This article deals with the problem of assessing the economic efficiency of the operation of a cascade of hydroelectric power plants in the conditions of the wholesale electricity market. The definition of economic efficiency is based on the choice of the optimal plan for the available capacity of the hydropower plants, depending on the type of distribution of available capacity, as well as the size of the penalty for the difference between the actual available capacity and the planned one. The calculation was made in the MathCad computer algebra system for two hydropower plant cascades (the Pamir hydropower plant cascade and the Bureyskie hydropower plant cascade). The obtained results have shown that the influence of the selected distribution function of the available power has a stronger effect on more powerful stations. The cascade connection of hydropower plants allows increasing the value of the minimum capacity, thereby reducing the range of uncertainty and possible penalties for the declared capacity, thereby ensuring the most cost-effective financial result for generating companies. © 2023 IEEE.