The main electric grid in Texas returned to normal operations this morning, ending five days of winter storm-induced power outages that crippled fossil generators and wind turbines and left millions of residents in the dark and near-arctic cold.

News reports said at least 21 people died from the cold and other storm-related complications, some from hypothermia in their homes without electricity, while millions of residents are under a boil-water notice as frozen pipes burst at ice-locked water processing facilities,

“I want to acknowledge the immense human suffering we saw during this event,” Bill Magness, CEO of grid operator Electric Reliability Council of Texas (ERCOT), told reporters. “Texas can't afford to have this happen again.”

He said ERCOT operators early Monday had to impose emergency rotating blackouts as power plants began tripping off the grid that serves 90% of the state's electric load in rapid succession as the intense cold and icing interrupted operations at generators.

By Tuesday, ERCOT had lost 40% of its generation capacity creating supply imbalance as much as 14GW as demand spiked to a winter peak record 69.1GW. At least 185 power plants of the more than 700 in its system had tripped offline during the crisis.

“Doing nothing was not an option,” said Magness, as this would have resulted in cascading blackouts and caused the grid to crash, a situation that would have taken weeks and perhaps months to fully revert from a cold start. Real-time wholesale power prices hit the market cap of $9,000/MWh this week.

During the crisis as much as 46GW of generation was off-line including about 28GW of thermal – coal, natural gas and nuclear – and 18GW of renewables, mainly wind. Bone-chilling temperatures froze wellheads throughout West Texas, the nation's top natural gas region, preventing or curtailing flow into pipelines to power plants.

Icing on wind turbine blades forced half the state’s 22.9GW of installed capacity off line, Dan Woodfin, senior director of ERCOT grid system operations, said on today’s call. As of 0730CST , there was 20GW of thermal and 14GW of renewable generation, mainly wind, in forced outage.

“No generation was immune from damage,” said Magness, with coal and nuclear plants also underperforming for much of the week. Over the last decade, those technologies have steadily lost share in the ERCOT market to cheaper gas and renewables that supplied about 68% of energy consumption in 2020.

Daily available wind capacity gyrated between 10GW despite thousands of idle turbines to a low of about 800MW. Last year, ERCOT forecast wind would provide 7% of system capacity or 6.5GW this winter assuming an average 30% capacity factor (also for solar arrays).

Owners of affected wind farms have not publicly said if turbines suffered other mechanical or operational issues from the cold temperatures.

A plus for the system has been the strong rebound in solar output starting Wednesday afternoon as skies cleared to some extent in West Texas for most large arrays are installed.

“Once the solar generation was online, we started trying to bring back load in a deliberate manner,” said Woodfin. Solar has been providing about 1GW of capacity more than ERCOT had planned for, according to Solar Energy Industries Association, a national trade group.

ERCOT has about 3.9GW of installed solar capacity in its service territory but most of it lacks energy storage capacity.

Both gas and wind have come under fire from critics for their roles in the grid crisis, as did generators for inadequate efforts to weatherise their plants. Also under the microscope is the deregulated structure of ERCOT's energy-only power market and Texas being the only US state with an independent electric grid outside federal control.

Other US states form part of either the Eastern or Western Interconnection that is overseen in Washington, DC. The ERCOT network has three direct current ties to Mexico totalling about 300MW carrying capacity and two others to the Eastern Interconnection with 820MW capacity.

A joint investigation into ERCOT’s winter preparedness and its handling of the grid crisis was launched by the Federal Energy Regulatory Commission (FERC) and the North American Electric Reliability Corporation (NERC), which regulate interstate transmission and bulk sale of electricity and gas and reliability and security of the bulk power system, respectively. FERC oversees NERC.

President Joe Biden's appointee as FERC chair Richard Glick told KHOU-11 television station in Houston that Texas policymakers need to rethink the state's "go-it-alone" approach with an isolated grid that limits outside help in an electricity supply crisis.

"“That strikes me as the proverbial cutting off your nose to spite your face," he said. It's unclear whether the Southwest Power Pool which operates a multistate midwestern grid whose service territory includes the northern Texas Panhandle region could have been much help to ERCOT given its own power problems this week.

Xcel Energy, the utility serving the Panhandle, had natural gas supply issues plus early week problems with icing on turbine blades at its biggest wind farm there and weak wind resource, Wes Reeves, senior media representative, tells Recharge.

When asked about failure to weatherise numerous thermal plants in ERCOT after a less several 2011 winter freeze, Glick said not enough action was taken after detailed FERC/NERC autopsy report. “We had a warning in 2011 but people didn't take it seriously enough," he said.

The FERC chief said he believes NERC has the authority, as as long as it relates to power electric reliability standards, to pursue mandatory action to weatherise power plants "even in Texas." That could include wind turbines.

This week's events prompted other investigations in the coming weeks by the Texas legislature and Congress into ERCOT's grid resilience and resource planning, and how operators and regulators can better protect and support critical infrastructure nationwide given intensifying climate change.