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Based on the working principles of solar cells, the photovoltaic module mismatch model was constructed to simulate the heat dissipated by one single cell with different shading percentage ranging from 10% to 100%. ANSYS simulation was utilized in this paper to explore the relationship of hot spot temperature and type of solar cell defects (for example point defect and planar defect) with the module output power. The simulation results showed that the module hot spot temperature is inversely correlated with the solar cell defective area, and positively correlated with module output power. Solar cells with different type of defects and solar modules with different output power were picked to conduct the hot spot experiments, in which the leakage currents for the defected solar cells and the high-efficiency module cells (normal cells) were less than 1.5 A and 0.1 A, respectively, for an applied negative bias of 12 V. The results showed that the temperature of the module with point defected solar cell and the high-efficiency module reached up to 200 and 170°C, respectively, which could lead to encapsulation failure. The experimental data was consistent with the simulation, demonstrating the accuracy of the simulation model and providing directives for solving the hot spot problem of the high-efficiency module.

Fatigue of the cell interconnectors is one of the main reasons for module failure. Especially with respect to module application in extreme climates new demands on solar cell interconnectors will arise. Optimizations in the manufacturing process to generate a product demand related microstructure are a key to improve the material behavior of interconnectors with respect to extreme climate loading conditions without increasing costs. For achieving this goal several aspects were considered in this paper: Influence of the annealing process on the fatigue behavior: Due to an optimization of the annealing process an increase in ribbon fatigue strength by a factor of four could be achieved. The effect consists of two parts: Firstly, annealing influences the geometrical shape generated during the fatigue experiment. Secondly, it affects crack formation and crack growth during fatigue. Influence of temperature on fatigue behavior: an increase in temperature leads to a significant reduction in fatigue strength (from 25 to 100 °C by factor 3). This results from increased dislocation creep at higher temperatures. Microstructural comparison of fracture patterns: The loading amplitude determines the roughness of the fracture surface: Smaller amplitudes lead to a coarser surface structure. This is important to compare accelerated lifetime testing in the lab and modules failures from the field. Simulation of temperature and microstructure dependent fatigue for lifetime prediction: Exemplarily it will be depicted how optimized fatigue behavior in the lab translates into real module lifetime under extreme climate conditions. Despite the actual numbers which show the potential of the approach, but could vary from sample to sample, the focus of the paper is the method itself and its physical background.

A bifacial photovoltaic model was developed not only to calculate the power and energy yield for bifacial modules for various setup and installation conditions but also to identify suitable bifacial module applications and markets. The bifacial model shows that the energy yield for bifacial modules is very much location dependent and hugely influenced by how they are setup and installed. There is a need to have the modules mounted at a certain elevation above the ground to gain maximum energy yield. It is also important to ensure there is no blockage for the direct sun to shine on the area directly beneath the module. For locations at low latitude, a higher elevation is required. For locations at high latitude, the probability of the direct sunlight reaching the ground directly under the module is higher. Therefore, less module mounting elevation is required. However, there is a saturation point for energy yield improvement with increased module mounting height. In addition to the mounting height, a sufficient length of clearance path in front of the module array should be considered. The model also shows that the ground reflectance is one of the key parameters for bifacial module performance. The model indicates that >10% of energy yield gain with 20% background reflectance from REC bifacial multi-crystalline silicon solar module array with a bifaciality of 0.6 is achievable in Konstanz, Germany. This correlates well with the measured field energy yield data of the bifacial prototype modules.

A laboratory type PID-test system was used to measure degradation curves of the shunt resistance during the stress test. It was found that these curves feature typically an initial plateau without significant changes and a mono-exponential decay, both having temperature depended time constants: The plateau length as well as the decay time constant behave Arrhenius-like. Performing these degradation measurements under various temperatures enable the identification of PID relevant activation energies. A solar module compound made of industrial-type crystalline silicon solar cells was investigated and an activation energy of the decay was determined to (0,95 ± 0,14) eV.

Encapsulation of a solar cell affects its optical performance, a fact that is often overlooked when the efficiency of different types of solar cells is compared. In this work we have measured the reflectivity of silicon wafers with textures typically applied in the industry, i.e. random pyramids and isotropic texture with conventional silicon nitride anti-reflex coatings, as well as a graded porous silicon anti-reflection coating. We investigate how the reflectivity is affected by angle of incidence for all surfaces both with and without encapsulation. The reflectivity of the random pyramidal structure is compared with a ray-tracing model, and we achieve good correspondence both with and without encapsulation for various angles of incidence. The ray-tracing model allows us to do a complete optical loss analysis of the solar module. We apply this loss analysis methodology to four different configurations, and show that encapsulation does not necessarily imply a large optical loss, particularly when we consider higher angles of incidence.

The “snail trail” discoloration effect observed at many PV modules after some time in the field was investigated with regard to their microscopic and chemical properties and environmental conditions. We show here the combined results of studies on defect modules after outdoor exposure as well as on mini modules after laboratory DH tests and provide a mechanistic model for the snail trail formation. Finally, we can show that a detailed chemical and physical characterization of encapsulation polymers is a fundamental prerequisite for quality assurance and reliability in solar module production.

In recent years, a discoloration defect called as the snail trials emerged on crystalline silicon solar module in urban photovoltaic energy systems. It resulted in power degradation, and caused a serious concern about effects of this phenomenon on crystalline silicon solar modules, but very few publications have dealt with this phenomenon. In this paper, the crystalline silicon solar modules with snail trials are investigated by I-V and P-V characteristics, electroluminescence (EL) technique, thermography analysis, and energy production in photovoltaic power plant. The obtained results show that the snail trails may affect output of power for crystalline silicon solar modules compared with reference module, the energy production measured was about 9.1% lower than the normal array.