<p>This article investigates the propagation path of solar radiation through the Earth’s atmosphere and its impact on the performance of photovoltaic (PV) <br /> systems. The study provides an in-depth analysis of the concept of “Air Mass” (AM) and examines the physical foundations and practical significance of international standard spectra, such as AM0 (extraterrestrial conditions), AM1.5D (direct radiation), and AM1.5G (global radiation). The influence of the atmosphere on the solar spectrum — namely, the reduction of intensity and changes in spectral composition — and its effect on the operation of PV devices under various geographical conditions are explored. The article presents theoretical and experimental methods for evaluating the power output and energy effciency of PV panels based on standard spectra (ASTM G173-03 and others). Special attention is given to the roles of direct and diffuse radiation components in concentrator systems. The results show that selecting an AM standard appropriate to a region’s geographic location and atmospheric characteristics is critical for the design, testing, and performance forecasting of photovoltaic systems. The study proposes methodological foundations for using AM standards in PV system modeling and predicting real-world performance. Moreover, the research examines the relationship between spectral variations caused by absorption in specifc solar spectrum bands by atmospheric constituents (water vapor, CO₂, ozone) and the spectral sensitivity of photovoltaic <br /> modules. This enables a deeper understanding of operational differences among photovoltaic converters based on various semiconductor materials (e.g., crystalline silicon, thin-film technologies) under real atmospheric conditions. The article also considers the altitude-dependent increase in solar irradiance and presents an empirical model that accounts for this factor. The model is applied to more accurately assess the energy production potential of photovoltaic power plants in the high-mountain regions of Uzbekistan (e.g., the Alpomish and Adelung peaks).</p>