I work in a power station and can I can tell you the spot price...

I work in a power station and can I can tell you the spot price per MW around Australia at the moment is anywhere between $30 and $60. Apart from Tasmania due to bass link failing they are paying through the nose.
Also are you factoring in the expensive of pumping the water back up at night?
This set up will use more electricity than it will produce.
One more thing with the reduction of big industry in Australia such as car manufacturing, outlook for electricity price is uncertain.
Cheers