Governments are hesitating to use this because pump storage has major environmental impact. It just needs _a lot_ of space. You also need mountains for that and

Governments are hesitating to use this because pump storage has major environmental impact. It just needs _a lot_ of space. You also need mountains for that and not every country has those. There is some research going into putting concrete spheres into the ocean and pumping water in and out of them. The principle is the same but it doesn't need hundreds of hectares of forest to be cleared.