THE NATIONAL Grid Corp. of the Philippines (NGCP) raised red and yellow alerts over the Luzon grid Monday, as demand peaked following a rise in temperatures over the weekend.

The system operator said on Viber that it placed the grid on yellow alert between 11 a.m. and 1 p.m. Monday, moving to a red alert from 1 p.m. onwards.

A yellow alert is issued when reserves fall below ideal levels. A red alert is declared if the supply-demand balance deteriorates further to the point where power interruptions must be resorted to.

“We have a projected system peak demand of 11,514 megawatts (MW) and our available capacity for today is about 11,729 MW. The difference is small — a little over 200 MW. That is already a concern,” Mario C. Marasigan, the Department of Energy’s (DoE) Electric Power Industry Management Bureau director, said during a briefing.

He also noted the rise in its heat index over the weekend. The government weather service reported that Aparri, Cagayan posted a reading of 46 degrees Celsius on the index on May 30.

“As a rule of thumb, an estimated 100 MW must be allotted for every degree (of) increase in temperature,” Mr. Marasigan said.

He added that unplanned or forced outages accounted for 1,285 MW of unavailable capacity Monday.

Manila Electric Co. (Meralco) said areas affected by manual load dropping or rotational power cuts include parts of Bulacan, Cavite, Laguna, Metro Manila, Quezon, and Rizal.

The rotational outages are due to last less than an hour, Energy Undersecretary Felix William B. Fuentebella said Monday.

At 4 p.m., Meralco said power has been restored to all affected areas.

In a separate statement issued on Viber, the DoE said that it will continue to monitor the power situation and submit updates to consumers and enforcement agencies. The department also reminded distribution utilities and the system operator of their duty to address the required capacity increases to ensure a reliable power system.

Last month, the Energy department said that it did not expect any red alerts to take place on the Luzon grid during the dry months until July after it met with the NGCP to discuss the island’s power outlook. — Angelica Y. Yang