Showing papers by "Peter Hacke published in 2016"

Sodium Accumulation at Potential-Induced Degradation Shunted Areas in Polycrystalline Silicon Modules

Abstract: We investigated potential-induced degradation (PID) in silicon mini-modules that were subjected to accelerated stressing to induce PID conditions. Shunted areas on the cells were identified with photoluminescence and dark lock-in thermography (DLIT) imaging. The identical shunted areas were then analyzed via time-of-flight secondary-ion mass spectrometry (TOF-SIMS) imaging, 3-D tomography, and high-resolution transmission electron microscopy. The TOF-SIMS imaging indicates a high concentration of sodium in the shunted areas, and 3-D tomography reveals that the sodium extends more than 2 μm from the surface below shunted regions. Transmission electron microscopy investigation reveals that a stacking fault is present at an area identified as shunted by DLIT imaging. After the removal of surface sodium, tomography reveals persistent sodium present around the junction depth of 300 nm and a drastic difference in sodium content at the junction when comparing shunted and nonshunted regions.

Automatic detection and evaluation of solar cell micro-cracks in electroluminescence images using matched filters

Abstract: A method for detecting micro-cracks in solar cells using two dimensional matched filters was developed, derived from the electroluminescence intensity profile of typical micro-cracks. We describe the image processing steps to obtain a binary map with the location of the micro-cracks. Finally, we show how to automatically estimate the total length of each micro-crack from these maps, and propose a method to identify severe types of micro-cracks, such as parallel, dendritic, and cracks with multiple orientations. With an optimized threshold parameter, the technique detects over 90 % of cracks larger than 3 cm in length. The method shows great potential for quantifying micro-crack damage after manufacturing or module transportation for the determination of a module quality criterion for cell cracking in photovoltaic modules.

Assessing the causes of encapsulant delamination in PV modules

Abstract: Delamination of the encapsulant is one of the most prevalent PV module field failures. This paper will present examples of various types of delaminations that have been observed in the field. It will then discuss the development of accelerated stress tests designed to duplicate those field failures and thus provide tools for avoiding them in the future.

Elucidating PID Degradation Mechanisms and In Situ Dark I–V Monitoring for Modeling Degradation Rate in CdTe Thin-Film Modules

Abstract: A progression of potential-induced degradation (PID) mechanisms is observed in CdTe modules, which are dependent on the stress level and moisture ingress. This includes shunting, junction degradation, and two different manifestations of series resistance. The dark I–V method for in situ characterization of P max based on superposition was adapted for the thin-film modules undergoing PID in view of the degradation mechanisms observed. An exponential model based on module temperature and relative humidity (RH) was fit to the PID rate for multiple stress levels in chamber tests and validated by predicting the observed degradation of the module type in the field.

Fault identification in crystalline silicon PV modules by complementary analysis of the light and dark current–voltage characteristics

Abstract: This article proposes a fault identification method, based on the complementary analysis of the light and dark current-voltage (I-V) characteristics of the photovoltaic (PV) module, to distinguish between four important degradation modes that lead to power loss in PV modules: (i) degradation of the electrical circuit of the PV module (cell interconnect breaks; corrosion of the junction box, module cables, and connectors); (ii) mechanical damage to the solar cells (cell microcracks and fractures); (iii) potential-induced degradation (PID) sustained by the module; and (iv) optical losses affecting the module (soiling, shading, and discoloration). The premise of the proposed method is that different degradation modes affect the light and dark I-V characteristics of the PV module in different ways, leaving distinct signatures. This work focuses on identifying and correlating these specific signatures present in the light and dark I-V measurements to specific degradation modes; a number of new dark I-V diagnostic parameters are proposed to quantify these signatures. The experimental results show that these dark I-V diagnostic parameters, complemented by light I-V performance and series-resistance measurements, can accurately detect and identify the four degradation modes discussed.

Module degradation mechanisms studied by a multi-scale approach

Abstract: A key pathway to meeting the Department of Energy SunShot 2020 goals is to reduce financing costs by improving investor confidence through improved photovoltaic (PV) module reliability. A comprehensive approach to further understand and improve PV reliability includes characterization techniques and modeling from module to atomic scale. Imaging techniques, which include photoluminescence, electroluminescence, and lock-in thermography, are used to locate localized defects responsible for module degradation. Small area samples containing such defects are prepared using coring techniques and are then suitable and available for microscopic study and specific defect modeling and analysis.

Modeling current transfer from PV modules based on meteorological data

Abstract: Current transferred from the active cell circuit to ground in modules undergoing potential-induced degradation (PID) stress is analyzed with respect to meteorological data. Duration and coulombs transferred as a function of whether the module is wet (from dew or rain) or the extent of uncondensed surface humidity are quantified based on meteorological indicators. With this, functions predicting the mode and rate of coulomb transfer are developed for use in estimating the relative PID stress associated with temperature, moisture, and system voltage in any climate. Current transfer in a framed crystalline silicon module is relatively high when there is no condensed water on the module, whereas current transfer in a thin-film module held by edge clips is not, and displays a greater fraction of coulombs transferred when wet compared to the framed module in the natural environment.

Development of Cu(In, Ga)Se 2 test coupons for potential induced degradation studies

Abstract: We report on the design, fabrication and accelerated testing of fully encapsulated small area coupons (approximately 7.5cm × 7.5 cm) for the purpose of researching potential induced degradation in Cu(In, Ga)Se 2 based PV modules. The fabrication of these coupons enables the study of the solar cells and the materials used in PV module manufacturing such as top and bottom glass covers of different composition (soda-lime glass, high temperature glass, alkaline-free glass, etc), plastic-based top covers, ethylene vinyl acetate and edge seal encapsulation materials. The coupons can also be used to emulate framed and frameless modules that utilize either monolithically interconnected modules or singular cell type of modules. The design of the coupons, their fabrication, the materials used and their testing for 1000 hours under 85°C and 85% RH conditions are presented.

A novel technique for performing PID susceptibility screening during the solar cell fabrication process

Abstract: Various characterization techniques have historically been developed in order to screen potential induced degradation (PID)-susceptible cells, but those techniques require final solar cells. We present a new characterization technique for screening PID-susceptible cells during the cell fabrication process. Illuminated Lock-In Thermography (ILIT) was used to image PID shunting of the cell without metallization and clearly showed PID-affected areas. PID-susceptible cells can be screened by ILIT, and the sample structure can advantageously be simplified as long as the sample has the silicon nitride antireflection coating and an aluminum back surface field.

Monitoring the recovery of c-Si modules from potential-induced degradation using suns-V oc curves

Abstract: Potential-induced degradation (PID) has recently been shown as an important failure mode in c-Si modules. We demonstrate the utility of Suns-V oc analysis for measuring shunt effects caused by PID at the module level. Our results show an expected positive correlation between module shunt resistance and power during recovery from the degraded state.