Repowering of worn-out coal-fired power plants is an alternative regarding costs and efficiency due to both increased installed capacity and reduced emissions per installed power. The exergy approach in examining repowering alternatives can provide data for designers and operators in the identification and comparison of losses. In this study, hot windbox (HWB) and feedwater heating (FWH) repowering alternatives are compared in terms of exergy for a coal-fired thermal power plant. The design data (Case 1) of the existing Soma-A Thermal Power Plant (Manisa, Turkey, with 44 MWel capacity) are used for energy and exergy calculations to investigate irreversibilities in the cycle and these calculations are repeated for each repowering option, FWH (Case 2), and HWB (Case 3). Energy simulations are performed by THERMOFLEX software, and exergy simulations are performed with a user-defined EXCEL calculation tool, in which the related first and second law equations are embedded, by using THERMOFLEX results of Soma-A. The total exergy destruction rate is increased after repowering applications by 22.5% after FWH repowering and 22.4% after HWB repowering. However, the total exergy destruction per installed power is decreased by 15.1% and 13.8%, and exergy efficiency is increased from 29.1% to 33.9% and 34.7% after FWH and HWB repowering applications, respectively. Also, CO2 emissions per installed power for the current power plant is decreased by 17.0% and 13.5% kg per kWh(el) after FWH and HWB repowering, respectively. Repowering alternatives have a significant impact on existing thermal power plants in terms of both energy efficiency and environmental impact. For this reason, it is one of the most powerful applications for short-term carbon emissions reduction by supporting these practices with various economic incentives to meet the ever-increasing energy demand.