The Electric Reliability Council of Texas on Sept. 13 filed a report with the Texas Public Utility Commission detailing the grid operator’s response to a spike in power demand earlier this month in the wake of soaring temperatures.
The report specifically addresses the Energy Emergency Alert condition that affected the ERCOT System on September 6,2023, including a description of the events leading up to and following that condition.
The report notes that on September 6, 2023, from approximately 7:10 p.m. until approximately 7:25 p.m., ERCOT observed a decline in the system frequency from 60 Hz to 59.77 Hz, which is outside the target range of 59.9 to 60.1 Hz.
In order to access additional power reserves to restore and maintain frequency, ERCOT declared an EEA Level 2 at 7:25 p.m.
Due to tight reserve margins that evening, ERCOT had already deployed ancillary services, including non-spinning reserve service, ERCOT Contingency Reserve Service, generation-provided Responsive Reserve Service, and Fast Frequency Response at the time of the EEA2.
ERCOT had also already deployed emergency response service and requested that Transmission Operators implement distribution voltage reduction measures, if available.
As part of the EEA2 declaration, ERCOT requested deployment of load management program capacity.
And immediately after the EEA2 declaration, load resources were deployed through responsive reserve service to stop frequency decay.
At 7:37 p.m., system frequency was restored to 60 Hz through these actions, and no additional measures, including firm load-shedding, were necessary.
At 8:27 p.m., the ERCOT System moved from EEA2 up to EEA1, and at 8:37 p.m., the ERCOT System exited EEA1 and returned to normal operations.
Operating reserve levels remained tight the following day on Thursday, September 7, at their lowest reaching 3,685 MW, but conditions improved on Friday, September 8 with the lowest reserves of 4,612 MW on that date.
Variety of Factors Contributed to Low Power Reserve Conditions
ERCOT said that a variety of factors contributed to the low power reserve conditions that resulted in the system frequency decline on September 6.
“The most significant factor is that the ERCOT region has experienced an unusually hot summer, resulting in abnormally high electric power demand,” the report said.
This summer' s peak demand of 85,464 MW, which occurred on August 10, surpassed the summer 2022 peak demand of 80,148 MW by approximately 6.6%.
The week of September 4 through 8 was particularly abnormal, with the peak load of 84,182 MW on September 8 exceeding the previous September demand record of 72,370 MW (set in 2021) by approximately 16%.
On September 6, the day of the EEA, high temperatures contributed to a very high peak demand during Hour Ending 18:00 of 82,705 MW.
“As has been true on many days this summer, abnormally high demand on September 6 persisted into the evening hours, overlapping with the period during which solar generation output decreases,” the report said.
“With a decline in solar output, other generation must be used to meet system demand and ensure sufficient reserves. However, because the sunset in early September occurs approximately half an hour earlier than it does in early August and about 45 minutes earlier than it does in July, the risk associated with the solar ramp is greater in early September than it has been in other periods of extreme demand this summer because of the greater proximity to the demand peak.”
Transmission Constraint Cited
On the evening of September 6, the decline in solar generation output was accompanied by limitations on other generation. Wind generation output that evening was relatively low across most of the system.
A high-risk transmission constraint in South Texas restricted the flow of generation out of that area to the rest of the ERCOT Transmission Grid, the report said.
Following the solar generation ramp-down on September 6, and with low wind generation output in the North, Central, and West regions but high wind generation output in the South region, energy flow out of the South increased the loading on a significant 345 kV transmission line beyond that line's post-contingency limit.
“Because the overload of this element following a contingency could have had significant consequences for grid reliability, ERCOT was forced to direct manual curtailment of 1,590 MW of generation from the South region,” the report noted.
ERCOT also moved ancillary services from certain generation resources immediately north of the constraint to other units in order to allow more generation capacity to provide energy north of the constraint.
Additionally, although some generation resources were experiencing ongoing forced outages during the EEA, the total amount of forced outages was at a lower level than the immediately preceding days and was in line with the level of forced outages observed throughout the 2023 summer season.
Based on the occurrence of the EEA and the need for additional generation, ERCOT initiated communications with the Texas Commission on Environmental Quality to request enforcement discretion with respect to exceedances of state air permits.
Under the TCEQ' s existing policy, if ERCOT determines that it is unlikely to be able to meet electric demand and reserve requirements on the ERCOT System, ERCOT may request that TCEQ exercise its enforcement discretion with respect to potential violations under its jurisdiction.
On September 6 at 7:29 p.m., immediately after the EEA2 was declared, ERCOT requested that TCEQ exercise enforcement discretion beginning immediately and extending through midnight. TCEQ approved the request shortly thereafter at 7:49 p.m. and ERCOT issued a Market Notice to notify Market Participants. ERCOT placed another such request the following morning of September 7 to extend from noon through midnight on September 7 and 8, and TCEQ approved that request.
Additionally, based on ERCOT's assessment that conditions similar to those observed on September 6 could arise again on September 7 and 8, ERCOT contacted the Department of Energy on the morning of September 7 to inquire about the possibility of securing an order under Federal Power Act Section 202(c) for the evening hours of September 7 and 8. DOE subsequently approved ERCOT’s request.
Energy Storage
In related news, Enel North America on Sept. 14 reported that it has more than tripled its operational utility-scale storage capacity this summer by bringing five new battery energy storage systems online in Texas.
The new batteries add over 369 MW/555 MWh of dispatchable energy storage to the Texas power grid.
With a total of 520 MW/780 MWh of operational utility-scale battery storage capacity across the state, Enel can dispatch flexible capacity, providing services to support resiliency amid shifting grid conditions in ERCOT, it said.
All of Enel's utility-scale batteries participate in ERCOT's Ancillary Services, dispatching electricity during grid emergencies to help prevent blackouts and maintain the grid's frequency on a daily basis.
As a participant in ERCOT's Ancillary Services, Enel maintains high availability of its seven operating BESS assets, storing up to 325 MW of available electricity at all times that can be discharged to the grid within seconds if needed, it said.
With respect to Sept. 6, when ERCOT declared an Energy Emergency Level 2 alert, Enel said that in order to help prevent rolling outages, Enel delivered around 524 MWh of electricity from its seven operational battery storage systems to the grid, while Enel's renewable portfolio in Texas generated approximately 19.9 GWh of wind and solar electricity throughout the day.
ERCOT and local utilities also called on approximately 145 MW of critical load relief from Enel's demand response (DR) portfolio, the company said.
The five new BESS, all of which are located at or near renewable generation plants in Texas, include:
- Two 59 MW/89 MWh batteries at Enel's Blue Jay Solar project near Iola and Roseland Solar project near Riesel;
- Two 57 MW/86 MWh batteries at the High Lonesome Wind and Roadrunner Solar projects near McCamey; and
- A 137 MW / 206 MWh battery at the Azure Sky Wind project near Throckmorton.
The company has over 3.3 GW of installed wind and solar capacity in the state, with an additional 1.8 GW of solar and 823 MW/1,234 MWh of utility-scale storage capacity under construction.
Enel also manages around 200 MW of DR capacity on behalf of commercial and industrial (C&I) entities in the ERCOT market and launched a retail energy offering in Texas late last year.
ERCOT Says Storage is Starting to Play a Major Role in Electric Market
ERCOT told Public Power Current on Sept. 14 that energy storage is starting to play a major role in the ERCOT electric market, particularly in the provision of Ancillary Services.
“In addition to current generation participation, we’re also seeing a significant number of energy storage resources in the queue,” as shown in the Generation Interconnection Storage (GIS) report, ERCOT said.
On top of these larger, single-site energy storage applications, ERCOT administered an Aggregate Distributed Energy Resource (ADER) pilot program.
ERCOT noted that its Fuel Mix Dashboard shows what type of generation is powering the grid at any moment. The Power Storage category includes the output from Energy Storage Resources when discharging power. Under current market rules, the power consumed by these devices when they are charging is included in the system load.
