Hmmm ...
100 MWh = 360 billion joules.
I'm going to guess that this contraption is roughly a 100 metre cube.
360 billion joules = 36 billion kg . m (ok I rounded the gravitational constant from 9.81 to 10, bite me) = 360 million kg lifted 100 metres.
360,000 tonnes. Using density 2.4 kg/m3 that's a block 100 x 100 x 15 metres of solid concrete. Or 100 x 100 x 5 metres of solid iron/steel.
Yikes.
100 MWh = 100,000 kWh. About a thousand Tesla Model S battery packs, each one weighing something less than a tonne but call it a tonne in the interest of possibly using a less-energy-dense, but more durable, battery formulation, than what the car uses.
A 10x10x10 array of Tesla Model S battery packs would be about 30 x 20 x 2 metres.