Pumped hydro is both very geologically limited and environmentally detrimental.
If you are willing to live with the very considerable impact and are willing to do a costly megaproject, one possibility that I've raised before: it'd be possible to go implement Atlantropa, but instead of using it (exclusively) to generate hydroelectric power, as its creator envisioned, use it for pumped storage. The world will never need more energy storage than that could provide.
Atlantropa, also referred to as Panropa,[1] was a gigantic engineering and colonisation idea that German architect Herman Sörgel devised in the 1920s, and promoted until his death in 1952.[2][3] The proposal included several hydroelectric dams at key points on the Mediterranean Sea, such as the Strait of Gibraltar and the Bosporus, to cause a sea level drop and reclaim land.
The central feature of the Atlantropa proposal was to build a hydroelectric dam across the Strait of Gibraltar, which would have generated enormous amounts of hydroelectricity[4] and would have led to the lowering of the surface of the Mediterranean Sea by as much as 200 metres (660 ft), opening up large new areas of land for settlement, such as in the Adriatic Sea. Four other major dams were also proposed:[5][6][7]
- Across the Dardanelles to hold back the Black Sea
- Between Sicily and Tunisia to provide a roadway and to lower the inner Mediterranean further
- On the Congo River below its Kasai River tributary, to refill the Chad basin around Lake Chad, provide fresh water to irrigate the Sahara, and create a shipping lane to the interior of Africa
- Extending the Suez Canal and locks to maintain connection with the Red Sea
Sörgel saw his scheme, which was projected to take more than a century, as a peaceful pan-European alternative to the Lebensraum concepts that later became one of the stated reasons for Nazi Germany's conquest of new territories. He envisioned Atlantropa as a way of providing land, food, employment, electric power, and, most of all, a new vision for Europe and neighbouring Africa.