Small reverse osmosis (RO) based desalination plants driven by wind and solar energies are attractive options to meet the requirements of autonomous areas. The complexity of these systems requires proper optimization of the solar and wind energy generation with storage needs. The main contribution of this study is a design optimization method of a hybrid reverse osmosis desalination plant powered by solar and wind energy. There are many investigations based on hybrid energy systems but the investigation of a useful model and effective methods are rarely found. Here, the possibility of three autonomous hybrid arrangements, namely, solar-wind-battery-RO desalination, solar-battery-RO desalination, and wind-battery-RO desalination, are investigated. Integer and continuous variables in the optimization model of the hybrid schemes for an autonomous region of Iran are considered. The main optimization function of minimizing the life cycle cost is used to evaluate different types of renewable energy systems for powering reverse osmosis desalination. Also, the probability of power interruption is used to measure the reliability of the hybrid schemes. For this aim, a new hybrid search algorithm is developed for simulating annealing and chaotic system. The results are compared with those from original chaotic search and simulated annealing algorithms. The simulation results show that the relative error in the hybrid scheme between the best performances of the hybrid search algorithm and the simulated annealing algorithm is 47.75%, and 4.08% for the hybrid search algorithm and chaotic search algorithm. In overall terms, the results demonstrate that the hybrid search algorithm provided the best performance between the original simulated annealing and the chaotic search algorithm. Additionally, the hybrid renewable energy system decreases system cost and increases system reliability for increasing fresh water availability and meeting the electricity load demands.