Within the last years, a new characterization method for solar modules called Magnetic Field Imaging (MFI) has been introduced. MFI reveals the strength as well as the direction of currents flowing within solar modules by analyzing the magnetic field distribution and thereby allows to trace back electrical defects. Within our work, we demonstrate how MFI can be exploited to characterize solar modules that contain stripe-like solar cells interconnected in a roof tile manner - so called shingle solar modules. In comparison to conventional solar modules, shingle modules yield the potential for higher power densities, exhibit a more homogeneous appearance and are less prone to power losses when being partially shaded. Due to these advantages, shingle solar modules are expected to gain a growing share of the solar module market within the next years, reaching 11% by 2027. As we demonstrate, MFI allows to detect different defects that are typical as well as unique for shingle solar modules, namely a local shunt by smudged electrically conductive adhesive (ECA), a systematic tilt between individual shingles, and locally poor shingle interconnection. Each defect type shows a fingerprint-like characteristic within MFI measurements and thus can be identified without ambiguity. Compared to electroluminescence (EL), MFI tends to display the defects more prominent and clearer. Furthermore, we demonstrate that MFI can be used to study the response of shingle modules to partial shading and observe that the module current bypasses shaded regions, as predicted by theory. We conclude that MFI would allow to investigate any kind of module under partial shading revealing the current flow through the solar cells, the connectors, and the bypass diodes.

The electrical potential between the cells and ground can cause leakage currents that are a necessary but not sufficient indicator for potential induced degradation that is because of the migration of sodium ions into the silicon cells. Outdoor exposure of modules with high-voltage bias in two different climate regions with monitoring of the climatic data, the module temperatures as well as the leakage currents was used to investigate the effect of rain-induced and soiling-induced increase of the surface conductivity, the leakage current and the decrease of the module performance.

Temperature, temperature cycling, moisture, ultraviolet radiation, and negative bias voltage are considered as main degradation factors for photovoltaic modules by causing hydrolysis and photo-degradation of polymeric components, corrosion of glass, and of metallic components like grids and interconnectors. Commercially produced photovoltaic modules with crystalline silicon cells were exposed to accelerated damp-heat testing in the lab. Test temperatures were 75, 85, and 90 degrees C. The tests were continued until a final degradation state was reached (3500-7000h). The degradation function could be modeled by a Boltzmann function allowing the determination of the time to failure (20% power loss). The time to failure as function of the test temperature follows Arrhenius relations allowing the evaluation of the activation energy of the dominating degradation process. These time-transformation functions could be used for service life estimation. Electroluminescence pictures illustrate the degradation behavior and the differences of the modules, indicating no changes in the degradation mechanisms for the different temperatures. A procedure for the evaluation of outdoor operation conditions towards accelerated service life testing with respect to moisture impact is proposed. Copyright (c) 2016 John Wiley & Sons, Ltd.

The electrical ageing of photovoltaic modules during extended damp‐heat tests at different stress levels is investigated for three types of crystalline silicon photovoltaic modules with different backsheets, encapsulants and cell types. Deploying different stress levels allows determination of an equivalent stress dose function, which is a first step towards a lifetime prediction of devices. The derived humidity dose is used to characterise the degradation of power as well as that of the solar cell's equivalent circuit parameters calculated from measured current–voltage characteristics. An application of this to the samples demonstrates different modes in the degradation and thus enables better understanding of the module's underlying ageing mechanisms. The analysis of changes in the solar cell equivalent circuit parameters identified the primary contributors to the power degradation and distinguished the potential ageing mechanism for each types of module investigated in this paper. © 2016 The Authors. Progress in Photovoltaics: Research and Applications published by John Wiley & Sons Ltd. © 2016 The Authors. Progress in Photovoltaics: Research and Applications published by John Wiley & Sons Ltd.

To test reproducibility of a technical specification under development for potential-induced degradation (PID) and polarization, three crystalline silicon module types were distributed in five replicas each to five laboratories. Stress tests were performed in environmental chambers at 60 °C, 85% relative humidity, 96 h, and with module nameplate system voltage applied. Results from the modules tested indicate that the test protocol can discern susceptibility to PID according to the pass/fail criteria with acceptable consistency from lab to lab; however, areas for improvement are indicated to achieve better uniformity in temperature and humidity on the module surfaces. In the analysis of variance of the results, 6% of the variance was attributed to laboratory influence, 34% to module design, and 60% to variability in test results within a given design. Testing with the additional factor of illumination with ultraviolet light slowed or arrested the degradation. Testing at 25 °C with aluminum foil as the module ground was also examined for comparison. The foil, as tested, did not itself achieve consistent contact to ground at all surfaces, but methods to ensure more consistent grounding were found and proposed. The rates of degradation in each test are compared, and details affecting the rates are discussed.

To design realistic and quick accelerated aging tests, the comparison between the degradation mechanisms induced by outdoor exposure and by accelerated aging tests is indispensable. Various accelerated aging tests, i.e. heat aging, UV aging, damp-heat aging and combined UV / damp-heat aging, were performed on full-size PV modules from different PV module manufacturers. The climate-dependence of the degradation was investigated on identical PV modules which have been exposed in different extreme climates for up to six years. A comprehensive degradation analysis was performed, i.e. by means of power measurements, electroluminescence imaging and Raman spectroscopy. The electrical characterization showed a high stability of all investigated modules.

In this study, the influence of the PV laminate design on the silicon cell degradation was investigated. Laminates consisting of two different kinds of encapsulation (EVA and PVB) and three different back-sheet materials (TAPT, PA and a TPT foils) were manufactured. Standard cells with a two and three bus bar design were used as well as MWT cells. The laminates were subjected to a UV, heat and damp-heat aging tests. The degradation of the cell metallization was investigated by means of electroluminescence imaging, the degree of polymeric aging was determined by Raman spectroscopy. Special attention was paid to the spatial distribution of corrosion effects on the cell. A severe influence of the solar cell type, i.e. the metallization paste, could be shown. Furthermore, a strong dependence of the degree of metallization degradation on the type of back-sheet material was found. An extensive UV aging for up to 180 kWh appeared to have no influence on the metallization corrosion.

The climatic conditions play an important role for a degradation mechanism of photovoltaic modules, known as potential induced degradation (PID). The influence of ambient humidity, precipitation and temperature on the leakage current has been investigated with high voltage stress in two different climate regions. This work focusses on one of them (Freiburg, Germany) It was found out, that for this test sit, rain seems to be a serious problem as a conductive layer is established that leads to a high leakage current. A temperature dependency such as found in indoor test was found as well.

This paper focusses on the physical conditions for a degradation mechanism of photovoltaic modules, known as potential-induced degradation. The analysis was made on several levels. At first, the influence of humidity and temperature on the potential-induced leakage current has been investigated, the second step consists of an accelerated test scheme in a climatic chamber and the third one is outdoor exposure with high voltage stress in two different climate regions. The humidity has a huge impact on the leakage current. Therefore, a test in the climate chamber accelerates the stress found in the field of some orders of magnitude. Copyright (c) 2012 John Wiley & Sons, Ltd.