The Mindanao power grid came under renewed pressure on Wednesday, September 9, as the National Grid Corporation of the Philippines (NGCP) placed the island grid under yellow alert because of limited generating capacity.
But the situation later deteriorated.
According to an updated NGCP advisory reported by the Philippine News Agency (PNA), the Mindanao grid was subsequently placed under red alert during parts of the afternoon and evening, underscoring how quickly a tight power reserve can become a more serious supply problem.
This makes the original GMA report about the yellow alert only part of the developing story.
From yellow alert to red alert
Earlier on Wednesday, NGCP reported that Mindanao had around 2,731 megawatts (MW) of available capacity, while peak demand was projected at approximately 2,600 MW.
The yellow alert was scheduled from 1 p.m. to 9 p.m.
NGCP said the forced outage of GNPower Kauswagan Units 2 and 3 was among the major factors behind the tight operating margin. PNA reported that 13 Mindanao power plants had already become unavailable during September, while another 16 had been unavailable since 2024. Six additional plants were operating at reduced or derated capacity.
Later in the day, however, available capacity fell further.
At around 2 p.m., NGCP reported approximately 2,641 MW of available capacity against 2,591 MW in demand, prompting red-alert periods from 2 p.m. to 4 p.m. and 5 p.m. to 8 p.m. Yellow alerts were also scheduled between those periods and later in the evening.
The reduction was linked in part to the derated capacity of Therma Marine Inc. Mobile 2 in Agusan del Norte, together with other unavailable or derated diesel- and hydropower facilities. NGCP said the total capacity loss had reached about 827.7 MW.
What does a yellow alert actually mean?
A yellow alert does not automatically mean that consumers are experiencing brownouts.
It means the grid still has enough capacity to meet demand, but its operating margin is below the required contingency reserve.
In other words, the system has less room to absorb another unexpected power-plant failure or a sudden jump in electricity consumption.
A red alert is more serious.
NGCP uses the red-alert classification when available supply is insufficient to meet demand and the transmission grid’s regulating requirement. Under such conditions, controlled or rotational power interruptions can become necessary to protect the wider grid.
This is not an isolated Mindanao problem
The latest alert follows several days of power-supply pressure across the country.
On September 8, Mindanao was again placed under yellow alert, with NGCP reporting about 2,805 MW of capacity against expected peak demand of 2,627 MW.
At that time, NGCP identified the unavailability of GNPower Kauswagan Units 2 and 3 as a major factor. Around 756.9 MW of capacity was unavailable because of plant outages and derated generation.
The previous day’s situation was even more severe.
The Inquirer reported that Mindanao experienced alternating red and yellow alerts on September 8 after the unexpected tripping of Minergy Coal Unit 2 removed another 50 MW from the system while the demand forecast increased by roughly 100 MW.
The repeated alerts show that Mindanao’s power system is operating with increasingly thin reserves whenever multiple generating units are unavailable at the same time.
Why are so many plants unavailable?
NGCP’s recent advisories show that the problem is not being caused by a single generating facility.
Several plants are dealing with forced outages, maintenance issues or reduced operating capacity.
On September 9, NGCP reported that 15 Mindanao plants were unavailable during the month, while another 15 had been unavailable since 2024. Eight additional plants were operating at derated capacity. Together, these conditions represented an estimated 827.7 MW in lost capacity, according to PNA.
This continuing pattern is significant because the Mindanao grid must maintain enough reserve not only for ordinary electricity consumption but also for unexpected disruptions.
When several large plants are simultaneously offline, even a relatively modest increase in demand can rapidly narrow the margin.
Mindanao also matters to the Visayas
The situation has implications beyond Mindanao.
The Philippines’ interconnected grid allows power to move between regions, meaning reduced generation in Mindanao can also affect the country’s ability to support the Visayas during periods of tight supply.
PNA reported that lower power imports from Mindanao were among the factors contributing to supply problems in the Visayas.
The Visayas grid itself was placed under a lengthy red alert on September 9, with PNA reporting available capacity of about 2,124 MW against expected peak demand of 2,555 MW.
That means the country is confronting simultaneous reliability concerns in two major island grids.
Government is pushing new power capacity
The government has also been working to increase Mindanao’s generation capacity.
In July, the Department of Energy announced that Phase 1 of the Tantangan Solar Power Project in Sultan Kudarat had been energized. The first phase provides 74.5 MWp, while the full project is targeted to reach 99 MWp, alongside a battery energy storage system capable of delivering 4 MW and storing 16 MWh.
The DOE said the project is intended to strengthen Mindanao’s power supply and diversify its generation mix.
However, renewable projects such as solar do not immediately eliminate the need for sufficient dispatchable and reserve capacity, particularly during periods when demand rises or conventional generating units unexpectedly go offline.
What consumers should watch
For ordinary consumers, the most important distinction is between a yellow alert and a red alert.
A yellow alert is essentially a warning that the grid’s safety cushion has become thin.
A red alert means the system has entered a much more critical condition, with the possibility of controlled interruptions increasing if supply cannot keep pace with demand.
Consumers should therefore continue monitoring announcements from NGCP and their local distribution utilities, particularly during peak-demand periods.
NGCP itself has repeatedly urged stakeholders to ensure generating plants remain available and has warned that unplanned outages of critical facilities can be a major factor behind power interruptions.
The bigger warning for Mindanao
The latest developments reveal a bigger issue than a single day’s yellow alert.
Mindanao’s electricity system is increasingly vulnerable whenever multiple power plants are simultaneously unavailable and demand remains high.
Wednesday’s progression from yellow alert to red-alert periods is a reminder of how quickly that margin can disappear.
And with the Visayas also facing severe supply constraints, the question is no longer simply whether Mindanao has enough electricity today.
It is whether the country’s interconnected power system has enough reserve when the next major plant unexpectedly goes offline.
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