As many as 9 million Californians could lose power tonight as record-breaking heat taxes the electric grid and rampant wildfires knock out power plants and transmission lines.

The blazes have already cut electricity to more than 40,000 customers, most of them in Los Angeles, San Diego and Fresno counties — in some cases for as long as 36 hours. The real test will come after 2 p.m. Hawaii time today when electricity demand is forecast to peak and the state’s solar production begins to wane. Without significant conservation, rolling blackouts will begin, plunging scores of people into darkness for the third time in less than a month.

“Today is sizing up to be the most challenging day of the year,” said Eric Schmitt, vice president of operations at the California Independent System Operator, which runs most of the state’s grid.

The crisis comes just three weeks after an August heat wave triggered California’s first rotating blackouts since the 2001 energy crisis and fueled hundreds of wildfires across the state. As climate change contributes to more extreme weather, the region’s heat, wildfire and blackout woes are only getting worse.

The heat gripping the state is unprecedented. San Francisco hit 100 degrees Fahrenheit today, smashing a prior record of 92 set in 1904, according to National Weather Service. Los Angeles reached 111 and San Deigo topped 100, also records.

“Temperatures during this current heat storm are expected to peak today, pushing demand for energy beyond levels of available supply,” the California ISO said in a statement. “There is currently not a sufficient supply of energy to meet the high amounts of demand during the heatwave.”

With the state predicting a massive, 4-gigawatt electricity shortfall starting this evening, the Department of Energy issued an emergency order allowing more power plants, generators and even boat engines to produce electricity over the next seven days, even if anti-pollution laws or other regulations might normally block them from running.

In the meantime, wildfires are wreaking havoc on the grid. The Creek Fire yesterday knocked out transmission from a hydro plant, while a fire in Southern California cut off a solar farm, the California ISO said. Together, the blazes sucked 1.6 gigawatts from the power system, enough to power 1.2 million homes.

About half of that had been re-connected by midday today — and then another fire in Southern California cut out 500-600 megawatts.

Wholesale electricity prices in the southern part of the state spiked to the highest level in nearly a year, diverging sharply from prices in Northern California.

At the state grid operator’s request, the Energy Department said it was authorizing power plants in the City of Industry, El Segundo and Long Beach to run at their maximum output levels — even though it may unleash additional air pollution.

The Los Angeles Department of Water and Power reported Sunday that it had restored power to more than 37,000 customers who lost it during the heat wave Saturday, but roughly 7,000 more remain in the dark. Some of those could be without electricity for 36 hours, the municipal utility warned. Some of LADWP’s equipment was running at 200% of capacity due to the extreme demand for power, and the high night-time temperatures weren’t letting the gear cool off.

Utility giant PG&E Corp. which powers much of Northern and Central California, warned on Saturday that it may decide to cut power to about 103,000 customers in parts of the San Francisco Bay area and Sierra Nevada foothills starting late Monday to keep its power lines from igniting fires. Hot, dry winds are forecast to blow across the region, threatening to knock tree limbs into power lines.

This is the first time PG&E has warned of shutoffs during this year’s fire season. Last year, when California’s utilities first began carrying out widespread blackouts like this, some homes and businesses were left in the dark for days. That drew outrage from state and local officials, triggered investigations and prompted PG&E to reassess the scope of future shutoffs.

The utility’s weather models show that warm, offshore winds will develop Monday evening on the heels of the heat wave. The soaring temperatures will further dry out grass, bushes and other vegetation, PG&E said.

Years of deadly fires started by PG&E’s wires in wind storms forced California’s largest utility to declare bankruptcy last year. The company emerged in July after agreeing to pay $25.5 billion to settle wildfire lawsuits. The state has since set up a wildfire liabilities fund, essentially an insurance pool for the region’s utilities, but just one catastrophic blaze could wipe it out.