There are very few details on how much they've actually generated on any of these. The MIT one doesn't specify how it's getting the original water at all.
The IEEE one does actually list it out:
Researchers have built a kilowatt-scale pilot plant that can produce both green hydrogen and heat using solar energy. The solar-to-hydrogen plant is the largest constructed to date, and produces about half a kilogram of hydrogen in 8 hours, which amounts to a little over 2 kilowatts of equivalent output power.
Yeah, that's about what I'd expect. You are not going to power cars with this.
The one in the Guardian article seems to be targeting it a as a replacement for natural gas in home heating and cooking, which is a maybe.