A hundred years on means a hundred years later; i.e. a hundred years after superconductivity was first observed.
I looked in the Oxford Advanced Learner's Dictionary, the Oxford English Dictionary that's built into my Kindle and en.wiktionary.org, and the best I could find was:
further forward; in an advanced state: I'll see you later on; time's getting on
-- Oxford English Dictionary
I agree that's not very helpful when you're trying to make sense of the phrase a hundred years on when there are so many other possible meanings. You have to rely on context. Look at the headline of the article you were reading:
Superconductors: A century after their discovery, superconductors are finally moving beyond scientific and medical uses and into power grids
or the preceding paragraph:
exactly a century ago, he ... discovered superconductivity.
I should also mention that the The Economist is notable for it's sophisticated-yet-playful use of English (plus the occasional foreign word, just to make things interesting). I consider The Economist the ultimate challenge for learners of English. I'm sure there are lots of words and usages in The Economist you won't find in most dictionaries.