The rare deep freeze in Texas that left millions without power this past week forebodes greater challenges for the U.S. power grid in a future where extreme weather is more common and the economy relies increasingly on electricity to fuel vehicles and heat homes.

At its peak, the extreme cold snap in Texas left more than 4 million without power for multiple days and forced offline more than 180 power plants unable to withstand the wintery conditions. The Electric Reliability Council of Texas, or ERCOT, the state’s grid operator, finally lifted emergency conditions Friday morning once temperatures began to warm slightly, and it was able to bring the lights back on for most Texans.