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(Reuters) - Texans' set an hourly electric use record for June on Tuesday, the second record in as many days, as the state's largest cities baked under triple-digit temperatures.
Power demand reached 66,583 megawatts in the hour between 4 p.m. and 5 p.m. CDT (2200 GMT), passing Monday's peak of 65,047 MW, according to preliminary grid data.
The early summer heat wave, which produced temperature records in Houston and San Antonio, also pushed electric consumption above the highest hourly amount in any July on record, according to grid records.
Late afternoon thunderstorms around Houston and San Antonio pared rising demand, keeping it under the 67,000 MW forecast earlier in the day by the Electric Reliability Council of Texas (ERCOT), the primary grid agency for the state.
ERCOT and power companies across the state urged residents to limit afternoon power use, and ERCOT vice president Kent Saathoff said on a call it appeared the public was cooperating.
The grid agency issued an advisory to generators on Tuesday afternoon as power supplies tightened, but it avoided declaring a power emergency.
Real-time power prices rose above $1,000 per megawatt-hour for about two hours during the afternoon peak as power supplies tightened and briefly reached the $3,000 maximum allowed. Day-earlier real-time prices were less than $150 per MWh.
Houston's high temperature reached 103 degrees Fahrenheit (39 Celsius), 12 degrees above normal and breaking the record of 99 degrees. San Antonio hit 105, also a record, while the high in Dallas of 105 fell short of the long-standing 1980 record of 112 degrees.
Some relief is expected to start statewide on Wednesday, with highs dropping into the high 90s by Friday, giving power plants and air conditioners a break.
Last year, ERCOT set seven monthly peak-power records as extreme cold in February and an extended heat wave hit the state.
So far this year, Texas has exceeded the monthly records in May and June.
The state's all-time peak use was 68,379 MW last August during a heat wave and drought.
The grid agency has projected that power use will peak at 67,492 MW this summer, about 1,300 MW above what would be expected in a normal weather scenario.
One megawatt is enough to serve about 200 Texas homes during hot weather when air conditioners run for extended periods.
ERCOT has warned that rolling outages could occur this summer given the state's limited amount of surplus generation.
The state's shrinking reserve margin has led regulators to implement a number of wholesale market changes to encourage construction of power plants over the long-term.
Since no grid emergency was declared on Tuesday, the market has not yet tested the pricing changes regulators have implemented since last summer when an extended heat wave and drought forced ERCOT to declare emergencies on six days and to curtail power to some customers on two days in August to avoid widespread rolling outages.
The biggest transmission and generation companies in ERCOT include Luminant and Oncor, units of privately held Energy Future Holdings, CenterPoint Energy, American Electric Power, PNM Resources, NRG Energy, Exelon, NextEra Energy and Calpine.
Reporting by Eileen O'Grady in Houston and Scott DiSavino in New York, editing by Dave Zimmerman and M.D. Golan