The idea had apparently been around for a while, since 2008 or so, there were other, similar studies. I don't know if they were similarly flawed or not though.

I also would not completely dismiss the premise - trees are probably very good at converting solar energy.

And to add to that, I don't buy the counter argument that a tree arrangement can't be better than a flat panel - why not? The sun moves around so the flat panel might be optimal at one point in the day, but will certainly be sub-optimal at other times. This isn't a clear cut argument at all. There are many variables in play. Cloud cover; seasons; etc. Keep in mind the experiment was done in a cold climate.