Investigation of the Relationship between Shaded Cell Temperature and the Operating Point of PV Systems

Abstract

The building integrated photovoltaic applications (BIPV) are mostly affected by partial shading, which results in a significant decrease in energy efficiency and leads to the apparition of multiple power peaks on the I-V characteristic curve of photovoltaic generators. In mitigating this problem, sophisticated maximum power point tracking techniques (MPPT) are used to track the global peak among the other locals. These techniques do not take into account the overheating of the shaded cells given that, under some critical situations, shaded cell performances may degrade, thus affecting the lifespan of the photovoltaic modules. In this regard, the present work aims to investigate in which peak on the I-V characteristic curve the PV module should operate appropriately with less overheating risk. For that, the shaded cells’ temperatures and currents at different operating points were monitored. The results show that the worst-case scenario occurs for small shadow ratios (in the studied case, the shadow ratio ‘sr’ = 25%) where the temperature of the shaded cell reached approximately three times (300%) the temperature of non-shaded cells. This temperature decreases as the operating point is moved from the short circuit current towards the open-circuit voltage; as a result, the PV module works safely with minimum thermal stress for the maximum power peak near the open-circuit voltage.