How do friction and imperfect insulation reduce the efficiency of real power plants?

In real power plants, friction and imperfect thermal insulation act as sources of irreversibility that prevent the system from achieving its theoretical maximum efficiency, which is governed by the second law of thermodynamics.1

While the Carnot cycle defines the upper limit of efficiency based solely on the temperatures of the heat source and the heat sink, real-world operations are hindered by physical imperfections. Friction within moving parts and the inability to perfectly insulate the system lead to energy losses that do not contribute to useful work.12

Because of these factors, the actual efficiency of power plants is significantly lower than the theoretical maximum. For instance, while a plant might have a theoretical limit of 75 percent efficiency based on its operating temperatures, various mechanical and thermal imperfections typically restrict the actual efficiency to about 60 percent or less. No amount of engineering can bypass these fundamental thermodynamic constraints, as the second law requires that a portion of energy must always be exhausted as waste heat.1