This study compared three different steam power plants operating under ultra-supercritical, supercritical, and subcritical conditions. Energy and exergy determinations were conducted to define the performance of each system, and the efficiencies of the fundamental equipment, as well as the overall system, in the power plants were compared. According to the results obtained, higher overall exergy efficiency was found in the ultra-supercritical cycle because of lower coal consumption. The energy efficiencies of the subcritical, supercritical, and ultra-supercritical thermal power plants were determined to be 41.5%, 43.8%, and 46.0%, respectively. Also, the comparable exergy efficiency values of the thermal power plants were determined to be 39.1%, 40.8%, and 41.9%, respectively. The chemical reaction is the most significant exergy destruction source in a boiler system. Exergy destruction can be decreased with a preliminary heating procedure for air combustion and by decreasing the ratio of air to fuel. In all these situations, the highest level of exergy destruction was determined to be in the boiler unit.