The irradiance / solar related simulation engine for Honeybee (EnergyPlus)

May I ask what is the simulation engine for the irradiance / solar related calculation (E.g. the irradiance received by solar panel for the calculation of PV generation) engine that Honeybee or EnergyPlus uses?

Can I replace the simulation engine by RADIANCE (if RADIANCE is not the simulation engine) when I do PV output simulation by EnergyPlus?

Thanks.