Grid bottleneck leaves Visayas short of Luzon, Mindanao power

ILOILO CITY — Tight power supply in the Visayas is being compounded by the limited capacity of transmission lines to bring additional electricity from Luzon and Mindanao to the region, according to the Department of Energy (DOE).

The Visayas grid has been placed under recurring yellow and red alerts, the latter signaling that available supply is insufficient to meet demand and may require rotating outages, while a yellow alert means contingency reserves have fallen below required levels.

DOE Undersecretary Mario Marasigan said the Visayas receives electricity from both Luzon and Mindanao through the country’s interconnected transmission grid, which is operated by the National Grid Corporation of the Philippines (NGCP).

Power from Luzon reaches the Visayas through the Luzon-Visayas high-voltage direct current (HVDC) interconnection, which links Sorsogon in Luzon to Leyte in the Visayas.

From Leyte and Samar, electricity can be transmitted onward to Cebu and other parts of the Visayas grid, with Panay at the end of the line.

The region can also receive electricity from Mindanao through the Mindanao-Visayas Interconnection Project (MVIP), which allows Mindanao to export up to 450 megawatts (MW) to the Visayas when sufficient capacity is available.

The MVIP, a submarine cable link between Cebu and Zamboanga del Norte, went into full commercial operation in early 2024, connecting the Mindanao grid to the rest of the country for the first time.

However, Marasigan said the existing transmission capacity limits how much additional power can be delivered to the Visayas.

“As far as the transfer of capacities from Luzon, our limitation for the transfer capacity of the line from Luzon to Visayas is 250 MW. That is the limit. We cannot go higher because that is the limitation based on the capacity of the line,” Marasigan said during a House Committee on Energy hearing on Monday, Sept. 21.

“For Mindanao, the transfer capacity is 450 MW,” he added.

Marasigan said the existing transmission facilities need to be upgraded to allow more electricity from Luzon to be delivered to the Visayas.

“Perhaps it is time for us to significantly increase the capacity coming from Luzon because a larger transfer of power capacity from Luzon to the Visayas would greatly help,” Marasigan added.

The DOE official also clarified that the 250 MW figure for Luzon-to-Visayas transfers should not be interpreted as a guaranteed amount that can be delivered at all times.

“The 250 MW, we cannot guarantee that it is 250 MW every time. There are still limitations,” he said.

While the line has a higher physical line capacity of 450 MW, Marasigan said the actual amount of power that can be transferred at a particular time is determined by system operating conditions.

“That is already part of the operation of our system. The actual transfer at a specific time is determined by the system operator,” he said.

He explained that NGCP, as system operator, must consider the interaction of power plants and transmission facilities along the network to prevent overloading.

For example, Marasigan said, if a 400 MW power plant is already operating in an area and another 250 MW is brought in through a transmission line with a 440 MW physical capacity, the combined flow could exceed the safe operating limit of a particular section of the network.

“The interaction of the plant in the area and the line is being monitored by system operations because there could be an overload,” he said.

He said system operators therefore have to regulate how much electricity is transferred at a given time to maintain the stability of the grid.

“At that particular time of operation, the system operator needs to determine how much the line can safely transfer. Otherwise, the system will not be balanced and it could result in an outage caused by the line,” Marasigan said.

Marasigan also acknowledged delays in the implementation of some NGCP transmission projects.

At the same hearing, NGCP acknowledged that some transmission projects have been delayed due to external factors, particularly difficulties in securing rights of way.

NGCP, a privately owned concessionaire, has held the franchise to operate and maintain the national transmission grid since 2009 under a 25-year franchise granted by Congress in 2008.

Local generation still needed

Despite the need to expand transmission capacity, Marasigan said the Visayas also needs additional generation facilities within its different subregions to ensure that each area can continue operating independently in case of transmission disruptions.

“What we need are generation capacities in each of the subgroups to ensure that if a line trips, the island can still operate independently,” he said.

Marasigan said the Visayas has a total installed generation capacity of about 4,138 MW, which, on paper, is enough to supply the region’s requirements.

DOE data showed that the Negros Island Region has 1,099 MW of installed generation capacity, Western Visayas has 765 MW, Central Visayas has 1,256 MW, and Eastern Visayas has 1,017 MW.

Negros Island’s generation capacity is largely renewable, accounting for about 1,068 MW. The island currently has no coal-fired power plant.

Coal-fired plants, which generally provide baseload power, are concentrated in Western and Central Visayas.

Western Visayas has 452 MW of coal-fired capacity, while Central Visayas has 894 MW.

However, Marasigan said installed capacity does not necessarily translate into available capacity at any given time.

“Unfortunately, not all these power plants are capable of producing power based on their installed capacity at the moment,” he said.

Renewable energy sources, particularly solar, are subject to operating conditions. Solar plants generate power only during daylight hours.

Hydroelectric facilities may experience reduced output when water levels are low.

Biomass plants may also have reduced generation during the off-milling season, Marasigan said.

“So if there is a plant that goes on outage, we become short,” he said.