On your suggestion, a lot depends on who uses or relies on water down-stream from any hydro dam.
If down-stream river users don't matter then there is another option to pumped hydro. Use solar/wind during the day and only run the dam's hydro when renewables aren't generating. That way you don't have any energy losses from shifting water back up into the dam. Simple, except if the owner of the dam is used to receiving power income 24x7, they have lost a large chunk of their income as hydro is stopped during the day. If the dam capacity is going to be increased for similar total capacity over a shorter period of time, a massive MWH turbine and possibly other infrastructure upgrade is needed.
Another problem is that lots of pesky human and animal water/river users expect rivers to flow all the time, not just when a power company wants to send water down the river. If hydro is running during the day but the water is shifted back up with pumped hydro you generate the same effect as not running water down the river. This creates the common pumped hydro requirement of two nearby lakes at different altitudes which is not your normal Hydro scheme. A proposed project in New Zealand (Onslow) also identified the issue of evaporation. Pumped hydro superficially appears to be a closed systems where water is shifted to the upper lake in times of low power prices and generates electricity back to the lower lake during high prices. Evaporation however occurs all the time. The hotter the temperature and the larger/flatter the lake, the bigger the evaporation problem. Given temperatures in Australia this could be a bigger problem in Australia than in NZ.
The article below notes three pumped hydro schemes in Australia with no new schemes since 1984. They are rarer than lithium mines.
The Snowy 2.0 expansion is occurring. Its plan was 7 years from FID to planned completion (if it runs to time). Any big new scheme would need to add years to that planning and consenting to that timeframe. Any new large pumped hydro for the 2020's probably needs to already be under design. If solar load shifting is wanted in the 2020's, the project that could be consented and built is chemical batteries. While pumped hydro may have appeal and look like a good idea, IMO large scale pumped hydro its not part of the solution in the 2020's. Small scale may be possible to consent and build but with an emphasis on "small". What could be built and scaled in the 2020's is chemical batteries. Lithum?, Vanadium redox flow? Something else? who knows?
