The Sahara desert: it's hot, with lots of sand and not much else. To you and me that might look like nothing more than a recipe for boredom and an epic sunburn, but to Markus Kayser and his solar-powered sand printer, it's just a giant pile of raw materials which can be used to make anything you want out of glass.
When you get sand hot enough, it melts. Simple as that. Lightning bolts do it all the time, making weird glass portraits of themselves called fulgurites. You don't need that much energy, though, and with enough concentrated solar power, you can melt sand like sandy butter. Add a little extra cleverness in the form of solar panels to drive the electronics for a 3D printing platform, and you've got a self-sustaining glass object printer with enough raw material to last you until approximately the end of time:
Sand, by the way, can be used to make more than just glass. You can also use it to make high-quality solar panels. If you're thinking that making solar panels with a solar powered factory sounds like a self-sustaining solution to all of our energy woes, you're not alone, and that solar power breeding project we wrote about last year is trying to do exactly that.