Impact of string connection and contact defects on electrical current distribution in solar cells and modules: A model validated by magnetic field imaging
Ammar Tummalieh, Max Mittag, Julian Weber, Damla Yucebas, Levin Schäfer, Rüdiger Quay, Christian Reichel, Holger Neuhaus
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引用次数: 0
Abstract
Modeling of solar modules and their components is essential to quantify geometrical, optical, and electrical losses and to improve the designs and technologies in terms of performance. In most loss analysis models, the current share among the busbars of the solar cell is assumed to be equal since a symmetrical distribution of the metallization is given. The impact of string terminal connection on the current distribution among the ribbons and the resulting changes in ohmic losses has not been studied yet. In this study, a MATLAB model is developed to consider the impact of the string connector terminal position on the current distribution and the ohmic losses in the ribbons and in string connector. The model allows for the analysis of the impact of contact defects scenarios in ribbons and string connectors on the current distribution. Results show that the highest current flows at the closest busbar to the string connector terminal while the current decreases at the busbars farther away from the terminal due to higher ohmic resistance of the current path. The higher the ohmic resistance of the string connector, the more inhomogeneous the current share at busbars. Simulating a 9 busbar M6 half-cell with 1 × 0.08 mm2 string connector, positioning the string connector terminal at the leftmost or rightmost ribbon results in 0.4 W less power compared to center connection configuration, where the string connector terminal is positioned at the center ribbon. Furthermore, simulation results show that inhomogeneity of current causes about 2.1% reduction in module power compared to the case of evenly distributed cell current, considering a 120-haf-cell module with the same string connector. Regarding contact defect analysis, exemplary simulations show the impact of the position of detached ribbons on the power or efficiency loss. Considering left or right connection configuration, detaching the leftmost or rightmost ribbon results in higher power loss compared to other ribbons. Detaching one cell ribbon completely from the string connector results in about 0.2%abs decrease in cell efficiency, while detaching the outer ribbon along all strings of a 120-half-cell module results in power loss of about 0.8%. The developed model is validated by performing magnetic field imaging (MFI) measurements, in which the magnetic flux density induced by the current carried by the ribbons is measured.
期刊介绍:
Progress in Photovoltaics offers a prestigious forum for reporting advances in this rapidly developing technology, aiming to reach all interested professionals, researchers and energy policy-makers.
The key criterion is that all papers submitted should report substantial “progress” in photovoltaics.
Papers are encouraged that report substantial “progress” such as gains in independently certified solar cell efficiency, eligible for a new entry in the journal''s widely referenced Solar Cell Efficiency Tables.
Examples of papers that will not be considered for publication are those that report development in materials without relation to data on cell performance, routine analysis, characterisation or modelling of cells or processing sequences, routine reports of system performance, improvements in electronic hardware design, or country programs, although invited papers may occasionally be solicited in these areas to capture accumulated “progress”.