Standalone renewable energy (RE) systems hold the most promising solution to the electrification of remote areas without utility grid access, while a feasible energy storage is a core part for achieving a continuous and reliable power supply since RE is usually intermittent and weather dependent. In the present study, the pumped hydro storage system is proposed, which is considered as a promising technology for solar energy penetration and particularly for small autonomous systems in remote areas. The mathematical models for the major components are developed, and system reliability and economic criteria are discussed as a benchmark for optimization. The genetic algorithm (GA), along with Pareto optimality concept, is used for the system techno-economic optimization: to maximize power supply reliability and minimize system lifecycle cost simultaneously. The proposed methodology is applied on a real remote inhabited island without power supply. System sizing, simulation and optimization are carried out using single-objective and double-objective GA technique. The performance of the optimal case under zero LPSP is examined. This study demonstrates that the proposed models and optimization algorithm is effective and can be used for other similar studies in the future.