One assumes that Graham knows about 'peak lopping' i.e. matching demand spikes on the Grid which is were Dinorwig comes into its own (and the fact that you cant just turn a normal powerstation off at night, hence the 'spare' electricity on the grid at night which is when they pump it back up to the top.
"Synchronised and spinning-in-air emergency load pick-up rate from standby 0 to 1,320 MW in 12 seconds"
As for nicks assumption that you need a 'bloody big stream' to make it all work, that is not the case at all. Head is where its at.
"he economics only stack up as an alternative to sticking the money in the bank or building society at current interest rates for saving and borrowing, they certainly don't stack up as a viable long term business proposition"
Thats bollocks too, if you have a reasonable site, then payback can be relatively quick (5 to 8 years) after than - its just money in the bank with the Renewable Obligation Certificates you'll be earning, you can make a tidy sum selling them to the energy companies. They can have a very long lifespan too. Many of the Major hydro schemes where built over a 100 years ago (OK - so most have had a recent refit of new turbines/valves)
The 'Feed In Tariffs' that the Gov will probably introduce soon will help things along too.
He's right about grid connection though. It costs thousands to put lines in (think 3000 up front then an additional 1000 per pole as a rule of thumb).
It can still stack up though. There are tones of micro hydro schemes cropping up all over, especially in Wales at the moment.