Reassessment of cell to module gains and losses: Accounting for the current boost specific to cells located on the edges

Abstract

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 (≈+0.5%abs or ≈16% of the CTM gains) when reflective backsheets are used.

Silicon heterojunction solar cells: Recent technological development and practical aspects - from lab to industry

“…CTM power ratios can vary greatly depending on module type and features, e.g. white backsheet modules benefit from a ≈ 2% gain in short circuit current (I SC ) because of the light recollected after reflection on the backsheet between the cells [103,104]. Advanced interconnection techniques and improvements in light management at the module level are pushing CTM factors upward and they are expected to exceed 100% by 2020 [105].…”

“…8b where the distributions of the CTM factors of power, FF and I SC are shown of 5000 simulated modules comprised of cells with I SC in a 4% range. While the loss in power is low (CTM Pmpp around -0.15%), the cell-to-cell mismatch causes a strong negative ≈− CTM ( 1%) ISC partially counterbalanced by a positive ≈+ CTM ( 0.85%) FF [104]. This effect is important for a module manufacturer to accurately separate between ohmic and optical losses (e.g.…”

“…In red: simulated IV curve of the module constituted of these 60 cells connected in series. b) Distributions of the CTM factors of power, FF and I SC of 5000 simulated modules comprised of cells with I SC in a 4% range from ref [104]…”

Cell-to-Module Simulation Analysis for Optimizing the Efficiency and Power of the Photovoltaic Module

“…The reflected light is redirected back to the solar cells, providing another opportunity for absorption. Such a method is not accessible when calculating a solar cell parameter in open air, which can ensure a gain in CTM performance [14,[19][20][21][22][23][24].…”

“…Simulation input parameters for the optimized efficiency and power of the module[1][2][3][4]6,7,10,11,13,14,[17][18][19][20][21][22][24][25][26][27][31][32][33].…”