## 5 Results and Discussions  
Figure 5 depicted the simulated I-V and P-V characteristics of the RADITRC-PV structure and the bare PV cell at normal incidence. The simulations were performed under a solar irradiance of 1000 W/m\({}^{2}\) and at a temperature of 25 \({}^{\circ}\)C. From the simulations, the bare PV cell generated 0.0350 A of short circuit current, 0.5860 V of open-circuit voltage and 0.0165 W of maximum power output. The inclusion of RADITRC in the structure increases the short circuit voltage to 0.1460 A, the open-circuit voltage to 0.0627 V and the maximum output power to 0.0740 W. The simulated opto-electronic gain, (calculated by dividing the short circuit current generated from the concentrator by the one produced from a bare PV cell), is calculated to be 4.1714. Figure 4: The steps carried out at each angle of incidence to determine the angular response of the RADITRC from \(-50^{\circ}\) to \(50^{\circ}\) with an increment \(5^{\circ}\). A \(0^{\circ}\) incident angle means that the sun rays are perpendicular to the RADITRC. The performances of the RADTIRC-PV structure and the bare PV cell were investigated at different incident angles between \(-50^{\circ}\) and \(50^{\circ}\) to evaluate its angular response. In each simulation, the short circuit current (I\({}_{\text{sc}}\)), the open-circuit voltage (V\({}_{\text{oc}}\)), the maximum power (P\({}_{\text{max}}\)), the fill factor (FF) and the opto-electronic gain (C\({}_{\text{opto-e}}\)) were determined and recorded. The I-V and P-V characteristics generated from the simulations were compared with values obtained from the experiment. Figure 6 shows the comparison of the short circuit currents 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 short circuit current experienced a drop from a maximum value of 0.1460 A at the normal incidence to 0.1219 A at the incident angles of \(\pm 15^{\circ}\). The short circuit current's value reduced to less than half of the peak value when the incident angle is beyond \(\pm 30^{\circ}\). The value of the short circuit current produced from the RADTIRC-PV structure is less than the one generated from the bare PV cell outside the design half-acceptance angle of \(\pm 40^{\circ}\). This adheres to theory where outside the half-acceptance angle, the sun rays will not be directed to the exit aperture, rather they escape through the side profile of the concentrator [17]. It can be concluded that the RADTIRC-PV structure generates much higher short circuit current than the bare PV cell within the 'design' half-acceptance angles. Figure 5: Simulated I-V and P-V characteristics of the RADTIRC-PV structure and the bare PV cell at normal incidence. Figure 6: Comparison of the short circuit currents obtained from simulations and experiments for the RADTIRC-PV structure and a bare PV cell at STCs. A similar trend is demonstrated by the bare PV cell, where the value of the simulated short circuit current gradually dropped from the 0.0350 A at normal incidence to lower values when the incident angle was increased from 0\({}^{\circ}\) to \(\pm\)50\({}^{\circ}\). The simulation values of the short circuit current agreed well with the experiment values for both the RADTIRC-PV structure and the bare PV cell, with the highest relative error of 2.1229% for both recorded at the incident angle of \(\pm\)10\({}^{\circ}\). Specifically for the RADTIRC, the relative error for short circuit current value between simulation and experiment at normal incidence is 0.0000%, which is much better than the results obtained by [PERSON] et al. [43] which recorded a value of 1.5604% at similar setup. Figures 7 and 8 show the comparison of the open circuit voltages obtained from simulations and experiments for the RADTIRC-PV structure and a bare PV cell at STCs at a different angle of incidence, correspondingly.