An in-depth study on the hot spot case of photovoltaic modules (1)

0 Preface

First of all, this case is a classic case that the author actually encountered. The customer used an infrared camera to detect a photo of a solar power plant running for four months and found some hot components. In the infrared photo hot spot component sent by the customer, it was found that the heating of the four photovoltaic modules is somewhat different from the conventional hot spot, as shown in Fig. 1, in which two strings of the junction box and the component are abnormal in temperature. This batch of components is a 60-piece polycrystalline cell module with a power of 250W, using a snap-in junction box and a non-filled junction box. Through in-depth analysis, before going to the scene, it is inferred that this phenomenon is due to the contact of the corresponding bus bar is not good, forming an open state. After arriving at the site, the voltage was verified to be only 2/3. Further inspection of the cover revealed that the bus bar was not connected.

1. Infer the results by the following three points

1.1 Under the same environment, the open state of the same component is higher than the operating temperature.

On this point, everyone may feel very strange, can not understand, the following is a theoretical analysis:

First, for a single-cell battery, the equivalent circuit diagram is shown in Figure 2. In the open state, when there is illumination, the photo-generated carriers separated by the built-in electric field form the photocurrent from the N-zone to the P-zone. IL, and the photovoltage appearing at both ends of the solar cell, that is, the open circuit voltage Voc, generates a forward junction current ID from the P region to the N region. When the illumination is stabilized, the photocurrent is exactly equal to the forward junction current, that is, ID=IL, so Although the external part of the monolithic cell is open, there is current inside, and it is consumed by the monolithic battery itself, and it is converted into heat.