We found this small hydroelectric power scheme. It is said to be the biggest such in Cumbria.
https://www.itv.com/news/border/story/2015-10-09/cumbrias-biggest-hydro-electric-scheme-nears-completion/ It cost £2.8million. If 1kWh costs 12p and it generates 2400MWh a year, that would be £288000 a year and so would take 10 years to pay back. I would have thought it would be slightly more than that because some of the 12p will be needed for business running costs.
