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ERCOT is the power grid operator for about 90% of the state’s electricity load and serves over 24 million Texas electricity consumers. The summer of 2015 was an interesting time for the Texas grid operator. The ERCOT hourly peak demand record was broken five times between August 5th and August 10th. The prevailing ERCOT record demand of 69,621 MW was set on August 10th between the hours of 4-5 pm. This broke the previous record of 68,305 MW set in August of 2011. For reference, one MW can power about 200 Texas homes during peak usage. Residential and commercial electricity customers, with their high air conditioning usage, are the primary contributors to peak demand.
The summer of 2015 was fairly stout from a metrological perspective. This may not be apparent to most Texas electricity users due the media’s focus on days that reach or exceed the 100-degree mark. The Dallas-Fort Worth area, for example, had only 15 days where temperatures reached or exceeded 100 degrees in 2015. This seems pleasant when compared to the record-setting 71 days of triple-digit temperatures in 2011. So why was the Texas power grid so stressed during the summer of 2015?
To gain a better understanding of how Texas summer heat correlates to electricity demand, the concept of a cooling degree day is required. A cooling degree day is a measure of the cooling demand in a given area and is based on how much the average daily temperature deviates from a base temperature. The base temperature is set at 65° F. High temperature readings are important, however, cooling degree days take into consideration the temperatures throughout the day. When temperatures remain high during the evening and night, as often happens during Texas summers, cooling demand increases significantly.
| ERCOT Net Energy Load (MWh) | DFW Jun-Aug Cooling Degree Days | |
| 2011 | 108,214,852 | 2376 |
| 2012 | 100,934,354 | 1973 |
| 2013 | 101,414,421 | 1839 |
| 2014 | 102,098,583 | 1779 |
| 2015 | 106,264,030 | 1913 |
Texas experienced a brutal summer (June thru August) in 2011 with 2,376 cooling degree days in the Dallas-Fort Worth metroplex. This represents a cooling demand 35% above normal. By contrast, there were 1,913 cooling degree days in the summer of 2015 which is only 9% above normal. Weather is a big driver of Texas electricity usage, but there was another factor driving ERCOT’s record demand in 2015.
According to the Texas Department of State Health Services, the state population is surging. Between 2011 and 2015, Texas was projected to add over 2 million residents. This represents a growth rate more than twice the national average. This growing population comes with a need for additional schools, grocery stores, medical facilities and other service establishments. Texas has also been successful in growing it industrial sector.
The growth in Texas electricity consumption coupled with a slightly warmer than normal summer combined to create the ERCOT record-setting demands in 2015. With the growth Texas is experiencing, it will not take extreme weather events to continue setting records.