Multi-Decadal Surface Solar Radiation Trends Over Sumatra (1980-2025): Implications for Solar Energy Development

Abstract

The long-term stability of surface solar radiation (SSR) is a critical factor influencing photovoltaic (PV) performance and sustainable solar energy development. However, information on long-term SSR changes over tropical maritime regions, particularly Sumatra, remains limited. This study investigated the long-term temporal, seasonal and spatial trends of SSR over Sumatra during 1980-2025 using the ERA5-Land reanalysis dataset processed in Google Earth Engine. Annual and seasonal SSR trends were evaluated using Ordinary Least Squares (OLS) regression, the Mann-Kendall (MK) test, and Sen's slope estimator, while pixel-wise OLS regression was applied to characterize spatial variations. The results revealed a significant declining trend in annual SSR, with an OLS slope of -0.154 W m⁻² year⁻¹ (p = 0.0072), confirmed by the MK test (p = 0.0076) and Sen's Slope (-0.166 W m⁻² year⁻¹). Annual mean SSR decreased by approximately 7 W m⁻² over the 46 years, indicating persistent solar dimming. Seasonal analysis showed that SSR declined significantly in both the wet and dry seasons, with the greatest reduction occurring in the dry season. Spatial analysis showed that negative SSR trends dominated northern and central Sumatra, whereas relatively stable or locally increasing trends occurred in parts of southern Sumatra. These findings provide baseline information on the long-term stability of solar resources and highlight the importance of incorporating historical SSR trends into future photovoltaic planning and solar resource assessment.