The Curzon-Ahlborn (1975) result gives the efficiency of an endoreversible heat engine at maximum power: η_CA = 1 − √(T_c/T_h). This lies between the reversible Carnot efficiency η_C = 1−T_c/T_h (zero power) and η_C/2 (the Schmiedl-Seifert bound for Brownian heat engines). Real power plants operate surprisingly close to η_CA: Doel nuclear plant 40% (η_CA=40%), West Thurrock coal 36% (η_CA=35%). The efficiency-power curve shows the fundamental tradeoff.