Pumped hydro using existing dams is brilliant and should be maximally exploited but we already have dams on all the really good sites. We can improve by adding

Pumped hydro using existing dams is brilliant and should be maximally exploited but we already have dams on all the really good sites. We can improve by adding the pump-up stage to many of them but there is simply no scope for massive expansion in total reservoir / energy storage capacity.