Quantitative temperature measurement of photovoltaic modules using spectral-directional infrared thermography

This work presents a metrologically grounded approach for quantitative photovoltaic (PV) module temperature measurement using spectral-directional infrared thermography. The proposed measurement chain combines experimental estimation of the reflected sky contribution, spectral-directional radiometric modeling, instrument calibration, and uncertainty propagation according to the Guide to the Expression of Uncertainty in Measurement (GUM) framework. Outdoor experiments were conducted under clear-sky, partially cloudy, and cloudy conditions. The spectral-directional model was compared with conventional diffuse-gray thermographic processing and calibrated contact measurements. For the analyzed campaigns, the spectral-directional approach produced absolute deviations from the contact reference ranging from 0.14 ∘ C to 4.16 ∘ C, whereas the diffuse-gray model produced deviations from 0.58 ∘ C to 6.41 ∘ C. The results demonstrate that explicit consideration of reflected sky radiance and the spectral-directional behavior of PV glass improves the physical representativeness of thermographic temperature estimates. Despite the remaining limitations associated with optical-property characterization and sky-radiance estimation, the proposed methodology provides physically consistent and traceable temperature measurements while preserving the original thermal state of the module, supporting the use of infrared thermography as a quantitative tool for photovoltaic temperature assessment under real outdoor operating conditions. • A metrologically grounded approach for quantitative PV thermography is presented. • Reflected sky radiance is experimentally determined under outdoor conditions. • Spectral-directional modeling reduced deviations relative to contact measurements. • Expanded uncertainties between 1.3 ∘ C and 1.8 ∘ C were achieved outdoors. • Contact sensors can alter the thermal state of PV modules through shading.