> When fully charged, the upper reservoir can store enough energy to power the plant at full capacity for 10.8 hours
That's actually 38.8GWh so close enough.
Both the GW and GWh are important and independent characteristics
Gwh/Mwh and GW/MW are not the same units. One is a time based unit, scales to duration and the other is peak intensity. You can deliver 1 GW for an hour is 1 Gwh and the same Gwh can deliver 500 MW for 2 hours or 250 MW for 4 hours.
Ah yes I misread because it was written separately. Not sure where 36 GWh came from though.