A Flex Alert is declared by the California Independent System Operator, or CAISO, when the power grid is under enough stress that consumers are asked to conserve electricity to help avoid blackouts.
While electricity demand has not necessarily decreased, grid capacity has increased substantially in recent years.
CAISO said peak grid capacity often reached just over 50,000 megawatts five years ago. Today, peak capacity has reached nearly 70,000 megawatts.
"Batteries are really the story here," said Jayme Ackemann of CAISO. "In the last five years, we've added more than 17,000 megawatts of battery storage."
Ackemann said batteries play a critical role during the early evening hours, when solar generation begins to decline as the sun sets while electricity demand increases as people return home.
"We say between 4 p.m. and 9 p.m. It really is a rolling timeframe where people are arriving home from work and beginning to turn on things in their home," Ackemann said. "For example, they lower their air conditioning if it's been a hot day."
During the summer months, solar power often generates more than half of California's electricity supply.
Much of that energy is used to recharge batteries during the day so the stored power can be deployed at night.
"Generally speaking, it takes us until about 3 p.m. to fully restore our battery resources, at which time we're just about ready to begin deploying them throughout the state," Ackemann said.
Ackemann said California's energy reliability also benefits from a diverse mix of power sources.
"Having a diverse resource mix that includes wind resources, geothermal, hydropower. And of course, we do supplement as needed with natural gas resources during peak events," she added.