This work presents a comprehensive model of a commercially available flat-plate solar collector, including risers and headers, simulated using a custom-developed Python program. The program models each component of the collector, incorporating physical effects often neglected in other computational models but crucial for accurately predicting temperature profile changes at a sub-minute time scale. The flat-plate solar collector model employs a multi-node temperature arrangement, discretized along the horizontal or vertical axes. Each node consists of four temperatures: one for the glass cover, one for the aluminum casing, one for the absorber plate’s junction with the copper tubes, and one for the working fluid. The simulations were validated against experimental measurements conducted at a testing facility adhering to ISO 9806 standards, showing excellent agreement between simulation results and experimental data. The comparisons included data from three subtests: performance, incident angle modifier, and effective thermal capacity, all part of the steady-state testing method prescribed by the standard. All three subtests showed strong qualitative and quantitative agreement, with all parameters falling within the range of experimental uncertainty.