Sept. 19 — Many of the wind turbines could not operate because the wind was stagnant, a common occurrence on very hot days. As a result, energy costs skyrocketed. In Houston, wholesale power prices spiked 49,000% (to $9,000 per megawatt-hour). The Electric Reliability Council of Texas (ERCOT) warned that reserve margins were so low that it might have to institute rolling blackouts, or controlled interruptions of power service. The independent system operator called for the construction of more gas-fired generating plants.