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Reassessment of Cell to Module Gains and Losses: Accounting for the Current Boost Specific to Cells Located on the Edges
The power produced by a photovoltaic module is not simply the sum of the powers of its constituents cells. The difference stems from a number of so-called 'cell-to-module' (CTM) gain or loss mechanisms. These are getting more and more attention as improvements in cell efficiency are becoming harder to achieve. This work focuses on two CTM mechanisms: the gain due to the recapture of light hitting the apparent backsheet in the 'empty' spaces around the cells and the loss from the serial connection of 'mismatched' cells i.e. with different maximum power points. In general, for insulation purposes, the spaces on the edges of modules are larger than the spacing between cells. This study reveals that, when reflective backsheets are used, these 'edge spaces' provide an additional current boost to the cells placed at the edges that can lead to a 0.5% gain in the output power of modules (with 60 or 72 cells). This location-dependent current boost adds to the usual variations in cell characteristics dictated by the binning size and results in larger 'cell-to-cell mismatch losses'. However, the simulations reveal that for short-circuit current bin size smaller than 5%, this additional mismatch loss is lower than 0.05%. All considered, this study demonstrates that the spaces at the edges of PV modules have a significant impact on the cell to module ratios (approximate toand 0.5% abs or approximate to 16% of the CTM gains) when reflective backsheets are used.

Authors: O. Dupre, J. Levrat, J. Champliaud, M. Despeisse, M. Boccard, and C. Ballif

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