The period of highest power demand (and therefore price) is during the evening peak period when solar panels are no longer generating. During the day, the increasing amount of solar power (including that used for domestic self-consumption) is lowering the amount of power required from baseload fossil-fuelled power generators and thus the market price for power. This has been described as the "duck curve". I'm not sure about the contractual obligations GNX might have to sell power to the QLD Govt at the time it is generated, but certainly it could be beneficial to both the stability of the grid, and GNX's bottom line to store power generated during the "duck curve" period and sell it back to the grid during the evening peak when power demand and thus prices are high.
