It is far from clear which will be the cheapest storage medium, in each place. Count on people to install whatever is cheapest where they are at the time they b

It is far from clear which will be the cheapest storage medium, in each place. Count on people to install whatever is cheapest where they are at the time they build. Batteries are expensive right now, but costs are still falling. It is conceivable that a substantial fraction of installed storage will actually end up batteries. My favorite medium, at the moment, is heavy weights hung from a disused supertanker moored over a sea trench. Each weight would have its own cable reel, with clutch and brake, sharing a shaft with the rest, the shaft driven by a winch and motor/generator kept out of the weather. A net full of ironstone riprap would serve for the weight. The winch would be whatever is the biggest available off the shelf, with the weights chosen to match the winch. Maybe 1000 tons each? A supertanker is wide enough for multiple shafts, and you can rack together multiple supertankers. A smallish one can hold up 100,000 tons. Taiwan has an excellent trench right off the SE shore, but there are a lot of near-shore trenches, off SE India, SW Mexico, E Korea, SE Japan, and even Monterey and Monaco. Probably a deep trench is not even needed for viability; 1000 meters is probably plenty. A supertanker seems to run $50-100M new, probably a small fraction as scrap. There will be a lot of supertankers to scrap; it is already starting.