As problems stated, there's probably a bit of arbitrage going on behind the scenes. However, Texas also has a well connected grid across the rather large state that is only weakly connected to other grids. There's a lot of wind in Texas and a lot of wind power. On an average day 12% of the entire state is powered by wind. Some days it's 40%. Sometimes wind produces so much energy that the spot price goes negative and wind farms are paid to disconnect so they don't overrun the transmission system.