Wall Street Journal: "During peak daylight hours, California produces a surplus of solar energy, and power generators may be ordered or paid to cut back their production so the grid isn’t overloaded. On Friday and Saturday Caiso reported about 1,000 mega-watt hours (MWh) were curtailed—enough to power 30,000 homes. This year 1.3 million MWh of power have been curtailed."
"But this means supply shortages can occur in the evening when solar energy plunges but demand for power remains high. That’s what happened this weekend."
Rocky Mountain Institute: "Relatively high levels of curtailment are already an issue in California."