We propose and demonstrate a reliable and non-destructive spatially resolved measurement technique for ultra-fast hot-spot classification of solar cells. The method can deliver quantitative images of the local heat dissipation in hot-spots in measurement times below 10 ms. The high accuracy and sensitivity allow for reliable hot-spot testing and provide the basis for a reliable classification of solar cells into different hot-spot categories. The method can be applied to wafer-based silicon solar cells and in principle also to thin-film solar cells of all material compositions. This paper explains the measurement principle, gives a detailed step-by-step description of viable automated evaluation procedures, and assesses the sensitivity and accuracy of the method.