Dear All,
How's this for a scenario...
Using the 1920's & 30's as two decades of major privately generated utility electricity supply (hydro only). If all the hydro installations extant during those two decades in GB were reinstalled, this could equate to a 10% national usage contribution to the Grid. If, however, one looks at old water mills (wherever they might exist in a reinstatable position), this could equate to an additional 5% +. These are min. figures.
I am personally aware of many unused installations in this County alone. The first was a 150hp low head turbine unit (viz., used a large flow in through a 21" pipe from a leat (the latter from a small weir). The principal uses the falling weight of water after the turbine to create suction, which, after a fall of 17 feet is significant. This powered apx. 150 homes in the 1920's and 30's (24/7) - multiply this x 3 for three in tandem which could easily be done. The second was a pelton type of apx. 100hp that supplied apx. 50 homes during the same two decades (this source could easily be x 3 facilities). There are four locations around here where peltons were used to supply very significant supplies of elec. for lead mines (could be x 2 in tandem easily). There are apx. 200 miles of leats (in total), in this area that supplied water for mine water wheels (probably 100 + wheels in number ranging in size from 24 feet to 50 feet - so available hp. is very significant). The source supply of water is the same now as it was then. There is a disused woollen mill facility not far away that has/had four 25 foot wheels in tandem supplied by a good river - prob. about 45 to 50hp each: there are some ten similar wool and corn mill situations in this County alone - without looking very hard!
A surprising number of farms generated via peltons in the mountains, and many other lower lying farms had water wheels varying from 15 feet to 20feet dia.. Unknown hp. total of course, but a couple of thousand possibly anyway.
So, using this as a private supply situation guide for one county alone (and not considering any other potential sites - of which there are many), the hp. (horse power), potential could be said to be in the region of a min. of 20,000.. Additionally there is a Grid hydro station in the county, which, if the politicians were brave enough, could be significantly expanded, so add about 100 MW (existing supply), increase x 2, and then double again for three other potential sites, and we are talking about a lot of electricity. This from one County alone. Moving to Radnorshire (Elan Valley dams - Birmingham water supply), there is potential to construct two additional dams of significant size just to start with in that locality alone - the feeder streams for all the dams could supply a min. 300hp of drive.
The potential exists to generate huge quans. of hydro electricity in GB, it just needs some determined and decisive action from Govt. to stop the nonsense currently prohibiting an extremely climate friendly power source from being utilised. Alright, we get dry spells, so therefor increase hydro installations in areas historically less affected. The Severn Barrage should be built asap. (as others), if they don't it will be regretted - the more delay the more the cost. Don't forget there are also current flow turbines that can use tidal flow without barrages, indeed, such facilities can be placed wherever there is significant tidal flow.
The use of water power is not just possible, it is an inevitable necessity.
Regards, Bernard
p.s. In Scotland after WW2, there was a dam building programme in Scotland to employ recently returned servicemen. It is interesting that quite a few of these dams are not used for anything - I have seen one of them.