Underwater Solar and the Rupiah: Coastal Power, Aquaculture Sensors, and Diesel-Backup Exposure

Rupiah Stability Watch · 2026-09-16

The premise

Underwater solar will not defend the rupiah. It will not replace grid power, change Indonesia’s national energy balance, or remove the country’s dependence on imported petroleum products. The narrower question is more useful: whether a small, pre-commercial solar technology could someday keep coastal evidence and service nodes alive when diesel logistics, batteries, storms, haze, or earthquakes make ordinary operations fragile.

That makes it a watchlist item, not a procurement recommendation.

The new signal is specific. Research reported by pv magazine says a China-led team demonstrated lead-halide perovskite solar cells operating 10 meters below the South China Sea surface. The reported figures are impressive for a submerged device but small in system terms: 34.71% power-conversion efficiency under simulated 10-meter conditions, almost no degradation after 1,160 hours in that simulated environment, and 324 mWh generated over two hours at 10 meters when integrated with underwater robots near the Weizhou Islands. The researchers also noted that earlier underwater-solar studies had mostly stayed at two meters or less.

For Indonesia, the relevant ledger is not megawatts. It is degraded-mode days: the day a ferry route loses visibility data, an aquaculture pond loses water-quality readings, a tide or tsunami node goes offline, a port sensor needs a generator run, or a reef-monitoring site stops publishing data just when coastal stress is becoming economically visible.

That is why this piece belongs beside Rupiah Stability Watch’s earlier work on underwater visibility, civic sensor nodes, neglected energy buffers, blue-green coastal buffers, coral reef stress, small electric logistics, battery storage, and haze measurement gaps. The through-line is not gadget optimism. It is the operating ledger: Indonesia’s rupiah is pressured less by one dramatic failure than by repeated small outages that turn fuel, food, trust, and insurance into imported-cost problems.

What the evidence supports

The evidence supports three modest claims.

First, underwater photovoltaics have moved from shallow demonstration toward a more practical depth. The pv magazine report describes a 10-meter deployment, not just a lab cell under a film of water. The technology is still not proven as a durable Indonesian coastal asset. But 10 meters matters because many useful monitoring tasks live in the first coastal layer: aquaculture pens, harbour approaches, reefs, moored instruments, underwater cameras, turbidity sensors, and communications relays.

Second, the rupiah channel is fuel and maintenance exposure at the edge, not national generation. Indonesia’s petroleum ledger is already exposed. The U.S. Energy Information Administration’s August 2025 country brief put Indonesia’s 2024 petroleum-and-liquids consumption at 1.7 million barrels per day, while production was 868,000 barrels per day. It also reported that petroleum product imports rose 6.4% in 2024 to 791,000 barrels per day, with diesel and gasoil accounting for 16% of those product imports — about 126,560 barrels per day. Indonesia’s own 2024 energy handbook reported 2024 domestic fuel sales of 82.9 million kiloliters, fuel imports of 28.1 million kiloliters, and LPG imports of 6.9 million tons.

A submerged solar cell on a sensor will not move those totals. But the totals explain why every recurring diesel hour at the edge deserves scrutiny. A port authority, fish farm, reef team, or disaster office that avoids a generator visit has avoided more than a litre of fuel. It has avoided a chain of imported fuel, boat time, battery replacement, and deferred maintenance.

Third, Indonesia has enough coastal operating use cases for the question to be real. World Bank data, sourced to FAO, records Indonesia’s 2024 aquaculture production at about 15.75 million metric tons. That does not mean underwater solar should be installed across ponds and cages. It means the monitoring surface is large: dissolved oxygen, temperature, salinity, turbidity, pH, disease risk, feed control, pump status, weather, and cold-chain coordination. In those settings, power is valuable when it preserves readings and alarms, not when it produces impressive capacity numbers.

A nearshore comparison helps keep scale honest. Ocean Sun says a 160 kWp floating-solar installation at Emilsen Fisk’s fish farm in Norway is expected to generate 80,000–90,000 kWh annually and cut diesel use and emissions. That is floating solar, not underwater solar, and Norway is not Indonesia. But it shows the general operating fact: coastal aquaculture power is already an energy-resilience problem, and diesel displacement can matter before any technology becomes nationally significant.

The Indonesian use cases that are plausible

The most plausible Indonesian cases are small, exposed, and measurement-heavy.

Aquaculture monitoring is the first. A submerged or semi-submerged power source would be useful only if it improves sensor uptime without adding a harder maintenance burden than the battery or surface panel it replaces. The right first test is not “how many panels can be installed?” It is whether water-quality data remain available during storms, haze, supply disruption, disease events, and generator downtime.

Port and ferry visibility is the second. Rupiah Stability Watch has already treated underwater visibility as a logistics signal: shallow disruptions at ports and ferry corridors become larger costs when delays, accidents, spoilage, and rerouting accumulate. A low-power underwater or submerged device might support turbidity, current, camera, or buoy systems. The currency link would be indirect but real: fewer blind operating hours, fewer diesel inspection trips, and faster public records after an incident.

Reef and coastal-ecosystem monitoring is the third. Coral stress, fishery pressure, and tourism confidence all need continuous records. A cheap power source for submerged reef instruments could make those records more complete. But this is also where ecological caution is sharpest: a lead-halide perovskite module in marine water must be treated as an environmental object, not just an energy object.

Disaster-warning and tide nodes are the fourth. BMKG’s remarks in The ASEAN Magazine emphasized systematic observation, standard measurement, data exchange, and the gap between technological warning and community action. Indonesia’s warning problem is not only detection; it is continuity, maintenance, and trust. Antara reported in February 2025 that BMKG’s earthquake and tsunami mitigation budget line of Rp41.9 billion was preserved even as the agency’s broader budget was cut from an initial Rp2.8 trillion to a revised Rp1.7 trillion. That is the setting in which small power improvements matter: not as substitutes for public funding, but as ways to reduce the weak points that maintenance budgets have to chase.

Navigation aids and small island service nodes are the fifth. Surface solar already serves many of these functions. Underwater solar would have to beat existing surface panels on theft resistance, storm survivability, shading, salt exposure, visual footprint, or colocated underwater sensing. If it cannot beat surface solar on a named operating problem, it is a curiosity.

What the evidence does not support

The evidence does not support an Indonesian roll-out.

The reported underwater cell is a research-stage perovskite device. Perovskites can be efficient, and they can also be sensitive to moisture, encapsulation failures, ion migration, and end-of-life handling. In this case, the chemistry reported is lead-halide. That matters. A marine deployment would need proof of encapsulation, retrieval, recycling, and failure containment before procurement officers treat it as benign.

The evidence also does not support a claim that underwater solar is better than ordinary surface solar for most coastal needs. Surface panels are cheaper, more mature, easier to inspect, easier to repair, and easier to connect to batteries. Underwater solar has to earn its place where the load is underwater, the installation benefits from being submerged, or the surface environment creates specific problems: theft, storm exposure, marine traffic, visual constraints, or long cable runs.

Nor does the evidence support a meaningful national fuel-saving claim. If diesel and gasoil imports are around 126,560 barrels per day on the EIA’s 2024 product-import breakdown, sensor-level power savings are too small to register directly. The honest rupiah channel is second-order: fewer degraded-mode days, fewer emergency logistics trips, better fish and port records, less spoilage, and more credible disaster and environmental data.

The least-harm path

The least-harm path is a watchlist with field tests, not a program.

A serious Indonesian test would begin with three or four monitored sites, each tied to a real public operating problem: one aquaculture cluster, one port or ferry corridor, one reef or marine protected area, and one disaster or tide-monitoring node. Each site should compare underwater solar against the boring alternatives: surface solar plus battery, larger battery alone, scheduled battery swap, cable from shore, and hybrid diesel-solar backup.

The test should publish five numbers.

• Diesel litres displaced, including boat trips for maintenance.
• Sensor uptime during storms, haze, floods, quakes, and ordinary supply interruptions.
• Import content: panel, encapsulation, battery, inverter, telemetry, software, and service contract.
• Local repair share: which failures can be fixed by Indonesian technicians with stocked parts.
• Data availability: whether readings are public, timestamped, auditable, and preserved after outages.

The procurement rule should be plain: no purchase without retrieval and disposal obligations, no marine deployment without ecological review, and no “innovation” budget unless the data are public enough to improve the operating ledger.

That last condition matters. A sensor that does not publish usable records is not a resilience asset. It is a submerged invoice.

What policymakers should watch

The watchlist should stay narrow.

Watch whether the 10-meter perovskite result is reproduced by independent teams in seawater, turbid water, tropical biofouling conditions, and longer deployments. Watch whether encapsulation survives heat, salt, abrasion, fishing gear, storms, and maintenance neglect. Watch whether module makers disclose lead containment and end-of-life pathways. Watch whether batteries and telemetry, not the cell, become the real import bill.

Watch Indonesian pilots only if they name the avoided diesel work. “Powering coastal sensors” is too vague. “Reducing generator visits to an aquaculture oxygen-monitoring buoy by 40% while publishing continuous dissolved-oxygen data” is a claim that can be audited.

Watch whether the technology strengthens existing public systems rather than bypassing them. BMKG, port authorities, fisheries offices, local governments, universities, and community monitors need interoperable data more than they need isolated devices. The lesson from haze records and disaster warnings is the same: a measurement chain is only as strong as its weakest public link.

What I am uncertain about

The largest uncertainty is durability in Indonesian water. A 1,160-hour simulated result and a short field deployment are not the same as multi-season survival in warm, fouling, sedimented, storm-exposed coastal sites.

The second uncertainty is cost. If the module is cheap but the enclosure, battery, telemetry, imported service contract, and retrieval obligation are expensive, the rupiah ledger may worsen rather than improve.

The third uncertainty is governance. Indonesia does not need another device category that produces proprietary records, breaks quietly, and requires foreign-currency maintenance. The technology becomes relevant only if it makes public operating records more complete at lower total exposure.

The conclusion is therefore restrained. Underwater solar is mostly a technology curiosity today. It becomes a rupiah-resilience watchlist item only where it powers the evidence chain itself: coastal sensors, aquaculture alarms, reef records, navigation aids, and disaster-warning nodes that keep Indonesia’s operating ledger visible when stress arrives.