Modeling of flat-plate solar collector operation in transient states

Solar energy is becoming an alternative for the limited fossil fuel resources. One of the simplest and most direct applications of this energy is the conversion of solar radiation into heat, which can be used in water heating systems. A commonly used solar collectors is the flat-plate. A lot of research has been conducted in order to analyze the flat-plate operation and improve its efficiency. This study presents a one-dimensional mathematical model for simulating the transient processes which occur in liquid flat-plate solar collectors. The proposed model simulates the complete solar collector system including the flat-plate and the storage tank. The model considers time-dependent thermo-physical properties and heat transfer coefficients and is based on solving equations which describe the energy conservation for the glass cover, air gap between cover and absorber, working fluid, insulation, and the storage tank. The differential equations were solved using the implicit finite-difference method in an iterative scheme and executed using the MATLAB. In order to verify the proposed method, an experiment was designed and conducted for several days with variable ambient conditions and flow rates. The comparison between the computed and measured results of the transient fluid temperature at the collector outlet showed a satisfactory convergence. The proposed method is an appropriate for the verification of the absorber and glass cover effectiveness, and to calculate the overall efficiency of the system along with the overall heat loss factor