I reckon you should stop guessing and start doing some reading to support your argument . There are huge amounts of information freely available on this subject . Projects already built , many engineering studies done , live data tracking price reductions etc .
Also , you seem to be assuming that we will need pumped storage for the whole demand during the day . That is wrong of course .
While storage will play an important part in managing peaks and picking up shortfalls , it doesn't have to do it all .
Rather than me bang on about it , here is a video by an expert in the field who demonstrates how a renewable grid will work . Do yourself a favour and spend 5 minutes learning something about the subject .
Btw . According to Wiki , 75 % of Australia's coal fleet is already beyond it's design life .
