The Visayas power grid faced severe supply constraints on Thursday, August 13, when it was placed under a red alert for the sixth time as available power capacity fell well below the forecast peak demand, according to the National Grid Corporation of the Philippines (NGCP). In an 8 a.m. advisory, the NGCP reported an available capacity of 2,283 megawatts (MW) against a forecast peak demand of 2,360 MW, creating a 77-MW shortfall across the region.
Grid Alert Statuses and Operating Margins
The National Grid Corporation of the Philippines (NGCP) enforced a red alert across the Visayas grid from 6 p.m. to 8 p.m. on Thursday, August 13. Based on standard grid criteria, authorities trigger a red alert whenever generation capacity falls short of what is required to satisfy consumer needs alongside the necessary regulating reserves for grid frequency stability, thereby elevating the likelihood of rolling blackouts unless usage drops. In addition to the red alert, yellow alerts were declared from 2 p.m. to 6 p.m. and again from 8 p.m. to 9 p.m. A yellow alert becomes necessary when available operating margins drop below the specific contingency reserve threshold required to safely handle the sudden disconnection of the largest running generator without impacting power consumers. In separate coverage of the same period, Business Inquirer noted that the NGCP’s initial advisory issued late Wednesday had also encompassed the Visayas grid under a red alert from 3 p.m. to 9 p.m. and a yellow alert from 9 p.m. to 11 p.m., driven by thin power supply and the temporary tripping of the Daanglungsod-CalongCalong 138-kV L1 and Daanglungsod-Magdugo 138-kV L1 transmission lines. Both of those transmission lines resumed operations at 4:17 p.m. on Wednesday, restoring connections to the affected power facilities according to Business Inquirer.
Causes of the Visayas Power Shortfall
The tightening power supply was driven by multiple simultaneous generation and transmission constraints. According to the National Grid Corporation of the Philippines (NGCP), the alerts stemmed from the continued unavailability of three major coal-fired units in the Visayas, combined with reduced power imports from Mindanao. GNPK 2 underwent a planned maintenance service, while GNPK 1 experienced an unplanned halt triggered by a leaking boiler tube, both of which contributed to the drop in incoming power. High forecast system demand further exacerbated the tight supply situation.
Forced Outages and Plant Derations Across the Region
The tight conditions highlight a wider issue of widespread generation unavailability across the Visayas grid. NGCP figures revealed that 27 generating facilities experienced forced shutdowns, with these units dropping off the network incrementally over multiple years: six in August, two in July, three in June, seven in May, one in March, three in 2025, two in 2024, two in 2023, and one dating back to 2021. Furthermore, 13 additional plants were operating at derated capacities. Combined, these forced outages and derations stripped 903.2 MW of capacity out of the grid. While restoring all of that offline capacity would easily cover Thursday’s projected 77-MW supply deficit, the continued downtime of these facilities means the grid could remain vulnerable to subsequent shocks if plant repairs and transmission stability are not rapidly addressed.
