I think the parent is suggesting that these things could be maintained in a cost effective way indefinitely. It's not like you hit year 50 and throw it away because of some inherent quality of the tech (as with nuclear plants or lithium batteries which fundamentally degrade in ways that are cost prohibitive to "fix").

The thing is, I'm unsure whether this holds true. Could you actually replace pipes inside a huge sand battery without bringing the entire thing offline? And at some point are you basically rebuilding it?