How to build user-defined solar radiation in mfix

hello everyone, I realize that MFiX has powerful user-defined functions.I started to read the mfix.f and dem codes line by line and i wonder if i can add solar energy radiation model to it… I get confused and i want to know how to start my codes, thank you !!!

See the implementation of radiation available online. MFIX-RAD / Code / [88d4b9]

Thank you for your recommendation. In fact, I have seen this program, but it is not what I want. I want add external incident solar photon as a new radiation source into the system.