The objective of this work is to study the heat transfer and fluid dynamics phenomena which take place in flat plate solar collectors. The resolution of the steady and unsteady conduction in 1D and 2D domains including composite materials, Smith Hutton problem, Navier-Stokes equations and energy equation are carried out by means of numerical methods. The acquired knowledge in heat transfer and fluid flow is then applied to flat plate solar collectors. A numerical model is created to simulate flat plate solar collectors. The numerical model which is suitable for flat plate solar collector design is validated by means of comparison with the existing experimental data. The results and the relevance of the assumed hypothesis are analyzed.