> BTW, everybody in Arizona has A/C. Amazingly, A/C demand peaks when the sun is high in the sky.

Here in California, peak AC demand is late afternoon. Environmental thermal mass means peak outdoor temperature happens a fair bit after peak insolation. Structures take even more time to heat up and add additional delay. Finally, people arriving home from work means increased AC use, too.

Demand stays fairly high after it gets dark.

(And it's my understanding most other places keep daytime heat later than here).

We have had "off peak hot water" for many decades. Multiple different rates for peak and off-peak.

It is not useless but it does have its price in terms of complexity and usability. With off peak at night you tend to run out of hot water during the day at times e.g. if you have visitors.

It is not a new idea and it is no panacea.

My house has a 25 year old gas furnace and it is still in solid condition. Had to get the blower motor replaced but that is about it. Our AC unit did not fare as well so we may be upgrading both next year. But yeah, they can last a lot longer than 10 years.

> BTW, everybody in Arizona has A/C. Amazingly, A/C demand peaks when the sun is high in the sky.

Magically when solar production is at it's peak!