The size of a little hydropower plant for the run-of-river type is extremely crucial for the price effectiveness of investment. In our work, a numerical method is employed for optimal size of such a plant that includes two hydraulic turbines running in parallel, which are often various type and size being improve its efficiency. The research and evaluation of plant overall performance is performed utilizing a newly developed analysis algorithm that simulates in detail the plant procedure throughout the 12 months and computes its production outcomes and financial indices. A parametric research is completed first-in order to quantify the influence of some important building and procedure factors. Then, a stochastic evolutionary algorithm is implemented for optimization procedure. The analyzed optimization issue utilizes data of a particular site and is fixed within the solitary and two-objective settings, considering, as well as economic, some extra goals, as maximization of produced energy while the best exploitation of the water stream potential. Examining the outcomes of numerous optimizations works, it becomes possible to identify the absolute most beneficial design choices to realize the task. It was found that the utilization of two turbines of various dimensions can raise sufficiently the energy production of the plant in addition to economic results of the investment. Finally, the susceptibility for the plant performance with other external parameters can easily be examined utilizing the current strategy, and some indicative results are offered for different financial or hydrologic conditions.