Impact of Optimizing Cell Metallization for Local Conditions on the Module Energy Yield

The metallization of silicon solar cells is often optimized for their performance under standard test conditions (STC) at 1000 W/m2 of AM1.5G illumination and 25 °C cell temperature. However, solar modules in field installations, experience a range of illumination intensities and distributions, spectral conditions and operating temperatures, depending on location and type of installation. In this work, we aim to answer the question of whether significant energy yield increases can be realized with solar cells that are optimized under average local conditions. We systematically optimize the metallization of monocrystalline PERC solar cells for a range of irradiance and temperature values. We find the optimum number of fingers to vary between 75 to 175 and the number of busbars between four to eight for 800 μm wide planar standard ribbons. We assessed the impact of these cell designs on energy yield of modules in a single-axis tracking scenario in Alice Springs, Australia, as well as in a building-integrated façade in Cabauw, Netherlands. A module with cells optimized for 600 W/m2 and 30°C, which is the average plane of array irradiance and cell operating temperature for a façade installation in Cabauw, will produce 0.4% higher annual yield than a module with cells optimized for STC. For our module scenario in Alice Springs, the cells with optimized metallization do not significantly increase the module yield since the average irradiance is close to STC. However, with our assumed finger geometry we observe a strong sensitivity for cells with less than approx. 100 fingers with yield losses up to 2.5%. Overall, we find this impact of locally optimized cell metallization is comparatively low, despite the significantly lower average irradiance received by the module.