What is interesting about a quick look at the Heindl Energy solution is that it looks like basically pumped hydro. The difference is that the water is sitting

What is interesting about a quick look at the Heindl Energy solution is that it looks like basically pumped hydro. The difference is that the water is sitting in a large cylindrical space underground with a large (minimum 100m / 300ft diameter) rock piston sitting on top of the water. Eliminates the need for mountainous terrain with a high lake-like geometry to pump the water up out of the gravity well — they can build this in the flatlands