## 5 Results and Discussions
The simulated open circuit voltage for the RADTIRC-PV structure experienced a gradual drop from a maximum value of 0.6270 V at the normal incidence to 0.5440 V at \(\pm\)50\({}^{\circ}\) angle of incidence. The simulation values of the open-circuit voltage agreed well with the experiment values for the RADTIRC-PV structure, with the maximum relative error of 5.3913% recorded at the angle of incidence of \(\pm\)50\({}^{\circ}\). Meanwhile, the simulated open circuit voltage for the bare PV cell experienced a gradual drop from a maximum value of 0.5860 V at the normal incidence to 0.5740 V at \(\pm\)50\({}^{\circ}\) angle of incidence. The maximum relative error of 3.0769% recorded at the angle of incidence of \(\pm\)15\({}^{\circ}\) when the simulation was compared with the experiment. Looking at the maximum power generation, Figure 9 shows the comparison of the values obtained from simulations and experiments for the RADTIRC-PV structure and a bare PV cell at STCs at different incident angles. For the RADTIRC-PV structure, the simulations indicated that the peak value of 0.0740 W was achieved at normal incidence. This value reduced to 0.0613 W at \(\pm\)15\({}^{\circ}\) angle of incidence. The maximum power value continued to drop reduced to less than half of the peak value when the incident angle is beyond \(\pm\)30\({}^{\circ}\). The maximum power value produced from the RADTIRC-PV structure is less than the one produced from the bare PV cell outside the design half-acceptance angle of \(\pm\)40\({}^{\circ}\). Figure 7: Comparison of the open-circuit voltages obtained from simulations and experiments for the RADTIRC-PV structure at STCs. A similar trend is demonstrated by the bare PV cell, where the value of the simulated maximum power gradually dropped from the peak value of 0.0165 W at normal incidence to lower values when the incident angle was raised from 0\({}^{\circ}\) to \(\pm\)50\({}^{\circ}\). The maximum power simulation values showed a good agreement with the experiment values for the RADITRC-PV structure, with the highest error of 9.9681% recorded at the incident angle of \(\pm\)50\({}^{\circ}\). As for the bare PV cell, the maximum relative error of 3.7463% was recorded at the angle of incidence of \(\pm\)15\({}^{\circ}\) when the simulation was compared with the experiment. Figures 10 and 11 show the comparison of the fill factor obtained from simulations and experiments for the RADITRC-PV structure and a bare PV cell at STCs at a different angle of incidence, respectively. The simulated fill factor for the RADITRC-PV structure varied between 77.6704% and 80.9228%. The simulation values of fill factor agreed well with the experiment values for the RADITRC-PV structure, with the maximum relative error of 4.4231% recorded at the angle of incidence of \(\pm\)50\({}^{\circ}\). Figure 8: Comparison of the open-circuit voltage obtained from simulations and experiments for the bare PV cells at STCs. Figure 9: Comparison of the maximum powers obtained from simulations and experiments for the RADITRC-PV structure and a bare PV cell at STCs. Meanwhile, the simulated fill factor for the bare PV cell varied between 79.7782% and 80.3597%. The maximum relative error of 2.4014% recorded at the angle of incidence of \(\pm\)15\({}^{\circ}\) when the simulation was compared with the experiment. Figure 12 shows the assessment of the opto-electronic gains obtained from simulations and experiments for the RADTIRC-PV structure and a bare PV cell at STCs. The simulated opto-electronic gain experienced a drop from a maximum value of 4.1714 at the normal incidence to 3.6047 at \(\pm\)15\({}^{\circ}\) angle of incidence. The opto-electronic gain value reduced to less than half of the maximum value when the incident angle is beyond \(\pm\)30\({}^{\circ}\). The opto-electronic gain value is less than one beyond the design half-acceptance angle of \(\pm\)40\({}^{\circ}\). The simulations shows very good agreement with the experiment, with no error relative error recorded at 4 decimal points.