Flat plate solar collectors remain one of the simplest and most widely used devices for converting incident solar radiation into low-grade thermal energy. This paper presents a numerical study of two-dimensional transient heat conduction in the absorber plate of a flat plate solar collector, based on a finite difference formulation of the governing energy balance equation. A symmetric region of the plate bounded by two adjacent fluid-carrying tubes is modelled, with convective losses at the top and bottom faces, an insulated (symmetry) condition at the centreline, and a temperature boundary condition coupling the plate to the working fluid at the tube side. The governing equation is non-dimensionalised and discretised using a forward-time, central-space (FTCS) explicit scheme, including separate treatments for edge and corner nodes. A FORTRAN code was developed to generate the transient temperature field for copper as the plate material and water as the working fluid. Results are presented as temperature contours at successive non-dimensional time steps, temperature profiles along the plate length and width, mean plate temperature, fluid exit temperature, and collector efficiency, each examined against varying solar irradiance and mass flow rate. The results show that the absorber plate approaches steady state at a non-dimensional time of approximately unity, that mean plate and fluid exit temperatures rise with irradiance, and that both quantities fall—while reaching steady state sooner—as the mass flow rate increases. Collector efficiency is found to increase moderately with irradiance but to fall sharply with increasing mass flow rate.

Keywords— Flat plate solar collector; absorber plate; transient heat conduction; finite difference method; two-dimensional analysis; collector efficiency.