36000 tons... doesn't actually sound like that much? That's a ~30x30m cube of dirt.

But I have no reference for the cost of setting up such a storage and how it compares to battery or hydro.

adgjlsfhk1 4 hours ago | parent | next [-]

The ~grid scale design of this for reference is somewhere around 200mx200mx50m for above ground, or ~100m cube (or bigger) for quarry infill. Such a design is going to get crushed by battery/hydro over the hours/days, but wins on cost for seasonal usage.

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pfdietz 6 hours ago | parent | prev [-]

The cost of putting dirt in a pile is $1-2/ton.

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PaulDavisThe1st 5 hours ago | parent | next [-]

so $36-72k for days of 1GW of power? Sounds pretty cheap to me ...

	▲	pfdietz 5 hours ago \| parent [-]
		They also state the cost per kWh(th) of storage capacity is about $0.10, or $100,000/GWh(th). This is thermal energy, which is converted to work at maybe 40% efficiency, mind you. There are costs over and above the dirt (for example, pipes laid through the dirt to carry heat in/out).

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cyberax 5 hours ago | parent | prev [-]

The biggest expense will be the pipework inside that pile. That you won't be able to service easily. And you'll also need a LOT of insulation around it to prevent heat from leaking out too quickly.

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adrianN 3 hours ago | parent | next [-]

Thermal storage benefits from the square/cube scaling, so the amount of insulation goes down as you scale up the storage.

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pfdietz 4 hours ago | parent | prev [-]

The insulation is just more dirt.

	▲	cyberax 3 hours ago \| parent [-]
		Homework: compute the heat flux from a 40 meter radius sphere, given the surface temperature 600C and the ambient temperature 0C. Now compute the amount of insulation needed to keep its temperature above 500C for 3 months, given that dry sand has an R value of 0.25 W/mK.