Would be nice, but Australia has a deep problem of carbon-brain, when they could be a major solar power producer/panel exporter.
I'm not liking their maths.
For a large shaft, we move weights up to 40 metric tonnes, which give us the capability to store up to 10 kWh of energy per 100 metres of depth.
40t ~= 400kN, so at 100m that's 40MJ. Sure, that's 11.1kWh mechanical, perhaps a little optimistic to say you'll get 10kWh back. That's a smallish home battery.
Where do you get another five-and-a-bit orders of magnitude from, to get to two gigawatt-hours?
Pumped hydro works because water is really really cheap and pretty easy to store, so millions of tonnes of water is doable, whether the height is tens or hundreds of meters.
Steel/iron/concrete is just too expensive. And you can't fit much in a five meter shaft compared to a lake.
I also think their numbers are too optimistic. You probably could store about 2 GWh energy if you equip all of the supposedly 100,000 mine shafts in Australia with their storages. Yet, this would not only mean 100,000 facilities to be constructed, but also mean 100,000 facilities to be checked and maintained regularly.
If I understand them correctly, they intend to use heavy materials from scrap for the weights, e.g. some steel container filled with concrete rubble. Thus, the price of them will be relatively low.
I would hazard a guess that a 40t-rated winch, 40t-rated 100m wire rope, and 40t-rated steel bucket to hold the scrap each cost more than a 10kWh battery.
Don't forget the generator/engine.
I didn't claim it was cost or ressource efficient in any way.
That would likely be the winch, but yes, you'll need a nice large regenerating motor drive.
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