This paper presents a simulation software initially developed by the author for educational purposes. The computational tool supports the design of power systems with large penetration by renewable energy sources. In particular, the problematic of power intermittency and its counter strategies are targeted. The main innovation of this simulation is the detailed transient analysis of the essential balance between power generation and consumption. Even so, the focus of the simulation tool is simple usage and interpretation of results, it successfully captures important characteristics of renewable power systems. The user selects the composition of a power system from conventional power plants, photovoltaic, windpower and tidal power. Following system definition, power generation and power demand are calculated based on local weather data. Energy storage can be added to balance mismatches between power demand and supply. Following the completion of a simulation system autonomy, carbon emission and electricity cost are evaluated to assess the performance of energy systems. (C) 2018 Elsevier Ltd. All rights reserved.