There's no such thing as "what they need". At any given price there's a quantity that will be economical to use (demand) and an amount that will be economical to produce (supply). 

When prices are artificially suppressed demand > supply, which means there's a shortage.

Isnt that finite amount usually 125% of what they need?


Satosora

At any given moment there's a finite amount of power being generated from hydro plants, even if they were to produce energy indefinitely.