This is such a clear and obvious way to store energy that I assumed it had long ago been analyzed and assessed to fall short of other options in terms of energy

This is such a clear and obvious way to store energy that I assumed it had long ago been analyzed and assessed to fall short of other options in terms of energy efficiency, capacity, and cost. Those and other numbers are what matters, and the article doesn't provide any of them. Without data on how its efficiency, capacity, and cost compare to pumped hydro, batteries, flywheels, and other alternatives, it looks like a student science project done at larger scale.