One thing they neglect to mention (which is by no means a deal-breaker) is that you waste a good portion (about half) of the electricity in the process of charging and discharging the pile of dirt. Chemical batteries are much more efficient in this regard.

Solar prices are coming down quite fast, I don't think a factor of two is going to be a killer here if the storage is cheap and long-lasting enough. Some people are already considering over-provisioning solar panels relative to available transformers/grid connections so that they can maintain output on cloudier days. "What do we do with all the extra power when the belly of the Duck Curve [1] hits the ground" is a problem lots of people are thinking about.

[1]https://en.wikipedia.org/wiki/Duck_curve

They mention it:

> There is an efficiency penalty converting back to electricity; round-trip efficiency is 40%-45%, but sometimes the steady supply of electricity is worth it.

One thing they also mention is how incredibly cheap storage of natural gas is. https://en.wikipedia.org/wiki/Power-to-gas#Efficiency The efficiency of power to gas is not great, but it's about the same as this thermal storage method, with probably much longer lifetimes,easier transportation and more general utility (the natural gas could for example be converted to methanol using the holy grail catalyst that was in the news recently).

The power to gas is also carbon neutral, even negative depending on what you decide to do with the natural gas (if you don't burn it for power but use it for industrial chemistry, you get some sequestration out of it).

More efficient, but much more expensive. I'm sick of people handwaving $100 per kWh. That is two orders of magnitude off where it needs to be to do anything more than virtue signal.

Meanwhile multiple grids are now paying renewable to curtail, because guess what, the variability is correlated (it's the exact same damn mathematics we used to fuck up the entire global economy in 2008, which is why I'm so surprised people are handwaving that too, but whatever). If you want to minimise cost without relying on gas to save you on dark still days, you want a cheap use for the surplus, round-trip be damned.

I didn't have time to read the whole thing so I don't know if they mention it, but another article about about using sand as heat storage pointed out one of the advantages is that the material isn't toxic, unlike chemical batteries.

They do mention it, but it’s downplayed relative to how much of a problem it can be.

In a situation where you have a lot of energy generation that would go to waste, storing it in a system with low round trip efficiency could be better than losing it.

For planned installations where the generation cost is nontrivial (like a solar install) then increasing the generation to compensate for poor battery efficiency isn’t as easy of a decision.

But chemical batteries cost a lot more and don't have lifespans of hundreds or thousands of years in seasonal storage scenarios.

And when electricity is in essence too cheap like with solar and wind it can be, losing half in efficiency actually doesn't matter too much.

However, for long term storage, the "cost of inefficiency" is swamped by the amortized capex of the batteries. The goal is to minimize capex, not maximize efficiency. This becomes even more true as the cost of the input energy declines.

Another thing they don't seem to mention is environmental impact (if there even is any worth mentioning, not sure).