A bypass circuit for avoiding the hot spot in PV modules

The hot spot occurring in outlier solar cells is recognized as one of the main reliability issues for photovoltaic modules. Even though PV modules are qualified to sustain over-temperatures the hot spot can lead to accelerated aging and, sometimes, to unexpected failure, with the possible risk of fire. The standard countermeasure to contrast this phenomenon is the adoption of bypass diodes, whose role is to limit the maximum reverse voltage across outlier cells. However, since the current is not limited, power dissipation can be high. In this paper a bypass circuit, suited to completely avoiding the onset of the hot spot, is presented. The circuit is a substantial improvement of a previous version that was able to reduce power dissipation by reducing the voltage across the reverse biased solar cell. The improvement presented in this paper allow to completely cancel the current, thus avoiding power dissipation and, therefore, preventing the rising in temperature of the solar cell. The novelty with respect to comparable approaches is that the intervention of the circuit doesn't require the preliminary detection of the hot spot. Indeed, the circuit self-activates in the same operating conditions of standard diodes, without needing neither control logic nor power supply. Detailed circuit simulations and experiments are presented to evidence the capability of the circuit to fully prevent power dissipation, and consequent rising in temperature, in outlier cells.