Avoiding the Hot Spot Occurrence in PV Modules

Failures involving PV cells affect the global reliability of the whole PV plant. Malfunctioning cells experience dramatic reverse biasing, causing over temperature and often leading to permanent damages. Even though traditional bypass diodes limit severe reverse biasing, they are not able to avoid over-temperature and hot spot occurrence. The circuit proposed in this paper replaces traditional bypass diodes, providing bypass action of sub-panel in case of significant reduction of the operating voltage; therefore, the operating area of the sub-panel is reduced to a safety area close to the MPP. Moreover, in case of bypass, the proposed circuit zeros the current in the bypassed cell by means an automatic disconnection section, thus avoiding power dissipation and the resulting hot spot. Experiments performed on a partially shaded PV module evidenced the reduction of the operating temperature in malfunctioning cells with respect to the traditional bypass diode.