Texas’ power grid came within a hair’s breadth of rolling blackouts on Thursday as high temperatures combined with unplanned outages for as much as 7 percent of the state’s power generation capacity.
The Electric Reliability Council of Texas, the manager for the high voltage transmission system that covers 85 percent of the state, issued a Level 2B warning Thursday afternoon, just one step away from rolling blackouts.
ERCOT called on all available power units, tapped power from neighboring power grids, including about 200 megawatts from Mexico, and turned to some large commercial customers to cut some 1,500 megawatts of power demand.
The measures were just enough to avoid what would have been the second instance of rolling blackouts this year and just the fourth instance in Texas in the past 21 years.
It was the third day in a row the state issued a power conservation warning, but the 1,500 megawatts of reduced demand meant the state didn’t break the record set Wednesday, when Texans used 68,294 megawatts during the 4 p.m. to 5 p.m. hour.
Thursday’s peak was just 66,815 megawatts.
One megawatt of power is enough electricity to power about 200 homes in Texas during hot weather when air conditioners are running for long periods of time.
Wholesale power prices were at the highest level allowed under the ERCOT system — $3,001 per megawatt-hour, or $3 per kilowatt-hour– for more than 2 hours at the height of demand.
The main difference between Wednesday and Thursday was the larger number of power plants offline, according to ERCOT spokeswoman Dottie Roark.
Texas has about 400 power plants, capable of generating roughly 70,000 megawatts of power in total. It’s not unusual for about 5 percent of the units to go off line for mechanical reasons during summer days, said Kent Saathoff, vice president of system planning and operations.
But Thursday’s outages may have been closer to 7 percent of the total fleet, or 5,000 MW.
ERCOT steadily issued warnings of the possible power problems throughout the day, beginning with a warning shortly after midnight that there would be tight demand in the afternoon.
At 1:25 p.m. ERCOT issued a warning that reserves had fallen below 2,500 MW, and at 1:46 issued a Level 1 Emergency as reserves fell below 2,300 MW.
At Level 1, ERCOT asks all available power plants to come online, begins drawing on power from neighboring grids, including Mexico, and asks consumers to cut back usage through 7 p.m.
At 2:33 p.m. ERCOT went into a Level 2A Emergency, at which time industrial customers who have agreed previously to shut-down equipment in an emergency were called on. That relieved about 1,000 megawatts of demand.
At 3:44 p.m. ERCOT entered a Level 2B Emergency, calling on another 300 to 400 MW of emergency interruptible loads and warning there was a “high probability” of rolling blackouts.
A Level 3 emergency is called when the outages begin to threaten the integrity of the entire grid. At that point local utilities — such as CenterPoint Energy in the Houston area or Oncor in the Dallas area — would be called on to do rotating blackouts, where certain circuits are cut off for 15 to 45 minutes — or longer — at a time.
If rolling blackouts are used, local grid operators like CenterPoint Energy in the Houston area and Oncor around Dallas and Ft. Worth, will turn off pre-selected circuits for anywhere from 15 minutes to an hour in order to avoid a system-wide failure.
Customers won’t get a warning beforehand, but in Houston the areas hit will likely be the same as those affected during the Feb. 2 rolling blackouts. Here is an explanation of how CenterPoint choses the circuits that go out, including a rough map.
Thursday was the third day in a row that Texas’ grid operators declared an energy emergency, calling on all available power generators, tapping power from neighboring grids and asking customers to conserve their usage.
ERCOT made the same call Wednesday as power use broke a record for the third straight day and nearly 4,700 megawatts of power plant capacity was offline due to unplanned maintenance issues.
The grid came within 50 megawatts of going to the next emergency level on Wednesday.
Wholesale power prices hit their peak level of $3,001 per MWh shortly before the Level 1 announcement on Thursday. Prices hit that level for about 15 minutes on Monday, 1.5 hours on Tuesday and 2.5 hours on Wednesday.
The spikes shouldn’t have a direct impact on retail customers.