## 1 Introduction
### Detailed System Performance Observations, Evaluation, and Analysis
These irradiances correspond to the smaller Sun altitude angles during the morning hours, when a stronger UV irradiation background is usually present (compared to the afternoon hours), and colder ambient air temperatures. A combination of incidence angles (in both the horizontal and vertical planes) thus exists, favoring the power generation from the east-tilted roof and also the north-facing wall sections. A maximum electric power output registered so far was 232 W, recorded on May 08, 2019, shortly after 11 am. Since this data point was acquired outside a systematic study conducted later, it hasn't been included in the dataset of Figure 5. For sunny Australian autumn days in May, each 1 kWh (3.6 MJ) of harvested electric energy corresponded to approximately 11 MJ/m\({}^{2}\) of daily  
Figure 4: Energy harvesting performance of 18-window solar atrium versus time of day. **(a)** Electric power output readings recorded over several days in May-June 2019; **(b)** the amounts of stored electric energy vs time of day; the data points used are from the same dataset of system-state records as in part **(a)**. land-area cumulative solar exposure. Considering the land-area footprint of this atrium structure being approx. 12.5 m\({}^{2}\) (5m \(\times\) 2.5 m), the combined (installation-scale) direct estimate of its actual solar energy harvesting efficiency is then approximately 2.6%. This figure is only marginally smaller than the rated efficiency of individual solar windows at standard test conditions (\(\sim\)3.0%), despite the absence of any optimally-tilted deployment areas and seasonal weather conditions without strong UV irradiation background. Interestingly, these field-measured performance data show some contrast with the recently reported figures for the \"real\" (field-measured) energy harvesting efficiencies of conventional PV generator types (solar panels) evaluated in major Australian cities [38]. In particular, these field-evaluated (\"real\") efficiencies of most conventional solar panel types stood at only about one-half of their rated energy conversion efficiency specifications. Environmental factors such as partial shading and soiling of solar panels, and installation-related geometric factors such as panel orientation and tilt angles, all affect the energy harvesting performance characteristics significantly [39; 40; 41; 42]. Table 1 shows an example of a typical daily system-related and environmental data-related dataset obtained during the study. It is important to note, that Enphase data interface has always rounded the output power readings to the nearest even number of Watts; this is possibly related to the fact that  
Figure 5: Energy harvesting performance vs solar exposure parameters. (**a**) Output power vs solar irradiation intensity measured in the horizontal plane by a local weather station; (**b**) generated electric energy vs daily land-area cumulative solar exposure (measured by the same weather station since midnight of the same day). the live data were sampled in 3-minute intervals, followed by the data averaging occurring every 15 minutes prior to internet broadcasting. Also, the cumulative solar exposure figures have apparently been adjusted by the weather station (however infrequently), to sometimes correct the sensor readings towards smaller values (compared to the data published at previous data sampling intervals) during the course of day. The datasets shown in Figure 6 illustrate the details of the atrium's power generation trends with respect to the variables such as the solar path-related angles, instantaneous irradiance intensity, time of day, and weather conditions. During this study conducted over autumn and winter months, the Sun altitude angle reached a maximum of only about 36\({}^{\circ}\) near mid-day, and therefore the solar atmospheric path-length always exceeded its standardized value (air-mass 1.5, corresponding to the AM1.5 NREL standard for solar spectrum measurements).