Simulating the generation of solar power plants is necessary for resource integration planning studies and flexibility analysis. However, most simulation tools fail to capture realistic sub-hourly variability and have limited usability. Here we present work on modeling sub-hourly variability at the plant and fleet levels, with an emphasis on usability for system planners. We validate our approach on a year of 6-second power measurements for a PV fleet with a total installed capacity of approximately 1,750 MW. Additionally, we report on efforts to develop a user-friendly tool integrating the approach, which will be released as an open-source Python 3 library and accompanying graphical user interface (GUI).