Permanent partial shading detection for protection of photovoltaic panels against hot spotting

Hot spot of photovoltaic (PV) panels leads to early degradation and even permanent damage of them. Partial shading is the main cause of hot spotting. Conventional bypass diodes are not able to rectify hot spotting perfectly and more efficient techniques are necessary. In this study, a simple technique is proposed for detection of partial shading and protection of the panels against hot spotting. Moreover, a strategy is used for discrimination between permanent and temporary partial shadings. Equivalent DC impedance of the panel is utilised to detect partial shading. Then, the shaded panel is open circuited using a simple relay to prevent hot spotting. The detection is confirmed or declined by measuring Thevenin impedance of the panel in a reclosing strategy. In the reclosing strategy, the panel is reconnected to the PV system for temporary partial shadings or disconnected from the system for permanent partial shading. The Thevenin impedance is calculated using open circuit voltage and short circuit current of the panel measured by a current sensor and a simple resistive voltage divider. The performance of the proposed method is evaluated using some experiments. The results confirm the performance of the technique for prevention of hot spotting.