(Reuters) - The Texas power grid operator on Wednesday imposed rare rolling blackouts as frigid weather swept across the state, leaving nearly 1 million homes temporarily without electricity. After the cold snap caused 50 generation units with the capacity of 7,000 megawatts to shut down, the Electric Reliability Council of Texas (ERCOT), the grid operator for the second most populous state behind California, declared an energy emergency.
ERCOT called on state energy suppliers to cut about 4,000 megawatts worth of power demand in the early hours of the day -- equal to 800,000 homes, using ERCOT's estimate of 1 megawatt per 200 houses in extreme temperatures.
The grid operator reduced that call to about 2,000 MW by noon local time as some generation returned to service.
Texas Gov. Rick Perry said Texas grid officials are working closely with ERCOT and utility providers to restore power.
"Until that happens, I urge businesses and residents to conserve electricity to minimize the impact of this event," Perry said in a statement.
The blackouts left homes dark and without heat for up to an hour, caused some schools and businesses to shut and spurred traffic snarls as some traffic lights stopped working.
"Rolling blackouts in Houston: you would have never thought you would see the day in the energy capital of the world," Jack Moore, chief executive of oilfield services equipment maker Cameron said on a conference call conducted from a division office because its Houston headquarters had no power.
There was no sign of significant outages at Houston's massive "refinery row" complex, which comprises about 13 percent of U.S. refining capacity.
Shell Oil Co said severe winter weather triggered a malfunction in fuel production units at its 329,800 barrel-per-day (bpd) joint-venture refinery in Deer Park, Texas.
Freezing weather shut at least 600 million cubic feet per day of natural gas production in three Texas basins, according to data from Bentek Energy [ID:nN02231787].
"Houston faces rolling blackouts, which should be disruptive to residential users. This is not likely to have any major effect on the oil industry," Mark Routt, oil engineer and consultant at KBC in Houston told Reuters.
Refineries and other critical infrastructure have separate power supply agreements with utilities and are less susceptible to interruptions than residential or commercial customers.
In Houston, the state's most populous city, power supplier CenterPoint Energy, started 45-minute "controlled rolling outages" at about 5:45 a.m. local time, affecting about 330,000 customers on a rotating basis.
"These controlled rolling outages are planned emergency measures designed to avoid potentially longer, and more widespread power outages," CenterPoint official Scott Prochazka said in a statement.
