It is not ridiculous and as a physicist I learned long ago not to make predictions about technologies. However, there is no demonstrated path to energy storage on that scale and one thing I have learned is not to rely on theoretical "technologies." Of course if it isn't demonstrated it isn't actually a technology. But, at this point there is no practical economic power storage system, and there is a theoretical limit based upon physical chemistry/physics, engineering, chemical engineering and economics as to what can be done. There exists no demonstrated laboratory technology that is ready for scale-up to these scales.
I do know a concept that is ridiculous - mining of asteroids for bulk raw materials. The energy costs of getting something to the asteroid so that you can get mined material back, and reenter the atmosphere without burning up or destroying our civilization are unachievable. That is a back of the envelope calculation based upon Newton's laws.
Pumped water energy storage is not a theoretical technology.