Critics such as Heartland and ALEC are saying that most base-load generators are designed to go all-day, every-day and not to crank up and down so that they can back up wind and solar.
That is well above the base power load and the surge is supplied by less efficient fossil fuel power generators as well as some peak pumped water storage.
Google is testing a fleet of plug-in hybrids and software that would turn them into load-balancing tools for utilities flooded with variable power from wind and solar generators.