Cebu power deficit drags Visayas grid into repeated alerts

By Francis Allan L. Angelo

ILOILO CITY — Cebu’s simulated 422-megawatt shortfall during the evening peak has emerged as the weak link in the Visayas grid, forcing the island to draw electricity from four separate grids at the same time to keep supply and demand in balance.

Engr. Keelvin Dajao of the Department of Energy presented the power load transfer simulation before the Iloilo Business Club last week, showing every other island or subgrid with a surplus while Cebu alone faced a substantial deficit.

The simulation modeled a normal weekday scenario during the evening peak of approximately 6 p.m. to 8 p.m.

Cebu registered a peak demand of 1,077 MW against a dependable capacity of 655 MW, leaving the negative 422-MW reserve at the center of the presentation.

The imbalance helps explain why consumers in Iloilo and elsewhere in the Visayas can experience power interruptions during grid alerts even when their own islands have enough generation to meet local demand.

Under the simulation, Cebu covers the deficit by drawing roughly 200 MW from Leyte-Samar through the 250-MW Cebu-Leyte-Samar interconnection, about 178 MW through the Bohol corridor, and around 46 MW from Mindanao through the 450-MW Cebu-Mindanao link.

The pressure does not stop there.

Luzon sends about 200 MW to Leyte-Samar through the 440-MW Luzon-Leyte-Samar interconnection, effectively replenishing the power that Leyte-Samar transfers toward Cebu.

Panay, meanwhile, sends its entire 40-MW reserve toward Negros under the simulated conditions.

The result is a tightly interconnected system in which Cebu can hold its supply-demand balance only by drawing power through multiple transmission corridors simultaneously.

The DOE presentation showed Cebu accounting for about 45% of Visayas demand but only 26% of the region’s available generating capacity.

Across the Visayas, the simulated generation surplus amounts to only about 126 MW, equivalent to 5.2% of regional demand.

That leaves little room to absorb an unexpected loss of a major generating unit.

Much of the available surplus is also geographically separated from the region’s biggest load center.

Leyte-Samar, with a peak demand of 312 MW against a dependable capacity of 783 MW, holds a significant portion of the excess supply, but transfers toward Cebu are constrained by the 250-MW Cebu-Leyte-Samar interconnection.

Panay and Negros, by comparison, carry simulated reserves of 8.4% and 7.6%, respectively, while Bohol has only about 5 MW of headroom.

Panay posted a peak demand of 474 MW against a dependable capacity of 514 MW, Negros 419 MW against 451 MW, and Bohol 128 MW against 133 MW.

The figures illustrate why local generation sufficiency does not necessarily protect an island from manual load dropping when the interconnected Visayas grid comes under stress.

If a major Cebu generating unit trips or a critical transmission link becomes unavailable, the resulting imbalance can threaten grid frequency across the interconnected system.

The National Grid Corporation of the Philippines may then order distribution utilities in other parts of the Visayas to shed load to stabilize the grid, meaning consumers in Iloilo and Panay can lose electricity even when Panay itself has enough generation for its local requirements.

The problem has become increasingly visible this week as the Visayas grid repeatedly entered yellow and red alert conditions amid prolonged and forced outages of generating plants.

As of Friday morning, Aug. 28, some 979.6 MW of capacity was unavailable to the Visayas grid.

NGCP cited the unavailability of major coal-fired units TVI 1, TVI 2, and KSPC 1, along with limited imports from Mindanao, as factors behind Friday’s red and yellow alert declarations.

The DOE simulation points to a deeper issue beyond the immediate plant outages.

The Visayas does not merely need additional generating capacity. It needs sufficient reserves in the right locations and enough transmission capacity to move electricity from areas with surplus generation to major demand centers when the system is under stress.

For Iloilo consumers, that means Panay’s own power balance tells only part of the story.

As long as the islands operate as an interconnected grid with tight reserves and transmission constraints, a serious shortage hundreds of kilometers away can still switch off the lights at home.