Beyond Oʻahu: How The Other Hawaiian Islands Will Decarbonize

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Oʻahu was the test case, but it was never the whole question. The real question for Hawaiʻi was always whether the same logic that makes decarbonization viable on the most populous island would also hold across the rest of the inhabited archipelago. If Oʻahu could get to a clean, resilient, lower-carbon energy system with electrification, solar, storage, demand shifting, selective wind, and a narrow role for firming resources, did that mean the same architecture would work on Maui, Hawaiʻi Island, Kauaʻi, Molokaʻi, Lānaʻi, and even Niʻihau in some form? Or was Oʻahu a special case, shaped by its load, density, and infrastructure in ways that would not carry across to the neighbor islands.

The answer is that the broad architecture does carry across, and that is encouraging. But it does not carry across in a lazy or uniform way. Hawaiʻi is not one energy problem repeated several times. It is a family of related island problems, all sharing the same direction but not the same proportions. The common pattern is still clear. Electrify as much end use as possible. Build around local renewables, especially solar. Add storage and demand flexibility so local generation can serve more of the day. Use wind where it makes sense economically, ecologically, and socially. Keep combustion on a narrowing leash, with retained firm capacity where reliability still requires it. But once you step away from Oʻahu, three things start to matter more. Small grids change the physics and operating margins. Interisland transport starts to matter more. And the resource mix becomes more island-specific, especially on Hawaiʻi Island and Kauaʻi.

The first lesson from looking beyond Oʻahu is that smaller grids do not make decarbonization less possible, but they do make it less forgiving. Continental systems have size, diversity, and interconnection to absorb mistakes. If a utility-scale solar plant trips offline in California or Texas, the broader system can usually absorb it. If a charging cluster ramps unexpectedly on a continental grid, it is a planning issue, not a system-wide event. On smaller islands, every increment matters more. The same 5 MW of new charging load that would disappear into the noise on a mainland grid can become material on Molokaʻi or Lānaʻi. The same increase in rooftop solar that looks welcome in annual energy terms can create midday operating challenges if there is not enough storage, controllable demand, or retained spinning capability. As a result, the smaller the island, the more the energy transition becomes an exercise in operating stability, reserve margins, and local balancing, not just annual energy volumes.

That matters because there is a temptation to look at the neighbor islands and assume that having more open land or lower demand automatically makes decarbonization easier than on Oʻahu. In one sense that is true. The National Renewable Energy Laboratory and Hawaiian Electric resource work found that Oʻahu had about 97 MW of constrained onshore wind potential, while Maui had about 648 MW, Molokaʻi about 593 MW, Lānaʻi about 451 MW, and Hawaiʻi Island about 1,855 MW. On the utility-scale solar side, Oʻahu had about 1,271 MW of constrained potential, Maui about 1,274 MW, Molokaʻi about 1,442 MW, Lānaʻi about 919 MW, and Hawaiʻi Island about 14,260 MW. Those are not small differences. Oʻahu is the most constrained major island for large-scale renewable buildout. The other islands often do have more technical room for wind and solar.

But more room for projects is not the same thing as lower overall constraint. The bottleneck often shifts. On Maui, Hawaiian Electric’s renewable energy zone work has pointed to transmission distance, substation upgrades, and voltage support as important limits. On Hawaiʻi Island, grid studies have shown that generation has to be geographically balanced because too much concentration in one region creates cross-island congestion and voltage problems. On Kauaʻi, the issue is not just resource quality but ecological compatibility, with the Hawaiʻi State Energy Office and Kauaʻi Island Utility Cooperative both tied to a real constraint around endangered seabirds that has limited onshore wind development. On Molokaʻi and Lānaʻi, the issue is not land scarcity so much as the fact that small systems have narrow margins and limited tolerance for imbalance. The practical conclusion is that the neighbor islands often have more siting room than Oʻahu, but they do not have fewer planning constraints. They just have different ones.

Interisland transport sharpens this. It is one thing to decarbonize island electricity in the abstract. It is another to do it while assuming that some share of interisland aviation and marine transport also electrifies. Hawaiʻi’s Department of Transportation has already put sea and air interisland transportation inside its statewide zero-emission framing, even while acknowledging in its planning documents that aviation and marine are unlikely to reach zero emissions on the same timetable as surface transport. That is a sensible stance. The question is not whether electric planes and interisland electric vessels change the overall thesis. They do not. The question is what they do to local load shapes, airport and harbor infrastructure, and storage requirements.

Electric planes are the easier part of that future to imagine. My work as an advisor to electric aviation startups, my technoeconomic assessments of multiple aviation decarbonization pathways, and my discussions with CTOs, aerospace engineers and entrepreneurs in electric aviation make it clear that interisland aviation will be able to electrify. None of that means Hawaiian interisland aviation will pivot overnight. It does mean the route lengths and service patterns make Hawaiʻi one of the better geographies on the planet for electric flight trials and then scaled adoption, especially on high-frequency short-haul links. Also, Hawaiian firms and organizations should be cautious about current claims circulating from startups that don’t pass due diligence in the space.

The electricity requirement for that is meaningful but not system-breaking on the larger islands. A daily schedule with multiple turns could easily create several MWh of concentrated airport or harbor demand. On Oʻahu, that is manageable. On Maui and Hawaiʻi Island, it is still manageable with planning. On Molokaʻi and Lānaʻi, the same concentrated charging need could be material enough to require dedicated storage, feeder upgrades, or tightly managed charging windows. The point is not that electric aviation breaks the system. It is that it makes the system more clearly a timed and operated one, not just a bulk annual energy balance. The right answer is likely daytime charging supported by airport batteries and careful scheduling, not a separate energy strategy.

Interisland marine transport is more practical if the charging problem is shifted off the berth. Small passenger ferries and port craft are the easy cases, but freight does not have to depend entirely on delivering very high charging power during a short dockside window. A more plausible model for Hawaiʻi is containerized battery packs charged on land when ships are away, using solar, grid power, and stationary storage over many hours instead of trying to force all the energy transfer into the turnaround at the pier. That changes the problem materially. It reduces peak power demand at the harbor, makes better use of midday solar, and allows energy to be accumulated steadily between vessel calls. Ships would still need battery handling systems, standardized interfaces, and enough operational slack to swap packs without disrupting schedules, but the grid challenge becomes more manageable because the port is charging batteries over time rather than trying to refill a vessel in one burst. That does not make battery-electric interisland freight trivial. The batteries are still large, the logistics still matter, and reliability remains critical in an island system. But it does make the pathway look less like a heroic bet on extreme dockside power and more like an extension of the same solar-plus-storage logic shaping the rest of Hawaiʻi’s energy future.

Northern Europe has already shown that fully electric roll-on, roll-off and ropax operations are not theoretical. Norled’s MF Ampere, the world’s first fully electric car ferry, has been in service since 2015 carrying 120 cars and 350 passengers, and Norled says its success helped trigger a broader Norwegian battery-ferry buildout. At the larger freight end, Scandlines’ new Baltic Whale entered service in 2026 on the Puttgarden-Rødby route with a 10 MWh battery and berth charging infrastructure rated up to 25 MW, showing that scaled electric ro-ro freight service is now real, not aspirational.

China is proving the container side. COSCO’s Green Water 01 and 02 are 700 TEU, 10,000 ton pure battery containerships now in service on the 1,000 km Yangtze corridor, and they matter for Hawaiʻi because they are built around swappable battery containers rather than relying only on burst charging at the dock. Reports on the class indicate more than 50,000 kWh of battery capacity, with 24 battery containers installed and room for up to 36, allowing charged battery boxes to be loaded while depleted ones are removed and recharged ashore.

That distinction matters because it lets the main thesis stay intact. If interisland electric aviation scales, it reinforces a solar-heavy, storage-rich system. Aircraft charging can be shifted toward daytime, supported by airport batteries, and integrated into island grids with planning. As battery-electric ships scale for interisland passenger routes, the same logic largely holds. Even where marine electrification proves harder, that does not overturn the core decarbonization pathway for the islands’ domestic energy systems. It just means that some transport segments may remain separate problems for longer. Hawaiʻi should not let the hardest pieces of transport define the architecture of every island’s electricity future.

Oʻahu still remains the reference case. Hawaiian Electric reported that Oʻahu’s renewable share was 30.8% in 2024 and 32.3% in 2025, with customer-sited renewables already contributing 15.5% in 2024, utility solar 6.8%, and wind 3.8%. Those figures fit the picture that emerged in the Oʻahu analysis. Oʻahu is the tightest island for land use and siting, the largest in load, and the biggest challenge to decarbonize without the crutches available on the mainland. Yet it is also the island where distributed solar, parking canopies, managed charging, district cooling, storage, and demand shifting have the deepest opportunity set because there is so much load concentrated in one place. If that architecture works on Oʻahu, it is reasonable to ask whether the neighbor islands can follow variations on the same playbook.

Hawaiʻi Island is where the answer is yes, but with a major correction. The Big Island is not simply a solar-heavy version of Oʻahu with a little geothermal on the side. It is the island where geothermal changes the shape of the system. Hawaiian Electric’s portfolio reporting shows Hawaiʻi Island at 58.7% renewable in 2024 and 57.3% in 2025. In 2024, its delivered energy mix included 19.1% geothermal, 18.0% customer-sited renewables, 11.2% wind, 4.8% utility solar, and 2.6% hydro. That already makes it the most renewable of the Hawaiian Electric islands. The approved 46 MW expansion of Puna Geothermal Venture points toward geothermal becoming an even more central pillar. Hawaiian Electric’s planning referenced in the project environmental review indicates geothermal could reach 27.2% of Hawaiʻi Island’s generation by 2045.

That is a different kind of system. Solar is still a major pillar. The Big Island has enough solar resource and land potential that it would be strange to imagine anything else. But geothermal gives Hawaiʻi Island something no other major Hawaiian island has at that scale, which is a local resource that behaves much more like firm supply while also contributing inertia, frequency support, and reactive power. In plain terms, it is not just clean energy. It is grid help. That means the Big Island can support a decarbonized pathway that is still solar-heavy in annual generation, but much less dependent on batteries and retained combustion for every increment of reliability. Wind and hydro still matter, and storage still matters, but Hawaiʻi Island is best understood as a solar-geothermal island with supporting wind, hydro, and batteries, not as a simple solar-plus-storage system.

Even on the Big Island, the details are not trivial. Hawaiian Electric’s grid work has emphasized that generation cannot just pile up in one corner of the island. The loads are distributed and the network is constrained by geography. Too much generation on one side means voltage and transmission issues across long distances. The right architecture is not one giant renewable zone feeding everyone else. It is a balanced system with resources spread in a way that respects the network. That becomes important if interisland aviation charging expands at Kona or Hilo. Hawaiʻi Island has the renewable base to handle it, but it still has to be placed and operated intelligently.

Maui looks closer to Oʻahu in structure, but with a larger wind role. Hawaiian Electric reported Maui County at 41.1% renewable in 2024 and 41.6% in 2025. The county’s 2024 delivered mix included 19.8% customer-sited renewables and 16.5% wind. Hawaiian Electric has also pointed to major clean resources either in service or in development, including the 60 MW and 240 MWh AES Kuihelani solar-plus-storage project, 72 MW of wind already in service, 159 MW of customer-sited renewable capacity, and a 40 MW and 160 MWh Waena battery project in development. Those are not edge-of-system experiments. They are the bones of a new power system.

The likely Maui mix remains solar-heavy, but not as solar-dominant as Oʻahu. Maui has enough wind resource and enough room for wind to carry a larger share of annual generation if projects can clear the hurdles of siting, community acceptance, substation capacity, and transmission upgrades. In practice that means Maui is likely to settle into a system where solar is the lead resource, wind is a large supporting resource, batteries are everywhere, and flexible demand becomes more important as electric vehicles, building electrification, and perhaps airport charging grow. If Oʻahu’s story is that wind is useful but modest, Maui’s story is that wind may remain one of the main pillars, even if solar still sits at the center.

Kauaʻi is where the statewide pattern remains intact but the companion resource changes again. KIUC reported a 51% renewable share in 2024 and has stated that it can operate at 100% renewable on many sunny days, in part by using its gas turbine as a synchronous condenser rather than a fuel-burning generator during some operating periods. The cooperative’s mix already includes utility solar, customer solar, hydro, biomass, and large-scale batteries. KIUC has said that two additional solar-plus-battery projects, Mānā and Kaʻawanui, would each provide about 20% of Kauaʻi’s energy and could push its renewable performance above 80%. That is a major statement about direction. Kauaʻi is not searching for a different architecture. It is deepening the same one.

What is different on Kauaʻi is that wind appears constrained less by lack of resource than by ecological conflict. State and utility sources have pointed to endangered seabirds as a reason onshore wind has not developed there. That changes the mix. If Oʻahu is solar plus storage with a modest wind role, and Maui is solar plus storage with a stronger wind role, then Kauaʻi looks more like solar plus storage plus hydro, with some biomass in the background and a narrow thermal role retained for reliability and system services. Hydro is not going to carry the entire system, but it is a meaningful complement to solar on an island where wind faces obstacles. That makes Kauaʻi one of the clearest examples of the broader thesis. The destination is similar, but the supporting cast is local.

Molokaʻi is where the small-grid reality becomes impossible to ignore. On paper, the island has substantial solar potential and respectable wind potential. In practice, it is a system where even a few megawatts matter a great deal. Hawaiian Electric and Hoahu Energy Cooperative have said that the Palaʻau and Kualapuʻu community solar-plus-battery projects could together provide more than 20% of Molokaʻi’s electricity needs. University of Hawaiʻi and Hawaiian Electric work has also demonstrated the use of a 750 kW dynamic load bank and a 2 MW battery to allow the grid to absorb more rooftop solar generation. Those are signs of a system moving in the same direction as the larger islands, but with much narrower margins.

Reliability modeling makes the point clearer. Hawaiian Electric’s planning documents indicate that with only about 4.4 MW of retained firm generation, Molokaʻi would fail to meet the 0.1 loss-of-load expectation standard even with community renewable buildout and roughly 12 MW of paired photovoltaic capacity. With about 6.6 MW of retained firm generation and around 6 MW of added paired photovoltaic, the island can meet the reliability target. That is the kind of detail that matters. Molokaʻi can absolutely become much more solar-heavy. It can lean into rooftop solar, community solar, batteries, and managed demand. But it is also likely to retain firm capacity longer than Oʻahu or Maui, not because solar fails there, but because the grid is small and the cost of being wrong is high.

That same logic applies to transport. A handful of electric aircraft arrivals or a new charging cluster at the harbor might be trivial in annual energy terms, but material in operating terms. On Molokaʻi, the answer is likely not to avoid electrified transport. It is to integrate it tightly with on-site or near-site batteries, daytime charging windows, and conservative planning. The more the island moves toward solar as its dominant energy source, the more valuable those timed and buffered charging strategies become. Molokaʻi does not weaken the statewide thesis. It just reveals its operating assumptions.

Lānaʻi is even more concentrated in this sense. Hawaiian Electric’s selected Lānaʻi Solar project, sized at 17.5 MW with 89 MWh of storage and 3 MW set aside for shared solar, is large relative to the island’s load. It points toward a very high renewable future driven by utility-scale solar and batteries. Yet the same reliability studies that clarify Molokaʻi’s challenge show a similar pattern on Lānaʻi. Around 4 MW of retained firm generation misses the reliability target badly even with a large photovoltaic and battery buildout, while around 6 MW of retained firm generation keeps the system near the standard. Again, the lesson is not that solar is the wrong answer. It is that high-renewable small grids are not the same as large high-renewable grids. They need batteries, reserves, and retained firm support in larger proportion to their size.

That makes Lānaʻi a clean expression of what the statewide strategy should look like. It is still solar first. Storage is still central. Demand flexibility still matters. Electrification still reduces the total amount of energy the island has to supply. But the final stretch to very high renewable penetration is not just about adding more megawatts. It is about ensuring the island can ride through cloud cover, outages, charging spikes, and operational swings without losing reliability. Lānaʻi is not evidence against a solar-heavy decarbonized future. It is evidence that the smaller the grid, the more the transition is a control and storage story as much as a generation story.

Niʻihau sits outside most of the utility-centric discussion for a simple reason. According to the Public Utilities Commission, the island does not have electric utility service in the same sense as the other inhabited islands. That means the right frame is not a Hawaiian Electric or KIUC grid plan. It is a microgrid plan. In that context, the statewide thesis still points in the same direction. Solar and batteries are the natural core of a lower-carbon local power system. Backup generation remains useful, perhaps necessary, depending on the reliability requirement and what services must be maintained. But the scale and structure are different. Niʻihau is not a counterexample. It is a reminder that on the smallest and most isolated systems, the future may look more like stand-alone resilient microgrids than like a miniaturized version of a utility island grid.

When all of this is pulled together, the pattern across the archipelago becomes clear. Oʻahu remains the hardest land-constrained, load-heavy case, and it still supports a viable path centered on electrification, solar, storage, flexible demand, selective wind, and targeted efficiency measures like district cooling. Maui follows much the same pattern but with wind playing a larger role. Kauaʻi follows the same broad path but with hydro as a stronger supporting resource and wind constrained by ecology. Molokaʻi and Lānaʻi are also solar-heavy futures, but ones where storage, retained reserve, and careful operations matter more because the grids are small. Niʻihau points toward solar microgrids with batteries and backup. Hawaiʻi Island is the outlier in the best sense, because geothermal becomes large enough to change the system and provide a source of local firmness no other island can match.

That is a stronger result than it might appear at first. The other islands do not force Hawaiʻi to discover a different miracle technology or invent a different clean energy ideology for every grid. The same broad recipe works across the state. Electrify demand. Build around local renewables. Lean into solar because it is local, modular, and abundant. Add batteries and flexible demand so those renewables can serve more hours. Use wind where it is compatible with local conditions. Use island-specific resources where they exist, especially geothermal on Hawaiʻi Island and hydro on Kauaʻi. Retain firm generation only where reliability still requires it, and reduce its role over time rather than letting it define the whole architecture.

There is also a policy lesson in this. Hawaiʻi should have a statewide decarbonization framework, but it should resist a one-size-fits-all procurement mindset. The state does not need one island to imitate another. It needs the islands to move in the same direction with their own local balances of solar, wind, storage, firming, and demand flexibility. That means integrated planning across utilities, transport agencies, ports, airports, regulators, and local communities. It means recognizing that a 2 MW charging cluster at one airport can be a rounding error on one island and a planning event on another. It means understanding that one more utility-scale solar plant can be easy on a land-rich island and politically or ecologically impossible on another. It means building systems that are similar in logic but adapted in detail.

The deeper conclusion is that looking beyond Oʻahu strengthens the original case rather than weakening it. If the most constrained large-load island can make a clean, resilient, solar-heavy future work, and if the smaller islands can follow the same architecture with local variations, then Hawaiʻi does not face a fragmented energy future. It faces a coordinated one. The islands are different enough that each needs its own plan, but similar enough that the state can commit to a shared destination. That destination is not one of endless imported fuels with changing labels. It is one of local electrons, lower dependence, storage-rich operations, and island-specific clean resources doing most of the work.