Heat loss. That's going to cause entropy in your system. There's always that little bit of wasted energy that's going to pull your system down if you don't keep providing energy. Perhaps it could work in theory, but I doubt it could in reality.
Thanks. A follow up question, though: why can't the sun work as the power supply, making the intensifying lenses and mirrors all that remains to create such a reaction?
I'm assuming that, in theory, it could. Of course, you would have to do all the work of designing such a system to make it feasible. It's probably a little more complicated than you think. You'd have to think of the costs of such a project. I would bet that the current lens intensification technology necessary to generate substantive power would cost more than traditional solar panels. Then again, who knows? Maybe nobody's given this idea any thought before. Better take a patent out quick