The impact of cracks on photovoltaic power performance

This paper demonstrates a statistical analysis approach, which uses T-test and F-test for identifying whether the crack has significant impact on the total amount of power generated by the photovoltaic (PV) modules. Electroluminescence (EL) measurements were performed for scanning possible faults in the examined PV modules. Virtual Instrumentation (VI) LabVIEW software was applied to simulate the theoretical IV and PV curves. The approach classified only 60% of cracks that significantly impacted the total amount of power generated by PV modules

Cracks in Solar Cell Metallization Leading to Module Power Loss under Mechanical Loads

AbstractWe investigate the mechanisms leading to electrically insulated cell parts in a photovoltaic module under mechanical load. For this we measure the resistances across a crack in a laminated solar cell during bending that is typical in the field. The cracks in the solar cell are detected with electroluminescence imaging. The resistance over the aluminum paste increases continuously by negligible 30 mΩ whereas the front finger resistance increases by 15.4 kΩ stepwise. This difference is the result of the higher ductility of the aluminum paste in comparison to the front finger metallization. We associate the steps in the front finger resistance measurement to breakage of single fingers with an equivalent circuit model. Furthermore we found that a silicon crack widths lower 2μm has no influence on the resistances. Crack widths higher than 7μm leads to a complete front finger interruption. We determine that the specific resistance of such a crack causes nearly 100% of the power loss, which is caused by a completely electrically insulating crack in a photovoltaic module

Ni:Si as Barrier Material for a Solderable PVD Metallization of Silicon Solar Cells

AbstractWe study Ni:Si as a barrier material for the PVD metallization of silicon solar cells and investigate the long term solderability of Al/Ni:Si/Ag metal stacks in terms of peel forces and contact resistances. For this purpose, solar cell connectors are soldered on the Al/Ni:Si/Ag stacks in three different aging states: directly after metallization, after accelerated storage and after storage for six months. The thickness of the Ni:Si layer is varied in these tests. Furthermore we measure the contact resistance between cell interconnect ribbons and the test stack. To assess possible contamination of the Si by the metals we measure the effective lifetime of electron hole pairs during a regularly interrupted thermal treatment procedure. The samples with 200nm or thicker Ni:Si layers soldered with the lead-containing solder and the flux 952S perform best and pass all tests

COREPRO-Sim: A Tool for Modeling, Simulating and Adapting Data-driven Process Structures

Industry is increasingly demanding IT support for large engineering process structures consisting of hundreds up to thousands of synchronized processes. In technical domains, such process structures are characterized by their strong relation to the assembly of a product (e.g., a car); i.e., resulting process structures are data-driven. The strong linkage between data and processes can be utilized for automatically creating process structures as well as for (dynamically) adapting them at a high level of abstraction. This paper presents the COREPRO-Sim demonstrator which enables sophisticated support for modeling, coordinating and (dynamically) adapting data-driven process structures. COREPRO-Sim substantiates the COREPRO approach which provides a new paradigm for the integration of data and and process structures

Application of a new ray tracing framework to the analysis of extended regions in Si solar cell modules

While ray tracing of solar cells was established decades ago, ray tracing of entire modules has met obstacles, mainly because module optics are affected by geometric structures varying over a large scale of dimensions. In this paper, we introduce a ray tracing framework that is based on a modular structure made up of separate plugins. While existing plugins can be used for common effects such as light sources, absorption in materials, etc., specialized plug-ins can be written by users to handle problem-specific properties. We demonstrate the functionality of our approach by ray tracing a test module containing 9 crystalline Si solar cells. Good agreement between light-beam induced current (LBIC) measurements and ray tracing is achieved

Einfluss der ischämischen Remotepräkonditionierung auf die Mobilisierung endothelialer Progenitorzellen

Die Arbeit untersucht den Einfluss der ischämischen Remotepräkonditionierung (RIPC) auf die Mobilisierung endothelialer Progenitorzellen (EPC). Es wurden prospektiv, randomisiert, kontrolliert, doppelblind 50 Probanden im Rahmen herzchirurgischer Operationen zu 4 Zeitpunkten (präOP, 6h, 48h, 6d) untersucht. Die RIPC (4x5min) wurde unmittelbar vor der Operation durchgeführt. Es konnte kein signifikanter Gruppenunterschied im zeitlichen Verlauf festgestellt werden. Es konnte unabhängig von der Gruppenzugehörigkeit eine postoperative EPC-Mobilisierung mit biphasischer Verlaufsform gezeigt werden

Optimizing the Solar Cell Front Side Metallization and the Cell Interconnection for High Module Power Output

Improving the light trapping in a module results in an increase in the generated current. Consequently, an optimization of the front grid metallization of the cell is required for the best trade-off between series resistance, shading, and recombination losses. For this purpose, we combine ray tracing and electrical solar cell and module calculations that explicitly account for cell and module interactions. Our model bases on experimentally verified input parameters: We determine the electrical and optical properties of the front metal fingers of passivated emitter and rear cells (PERC). We show that the effective optical width of the front metal fingers in the module is significantly reduced by 54%. The optimized simulated module has 120 half-size PERC with 20.2% cell efficiency and has an output power of 295.2 W. This is achieved with an increased number of 120 front metal fingers per cell, four white-colored cell interconnection ribbons (CIR), and an increased cell spacing. Applying these optimized design changes to an experimental module we measure a module power output of 294.8 W and a cell-to-module (CTM) factor of 1.02. Measured and simulated power agree and the deviations in Voc, Isc and FF are less than 0.91%rel. We perform a module power gain analysis for the fabricated module and simulate a potential maximum module power of 374.1 W when including further improvements.German Federal Ministry for Economic Affairs and Energy/032564

Influence of Encapsulation Process Temperature on the Performance of Perovskite Mini Modules

Perovskite-on-silicon tandem solar cells are a promising candidate to significantly increase the efficiency of PV modules. Despite the fast research progress on material and solar cells aspects, there is still a lack of processes for an industrial module integration of these devices. One aspect hereby is the adaption of encapsulation materials and processes to the requirements of perovskite materials. Process temperatures of about 150 °C are necessary to use well proven, in silicon PV commonly applied encapsulation materials with a high reliability. However, perovskites start to decompose into their components at high temperatures. This limits the encapsulation process temperature, which in turn constraints the choice of encapsulation materials. This work presents an encapsulation process for methylammonium lead iodide (MAPhb) single junction perovskite solar cells (PSCs) with conventional production tools in glass-glass modules that serves as a model system for perovskite tandem applications. We evaluate the influence of the encapsulation process temperature between 120 °C and 160 °C on the performance of mini modules. The UV-absorbing encapsulation material is processable over the whole investigated temperature regime. We observe a difference in the IV-characteristics between the PSCs encapsulated in the temperature range of 120 °C - 140 °C to those processed at 160 °C. At lower encapsulation temperatures the IV-curves taken 1 h after encapsulation show a pronounced S-shape and no degradation of Foe. In contrast, the PSCs encapsulated at 160 °C exhibit a Foe decrease of up to 29% compared to the initial measurement shortly after PSC fabrication and no significant S-shape. Both, the S-shape that occurs at low encapsulation temperatures and the Foe loss after encapsulation at 160 °C, are no longer significant after one week of module storage under dark conditions. The presented encapsulation process therefore does not permanently damage the MAPbb PSCs even at a standard encapsulation temperature of 160 °C. To ensure long-term operation, we test the fabricated mini modules in a damp heat test at 85 °C and a relative humidity of 85%. We find no significant additional degradation caused by damp heat in 1250 h test duration compared to a reference module stored in ambient air

PV module current gains due to structured backsheets

We evaluate the optical performance of PV modules with respect to an increase in short circuit current density. Our evaluation is based on the combination of ray tracing simulations and measurements on test modules with four types of backsheets: Two of them are structured, the third is white and diffusively reflecting and the fourth reflects no light. Under normal incidence, structured backsheets reflect incoming light at an angle that causes total internal reflection at the glass/air interface, which guides the light to the solar cell surface. Three different irradiance conditions are studied: a) standard testing conditions (STC) with light incident perpendicular to the module surface, b) variation in the angle of incidence and c) light source with mean annual distribution of angles of incidence. Using the measured refractive index data in ray tracing simulations we find a short circuit current density (Jsc) gain of up to 0.9 mA/cm2 (2.3%) for monofacial cells and a structured backsheet, when compared to a white backsheet with diffuse reflection. For bifacial cells we calculate an even larger Jsc increase of 1.4 mA/cm2 (3.6%). The Jsc increase is larger for bifacial cells, since some light is transmitted through the cells and thus more light interacts with the backsheet. Our optical loss analysis reveals the best performance in STC for edge-aligned Ag grooves. This structure reduces absorption losses from 1.8 mA/cm2 to 0.3 mA/cm and reflection losses from 0.7 mA/cm to 0 mA/cm. This trend also holds under various angles of incidence as confirmed consistently by Jsc measurements and ray racing simulations. Simulations using an annual light source emitting a mean annual distribution of angles of incidence reveal grooves in both orientations edge alignment and east-west alignment achieve similar current gains of up to 1.5% for mono- and of 2.5% for bifacial cells compared to modules with white back sheets. This indicates that for modules with light guiding structures such as these backsheets optimization for STC differs from optimization for annul yield

Increased Light Harvesting by Structured Cell Interconnection Ribbons: An Optical Ray Tracing Study Using a Realistic Daylight Model

A key for increasing the module efficiency is improved light harvesting. The structuring of solar cell interconnection ribbons (CIR) is a promising option for improved light harvesting as it can easily be integrated into current module production. We perform ray tracing simulations of complete PV modules in 3D exhibiting geometric features such as profiled CIR and surface textured cells. We evaluate the increase in module performance by a light harvesting string (LHS) under realistic irradiation conditions with respect to angular and spectral distribution. Using the realistic irradiation for a location in Germany, a location at the polar circle and a location at the equator we simulate the enhancement of short-circuit current density Jsc resulting from the use of LHS. Our results show Jsc gains between 1.00% and 1.86% depending on the location and module orientation. We demonstrate the applicability of our model by comparing measurements and simulations for a one-cell module that we measure and simulate under various angles of the light incidence