Engineering360: "What is gravitational potential energy?"

Missing from this presentation are:

1. frictional losses in fluid flows each way

2. efficiency of pumps and drive motors

3. efficiency of turbines and generators

4. if the generators are DC, efficiency of DC to AC conversion

5. if the generators are AC, synchronisation with grid frequency

6. cost of maintenance of the up and down flow piping

In South Africa these pumped water schemes are in operation as a way to supplement peaking capacity. The fundamental difference is that excess power generated during low demand is used for pumping the water. In the case proposed the use of solar only to pump the water makes more sense to me. The efficiency of the system will depend on all the factors mentioned in the comment. However, I applaud the idea of using solar energy to build the peaking capacity rather than being dependent on system excesses, both of which are not fully predictable.

There are 3 pumped storage hydroelectric schemes that I am aware of in the UK. They contribute only a small portion of the National Grid's output, but have the virtue that they can be switched on extremely rapidly to meet a sudden demand

It helps, of course, to have a mountain with a lake at the top and space for a dam at the bottom