The equation for potential energy is U = m ⋅ g ⋅ h, so higher density factors into higher mass (per unit volume) so directly into higher energy storage capacity.
But as they stated it translates into higher energy storage capacity (per unit volume). This translates into smaller footprints as volumes go down, but that’s it. Now, mercury is almost 14 times more dense than water so that’s nothing to sneeze at.
There is also craned power generation BTW.. Concrete blocks are stacked with a crane.. They are then dropped to the ground and the potential energy harvested by the cranes motor
Which falls under the category of component sizing. But assuming you have however much mass at a given height, a denser fluid won't let you extract the same amount of energy from a lower height, which is what the company is claiming.
