to enhance the PV system efficiency and robustness under partial shading. Here, by-pass diodes are connected parallel to a number of solar cells. Under normal operating conditions, the diodes are blocked compared to the voltage generated by the cells. When shading occurs, the reverse of the voltage was observed in that specific section which enables the by-pass diode in parallel to conduct the current. It was observed that; the current of the un-shaded flows through the by-pass diode and the power/voltage characteristics shows a second local maximum. Also, the shaded cell was only loaded with that fraction of power produced by the un-shaded cells of that section. I. Introduction Solar photovoltaic array is formed by series/parallel combination of SPV modules to attain a desired voltage and current level. The major challenge in using a SPV source containing a number of cells in series is to deal with its nonlinear internal resistance. The problem gets complex when the array receives non uniform irradiance or partially shaded. In a larger SPVA, the occurrence of partial shading is common due to tree leaves falling over it, birds or bird litters on the array, shade of a neighbouring construction, and so forth. In a series connected string of cells, all the cells carry the same current. Even though a few cells under shade produce less photon current, these cells are also forced to carry the same current as the other fully illuminated cells. The shaded cells may get reverse biased, acting as loads, draining power from fully illuminated cells. If the system is not appropriately protected, hot-spot problem [1] can arise and in several cases, the system can be irreversibly damaged. Nowadays there is an increasing trend to integrate the SPV arrays at the design level in the building itself. In such cases it is difficult to avoid partial shading of array due to neighbouring buildings throughout the day in all the seasons. In conventional SPV systems, these shadows lower the overall generation power to a larger degree than what is expected. Hence the SPV installation cost is increased, because the number of SPV modules must be increased [2] and as a result, SPV power generation will be less attractive. This makes the study of partial shading of SPV modules a key issue. Moreover it is very important to understand the characteristics of SPVA under partial shaded conditions to use SPV installations effectively under all conditions. In recent years, the impact of partial shading on the SPV array performance has been widely discussed [3–6]. With a physical SPV module it is difficult to study the effects of partial shading since the field testing is costly, time consuming and depends heavily on the prevailing weather conditions. Moreover, it is difficult to maintain the same shade under varying numbers of shaded and fully illuminated cells throughout the experiment. However it is convenient to carry out the simulation study with the help of a computer model. In most of the studies [7–10], the effect of partial shading in reducing the output power of the SPVA has been discussed. But little attention has been paid to the power dissipated by the shaded cells affecting the array life and utilization of the array for the worst shaded case. The harmful effects in basic configurations and their comparison have been discussed in [11]. Common use of bypass diodes in anti- parallel with the series-connected SPV modules can partially mitigate the power reduction due to partial shadow [11]. In such cases a more sophisticated Maximum Power Point Tracking (MPPT) algorithms capable to disregard local power maximums is required [12–14]. Alternatively, the maximum available DC power can be improved if the connection of the SPV modules can be reconfigured such that panels with similar operating conditions are connected in the same series string. Moreover the parallel configuration should be dominant under partial shaded conditions [3–5]. However, high output current at low voltage in parallel configuration will have to be properly conditioned to the required level by using suitable DC-DC converter. Hence it is required to opt for derived configurations. In this paper, for different configuration types, the generalized MATLAB programs have been developed which are capable of simulating any number of modules connected in series, parallel or combined for any type of shading patterns