The effectiveness and affordability of solar thermal collectors must increase to promote solar thermal energy systems further. To accomplish this, it is vital to make use of tools which enable the evaluation and potential optimization of the effectiveness of new designs. By concentrating on the computational (CFD) analysis of a direct absorption polymer (polycarbonate) flat plate solar collector's performance, this paper illustrates such an endeavor. The adoption of the suggested material may lead to the manufacture of flat plate collectors that are both more economical and environmentally friendly. The most important aspect in the performance of this collector focuses on the efficient solar energy absorption by the working fluid. This energy transfer is accomplished by employing a clear polymer honeycomb structure inside the collector. Inside the polymer honeycomb structure channels, solar energy is absorbed directly by the working fluid. For the maximization of energy efficiency, it is important to assess and optimize the flow field development and heat transfer inside the collector. For this reason, a CFD model of the solar collector was created in the commercial CFD software Ansys CFX. The model included all the basic geometrical and thermophysical characteristics defining the fluid flow and heat transfer taking place in the solar collector, also taking into consideration buoyancy and gravity effects. For the proper inclusion of the effect of the internal polymer honeycomb structure in the CFD model, a porous medium approach was adopted, and appropriate source terms were added in the Navier-stokes equations through which the macroscopic effect on the fluid flow development and heat transfer could be sufficiently captured. CFD computations were performed to investigate the temperature, velocity, and pressure patterns in different regions of the solar collector, and a broader insight regarding the flow field and heat transfer inside the solar collector design was achieved. The CFD results were also compared with reasonable agreement with available experimental and simulation data from the literature. The numerical results showed an acceptable performance of this polymer design in relation to more standard designs. The results also revealed some weak points of the design, such as the identification of recirculation regions which can be the target of future optimization actions in future works.