This particular research article is an attempt to unify two distinct classical theories i.e. (i)-principle of minimum entropy generation (MEG) and (ii)-Hottel Whillier (HW) model in view of thermal optimization of PV/T and FPC collectors. Solar conversion systems are highly susceptible to substantial exergy losses in particular to thermal exergy, hence it would be better to have some sort of generalized approach, which in this paper was put forward in the form of irreversibility. The entire canvass of the paper focuses to show that how the elementary concepts in thermodynamics can be validated against a heat transfer problem to yield almost similar results. Based on MEG principle and its HW validation it has been investigated that certain minimum amount of entropy generation is the necessary criterion in order to anticipate maximum exergetic values particularly associated with heat interactions. The optimized mass flow rates for PV/T and FPC using MEG and HW models were respectively found to be (17&20l/h)(PV/T) and (8&10l/h)(FPC). However, the conclusive difference in the two approaches comes from the fact that MEG model take care of the universal entropy generation optimization, while HW model was system specific only. The transition in diameter which occurs towards asymptotic minimum entropy generation per unit length was found to be at 0.00875 m and 0.01 m for the two collectors particularly associated with laminar flow and constant heat flux source. The maximum temperature of the modeled PV module (255Wp) was ideally predicted to be reduce by 18 degrees C through the proposed design which corresponds to 8.6% increment in the electrical efficiency. A parameter chi based on useful thermal gain per unit cost of thermal management was maximized in order to optimize the center to center tube spacing.