The utilities and several major environmental groups see time-of-use rates as a valuable tool to help clean up the state?s power supply. California has a growing abundance of cheap solar power during the middle of the day, so much that utilities sometimes have been forced to pay other states to take it. But the sun goes down every evening just as people get home from work, forcing utilities to fire up expensive, polluting gas plants.
Time-varying rates are meant to encourage homes and businesses to shift their power use away from high-demand periods, when energy is dirtier and more expensive, and toward low-demand periods when energy is cleaner and less expensive.
https://www.latimes.com/business/la-fi-time-use-electricity-rates-20190103-story.html