Real Testing Conditions (RTC) for photovoltaic systems: A climate-responsive framework based on the TruePower™ Alliance

Standard Test Conditions (STC) provide a universal laboratory reference for photovoltaic (PV) module characterization; however, they do not represent the wide range of environmental conditions experienced in real operation. To complement this framework, this work derives Real Testing Conditions (RTC) based on long-term, high-resolution meteorological datasets. The proposed methodology is applied to four geographically and climatically diverse sites, i.e., Singapore, Australia, Germany, and China, within the TruePower™ Alliance program, where multiple PV technologies are deployed alongside comprehensive weather monitoring. RTC parameters are derived using a plane-of-array (POA) irradiance-weighted methodology applied to irradiance, temperature, and spectral distributions, ensuring that all operational time steps contribute to the representative conditions. The results show noticeable differences between STC and site-specific RTC values, indicating that fixed laboratory conditions may not fully represent climate-dependent operating environments. Using the derived RTC framework, the theoretical energy production of different semiconductor technologies is evaluated. The comparative analysis indicates that the optimal PV technology for maximizing annual energy yield depends on local climatic conditions, with GaAs-based devices achieving the highest performance among the technologies considered, followed by crystalline silicon. The proposed RTC framework provides a climate-aware reference condition that complements STC and enables improved first-order benchmarking of PV technologies under realistic environmental conditions.