This is not the first time has happened. Summer of 2019 saw a heat wave with no wind that lasted a week. Energy prices were way up.
https://cpowerenergymanagement.com/why-doesnt-texas-have-a-c...
Ps - I just checked the prices for northern Hub - day ahead was over $6,500 and real time around $4,500 per MW for 8pm.
Last Sunday both prices were around $25.