Small-scale multi-source energy systems that accommodate distributed energy resources are increasingly serving the demand for efficient low-carbon energy systems. This paper investigates the relationship between carbon reduction targets and the optimal design and scheduling of a small-scale multi source energy system based on an energy hub model. A Monte Carlo simulation is conducted to represent the uncertainty of solar power generation, and reliability indices (loss-of-load expectation and expected energy not served) are considered to ensure a reliable energy supply within the system. The simulation results show a considerable change in the optimal energy resource mix corresponding to different carbon reduction targets in both the grid-connected and isolated systems, as well as the essential role of electrical energy storage in maintaining reliability. (C) 2018 Elsevier Ltd. All rights reserved.