The Electric Reliability Council of Texas expects to have sufficient capacity to meet demand this fall and winter, but under extreme circumstances this winter, the system might have to enter an Energy Emergency Alert status.
"Based on the scenarios evaluated, an extreme higher-than-normal number of forced generation outages occurring during a period of unusually high demand would be unlikely to result in insufficient resources," ERCOT said in its "Preliminary Seasonal Assessment of Resource Adequacy for Winter 2018-19."
The winter SARA shows resources totaling 80.2 GW and demand peaking at 61.8 GW, but typical maintenance and forced outages would reduce the resources to 72.7 GW, leaving 10.9 GW as reserves, well above the 2.3 GW below which an Energy Emergency Alert, or EEA, may be declared.
If extreme weather were to cause loads to spike to 67.4 GW, that could also reduce the resources to 71.2 GW, so the overall reserves could fall to 3.8 GW. If extreme weather coincides with extreme generation outages, the resources could fall to 67.8 GW, leaving less than 400 MW of reserves, which would likely result in an EEA declaration.
In a media call Sept. 6, Pete Warnken, ERCOT manager of resource adequacy, said the extreme scenario "assumes the gas companies issue Level 4 restrictions" to ensure that customers who rely upon gas heating can stay warm, which occurs when temperatures fall below 20 degrees F, in which case "all those plants are totally out of service."
"We view the probability of that happening as very low," Warnken said.
EEAs are declared at various levels, designed to ensure sufficient resources remain available to meet demand and to prevent uncontrolled or "cascading" blackouts. Therefore, if reserves get low enough, ERCOT could call on utilities to implement load shedding plans to ensure that at least emergency services have power.
Fall scenarios rosier
In contrast, the "Final SARA for Fall 2018," covering October and November, contains no scenarios in which insufficient resources are available. While the capacity of generation out for maintenance rises in the fall and spring, loads typically fall, which results in capacity reserves significantly exceeding the EEA level in all forecasts.
The fall SARA shows resources totaling 81.7 GW and demand peaking at 58.6 GW, but typical maintenance and forced outages would reduce the resources to 67.4 GW, leaving 8.8 GW as reserves. If a one-in-10 chance of high generation outages occur, that would reduce the reserves by another 1.7 GW to about 7.1 GW. If the fall weather resulted in an extreme peak, the reserves could fall to about 5.9 GW.
After a summer featuring several new record peak loads in July and other heat waves with high loads and prices, one might expect more thermal generation to shut down for maintenance in the fall, but the "Final SARA for Fall 2018" contains estimates of typical and forced outages — 10.9 GW and 3.4 GW, respectively — that do not differ from the "Preliminary SARA for Fall 2018," issued in late April.
The capacity of resources did fall about 700 MW between the preliminary and final fall 2018 SARAs, mainly because of the following:
* The 470-MW Gibbons Creek coal plant was announced to be mothballed in October through spring 2019.
* About 300 MW of "private use network" generation, which is behind-the-meter industrial generation, was deemed unavailable this fall.
* About 300 MW of wind projects were delayed, of which 108 MW would have been counted as available at peak.
* However, the final SARA counted an additional 240 MW of utility-scale solar power as likely to be available at peak.
The latest National Weather Service forecast indicates an enhanced likelihood for above-normal temperatures for the October-December period for all of Texas. The forecast for December, January and February indicates a probability of near-normal temperatures for that time of year.