# Spectrally-Selective Energy-Harvesting Solar Windows for Public Infrastructure Applications
## 3 Results  
### Principal Results and Future Directions  
The principal results of large-area solar window module development indicated that the technology of building transparent solar concentrator-type windows has now reached the stage at which practical test-bedding applications within public infrastructure installations were feasible. We report, for the first time, on the development of industrially-framed, large-area color-neutral solar windows of high (up to 65% to 70%) visible transparency and large glass panel dimensions (1200 mm \(\times\) 600 mm). All previous samples of framed solar windows reported by our group (e.g., in Reference [21]) used glass panels of dimensions not exceeding 500 mm \(\times\) 500 mm. Adshel Pty. Ltd. (Port Melbourne, Australia) has provided a public bus stop as a site for testing the applicability of ClearVue Technologies Ltd, Perth, Australia. solar windows for generating electric energy in self-sustainable bus stops fitted with backlit advertising panels and LED lighting appliances. At the same time, the ECU research team started considering the construction of a pilot greenhouse fitted with energy-generating clear windows. Figure 6 illustrates a range of previously-developed framed solar window types suitable for powering small electric loads such as ventilation fans. The pilot bus-stop installation included six framed solar windows placed vertically along the backside wall of an existing bus stop. Figure 7 shows the front view of this bus stop, which featured a charge controller and battery storage system and was being charged either from the combined (parallel-connected PV windows) output or from a combination of two Unisolar PVL-72 flexible PV modules rated at 72 W\({}_{\text{P}}\) with each mounted on the roof of the same bus stop. The data presented within Figure 7 also describes several optical transmission and thermal-insulation related parameters of these solar window systems and the electrical testing data summary are also shown. The battery-charging current was being measured by the charge controller (Powertech MP3739) with maximum power point tracking (MPPT) functionality in real time and was observed to be at around 4 A. Therefore, replenishing the energy stored in two 12 V parallel-installed batteries simultaneously with powering all electric loads (consuming 45 W in total) when the system was connected to the wall of solar windows. The design of novel MPPT systems suitable for optimized use with distributed-generation and energy-harvesting-type solar PV systems is an ongoing area of active research in which new developments are reported regularly [26; 27].The total electric power output observed from six solar windows in morning conditions (9:30 a.m., 7 February 2017, at about 20 \({}^{\circ}\)C ambient air temperature) reached 74 W and exceeded that obtained at the same time from two parallel-connected PVL-72 roof-mounted modules (up to 57 W). Figure 8 illustrates the main PV measurement data for both system types. Figure 6: Examples of several earlier solar window design types (**a**) and an illustration of their application potential (**b**). The actual measurement time was near 9:30 a.m. on 7 February 2017 (when the Sun altitude angle was near 32\({}^{\circ}\), according to the astronomical data from www.suncalc.org). The Sun azimuth angle was 84.8\({}^{\circ}\) and the direction of normal to the vertically-installed wall of PV windows was practically due East, according to Google maps data. A part of bus-stop roof area was overhanging and shaded some of the solar cell (and also glass) areas from the direct sunlight across the top row of windows. The magnitude of this shading effect was dependent on the Sun altitude angle and the shadow affected only a few percent of the total area of panels installed across the top row of windows. However, slight reductions in the open-circuit voltages generated by a number of individual solar-cell strips placed under this overhanging roof section were expected.