Wondering how plausible that is, the numbers match very closely to the Dinorwig pumped-storage hydroelectric power plant in the UK[3], which stores ~9.2GWh of energy by pumping 9.2 million cubic metres of water, 9.2 billion litres, up 536 metres to Marchlyn Mawr reservoir. And it takes 7 hours to do that[4].
If the same amount of water has to be lifted only ~5% of the height, assume 5% of the energy, that would be ~450MWh/day for the Panama Canal.
I see it wouldn't be good to dump ocean water into Gatun Lake, but could the lowest locks of freshwater be pumped back up, instead of released into the ocean?
[1] https://ctmirror.org/2023/08/27/the-panama-canal-is-running-...
[2] https://www.marineinsight.com/guidelines/10-important-panama...
[3] https://en.wikipedia.org/wiki/Dinorwig_Power_Station#
[4] https://www.thegreenage.co.uk/cos/dinorwig-hydroelectric-pla...