Close examination of localized hot spots within photovoltaic modules

Abstract

For photovoltaic modules, hot-spot phenomena are very common and influential, affecting device performance and causing irreversible damage. Researchers mainly pay attentions to hot-spot phenomena from a large-scale view that hot spots result from module failures, i.e., abnormal solar cells in photovoltaic modules are heated by other normal cells as loads. However, this heating process may not be the start of hot-spot phenomena. The large-scale hot-spot phenomena may develop from localized temperatures anomaly within a unit cell in the module while current researches generally ignored this small-scale but important problem. In this paper, close inspection of localized hot spots within photovoltaic modules is conducted with a xenon lamp of simulating the solar irradiation. An electronic load and an infrared thermal camera are utilized to detect and analyze electrical and thermal characteristics of the tested cells under different irradiation and surface conditions. With this experimental system, the localized hot-spot phenomena within a unit cell are experimentally revealed and the transient forming and variation processes of hot spots resulted from different mechanisms are explored, which are seldom reported to our knowledge. Attributed to localized hot spots, power conversion efficiency may fall to as low as 1.58% from 15.61%. In addition to the non-uniform irradiation, environmental obstructions falling on the cell surface may also form hot spots of very high temperature. Dust covering on the cell may lead to a hot spot above 64 °C, reducing cell efficiency by as much as 5.7 percent. The easily ignored localized hot-spot phenomena must be handled properly in case they get exacerbated and expand to the whole module.