The Grids That Stop at the Coastline
When Southeast Asian grid planners talk about ASEAN cross-border power interconnectors, the conversation moves quickly from regional summits to water depths, seabed surveys, and cable-laying vessels. The political will for a more integrated ASEAN electricity network has existed for decades, but the region’s geography means many of those links must cross open water. Submarine cables bring a set of engineering, operational, and financial constraints that land-based transmission lines do not share.
The ASEAN Power Grid concept has long envisaged a network of cross-border connections allowing electricity to flow from resource-rich areas to demand centres. Progress has been incremental. The most visible regional project to date, the Lao PDR–Thailand–Malaysia–Singapore Power Integration Project, is largely an overland line, but it demonstrates the alignment needed before physical infrastructure can be built. For the maritime majority of the region, the next step in that integration requires submarine cables. The current status of the ASEAN Power Grid shows how far the institutional framework has come, even as the physical network lags behind.
Why the Sea Changes the Engineering Calculus
Submarine cables are not simply underground cables laid in water. The marine environment introduces several factors that change how a link is designed, operated, and maintained. The two most important are electrical and thermal.
On the electrical side, alternating-current cables have significant capacitance. For long submarine routes, the charging current required to energise the cable can consume much of its thermal capacity, reducing the amount of real power the line can carry. High-voltage direct current (HVDC) avoids this problem, which is why long submarine interconnectors are typically HVDC. Shorter crossings can remain AC if the distance and voltage allow sufficient thermal margin. The crossover point varies with cable design and system voltage, but the principle is consistent: beyond a certain distance, HVDC becomes the more practical option.
On the thermal side, the seabed is not a uniform heat sink. Where a cable is buried in soft sediment, heat dissipation can be poorer than in open water, forcing a lower current rating. Where it lies exposed on rock, mechanical protection becomes the bigger concern. Utilities must therefore combine thermal modelling with marine surveys before committing to a route.
One constraint that rarely appears in regional policy documents is the global shortage of specialised cable-laying and repair vessels. A fault on a terrestrial transmission line can often be located and repaired within days. A fault on a submarine cable in deep water requires a vessel equipped with remotely operated vehicles and jointing crews, and mobilisation lead times can run into months. Only a limited number of such vessels operate worldwide, and they are heavily booked by the offshore wind and telecommunications industries. That bottleneck shapes how seriously utilities treat redundancy and spare capacity when planning submarine interconnectors.
The Commercial Logic of Submarine Interconnectors
The economic case for cross-border transmission in Southeast Asia rests on three pillars: resource diversity, demand complementarity, and reserve sharing. Different parts of the region have very different generation profiles. Laos has hydropower that can be exported during wet seasons; Singapore has a high demand density but limited land for renewable generation; Indonesia and the Philippines have substantial geothermal and solar potential distributed across many islands. A physical connection allows these differences to be traded rather than duplicated.
As examined in a separate article on the economic and reliability case for connecting Southeast Asia’s electricity systems, cross-border links can reduce the need for each country to hold its own reserve margin against its own peak. Shared reserves and access to lower-cost generation can lower overall system costs, but only if the commercial arrangements for using those links are clear. Submarine interconnectors add a further cost layer: marine surveys, cable protection, and the risk of long repair outages mean the upfront cost per kilometre is higher than most terrestrial lines, and the financing needs to reflect that risk.
Regulatory and Market Hurdles Remain
A submarine cable is a physical asset, but its economic usefulness depends on rules that often do not yet exist across ASEAN. Ownership and cost allocation are immediate questions: should a cable between two countries be jointly owned, or should one party lease capacity to the other? What tariffs apply to third parties that want to use the link? Without harmonised grid codes, even a built cable may not be able to operate at full capacity because the two connected systems have different frequency control, voltage, or protection requirements.
The experience of European market coupling offers a useful reference, though not a template. Europe’s internal electricity market took decades to develop, and its progress required institutions to set common rules for cross-border capacity allocation and congestion management. For ASEAN, the relevant near-term question is less about full market coupling and more about the basic frameworks needed to make a physical cable usable. Harmonizing grid codes is often treated as a technical detail, but it is one of the clearest prerequisites for any cross-border flow. Similarly, the lessons from European market coupling show that political commitment to shared rules is as important as the cables themselves.
What Happens Next
Several planned submarine interconnector projects in Southeast Asia are moving from concept studies to feasibility assessments, driven by national renewable targets and the desire to share surplus generation. Multilateral development banks have shown interest in financing regional transmission, recognising that the benefits of interconnection extend beyond the two countries directly connected. Marine spatial planning and environmental permitting add time to project schedules, however, and unresolved maritime boundaries can delay or reroute some links.
The physical layer alone does not integrate ASEAN’s grids. Market rules, grid codes, and commercial agreements must evolve in parallel. But without submarine cables, the broader integration agenda has little to move electrons over. The direction of travel points toward more cross-border marine links, but the pace depends on how quickly the non-physical foundations catch up.
References
- IEA — World Energy Outlook 2025: regional electricity demand growth and cross-border trade trends.
