Syncing the time over the internet would make them a lot more consistent.

Our non-smart thermostat has trouble keeping accurate time and drifts a minute per month or so. That would spread the load out more because “6am” is a ten minute window.

This doesn't make any sense, though, as nobody turns on a heater for 10 minutes. Even if there is drift of 10-15 mins, there would still be a peak usage at 6:15 when all of the 6AM 'starters' are sucking power from the grid.

Imagine a grid supplied by a single coal-fired power plant. When demand rises the voltage drops and the frequency reduces, and the power plant has to start adding coal to the fire faster to get the voltage and frequency back to normal.

If the demand rises over the course of 10 minutes, you get a small drop in voltage and the plant ramps up gradually.

If the demand rises by the same amount over the course of 3 seconds, you'll get a much bigger voltage drop and the power plant has much less time to speed things up.

There's further complexity because real power grids are the size of nations and have many power plants. If several power plants notice the voltage dropping and increase their production, a few seconds later you might have too much power. Then they might respond by cutting their production, and a few seconds later you have too little power and so on.

> If the demand rises by the same amount over the course of 3 seconds, you'll get a much bigger voltage drop and the power plant has much less time to speed things up.

More than that, if the voltage drops too low, like from a sudden large power draw, you could get a brownout or even a blackout in severe cases. Voltage level is monitored and wild swings indicate instability which trips various safety systems.

I believe the smart thermostats are all synchronized with NTP servers and are able to much more precisely coordinate their activities as a side-effect.

Non-smart thermostats (even digital ones) usually drift on the clock settings substantially over time.

It isn’t. The dumb timer thermostat my parents had in the 90s would, if widely installed, cause the exact same synchronized load problem.

The article suggests the difference is that smart thermostats have the timer feature enabled and configured the same by default, and most users do not change the defaults.

Even if most other thermostats have a timer feature, I guess they are not all turned on and set to the same time by default.

I think thermostats "smarter" than a simple bimetallic strip were relatively rare before modern internet connected thermostats.

every apartment i've rented in the last 20 years has had a thermostat with some kind of clock and program capability. never used any of it, but I don't think they are rare

Interesting, mind if I ask where you are? None of the ~6 apartments I've rented had anything beyond a temperature setpoint.

Until recently, most of the thermostats I've seen in newish buildings (in US northeast) since I've been aware of thermostats (1995?) have been digital with clocks and timers.

Older buildings have had the electromechanical thermostats you describe.