The global expansion of renewable energy for carbon neutrality is accelerating. Nevertheless, fossil fuels continue to 

account for a significant share of energy demand. Coal, in particular, cannot be fully replaced in the short term due to 

its economic feasibility and supply stability, which underscores the need for complementary technologies to enable its 

continued utilization. Against this background, the importance of Carbon Capture, Utilization, and Storage (CCUS) technologies

has been increasingly recognized. In this study, we propose an integrated energy resource system that combines 

salt-cavern-based CCUS with solar power generation. To capture both daily demand–supply fluctuations and seasonal 

cycles, a two-stage optimization framework was developed. This framework simultaneously maximizes daily profit and 

ensures long-term operational efficiency. A case study conducted in South Australia shows that the proposed system 

secures the seasonal periodicity of CO2 injection and withdrawal while increasing annual profitability by 25.1% compared 

with conventional methods. In addition, by converting the stored CO2 into methanol, the system can produce 452.6 tons 

of methanol per year, demonstrating a clear value-added benefit. These results suggest that coal-based power generation, 

when integrated with salt-cavern CCUS and renewable energy, should not be viewed solely as a phase-out target. Instead, 

it can serve as a competitive and viable option in the transition toward carbon neutrality