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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.
Hydro is used to smooth out peaks and troughs in the power supply. You're not even close to getting a useful estimate.
The fifth largest hydroelectric power station in the UK is 160MW
100MW by 2030 is a pretty big deal.