A study on the characteristics of a buoyancy-driven flow in a rectangular circulation channel in a solar-energy-harvesting device is presented in this paper. The solar-energy-harvesting device is projected to convert solar radiation into electrical energy. As a first step of the energy conversion in the device, a flow is generated by an imbalance of buoyancy forces in the heating and cooling sections for a liquid in the circulation channel. Whereas solar energy is collected to provide the heat, free convection of ambient air provides the cooling in the device. The fluid used in the circulation channel is electrically conductive and has high thermal expansion coefficient. The present investigation focuses on the effects of channel dimensions on the buoyancy-driven flow field and uniformities of velocities. Both analytical and numerical approaches are applied in the study. Analytical closed-form solution is obtained by assuming uni-direction flow. Steady-state two-dimensional laminar solutions are obtained by numerical computation using QUICK scheme and SIMPLE algorithm.