In solar power plants, both in photovoltaic (PV) and concentrated ones, the electrical output is a key parameter for the development of solar energy. To ensure relevant predictability of electrical output, the durability of photovoltaic panels or concentrating systems has to be warranted. The assessment of the optical performance durability of the front glass throughout the lifetime of the solar power plant involves using a nondestructive method in the field without disrupting the energy generation of such systems. The aim of this work is to experiment a new accurate nondestructive method to evaluate the aging impact of glass used in solar energy conversion systems. The results bring out a correlation between the apparent emissivity, used as an aging indicator, in a spectral bandwidth of 8–12 μm and the integrated transmittance in the visible range, i.e., 400–800 nm for a float glass of 2 mm thickness aged under damp heat (DH). The optical characterizations of the soda-lime glass exposed to the DH test highlight the relevance of apparent emissivity used like a nondestructive aging indicator. The sensitivity coefficient of apparent emissivity, which is defined as the ratio of partial derivative of integrated transmittance (δT) to the partial derivative of apparent emissivity (δε), reaches 3.83, meaning that the apparent emissivity is three times more sensitive than the integrated transmittance for the case study.