Introducing CASSYS: An Open-Source Software for Simulation of Grid-Connected Photovoltaic Systems

CASSYS is an open-source computer program used to simulate the performance of grid-connected photovoltaic systems at Canadian Solar Inc. Using a detailed description of the system provided by the user (arrays, inverters, and balance of system components), site location, and weather conditions (irradiance, temperature) at arbitrary time steps, it calculates the state of the system at each interval and provides a detailed estimate of the energy flows and losses in the system. The goal of CASSYS is to provide a reliable, automatable, transparent, user-friendly and free program to simulate grid-connected photovoltaic system performance for operational purposes. This paper describes the physical models used for the simulation of system performance and showcases the program's versatility, current limitations, and demonstrates use cases for the software in the operations and maintenance context.