Love this in depth reply! Thank you, I'm going to read it attentively

That's very true, but it's possible and doesn't have to be expensive. Especially in mountainous areas with rivers which already utilize hydropower or coastal areas with existing dykes.

Plans for PSH reservoirs spanning a few dozen square km with pump turbines that work both ways (pump water out, generate electricity when water flows in) are ready to be executed. The expertise required lies with the engineering companies that built the Delta Works in the Netherlands, the Thames Barrier, the Dubai Palm Islands, Bath County Pumped Storage Station etc.

I think the issue is the huge up front investment these projects require, despite PSH being the cheapest storage method at very high scale and capacity. There's just not much profit to be made in that market outside of China it seems

Wouldn't it need to scale up much, much further than modern battery capacities? Modern battery capacity and life expectancy seems to be a major bottleneck in the energy transition, as I understand it. Generating power from sustainable sources is relatively easy, storing large quantities and transporting it far from the source is really difficult. Home batteries are prohibitively expensive at very low capacities and slow charging rate. Even the cheapest large scale energy storage method, pumped storage hydropower, is being implemented at a depressingly slow pace.

Not to mention the difficulty in gathering the amounts of gold and building the large scale factories required, that's going to impact the environment negatively just like lithium mining and battery manufacturing does.

If this can be scaled up to high density, modular and relatively mobile multi-GWh applications it will be absolutely revolutionary. That's a huge if though...