One story that did provide some food for thought is a power storage device from a start-up called Energy Vault, which calls it "pumped hydro in a box".

I'll declare my biases straight up.

I don't see much of a future for pumped hydro in Australia, outside of whatever new dams and tunnels Snowy Hydro can conjure up.

Otherwise, in a country dominated by heat and dust and evaporation, it doesn't seem a particularly practical way to store energy.

I can't avoid thinking it's the environmentalists' version of carbon capture and storage (CCS) - something regularly trotted out for its potential, which then proves singularly difficult to realise.

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CCS is certainly achievable.

Carbon dioxide is routinely injected into oil wells to pressurise the cavity and push out the product in a process known as "enhanced" recovery.

Experiments have also been conducted to see if CO2 can replace water (with various dissolved lubricating additives) used in fracking for coal seam gas.

But on this one I think the greenies are right. CCS is a dud.

And it's my bet that pumped hydro will join it in the museum of ideas that did't quite work.

With these thoughts in mind, my first reaction to Energy Vault was a sceptical one.

Simply put, Energy Vault works by hoisting huge concrete blocks into the air - using electricity - and then letting them fall again, and using the kinetic energy released on their way to the ground to run a generating system.

The faster the blocks are allowed to fall, the quicker the energy is released, but the more work must be done to stop the blocks at the bottom.

Most builders will counsel against letting 35-tonne blocks slam repeatedly into your foundations.

Perhaps more importantly, the energy used to cushion the descent is then not available to be converted to electrical output.

The slower the blocks are allowed to slide, the fewer problems at the bottom, but the less peak energy you'll be able to generate.

And then Energy Vault brings with it the same problem inherent in all grid storage "solutions": the need for extra generating capacity to prime the storage systems - to winch the concrete blocks to the top of their run, in other words - as well as run the grid in daytime.

This need to double or even triple the capacity of the grid to supply "real-time" power demand, as well as power for storage at night and at other times when intermittent renewable energy is available, is confirmed in a draft "integrated system plan" published last year by the Australian Energy Market Operator.

The AEMO report made news again this week when another body, the Australian Energy Regulator, questioned some of its assumptions about coal-fired power station closures.

Add the much-vaunted hydrogen export industry and AEMO says the grid would have to "nearly quadruple" its present output.

Practical or not, the global pressure to decarbonise will not go away, which is why such companies as Korea Zinc and BHP are putting money into Energy Vault.

How much investor interest is due to Energy Vault's proposed listing on the New York stock exchange - and the ability to profit from share price rises - and how much is belief in the technology itself, remains to be seen.

Korea Zinc's Sun Metals refinery at Townsville was built in 1996 and the company says 25 per cent of the smelter's electricity comes from the 1.2 million solar panels in its nearby Ark Energy solar farm.

Energy Vault began operations in 2017. Co-founder and CEO Robert Piconi has acknowledged the practical problems with other "gravity-based storage systems".

He told the Australian Financial Review this week that no similar company had proceeded past seed funding and Energy Vault still had significant challenges in materials science, software and advanced engineering.

Energy Vault's website has some impressive videos, including a quite extraordinary film showing the design and construction of an 80-metre tower in Switzerland - the demonstration plant illustrated above.

I would embed them into this article but the settings are such you'll need to go to energyvault.com to watch them.

Individual wind turbines are typically rated at 1.5 to three megawatts: the Swiss plant is described as five megawatts in some literature and 7.8 megawatts in others.

Otherwise, the modular systems in the other images are all computer graphics, and there's not a lot of technical information to verify such claims as "industry-leading round-trip efficiency of 85 per cent plus".

Still, BHP had seen enough by December to sign an MOU with Energy Vault for its "potential to unlock cleaner energy solutions".

BHP also noted a potential use for mine tailings, in line with Energy Vault's "circular economy" use of power-station fly-ash and fibreglass recycled from old wind-turbine blades in its concrete blocks.

"Basically, anywhere you can build a 20-storey building, you can build our technology." Mr Piconi told the AFR.

Mmm. Just the thing for the empty Newcastle CBD I offered a few thoughts about on New Year's Day.

And with that, I'm off on holidays for a little while.

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