In this paper, a Monte Carlo-based three-phase power-flow method is proposed to evaluate the impact of a variety of hybrid energy-generation systems on residential distribution systems. The proposed deterministic power-flow method was based on graph theory, circuit theory and nonlinear numerical solution methods, and was extended to develop the proposed Monte Carlo based power flow method using the commercial software package OPTIMUS. Various technologies for distributed generation were combined in the proposed method. The hybrid energy system at the University of Yuan Ze was used in this research. It consists of a 5 kW photovoltaic system, a 3 kW wind power system and a 2 kW hydrogen-fuel cell system. Then, a comprehensive study of the hybrid-energy micro-grid system was performed to evaluate its impact on the residential distribution power grids. The factors studied included steady-state voltage deviations, power flows, power losses, reverse power flows, short-circuit fault currents, maximum allowable capacity for distributed generation, and voltage unbalance factor. The results of this research should be of value for pre-determining the impacts of hybrid energy systems on the residential distribution systems. (C) 2015 Elsevier B.V. All rights reserved.