PVSyst is energy modelling software that has been widely regarded as the standard for bankable yield projections of commercial and utility scale projects since the industry began rapid growth in the early 2000s.  The software can model all types of PV systems with module and inverter parameters specific to the real products used on a particular job.  The software is not used to generate array layouts, but it can be used to model shading from real obstructions through integration with SunEye, or by 3D modelling.   New users can make simple energy yield estimates using mostly default parameters, while advanced users have nearly unlimited ability to adjust thermal, shading, optical, and other parameters to fine tune the model of the physical system being built.  This flexibility is an asset that allows for sophisticated modelling, but can be a liability with inexperienced users.