> A fundamental limitation of concentrating systems is they only work well with direct solar irradiance - it's very hard to concentrate diffuse solar rays coming from random directions, as you have on any overcast day.

It's impossible. That said, every type of solar panel works best with direct solar irradiance, what you can get from scatter off clouds and on overcast days is a pittance even in the best situations compared with direct light.

So this isn't nearly as big a step (yet) as it is made out to be, it may work out commercially but that is definitely not clear at this moment, and if it does work out commercially then it remains to be seen how much of that efficiency gain ends up reducing the per KWh installed cost of the panels. Any net gain of course is good.