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'No-water' hydropower turns England's hills into green and pleasant batteries
(www.rechargenews.com)
This is a most excellent place for technology news and articles.
If you have the system always running most of the cartage back to the top could be handled by the siphoning effect, like draining a washing machine or siphoning patrol.
You'd need energy to get it started but after that it should keep siphoning as long as there's liquid to siphon.
I don't understand how that would work in this case; if this is true, I think I'd need to see a diagram.
My understanding is that they use energy to pump the liquid up during times of excess, and release it to generate energy when there's more demand.