The solar-hydroelectric (SHE) energy system is a renewable hybrid energy system consisting of solar and hydroelectric energy. An optimization algorithm has been designed to work out the installed power size of the SHE hybrid system, which is planned to be integrated into the existing hydroelectric power systems. This designed algorithm provides the optimum installed power with the benefit/cost approach. The value of the hydro cost and also the energy generation is taken from the actual values since it's an existing facility, and also the electricity production and price of the solar power are obtained from the algorithm that works iteratively. This study aims to indicate that more electricity will be produced by regulating water flows due to the reservoir of hydroelectric power plants. Hydro energy enables energy management to be administrated more effectively with the reservoir, which could be a natural enclosure, without using the other energy storage equipment/method. As a result of the study, it's been shown that with the regulation of the hydro facility flows with a reservoir, 180% more solar power capacity installation with 20.9 MW installed power and 12% more electricity production with 75.3 GWh electricity production is provided compared to the unregulated situation.