(Reuters) – The California power grid operator urged consumers to prepare to conserve energy this week to prevent the possibility of rotating or controlled outages as homes and businesses crank up their air conditioners to escape a brutal heatwave.

The California ISO, which operates most of the state’s electric system, projected that demand plus reserves required in case something goes wrong would exceed power supplies for several days this week.

High temperatures are expected to be in the low 90s Fahrenheit (about 33 Celsius) in Los Angeles on Wednesday through Saturday, which is more than 20 degrees Fahrenheit over the normal high for the time of year, according to AccuWeather.

The ISO projected the biggest deficit would occur Thursday after the sun goes down and solar power is no longer available.

A heatwave last August forced California utilities to impose rotating blackouts that left over 400,000 customers without power for up to 2-1/2 hours when supplies ran short.

The grid operator forecast peak demand would rise from 40,919 megawatts (MW) on Wednesday to 43,820 MW on Thursday. That compares with an all-time peak of 50,270 MW in July 2006.

The ISO said Thursday’s peak plus reserves was more than 3,300 MW over supplies expected to be available at that time.

The ISO has said it expects to have about 50,734 MW of supply available this summer, but some of that comes from solar.

At the start of June, the ISO, which does not count all solar as being available since it only works when the sun is out, said it had over 14,100 MW of solar capacity that produced a record 13,205 MW in May.

Moreover, the ISO warned it may not be able to rely on neighboring states for much more power because the heatwave baking California was also blanketing much of the West.

The ISO was currently getting 29% of its power, or more than 7,200 MW, from imports. That compares with a peak of 9,956 MW in May and a record 11,894 MW in September 2019.

(Reporting by Scott DiSavino; Editing by Bernadette Baum)