The power system flexibility assessment and application using the IRENA flexTool involves a comprehensive evaluation of the flexibility potential of a power system. The flexTool is an analytical tool developed by the International Renewable Energy Agency (IRENA) that provides a systematic approach to assess the flexibility of a power system in terms of its ability to balance electricity supply and demand. The flexTool considers various parameters that affect the flexibility of a power system, such as the demand profile, generation mix, storage capacity, and grid infrastructure. It also accounts for the variability and uncertainty of renewable energy sources, which are increasingly integrated into power systems worldwide. The assessment carried out using the flexTool can help identify the flexibility measures that can be implemented to improve the resilience and reliability of the power system. These measures may include energy storage, demand-side management, interconnection with other power systems, and flexible generation. The application of the flexTool involves analyzing the data obtained from the assessment to develop a flexible and optimized power system plan. The plan should aim to achieve a balance between electricity supply and demand, ensure grid stability and security, and promote the integration of renewable energy sources. Overall, the power system flexibility assessment and application using the IRENA flexTool is a valuable tool for power system planners and operators to ensure a resilient and sustainable power system that meets the evolving energy needs of society.