Quantifying the impact of spatial responsivity on thermopile pyranometer linearity measurements

Accurate broadband irradiance measurement underpins photovoltaic performance assessment and traceable calibration. Here we address spatial non-uniformity and irradiance-dependent nonlinearity in thermopile pyranometers by combining a physics-based response model with a laser-based measurement system. First, we develop an optical–thermal model derived from the internal geometry of a disassembled pyranometer, describing radiative transfer through the dome and heat conduction within the sensing stack to predict the position-dependent responsivity. The predicted spatial responsivity is validated by small-spot scans. Second, we establish a beam-shaped, chopper-modulated, continuous-wave laser facility and perform pyranometer linearity measurements over the range (100–1000) W / m 2 . We further propose a spatial-responsivity-based method to evaluate the influence of beam non-uniformity on nonlinearity measurements and propagate this effect into an uncertainty budget, providing a practical framework for pyranometer linearity characterization.