The numerical problem of steady, laminar and incompressible natural convection flow in a wavy solar collector is studied. In this investigation, two vertical walls are perfectly insulated. The top cover glass surface is continuously absorbing solar energy. The bottom wavy solid surface is uniformly kept at a constant temperature Tc. Numerical analysis is done by this article for the performance of natural convective parameter (Ra) on _ow and heat transfer phenomena inside a solar collector. The solar collector has the flat- plate cover and sinusoidal wavy absorber. Air (Prandtl number 0:7) is considered as the working fluid inside the solar collector. The governing partial differential equations with proper boundary conditions are solved by Finite Element Method using Galerkin's weighted residual scheme. The effect of Rayleigh number related to performance such as temperature and velocity distributions, convective heat transfer, mean temperature and velocity of air is investigated systematically. The results show that better performance of heat transfer inside the collector is found by using the highest value of Ra. Calculated average Nusselt number (Nu) is correlated with Rayleigh number (Ra) and Prandtl number (Pr). Then a semi-empirical relation is established from this correlation with experimental data.