Grid Bottlenecks Force Solar Curtailment Across Southeast Asia
Solar capacity installed across Vietnam, the Philippines and Thailand has outpaced the transmission infrastructure needed to carry it, prompting grid operators in all three countries to curtail output from utility-scale plants during peak generation hours. Vietnam Electricity, the state utility known as EVN, confirmed in a filing to the Ministry of Industry and Trade that curtailment affected roughly 8 percent of registered solar output in the southern provinces during the first half of 2026, concentrated in Ninh Thuan and Binh Thuan, where developers built plants faster than the 500-kilovolt transmission lines connecting them to demand centers around Ho Chi Minh City.
The Philippines faces a similar pattern on a smaller scale. The National Grid Corporation of the Philippines reported congestion on lines feeding Luzon from solar farms in Nueva Ecija and Tarlac, provinces that added a combined 900 megawatts of utility-scale capacity between 2023 and 2025 under the feed-in incentive scheme administered by the Department of Energy. Grid operator officials said in a briefing to the Energy Regulatory Commission that new transmission segments connecting those provinces to Metro Manila are not scheduled for completion before 2028.
Battery Storage Enters the Mix, Slowly
Thailand's Provincial Electricity Authority has begun pairing new solar approvals with mandatory battery storage requirements in three northeastern provinces where curtailment has been highest, following a 2025 policy revision. Developers must now include at least two hours of storage capacity for any new solar project exceeding 10 megawatts in the affected zones, according to the authority's public tender documents. The requirement adds an estimated 15 to 20 percent to project capital costs, based on figures cited by the Thai Solar Energy Industries Association in comments submitted during the policy's public consultation period.
- Vietnam's Power Development Plan 8, revised in 2023, calls for 6 gigawatts of battery storage by 2030, though only a fraction of that capacity has reached financial close.
- The Asian Development Bank approved a 300 million US dollar loan package in 2025 to support grid modernization in Vietnam's southern provinces, according to the bank's project database.
- Malaysia's Energy Commission has taken a different approach, capping new solar interconnection applications in Kedah and Perlis rather than mandating storage, and industry groups say the moratorium has no confirmed end date.
Cross-Border Transmission as a Partial Fix
Regional planners increasingly point to interconnection between grids, rather than domestic transmission alone, as a release valve for curtailment. The Laos-Thailand-Malaysia-Singapore Power Integration Project, which has moved limited volumes of hydropower southward since 2022, is being studied by ASEAN's energy ministers as a template for routing surplus solar generation across borders during peak daylight hours, when domestic demand in the exporting country is often lower than supply. Officials from the ASEAN Centre for Energy said in a working paper published this year that expanding such interconnections would require harmonized technical standards that several member states have not yet adopted.
Singapore's Energy Market Authority has separately approved import licenses for solar-linked power from Indonesia and Cambodia under its cross-border electricity import program, aiming for up to 4 gigawatts of imported low-carbon electricity by 2035. Developers involved in the Cambodian project told Singaporean trade media that curtailment risk in the exporting country was a key factor in structuring the power purchase agreement, with penalty clauses tied to guaranteed minimum offtake volumes rather than fixed capacity payments.
Manufacturers Watch Policy Shifts Closely
The curtailment trend has drawn attention from panel manufacturers with regional assembly operations, since reduced generation hours affect the economics of power purchase agreements signed years before construction began. Jinko Solar's Southeast Asia unit said in an investor update that project financing terms across the region increasingly include curtailment-risk clauses that were rare before 2024. Developers interviewed by regional energy publications have pointed to Vietnam's stop-start approach to transmission investment as the more immediate constraint, ahead of policy questions around tariffs or subsidies.
Indonesia's state utility PLN has avoided the worst of the bottleneck so far because its solar buildout remains smaller relative to installed thermal capacity, but the utility's own 2025 electricity supply business plan flags transmission capacity in South Sulawesi and East Nusa Tenggara as a constraint for planned additions through 2030. PLN has committed to adding roughly 4,000 circuit-kilometers of new high-voltage lines nationwide over the plan period, according to the document filed with Indonesia's Ministry of Energy and Mineral Resources.
Regional grid operators are scheduled to discuss cross-border interconnection standards at the ASEAN Power Grid working group meeting in Vientiane in October, where transmission financing gaps are listed as a standing agenda item.