The Visayas and Mindanao power grids were placed under red and yellow alerts Thursday, September 3, amid insufficient power supply and the unavailability of several large power plants.

The National Grid Corporation of the Philippines (NGCP) said the Visayas Grid would be under red alert from 1 p.m. to 10 p.m. and yellow alert from 10 a.m. to 1 p.m. and 10 p.m. to 11 p.m.

As of 8 a.m. Thursday, the Visayas Grid had an available capacity of 2,187 megawatts against a peak demand of 2,575 MW.

The grid operator said several power plants were on forced outage, while 16 others were operating at derated capacities, resulting in a total of 792 MW of unavailable capacity.

Among the factors cited for the alerts were the unavailability of the Visayas' large coal plants TVI 1 and PEDC 3, as well as limited or unavailable power imports from Mindanao.

Meanwhile, the Mindanao Grid was placed under red alert from noon to 9 p.m. and yellow alert from 10 a.m. to noon and 9 p.m. to 10 p.m.

The Mindanao Grid had an available capacity of 2,480 MW against a peak demand of 2,546 MW as of 8 a.m.

A total of 841.6 MW was unavailable to the grid due to forced outages and derated capacities. Seven plants were operating at reduced capacities, while several others had been on forced outage since previous months.

The unavailability of Mindanao's large coal plants GNPK 1 and 2 and TSI 2 contributed to the yellow alert declaration, according to the grid operator.

A red alert is issued when power supply is insufficient to meet consumer demand and the transmission grid's regulating requirement.

A yellow alert, meanwhile, is declared when the operating margin is insufficient to meet the transmission grid's contingency requirement.

The alerts indicate tighter power supply conditions in the two grids and do not necessarily mean that power interruptions are already occurring.