Definition and Context
Delta T (ΔT) is the temperature difference between an anomalous component and its surrounding nominal components. In solar thermography, this metric is critical for identifying irregularities in photovoltaic modules.
Common anomalies that exhibit Delta T differences include overheating junction boxes, cell hotspots, bypass diodes, and severe cracking. These issues can cause uneven temperature distributions, leading to energy inefficiencies and potential long-term damage to solar modules if not promptly addressed
Measuring Delta T (ΔT)
The calculation of Delta T in relies on analyzing thermal imagery, often in the form of radiometric JPEGs (RJPEGs). These images encode radiometric data, which can be converted into precise temperature measurements.
To measure Delta T, thermal imaging algorithms compare the average temperature within a defined measurement field of view (MFOV) of an anomaly to the average temperature of nearby nominal components. This process ensures a conservative and accurate estimation of temperature deltas, even for anomalies with complex patterns, such as cracked modules.
For a single-cell anomaly, Delta T is determined by subtracting the nominal average temperature of nearby cells from the average temperature of a 4×4 pixel MFOV within the anomalous cell. This approach ensures that the measurement captures a representative temperature of the anomaly, avoiding inaccuracies caused by relying on singular pixel readings. In cases of multi-cell anomalies, Delta T is calculated by comparing the average temperature of the largest affected region, measured using an MFOV, to the average temperature of nearby nominal cells. This method accounts for the complexity of multi-cell issues and provides a precise assessment of the anomaly’s severity.
Advanced algorithms may also incorporate irradiance levels and environmental factors to normalize Delta T measurements, ensuring consistency across varying conditions. The choice of MFOV, which can vary depending on the camera model and specifications (e.g., 4×4 or 10×10 pixel groupings), plays a critical role in delivering accurate and reliable temperature measurements for different types of equipment.
