The results of the assessment and analysis of the operating modes of the power complex with the constructive and technological combination of hydraulic power plants (HPPs) with solar power plants (SFEU) in the presence of seasonal or daily regulation in the environmental hydro system are presented. The aspects of the operation of a hydroelectric power station with non-self-regulating derivation are considered in detail: when working in a load schedule with a maximum power equal to the installed one, and when the average daily power along the watercourse is approaching the provided one. It was found that in the first case, the influence of the SPEU regime on the joint work with the hydroelectric power station is to move a part of the load graph of the hydroelectric power plant with the maximum power to the base part of the schedule. In the second case, the influence of the SPEU mode consists in changing the variable part of the load graph, but the HPP, in contrast to the first case, retains its position in the load graph of the power system. The mode of operation of the hydroelectric power station becomes more uniform and at the same time, a smaller volume of the daily regulation basin (DRB) is required. For the example considered, the maximum power of the hydroelectric power station during the day increased from 50 MW to 54 MW. It has been revealed that even with the production of SPEU in 18% of the daily production of hydroelectric power plants, the volume of DRB is required approximately two times less. As a result, it is possible to increase the operating head at the hydroelectric power station and obtain the corresponding effect on power and electricity generation.