|Fig. 1: An Energy3D model of the SAS solar farm
|Fig. 2: Daily production data (Credit: Xan Gregg)
The data are surprising because they show that the outputs of solar panels driven by HSAT actually dip a bit at noon when the intensity of solar radiation reaches the highest of the day, as shown in Figure 2. The dip is much more pronounced in the winter than in the summer, according to Mr. Gregg (he only posted the data for April, though, which shows a mostly flat top with a small dip in the production curve).
|Fig. 3: Energy3D results for four seasons.
|Fig. 4: Change of incident sunbeam angle on 1/22 (HSAT).
|Fig. 5: Change of incident sunbeam angle on 1/22 (fixed)
So we can conclude that it is largely the motion of the solar panels driven by HSAT that is responsible for this "surprise." The constraint of the north-south alignment of the solar panel arrays makes it more difficult for them to face the sun, which appears to be shining more from the south at noon in the winter.
If you want to experiment further, you can try to track the changes of the incident angle in different seasons. You should find that the change of angle from morning to noon will not change as much as the day moves to the summer.
This dip effect becomes less and less significant if we move closer and closer to the equator. You can confirm that the effect vanishes in Singapore, which has a latitude of one degree. The lesson learned from this study is that the return of investment in HSAT is better at lower latitudes than at higher latitudes. This is probably why we see solar panel arrays in the north are typically fixed and tilted to face the south.
The analysis in this article should be applicable to parabolic troughs, which follow the sun in a similar way to HSAT.