Pintohoo GNX listed on the ASX is looking at a 250MW pumped hydro system from a far smaller mine pit than the Kal super pit .
Mind you MW in itself is a bit disingenuous as you could create 250MW in a second but it would not represent a lot of power if borken down for an hour , so better to use MW per hour storage
Obviously you do not use the total pit volume to determine storage capacity as need a head , and really probably only need a couple of days storage . , many of the pits in WA have water in them naturally as well even though they are in what could be considered by some as desert there is a natural inflow from ground water ie perched water table .
http://www.asx.com.au/asxpdf/20170712/pdf/43kl81g69r7q6j.pdf
I could do the calcs for you but from memory 1 Watt is 100 grams lifted 1 meter in one second
There is 1000,000 grams in 1 cubic meter of water
1000,000 W = 1MW
10 W = 1 kg lifted 1 Meter one second
10 * 1000 W = 1 cubic meter lifted 1 meter one second
10,000 W = 1 cubic meter lifted 1 meter one second
10kw = 1 cubic meter lifted 1 meter one second
say dam has 100 meter head then 1000 kw per second from 1 cubic meter of water
or the same as 1MW per second or 0.00027 MWH
Lets say the pit is a the shape of trapezoid 100 meters * 100 meters on the base 300 meters * 300 meters at the top and the sides are 300 meters high
so an average of 200 * 200 * 300 = 12 Million cubic meters
but we only need 24 hours of storage
SO 0.00027MWH * 12 MM cubic meters = 3240 MWH
But only need 24 hours storage
3240/ 24 = 135 MW available for 24 hours
need about 1 MW per 300 homes
So enough storage capacity for 32000 homes for 24 hours assuming 80% efficiency about a city of 80k people (no industry )
Looks like I just did the calculations hmmm but then I use to work at Calpine , mind you above only took a few minutes and all based on memory
