RAPSim (Renewable Alternativ Powersystems Simulation) is a free and open source micro-grid simulation framework for better understanding of power flowing behavior in smart microgrids with renewable sources. It is able to simulate grid-connected or standalone microgrids with solar, wind or other renewable energy sources. The proposed software calculates the power generated by each source in the microgrid and then it conducts a power flow analysis. This software is helpful for optimal placement of distributed generation units in a micro grid.
RAPSim is designed for use in science and classroom with a simple to use graphical interface. It is an easily extendable framework that supports users in implementation of their own models, for grid objects, and algorithms for grid control.
Software provides an easy user interface with drag and drop. However if you want to add new components, you need to implement them in Java.
It is a very complicated software and help of this software also not provided so it is tough to use it.