Every time the smart grid comes up, I imagine the power company turning off my air conditioning because the ability to turn off my air conditioning made them feel safe to under-provision.
Such as:
* You may turn off my air-conditioning for $2.00/hour as long as my room's temperature is below 75 Fahrenheit.
* You may turn off my air-conditioning for $10.00/hour as long as my room's temperature is below 80 Fahrenheit.
* You may turn off my air conditioning for a maximum of 1-hour per day for $60.00/hour, as long as my room's temperature is below 85 Fahrenheit
* You may, at no point, turn off my air-conditioning between the hours of 10pm-6am.
I have absolutely no reason to trust them unless their incentives align with mine, and, here, they do not.
Even in that case, I would only agree to the 75F limit, because, for the other ones, it would take way too much time (and possibly too much energy, as well) to get back down. Air conditioning isn't instantaneous, and one can't just turn it on when one needs it, if there's more than a trivial temperature (or humidity[1]) drop.
[1] For some areas of the country, that's another, bigger problem with allowing an outsider to turn off the AC: go too long without and the humidity goes up too high. Now you have to buy a thermostat with a humidistat, just in case, even if you didn't need one before.
Your Nest can already do this:
https://nest.com/support/article/What-is-Rush-Hour-RewardsThe steel foundry down the road is a lot easier to convince - their profits are directly tied to the cost of energy, and it is relatively easy for them to scale energy use up or down.