This paper concerns the entropy generation and sensitivity analyses of fluid flow inside a porous solar heat exchanger. The governing equations have been solved numerically using a finite volume method. The simulations are developed using the commercial software ANSYS Fluent. The effects of different parameters such as Darcy number , radiation parameter , and the porous substrate thickness on velocity components, temperature distributions, and the local and averaged entropy generation rates are studied in detail. Beside this, a sensitivity analysis is performed by using response surface methodology. As an interesting result, it was found that the growths in the entropy generation rate due to increase in radiation parameter are in the vicinity of 44 and 51% for clear fluid and porous regions, respectively, at .