I had to look up "solar hydrogen". Found this wonderful article demonstrating this new technology which currently manages to produce a full 500 grams of hydrogen per day...

https://spectrum.ieee.org/solar-to-hydrogen

Further, your bulk precious resources comment is somewhat disingenuous, as it discounts building these devices in the first place. The 7 meter wide system uses a variety of expensive solar cells, mirrors, electronics and motors to control the system and position the device.

And even if one was so inclined as want to build these at scale, I'd have to question the idea of taking an increasingly precious resource (clean water) and turning it into fuel.