Ann: July 2016 Company Presentation-GNX.AX, page-11

The home battery market is only a small risk. The pumped storage facility is being advertised at about 450 MW with a run-time of 5 hours (2.25 GWh per day if fully utilised).

If my memory serves me right, the Tesla Powerwall only has a 3.3 kW inverter and 7 kW capacity (unless you go for the 10 kW model, but we'll stay mainstream for arguments sake).

That means that Genex hydro will have the instantaneous power output of about 136,000 Tesla Powerwalls.
Since Genex can go for twice as long (roughly), then that jumps to about 272,000 Tesla Powerwalls as far as total capacity is concerned.

Now when you consider that demand during peak time in QLD is approximately 6 to 7 GW, Genex can only accommodate for 6 to 8% of the required load. This means that the project is not too large so as to push down their own market pricing power but has enough power availability that it may push out a couple of the higher cost producers in the market (gas burners, hopefully not ERM Power, as I hold them too).

As for the effect of batteries on the market, I dare say it'll be negligible until grid scale battery banks are hooked up.