It was August 4, 2011 and Texas was in the midst of a brutal heat wave. The temperature in Dallas had reached 110 degrees Fahrenheit (43 degrees Celsius) for the past two days, and as Texans ran their air conditioners, the load on the state power grid had just hit an all-time high. System operators at the Electric Reliability Council of Texas (Ercot) feared that rolling blackouts might be necessary.

Instead, they declared a ‘level 2’ emergency, and Ercot’s main demand response (DR) programme