Comment by kurthr
The power could come from anything (solar, wind, wave) other than the dominant current source for all ammonia, the Haber Process. TFA mentions this in the headline? Could this be done before by just using water+air+solar, yes it could. Frankly, this is just a proof of concept and any commercial solution would be different for scaling reasons.
Professor Aldo Rossa started popularizing a lot of this in the 80s. https://patents.google.com/patent/US4107277A/en
Having something other than a fossil fuel source for the most common fertilizer in the world seems useful. Also, it's easier, cheaper and safer to ship ammonia around than Hydrogen since it's a low pressure liquid and more energy dense. People have been talking about using it as a shipping fuel for decades.
You didn't read the article? "The process requires no external power" right after the headline.