# Spectrally-Selective Energy-Harvesting Solar Windows for Public Infrastructure Applications
## 3 Results
### Discussion  
Since the main types of the already-industrialized solar glass and solar window technologies have been described in Section 1, it is of interest to evaluate the results achieved and provide some performance metrics-based comparisons with the current state of the field of transparent solar window development. An approach relying on the use of reabsorption-free luminophores and CuInSe\({}_{2}\)-based cell modules described in Reference [28] demonstrates theoretically the possibility of achieving up to 14.9% of power conversion efficiency (PCE) in colorless transparent solar windows. This predicted performance has been shown to exceed the efficiency metrics figures predicted in the same way computationally for systems relying on the traditional Lumogen Red F 305 luminophore by about a factor of four. A calculated performance figure of 3.7% for the PCE of LSC-based windows using Lumogen F Red 305 dye has also been reported in Reference [28], which corresponds to the peak-rated electric output of 37 W\({}_{\mathrm{P}}\)/m\({}^{2}\) at the optimal panel orientation and tilt. However, the practical implementations of this type of colorless highly-transparent solar windows demonstrate that the measured electric power outputs on the predicted scale of magnitude are yet to be disclosed. A notable example of using Lumogen F Red-based semi-transparent solar windows for the construction of a greenhouse demonstrates a significant energy self-sufficiency potential reported in Reference [29]. The averaged PCE of up to about 3.8% has been demonstrated during the field testing of red-colored solar windows by employing a custom-designed network of multiple monocrystalline silicon solar cells placed at the back side of window panels. This has also been reported in Reference [29] where a roof area of a California-based greenhouse employing these solar windows would need only approximately one-third coverage of LSC electricity-generating panels in order to produce all the electricity consumed in the greenhouse operation. The authors of Reference [30] describe the recent development and testing of yellow-colored semitransparent polymethyl methacrylate-based LSC solar windows employing edge-mounted single-crystalline silicon cells only and demonstrate up to 12 W\({}_{\mathrm{P}}\)/m\({}^{2}\) of electric power output. A standard way of describing the LSC window-type concentrator performance metrics used in the literature involves the parameters such as geometric gain (G, the ratio of the total energy collection area to the area at which the PV conversion takes place), photon collection probability at solar cell surfaces (P), and optical concentration factor (C\({}_{\mathrm{opt}}\)). These parameters are related through an expression C\({}_{\mathrm{opt}}\) = G\(\cdot\)P = G\(\cdot\)(\(\eta\)/\(\eta_{\mathrm{nom}}\)), where h is the concentrator PCE, and \(\eta_{\mathrm{nom}}\) is \"bare-cell conversion efficiency\"--the nominal efficiency of the solar cell module of the type used [31]. Considering only the solar cell modules installed internally within the concentrator windows and the data of Table 1, the following performance metrics-related parameters can be derived for the solar windows by employing glass panels of size 750 mm \(\times\) 1000 mm: G = 4.25; P = 11.585%, and C\({}_{\mathrm{opt}}\) = 0.492. This is calculated by accounting for the concentrator-generated efficiency contribution of \(\eta\) = 1.425% and the cell module efficiency \(\eta_{\mathrm{nom}}\) = 12.3%. These performance parameters are in line with the data reported in the literature [21; 31] for LSC-type concentrators of much smaller dimensions. To the best of our knowledge, no other research group worldwide have so far described the development and testing of large-area high-transparency glass-based clear solar windows in particular using CIS cells and demonstrating Ampere-scale currents at the maximum-power point, together with large corresponding system voltages (V\({}_{\mathrm{MPP}}\) near 30 V).