Finally, I see mention of the HVAC "battery" idea I've been flogging for years. Progress!

I hope this progresses to using the pile-of-rocks "battery" to store heat/cold in cheap hours and draw on it in expensive hours.

You might be interested to read about a seasonal thermal storage project in Vojens, Denmark:

https://deepresource.wordpress.com/2020/12/16/district-heati...

Looks like the Danes are very smart!

It was popular in the 1950s. Deployed near where you live, even.

I know Seattle has an old steam plant to supply the downtown with heat. Never heard of rock storage in the US. I'm interested in a reference.

If so, Americans have forgotten all about it, replaced with a desire to do it all with electric batteries.

"storing energy in millions of smart thermostat homes by overheating/cooling them during peak hours to reduce demand at other hours"

Who's going to go along with this? I suspect millions in the US alone would flip their lids if such an idea were even considered and rightfully so. IMO this would be a great idea if your ultimate goal was to cause smart thermostats to be banished from the home.

It already happens today with little complaint.. many utilities are offering discounted rates if you agree to let them reduce your consumption on a handful of days per year. One such example;

https://consumersenergy-faqs.tendrilinc.com/faqs/what-is-the...

Everything's fine as long as it's voluntary. And by voluntary I mean both not compulsory (mandated by some level of government) as well as not normalized to such a degree that virtually every electric provider independently offers no other option. These types of things have a way of worming their way into our everyday lives; I imagine I'm not the only one who is wary of loss of agency from this as well as other similar things as the Overton window is dragged farther and farther away over time.

I think GP meant overheating/overcooling during off-peak hours? In which case plenty of people in well-insulated buildings go along with this, motivated by lower electricity prices during off-peak hours.

I took it as over-heating/cooling during peak electric production time (daylight probably) when power is more available in order to reduce usage during off-peak times. I think it would require compulsion or a large amount of voluntary adoption on the part of the customers to really make much of a difference though, and I doubt that the latter is likely on a meaningful scale (though I could be wrong of course).