By Marcy de Luna
HOUSTON (Reuters) - A weekend call for Texans to restrict air conditioning and appliance use after six power facilities tripped offline highlights a weakness in the state's grid: congestion on its transmission lines.
Reliability of the power grid has been an issue since last year's February freeze, which led to more than 200 deaths amid widespread blackouts and power-price spikes that pushed at least five power marketers into bankruptcy. The state's grid operator, Electric Reliability Council of Texas (ERCOT), set mandatory reliability standards for utilities to prevent future outages.
But unlike natural gas shortages and frozen generation plants that led to outages, the weekend power advisory had nothing to do with fuel supply. Six plants providing 2,900 megawatts of power "tripped off" the state said, triggering the advisory.
The resulting wholesale prices in Houston of $4,000 per megawatt hour-plus and negative prices 150 miles (241 km) away showed that power was unable to reach demand elsewhere, energy experts said.
"A transmission issue would explain where the pricing inconsistencies and negative prices could have come from," said Ramanan Krishnamoorti, chief energy officer at the University of Houston.
“The chances of many power plants to be offline for their own individual reasons would be infinitesimally small,” said Joshua Rhodes, a research associate at the University of Texas at Austin Energy Institute and Webber Energy Group.
ERCOT declined to make an official available to comment on Monday, and a spokesperson would not discuss what caused the six generation plants to trip off. The operator said it would have sufficient power for the state this summer.
Neal Dikeman, a partner at investment firm Energy Transition Ventures and former director of a smart grid company that sells power flow controls, said congestion is likely to remain an issue as Texas heats up this summer.
"In the summer there's often congestion from people turning on their air conditioners, which makes the (transmission) lines tap out because the thermal limits get hit."