GNX had better start buying up sites and starting planning for additonal pumped hydro plants before batteries get cheaper -
http://reneweconomy.com.au/res-lloyds-consider-100mw-battery-storage-plant-in-south-australia-93039/
GNX has a great opportunity to take the cream for grid power maintenance (frequency control, renewable supply smoothing and interconnector failure carry through) if GNX acts now. Even a statement of intent backed with some putative site selection and back-of-the-envelope sizings will slow competitors hoping to enter the market.
Not only will batteries compete with pumped hydro for energy storage, time also has a cost with the early players in the market taking the highest returns from the highest power price spikes.
Later entries will be selling into a flatter market.
Hopefully GNX's solution to the Kidston hydro storage will be essentially modular. This will de-risk and reduce the cost of later units.