The National Grid Corporation of the Philippines (NGCP) is calling for more stringent grid-integration policies following the entry of the massive Terra Solar project, warning that the surge in intermittent renewable energy could jeopardize the stability of the nation’s power system.

While the privately led transmission operator welcomed the 2,500-megawatt development as a boost to the country’s clean energy transition, NGCP cautioned that such a significant infusion of variable power requires more than just infrastructure.

The Meralco PowerGen Corp.’s Terra Solar project includes a 1,125-megawatt battery energy storage system designed to sustain output for four hours, yet NGCP maintained that the inherent volatility of solar power remains an operational hurdle.

“Some technologies (such as wind or solar) are, by nature, variable or supply intermittently, and therefore need to be handled more carefully,” NGCP said in a statement on Wednesday, Jan. 7.

“There are operational considerations that must be carefully managed on both sides of the transmission, and more importantly, on the side of the generating plant. Doing so will help grid stability and mitigate any fluctuations inherent in variable renewable energy sources (VREs). In addition, all required facilities on the plant side, as determined in the system impact study, must be fully complied with.”

The company is now urging the Department of Energy (DOE) to adopt more progressive policies regarding variable renewable energy. NGCP argued that the entry of bulk solar power must be matched by dependable baseload plants and fast-ramping resources to prevent frequency fluctuations and potential outages.

Under current Philippine law, solar farms are classified as “must-dispatch,” meaning they receive priority scheduling on the grid regardless of their impact on system stability.

Operating experience at existing facilities has already exposed vulnerabilities in the network. NGCP cited a recent incident in North Luzon where unstable output from renewable sources triggered voltage fluctuations, requiring emergency mitigation. At the San Marcelino solar farm in Zambales, brief cloud cover has been known to cause sudden drops in generation of up to 300 megawatts.

Because conventional coal-fired plants have long ramping times, they are often unable to react quickly enough to these shifts, leaving the grid vulnerable to under-frequency load shedding or rotating brownouts.

Terra Solar is slated to provide 850 megawatts to Manila Electric Co. primarily during daylight hours, while the remaining 1,650 megawatts will be sold through the Wholesale Electricity Spot Market.

NGCP noted that the project’s developer must fully comply with all facility requirements identified in its system impact study to mitigate these inherent risks.

The grid operator stressed that while battery systems are a critical “fast-acting resource” for maintaining frequency, they are only one part of a complex balancing act required to integrate thousands of megawatts of green energy into a system traditionally reliant on steady thermal power.