Specificity of Measuring Thermal Resistance in Solar Cells

This paper describes a modulation method of measuring the thermal impedance of solar modules. The measurements are taken by varying heating power harmonically and measuring a variable component of the junction temperature, which changes in response to it. Analyzing the dependence of thermal impedance on modulation frequency allows the determination of thermal impedance components corresponding to the structural elements of a solar module. It is experimentally shown that the amplitude of the variable component of junction temperature is mostly independent of the value of the heating power. This is explained by current crowding, that is a nonuniform distribution of the current through the junction and formation of local heating areas of the semiconductor. The formation of local heating areas is confirmed by the experimentally detected thermal resistance component, which takes place due to the temperature difference between local heating areas and the other part of a semiconductor of a solar module. Another confirmation of the local heating areas is a sharp thermal resistance decrease with an increase in the heating current.