Evaluation of Performance Losses and Degradation of Aged Crystalline Si Photovoltaic Modules Installed in Minas Gerais (Brazil)

Abstract

This paper investigates and compares crystalline silicon photovoltaic (PV) module performances for two distinct cases, part of a PV reliability project relating modes of degradation to climate data in Brazil. The selected installations provide the opportunity to directly evaluate and contrast the losses, reliability, and durability of modules operating for a long period (~15 years) for the same distributed power applications. The focus is on modules (a) from two installations, (b) operating under the same climate conditions, (c) with modules from two different manufacturers, (d) manufactured and installed at about the same time, but (e) with very different resulting observed changes in their operational and physical characteristics over their long field exposures. The PV modules were located in a tropical climate zones, at northern region of the state of Minas Gerais, Brazil. Visual inspections of the two module populations concluded that one set (Case A) had almost no encapsulant discoloration and few indications of delamination and corrosion. In contrast, the other set (Case B) had significant yellowing and browning, widespread areas of delamination, and fairly extensive interconnect corrosion regions. These visual observations correspond to the measured changes in the electrical characteristics, with those from the first set having an average annual loss in power of 0.4–0.5% while those modules from the second set having average annual power losses in the range 2.3–3.7% over their installation time. Encapsulant discoloration and delamination provided the first clues to the measured differences in module performance and can be attributed to the existing climate conditions of high incidence of high ultraviolet (UV) radiation and high ambient temperatures. The module-encapsulated degradation mechanisms have been analyzed and identified using complementary electrical, physical, and chemical characterization of the module components (encapsulated glass). Distinct differences between the two cases were established. The encapsulation browning (Case B) was followed by delamination and interconnect corrosion, and the associated chemical changes are reported. The causes for the differences between the two module types are identified based upon the critical module material properties and their long-term exposure under these climate conditions.