More than half of the power plants driven offline during the deep freeze in Texas in February were due to the weather, underscoring that many of the state’s facilities were not prepared to withstand extreme cold.

At the peak of the power crisis, which put millions of Texans in the dark for nearly a week, 51,173 megawatts of electricity were offline, with 54% of those outages due directly to the cold, the Electric Reliability Council of Texas, the state’s grid operator, said in a preliminary report released Tuesday.