Don't forget power companies can also work with smart thermostat manufacturers and car manufacturers to implement demand side tweaks to reduce power consumption. If they need to drop demand by some number of megawatts, they can adjust everyone's thermostate by 1 degree temporarily and easily meet that need, or slow electric car charging by half a kilowatt. As long as there's a manual override for users who need to charge right then or need to change the thermostat right then, this can easily make a significant dent in the variability of the grid with renewables