The dependence of the refractive index "n" on the nanosilica concentration was studied for all the prepared samples of TLSC designs as shown in Figure 6.
The effect of nanosilica concentration on the values of [[eta].sub.trap] can be observed in Table 1; it is clear that the values of [[eta].sub.trap] for design (1) TLSC samples are lower than those of design (2).
Figure 7 shows the effect of nanosilica concentration on the fluorescence spectra of the prepared TLSC designs measured by using FSD.
For the prepared TLSC designs, it is clear that design (2) samples have higher efficiency parameters compared to design (1) samples.
Field Performance of TLSC. The average daily solar insolation on a horizontal surface [P.sub.G] was measured hourly for one year (Riyadh, 2011) and plotted as shown in Figure 11.
Figure 12 illustrates the average values of the short circuit current density, [J.sub.sc], over the year 2011 for the PV cell attached to the TLSC edge mounted horizontally as shown in Figure 2.
The performance of the investigated TLSC was evaluated under clear sky conditions, and the hourly values of the optical efficiency [[eta].sub.opt] were calculated for all seasons using the following equation :
where [I.sub.sc] and [I.sub.rc] are the short circuit currents of the PV cells attached to TLSC edge and the reference PV cells directly exposed to sunlight, respectively, G is the geometric gain defined as the ratio of the surface area to the edge area of the TLSC plate, and B is the ratio of PV cell response at the fluorescence wavelength to the corresponding response of solar spectra.