What I don't like about that design is that its using your precious solar power for moving the panel.
There's another one that an inventor has come up with (featured on a TV show called "The New Inventors") which uses a thermal hydraulic system to move the panel, as heat increases, it slowly moves the panel. Its completely passive, and seems to work quite well.
Not sure if it's for sale yet, but I'd be shocked if it didn't come to market!
Sean