Heat spell takes a toll on power plants

High temperatures were the driving force behind record power demand in Texas last week, but those challenges were pushed to the brink of crisis for one key reason – the large number of power plants that went offline due to unscheduled repairs.

As much as 5,000 megawatts of power generation capacity – more than 7 percent of Texas’ total fleet – was offline because of equipment problems last Thursday, when the state’s high voltage grid manager, the Electric Reliability Council of Texas, came close to calling for rolling black-outs.

Between 3,000 megawatts and 4,800 megawatts of capacity was offline for unplanned outages on other days last week.

Kent Saathoff, ERCOT’s vice president of system planning and operations, said it’s not unusual for about 3,000 megawatts to go offline during the summer since high temperatures and long running hours inevitably leads to some equipment failure.

But it still seems like an awful lot of downed power plants.

There are about 550 power plants in all of Texas. Some are owned by municipal utilities like CPS Energy in San Antonio or Austin Energy, but many are owned by publicly traded companies such as Luminant, NRG Energy or Calpine. Still others are owned by private firms that develop and operate just a few units.

An NRG Energy worker repairs a boiler tube on one of the company's Texas power plants (Photo: David Knox/NRG)

Generally speaking, they all have an incentive to remain operating during peak hours. Wholesale spot prices can reach as high as $3,001 per megawatt-hour, or $3 per kilowatt-hour, as they did for several hours repeatedly last week. If your plant isn’t online during that peak, you can’t reap the profits. A power plant operator could actually lose money if they had to buy power on the spot market to fulfill supply obligations a downed plant couldn’t meet.

But it could– and has been – argued that if a company owns several power plants it could help create an environmental of power scarcity that drives up prices by choosing to take a plant offline. They might lose revenue from that plant but make up for it with the higher prices its other units receive.

Many readers thought that was the case on Feb. 2 when dozens of power plants went offline during a lengthy cold snap, leading to rolling blackouts.

A report on the incident by the Texas Public Utility Commission’s independent market monitor concluded there wasn’t such manipulation, however, and that it truly was a problem with the cold overwhelming several systems.

Not everyone believes the weather is a good enough answer for the outages, however. An Oregon research firm said last month there are too many unanswered questions about the Feb. 2 event and another period of tight demand in June to believe weather was the main culprit for the plant outages.

But if one thinks of Texas’ fleet of power plants as a fleet of cars, all being driven at 90 mph with the a/c blasting for 18 hours a day over several weeks, the idea that some of them might be broken down on the side of the road some days doesn’t seem quite so far-fetched.

Kent Coleman, a senior manager with the Electric Power Research Institute, an industry research group, said as a rule there are more power reliability issues in the hot weather months.

“All the electrical components are running as hard as they can right now,” Coleman said. “There’s a greater chance of overheated motors, cooling towers not working at the same efficiency as in cooler weather.”

One of the most common maintenance problems in power plants are leaks in what are called boiler tubes, the pipes that run through boilers that contain water that turns into steam to drive power turbines.

Steam tube leaks don’t necessarily lead to plants shutting down fully, but plants may cut back on the amount of power they produce when they have such leaks in order to avoid making the problems worse.

Certain types of coal can also create a build up of debris in super-heater tubes – essentially tubes that run through the exhaust stream in order to reheat steam to feed back into the turbine. If units aren’t able to shutdown overnight or over the weekend, the debris can’t be cleaned out and plants aren’t able to run as efficiently.

At least one North Texas power plant has run into a problem where the reservoir that it draws cooling water from has become too warm.  That means the plant isn’t able to turn steam back into water for reheating as efficiently, leading to lower production from the plant.

The outages don’t have to be large to have an impact. On Monday, as ERCOT CEO Trip Doggett was on a conference call with reporters, an unnamed power plant trip offline right in the middle of the hour of peak demand between 4 p.m. and 5 p.m. The outage could have pushed the grid over the line into a Level 1 Emergency, in which ERCOT would turn to neighboring grids for power. But it appears the reserve margins were just enough to avoid further problems.

This past weekend gave power plant operators a chance to take some plants offline to repair equipment, but the extreme temperatures are expected to continue at least into next week.

“We’re far from out of the woods,” Doggett said.