<p>Solar radiation is a key climatic variable that requires investigation into its historical changes to assess its impacts on solar energy technology, the hydrological cycle, environmental ecosystems, and agricultural productivity. This study applied the Innovative Polygon Trend Analysis (IPTA) method to analyze 42 years (1981–2022) of monthly solar radiation data from 15 stations across Bangladesh. IPTA graphs were developed for the mean and standard deviation (std) of monthly solar radiation, and the results were compared with the Mann-Kendall (MK) test. All stations exhibited irregular polygons in the IPTA graphs, indicating unstable temporal trends in solar radiation. The IPTA method identified an increasing trend for Sitakunda and Bhola (except December and January) and a decreasing trend for Dhaka and Jessore across all months. July showed an increasing trend in 9 stations, while December and January exhibited decreasing trends in 14 and 13 stations, respectively. IPTA was more effective at detecting trends, identifying 145 months (81%) with increasing or decreasing trends out of 180 compared to only 89 months (50%) by the MK test. The observed trends are potentially influenced by anthropogenic aerosols and cloud cover variations. The findings highlight the effectiveness of IPTA in capturing significant changes in solar radiation both quantitatively and qualitatively, providing valuable insights for stakeholders in solar energy development, climate change assessment, water resource management, and agricultural planning.</p>