> What materials are they using?

"Just Have a Think" put out a video about this recently [1]. The project he reports on claims 30MW with 4MW available within 3s for frequency stabilization and the weight is not solid concrete (emissions penalty), but rather compressed refuse that otherwise cannot be recycled (coal ash, demolition debris).

The friction would occur as long term tensile strength durability of lifting cables and high torque electrical hoists, which are the primary material penalties. But these things may be relatively cheap to produce and rotate out of service as their known operational lifetime approaches (Tesla has designated labor that changes out public charger cables within a reasonable buffer before they are expected to wear out).

[1] https://youtu.be/lh1--ftWWvY

That’s where I got the link from

> This is not rocket science.

it is literally rock science ;)

Seriously, in Germany, concrete costs arount 100 EUR per cubic meter. So we would end up with around 150 EUR per kwh capacity. But they would not have to use concrete for the task. They could as well use 23 m^3 gravel (which goes down to 10EUR) and some steel scaffolding. Or even just plain water (35m^3).

They're using "composite" bricks that include waste material (I can't find any obvious references to exactly what kind of mix of materials), so my guess would be the material cost will be rather low.

But each weight can be reused almost infinitely... The cost doesn't matter too much.

That's not right. Refinforced concrete will suffer from environmental influences and have a durability from maybe 30 years. That means you have a cost overhead of 3-4% per year for the replacement value.

Water tanks certainly have a much worse life time, given that they will start lacking after a short time and you don't only have to repair the tanks but also provide liquid to refill.

Cycling stress like that is going to dramatically reduce the lifespan due to tress fractures. I think they would be lucky to get 10-20 years from the blocks.

Stress fracture are already a significant issue for concrete dams when you frequently vary the water levels, and this is much worse as different stacking is going to stress each block slightly differently every time. In theory they might be perfectly flat surfaces meeting evenly, but in practice that’s far from the case.

Wouldn’t you just grind them up and recycle them?

They can’t recycle it into blocks of the same material properties. It’s not worthless by any stretch, just a poor fit for such demanding applications.

I wonder how they've calculated the costs of building this giant crane and concrete block system, vs building small scale pumped storage hydroelectricity. Not by the usual method of impounding a reservoir at the top of a hill, but putting a giant array of load-balancing medium sized water tanks at the top of a hill, running a pipe to the bottom where there's the pump/generator, and a similarly sized array of tanks.

A big tank is overwhelmingly cheaper than a collection of small tanks.

Ground water makes a remarkably capacious reservoir, which may be deeper than your hill is high, doubling the energy storage capacity, for a possible upper limit on instantaneous wattage.

I would use depleted uranium for that. Many countries have to store thousands of tons of it, and governments will pay you for storing it. Instead of making it sit idle, you might as well use one of its finest qualities (density).

Let's make Fort Knox fully renewable by storing wind/solar in stacked gold bars.

Thousands of tons is a very small amount of mass for gravitational energy storage. The capacity of small pump storage reservoirs is measured in millions of tons. Also one probably wouldn't want to use a somewhat toxic and slightly radioactive material at large scale.

This was already busted by Thunderf00t: https://www.youtube.com/watch?v=NIhCuzxNvv0