This was where I was going too. (However, I'm not sure the power output of a panel is simply the sum of the individual cells. I thought that in a series array, the least illuminated panel essentially limits the panel current. Not that this matters in this case, since he wasn't actually measuring power. The voltage certainly adds.)
The experimental issue I thought about is that the experiment is situated next to a large wall. While the flat panel is facing away from the wall, it looks like some of the panels on the "tree" would also receive diffuse light from the wall. So effectively, the tree seems to have a larger collecting area than the flat panel. This would also make the tree less sensitive to shading.
The experimental issue I thought about is that the experiment is situated next to a large wall. While the flat panel is facing away from the wall, it looks like some of the panels on the "tree" would also receive diffuse light from the wall. So effectively, the tree seems to have a larger collecting area than the flat panel. This would also make the tree less sensitive to shading.