When I was a kid, my dad (Hi Dad!) brought home a parabolic reflector. Out in the full sun, we’d stick things into the focal point and watch while sunlight burnt a piece of paper, or Popsicle stick, or hotdog. Mostly we kept our fingers out of the way. It was pretty darn cool.
Dad also talked about how if we had a parabolic reflector six feet high, we could take it out to the Sahara Desert and use it to melt sand into glass. By pulling it along, we could create a road of glass. That was also pretty darn cool.
I had a flashback to those days when I saw (originally via BoingBoing) that a guy called Markus Kayser built a similar device — using a Fresnel lens with a sun-tracker rather than a parabolic reflector — but coupled it to the 3D printer technology that has been developed over the past decade, and powered the whole thing with photovoltaics. Excellent proof of concept!
Watch the video! Notice that a lot of these sequences are time-lapsed: the technology works, but not fast.