Emprirical Vs. Physical

I need to know that is difference between in Empirical and physical model in calculation , accuracy and physical meaning
and if i have to simulate or validate a plant which proposal is more suitable?

Dear Saeed Aziz,

Please see SAM's Help system for descriptions of the physical and empirical trough models. In general, the empirical trough is suitable for system designs similar to the SEGS systems in the United States because its equations are derived from regression analysis of performance data measured on those systems. The physical trough model is more flexible because it uses mathematical models that represent the geometry and heat transfer properties of the system components.

Best regards,
Paul.