The Role of Solar Radiation Ratios in Photovoltaic Asset Performance: A Global TMY Study

The Typical Meteorological Year (TMY) is a widely adopted input in the solar industry for simulating the performance of solar assets during the design and financing phase. A critical factor in shaping a TMY is the ratio of Global Horizontal Irradiance (GHI) to Direct Normal Irradiance (DNI), yet its relationship with photovoltaic asset yield remains poorly understood, and no one standard has been agreed upon. This study explores the impact of varying GHI:DNI ratios on the yield of simulated solar assets across diverse global locations and climate zones. The results reveal yield deviations of up to-5.7% (fixed-tilt) and-4.6% (single-axis trackers) when comparing simulations using different TMY variants to those based on long-term historical averages. Distinct trends emerge across climatological regions and system configurations (fixed-tilt vs. single-axis tracking). Additionally, the study demonstrates that differences in yield results between TMYs sampled at 15-minute and 60-minute intervals can be as high as-1.4 (fixed-tilt) and-1.3% (single-axis trackers). The findings provide actionable insights to inform the selection of appropriate TMY variants based on radiation ratios and assess the suitability of different solar resource data for specific applications.