The leakage of radiation from the optical cavity through the 0.05cm gap between the PV arrays and the reflector can be prevented by connecting the reflector to the PV arrays. Obviously, this will result in thermal conduction from the hot reflector to the cold PV arrays. However, this conduction loss can be minimized by using a very thin material to connect the reflector and the PV arrays. Consider an optical cavity with no gaps between the reflector and the emitter, and the emitter and the reflector and the PV arrays. Thus, the emitter width, wE = wC3 = 10cm in Figure 8.1. Using the same properties as used for Figure 8.2, the program in Appendix F was used to calculate the performance. With the gap eliminated, the temperature increases from TE = Tb = 1231K to TE = Tb = 1251K and the cavity efficiency increases from pc = 0.57 to pc = 0.64. While the PV efficiency remains the same, the TPV efficiency increases from pTPV = 0.18 to pxpV = 0.20, and the electrical power output increases from PEL = 44W to PEL = 49W.
Thus, eliminating the gap results in a significant increase in the cavity efficiency and TPV efficiency. Remember, however, the heat conduction loss between the reflector and PV arrays has been neglected. Inclusion of the conduction loss will reduce the gain in efficiency. However, as stated earlier, the conduction loss can be minimized by using a very thin material to connect the reflector and PV arrays.