Evaluation of Heat and Current Characteristics of Bypass Diodes for Fault Detection in Photovoltaic Module

In recent years, PV （photovoltaic） systems have been installed rapidly around the world. However, there is often a delay in the practical application of fault detection in PV systems. In this study, the temperature of BD （bypass diodes） mounted on PV modules was measured for simple and practical fault detection. The temperature of the BD of Module 31 was higher than other modules and a large current passed through one of the BDs. Measuring BD temperatures is easier than other conventional methods of fault detection. From the results of the rise in BD temperature under dark conditions, the increase in temperature increased linearly with increasing current flow. There is a proportional relationship between heat generated and the increasing temperature of the terminal box. The experimental results about surface temperature of the junction box in actual system operation suggested that the electric current through a BD in a terminal box can be known by measuring the surface temperature of the terminal box for PV module fault detection without a system shutdown. Moreover, we tried to evaluate temperature distribution of a terminal box using heat conduction equations. The evaluated results agreed well with the measured results.

Experimental research on the relationship between bypass diode configuration of photovoltaic module and hot spot generation

A hot spot is a reliability problem in photovoltaic(PV) modules where a mismatched or shaded cell heats up significantly and degrades the PV module output power performance. High PV cell temperature due to a hot spot can damage the cell encapsulate and lead to second breakdown, which both cause permanent damage to the PV module. In present systems, bypass diodes are used to mitigate the hot spot problem. In this work, five commercial polysilicon P V modules configured with different numbers of bypass diodes are used to study the influence of bypass diodes on the reverse bias voltage of a shaded cell and the resulting hot spot phenomenon. The reverse bias voltage of the shaded cell, and the hot spot probability and severity decrease as the number of bypass diodes increases. Negative terminal voltage of a shaded cell accompanied by a switched-off bypass diode are the necessary condition for hot spot generation. In an extreme case where each cell has an individual bypass diode in a P V module, it still cannot avoid the hazards of a hot spot under the shading areas of 5-7 cm2, but the probability of a hot spot is reduced to a minimum of 0.41%.

Study of crystalline silicon solar cells with integrated bypass diodes

This paper reported a novel method of integrating bypass diodes into crystalline silicon solar cells.Bypass diodes which have the opposite p-n junction were formed by printing specific paste on the local surface of solar cells using screen printing,while infrared laser was applied to isolate the diode from the cell after firing.A module of crystalline silicon solar cells with integrated bypass diodes was fabricated and the I-V characteristics were measured under different shade conditions.The experimental results clearly showed that the integrated bypass diodes can effectively stabilize module's short circuit current while reduce the module power loss when shaded as well.

Comparison of Different Solutions for Blocking Diode Applications in a Photovoltaic Panel under Varying Ambient Conditions

We characterized a crystalline silicon based mini-module under varying ambient conditions, developed a PSPICE model for this panel, including temperature and irradiation dependence and applied this model to the simulation of the impact of a blocking diode under different shadowing conditions. Different blocking diodes were examined, like germanium and silicon homojunction diodes and silicon Schottky diodes and compared to ＂intelligent＂ diodes, consisting of operational amplifiers with MOSFET switches. The simulations indicate a strongly reduced power loss in a panel integrating the new ＂intelligent＂ blocking diodes even when compared to silicon Schottky diodes, as the best performing traditional blocking diodes.