With the increasing adoption of renewable energy technologies in South Korea, the expansion of solar power plants in mountainous regions has raised concerns over slope instability and the risk of debris flows. This study analyzes the impact of solar power plants on landslide and debris flow occurrences in these regions. Geographic Information System (GIS) techniques and numerical simulation model were used to investigate slope stability and debris flow behavior under various rainfall conditions. Case studies were conducted in four domestic regions where recent landslides have occurred. The analysis revealed that steep slopes tend to form at the boundary between natural and artificial slopes during solar power plant installation, increasing the risk of slope failure during heavy rainfall. Rainfall data analysis indicated that slopes with intrinsic instability could fail with relatively low rainfall amounts. Furthermore, debris flow simulations demonstrated that landslides could transition into debris flows, causing damage to nearby roads and residential areas. It was confirmed that the slope stability assessments and debris flow analysis were needed during the design and construction of solar power plants in mountainous regions to effectively mitigate disaster risks.