Investigation of optimal cell-bonded optic for >1400× ultra-high experimental concentration factor for concentrator photovoltaics

To push toward the limit of potential ultra-high concentrator photovoltaics, various cell-bonded optic materials are experimentally evaluated within a highly concentrating multi-stage optic. Different refractive indexes could unlock smaller focal images at the cost of higher absorption and reflective losses. Materials used include polyurethane elastomers (Crystal Clear 200, OptaClear), silicon elastomer (Sylgard-184) and a custom Sapphire, in different cell relative configurations. Indoor and outdoor experimental measurements are taken, and a 2-stage configuration is compared to the 3-stage version with a higher effective concentration ratio. This allows us to evaluate the validity of using indoor experimental data to predict outdoor performance. The trends shown through indoor experiments were not consistently shown with outdoor experimentation, highlighting the need for real-world testing. An experimentally validated COMSOL model is used to add depth the analysis of the outdoor experimental data. Using Sylgard-184 as the cell-bonded optic material, the highest effective concentration achieved was a C e f f , P of 1475.9 ± 10.4 suns, with a geometric concentration of ∼6500 suns. Antireflective coatings were shown to improve performance slightly but had limited application due to the required hardness of the optic. To the knowledge of the authors, this is the highest experimental effective solar concentration factor reported thus far. • Record experimental effective concentration ratio achieved: 1475.9 ± 10.4. • Indoor experimental analysis could not accurately predict outdoor performance. • Thermally resistant optic materials are required for higher concentrations. • Designs must consider a balance between focal image size and absorptivity of optic.