From an engineering point of view, I don&#x27;t know if it is better or not, but the article implies that construction costs scale much better if you leave the rock there.<p>If you wanted to make an unadorned column of water underground, you&#x27;d have to remove all the rock where the column is. Without knowing anything about that sort of construction, I&#x27;d guess the cost is proportional to the volume of the cylinder.<p>The proposed design requires removing a ring of rock plus a disk at the bottom. The article claims that the construction cost is therefore proportional to the cylinder&#x27;s area.<p>There are also other reasons which are plausible, but they&#x27;re not as interesting. Rock is denser, so you get more energy storage per unit volume. (Because: potential energy is given by E = m g h, where m is the mass raised. Adding a rock on top means you get greater mass)