When I was a kid I had a Fresnel lens, probably 2' in diameter, out of an old projector or some similar thing. It would set asphalt on fire. Almost instantly. You could probably weld steel with sunlight, though not very conveniently.
Setting aside applications for moon base 1 and other sci-fi, there’s a lot of desert on earth. If the construction method is automatic or even semi automatic, and costs almost no energy, then who cares if it’s slow? A legion of robots that can’t even make other robots but can make glass bricks from sand seems like it could be paving the Empty Quarter one decade, finishing the glittering glass towers in the next.
https://www.youtube.com/watch?v=ptUj8JRAYu8
In theory if you could manufacture lenses and optical fibers, you could 3d print active solar powered structures anywhere where there is enough sun. Imagine a 3d printed little bottlegarden, with a water collector using a heated silicagel cycle printed in situ on mars. Still low atmospheric pressure, but warm and wetter.
Action around 1:25
Do you know the mirror area used here?