Three Bypass Diodes Architecture at the Limit

In this work, we demonstrate that partial shading of one solar cell in a state-of-the-art monocrystalline photovoltaic module with three bypass diodes results in hot cells with critical peak temperatures of 164.degrees C. We examine two solarmodules in the IEC 61215-2 MQT 09 hot-spot endurance test, one with 367.3WP featuring 72 full-cells and the other with 388.6WP featuring 144 half-cells. For the solar module with 72 solar cells, we measure a maximum temperature of 164.degrees C, which results in a degradation of the encapsulation material and increases the risk of solar module failure. The high temperature results from the hot cell effect due to the power dissipation in the reverse-biased solar cell caused by partial shading. Our experiments show that the half-cell solar module is advantageous in terms of solar cell shading compared to the full-cell solar module. Although the half-cell solar module has a higher power output than the full-cell solar module, we measure a cooler peak temperature of 150.degrees C. However, under certain shading conditions, the half-cell solar module can exhibit similar temperatures as the full-cell solar module. Based on our experimental results, we develop an electrical and a thermal model to predict the temperature of novel high-power solar modules with solar cells fromlarger silicon wafer formats in case of partial cell shading. Our predictions consider the trends of further increasing solar cell and module efficiencies, larger silicon wafer formats, and larger solar modules. We simulate a maximum peak temperature of 176.degrees C at the solar module's surface, which significantly increases the risk of solar module failure. Our results show that new high-power solar modules employing solar cells that are made from larger silicon wafer formats need a new protection against overheating. Three bypass diodes per solar module are no longer sufficient.