The current situation of depletion of energy resources and population growth makes feasible the use of the remaining potential in power plants already built and in operation. A recent research trend is the study of performance of photovoltaic- hydroelectric hybrid energy systems with PV modules installed on the reservoir surface. The hydroelectric power plant of Guarita was launched in 1953 and has an installed capacity of 1.86 MW, with 40 m height. This study assesses the feasibility of utilization of the residual flow of 370 l/s in a machinery house placed 12 m below the water level of the dam, operating in conjunction with PV modules installed over the surface of the water reservoir. The study was conducted based on simulations with well-known HOMER software, Legacy version. The hydroelectric potential will be deployed with low-cost alternatives such as the use of centrifugal pumps as turbines. The photovoltaic potential will be exploited with modules installed on floating structures. The optimization space obtained with HOMER indicates feasible solutions with the combination of 34.8 kW hydro and 30 kW PV. Lower costs of PV modules can make viable some solutions with 60 and 90 kW PV. This work also indicates useful conclusions in the design process and implementation of the hybrid system under study.