Light‐ and elevated temperature‐induced degradation impact on bifacial modules using accelerated aging tests, electroluminescence, and photovoltaic plant modeling

Abstract

The authors report on the light-and elevated temperature-induced degradation (LeTID) effect observed on bifacial photovoltaic modules and its potential impact on photovoltaic plants performance. Indoor LeTID quantification using indoor carrierinduced degradation (CID) is carried out using current injection. Power measurements yielded higher LeTID sensitivity for the rear side of bifacial modules compared to the front side, hence leading to a variation of the bifaciality factor by several percentage points. The difficulty in evaluating the maximal power degradation caused by LeTID is also highlighted as a reduced number of samples are used most of the time and as cells within a single module do not have always the same performance evolution trends. Using indoor CID results with the help of empirical fitting and Arrhenius relation, the yield impact of LeTID on a bifacial power plant is simulated under three different climates. Modeling results help to identify the main parameters related to LeTID modules sensitivity that impact photovoltaic (PV) plants yield: maximal power degradation, stabilized power value after regeneration, activation energy value, and LeTID kinetics. In some cases, the yield variation caused by LeTID sensitive modules could be mitigated by carefully selecting the modules as a function of climatic conditions.

Results from an international interlaboratory study on light‐ and elevated temperature‐induced degradation in solar modules

“…Mismatch loss would primarily manifest as I SC ‐related loss in the power loss attributions shown in Figure 6. Given the sizable power loss attributable to module I SC in Figure 6 and the cell‐to‐cell variation seen in EL in this and other work, it seems reasonable to suspect power loss contributions from mismatch [6]. In this section, we investigate whether the measured I SC loss associated with LETID (orange bars in Figure 6) could be due to cell mismatch.…”

“…A characteristic of previous studies of LETID‐affected modules is variation in cell‐to‐cell degradation, which is readily visible in EL images [2, 6, 37]. Figure 7 shows EL images at high and low injected current of a representative example of each module type before and after the detection phase, and after regeneration.…”

“…A characteristic of previous studies of LETID-affected modules is variation in cell-to-cell degradation, which is readily visible in EL images [2,2,6,37]. Figure 7 shows EL images at high and low injected current of Particularly for module types U* and P*, the low current images taken after detection and after regeneration are darker, relative to initial, than their high current counterparts.…”

“…To provide a reliable and consistent method of assessing LETID and ensure all future products are acceptably stable, the global community would benefit from standard procedures for commercial modules. While LETID‐related loss always seems to eventually recover with continued LETID stress (a phenomenon called “regeneration”), the process of degradation to regeneration might take years or decades to entirely run its course in the field, which would result in substantial energy yield loss in real‐world systems [5, 6].…”

A case study on accelerated light‐ and elevated temperature‐induced degradation testing of commercial multi‐crystalline silicon passivated emitter and rear cell modules

“…21 Dupuis et al used comprehensive experimental data of bifacial module degradation combined with predictive modelling to highlight the challenges accounting for the large variability between cells in a module as well as other uncertainties including activation energies. 22 All of this complexity and uncertainty can be disastrous for warranty claims, investors and consumers relying on accurate projections and costing of future output, designers sizing systems and so forth. If left untreated, the highly variable degradation could cause havoc for IEC qualification and reliability testing.…”