To add to this, there are numerous very large scale project already underway to use existing hydro capacity as pumped hydro storage. Eg, Bath County Pump Stora

To add to this, there are numerous very large scale project already underway to use existing hydro capacity as pumped hydro storage. Eg, Bath County Pump Storage is a 3GW plant[1] although ironically it is often filled using nuclear power because the hydro station can adapt better to rapid changes in demand. In the US there is 22GW total pump hydro storage already (compared to say 98GW total nuclear power capacity). [1] https://en.wikipedia.org/wiki/Bath_County_Pumped_Storage_Station https://en.wikipedia.org/wiki/Bath_County_Pumped_Storage_Sta...