The global energy system is moving toward sustainability to address critical challenges such as climate change, environmental pollution, and energy security. A key aspect of this transformation is shifting to renewable energy sources and reducing carbon emissions. However, integrating renewable energy into the power grid poses challenges for stability due to variability and intermittency. South Korea, with its high dependence on fossil fuels and an industrial-based economy, exemplifies the complexities of this transition. This study aims to support South Korea's energy transition by estimating future power demand and analyzing the power mix required to achieve the 2050 carbon-neutral target. The study employs linear regression and sigmoid-type logistic functions to forecast future demand and generation capacity, analyzing generator configurations based on seasonal and hourly usage patterns. Furthermore, the study calculates annual energy production and designs seasonal and hourly scenarios to provide insights into renewable energy integration strategies. The study also emphasizes the importance of Long-Duration Energy Storage (LDES) systems in addressing the variability of renewable energy and ensuring stable grid operation. It presents a stable grid operation model that minimizes fluctuations in the output of conventional generators while storing PV output and redistributing load during other time periods.