As usual, cost is the issue. Both the cost of the optics, the cost of tracking, the cost of imperfect tracking, and the cost of the complexity in the design and

As usual, cost is the issue. Both the cost of the optics, the cost of tracking, the cost of imperfect tracking, and the cost of the complexity in the design and installation. I know some academic research labs have looked into arrays of microlenses & prisms, which sound interesting, but I haven't heard of any commercial products. Googling for micro prisms and solar cells will show you some projects. Ultimately, I think it's just much easier to install a simple rectangular slab with two wires coming out. And the costs of solar cells are so cheap that they're probably comparable to the cost of the optics you'd want to lay above them. I also imagine that balancing the current-voltage characteristics of the cells could be challenging when light at different times of the day has different spectra (e.g., you wouldn't want diminished performance in reddish sunsets).