Impact of angular irradiance distributions on coupling gains and energy yield of cell interconnection designs in silicon solar modules in tracking and fixed systems

Abstract

Cell interconnector designs such as light redirecting films (LRFs) and various geometric ribbon layouts are all aimed at improving the performance of crystalline silicon solar modules. However, due to the usually specular reflecting surface, the angular-dependent module performance, which is typically quantified with an incidence angle modifier, depends on the rotation of the module. We find that typical power measurements under standard test conditions at 1000 W m-2 and 25 °C cell temperature are not suited to identify the best performing design in real-world conditions. In this work, we therefore determine the optimum ribbon geometry based on its simulated energy yield in common installation configurations for solar modules based on industry-standard full and half-cut solar cells. We compare the effects of planar, triangular, LRFs, pentagonal and wire ribbon geometries, as well as fixed optimal inclination, building-integrated (facade), and single-axis tracking installation scenarios of modules in portrait and landscape orientation. Energy yield gains of 1.8% can be achieved for full cell modules with LRFs or pentagonal ribbons in single-axis tracking installation compared to a reference module with five planar ribbons. Critically, we find that changing the module orientation to landscape reduces this energy yield gain by nearly 50% for the modules with LRFs. This directional dependence is significantly reduced with the pentagonal ribbon structure. The installation scenario can have a similarly dramatic impact. The expectation of power gains for certain designs inferred from standard test conditions may not only show significantly lower gains in annual energy yield, but may even lead to yield losses, especially for building-integrated photovoltaic systems. For a typical full-cell module, for example, we have found that LRFs perform 2.5% better than standard planar ribbons under standard test conditions but can result in a 0.2% lower annual yield in a facade installation. Therefore, to fully evaluate the effectiveness of a specific ribbon design, the annual energy yield must consider the angular irradiance distribution and weather conditions at a specific location, the installation scenario, and the module orientation.