Wind on Oʻahu: A Modest but Valuable Complement to Solar

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Any serious discussion of renewable energy on Oʻahu should begin with a clear understanding of how much electricity the island actually needs once fossil fuel end uses are electrified. Earlier analysis constructed a fully electrified civilian energy Sankey for Oʻahu that removed overseas aviation fuel, international maritime bunkering, and military energy demand. It also replaced gasoline vehicles with electric vehicles, electrified local marine transport and interisland aviation, and replaced fossil heating in buildings and industry with electric systems and heat pumps. When those changes are applied, the energy required to deliver the same useful services falls sharply because electric technologies waste far less energy than combustion engines and burners.

The resulting system requires roughly 6,000GWh of electricity delivered to loads each year. Total electricity flowing through the grid in that scenario is slightly higher once transmission losses are included, but the difference is small because grid losses are only a few hundred gigawatt hours. That number establishes the scale of the problem. The question for renewable energy planning on Oʻahu is not how to replace tens of thousands of gigawatt hours of fossil fuel consumption. It is how to produce roughly eight terawatt hours of electricity per year in a reliable way.

Solar energy is the largest renewable resource available to the island. Earlier analysis showed that rooftop solar, parking canopy solar, agrivoltaics, vertical photovoltaic installations, and utility scale solar farms could collectively produce far more than enough annual electricity to meet that demand. Solar is not the focus of this article, but the solar potential is an important reference point because it defines the role wind must play. Solar production on Oʻahu peaks around midday and declines in the evening when electricity demand often rises. Batteries can shift several hours of generation, but longer balancing requires either additional storage or complementary generation sources that produce power when the sun is not shining. Wind is the most obvious candidate for that complementary role.

The wind resource around Oʻahu is shaped by the trade wind climate of the central Pacific. Northeast trade winds dominate the island’s weather for much of the year, creating a steady flow of air across the surrounding ocean. Offshore winds are typically stronger and less turbulent than winds over land because the ocean surface is smooth and there are fewer topographic obstacles. Onshore winds can accelerate along ridges and valleys but are often more variable due to terrain effects. Understanding that pattern helps explain why offshore wind is often discussed as a major renewable resource for island systems.

Oʻahu already has several onshore wind farms that provide useful real world data. Kawailoa Wind, Kahuku Wind, and Nā Pua Makani together provide roughly 120MW of installed capacity. Their annual output indicates capacity factors between about 30% and 45%, depending on turbine design and site conditions. For example, a 30MW wind farm producing around 70GWh per year has a capacity factor of roughly 27%, while a 24MW project producing about 96GWh annually corresponds to a capacity factor of roughly 46%. These numbers illustrate both the strength of the wind resource and the variability between sites.

Two of Oʻahu’s existing wind projects are likely candidates for repowering over time, while the third is still too new for that to make sense. Kahuku Wind began operating around 2011 with turbines rated at about 2.3MW each, which reflects the technology available at the time. Kawailoa Wind followed in 2012 with similar generation technology. Modern onshore turbines use larger rotors and taller towers that capture more energy from the same wind resource, so replacing older turbines with newer machines can increase annual output without expanding the footprint of the project. Repowering often occurs after roughly 20 years of operation, which would place both Kahuku and Kawailoa in the early 2030s as potential candidates. Nā Pua Makani, by contrast, began operating in 2020 and already uses modern turbines, so repowering there would not be expected for at least another two decades. In practice this means that Oʻahu’s most realistic path to increasing onshore wind generation may come from upgrading existing sites rather than building entirely new wind farms.

Despite the strong wind resource, onshore wind development on Oʻahu faces significant constraints. The island’s strongest winds occur along ridgelines and coastal headlands that are also environmentally sensitive areas. Several endangered bird and bat species inhabit the island, and wind turbines have been the subject of extensive habitat conservation planning and mitigation requirements. Visual impact is also a major factor in a place where scenic landscapes are part of the island’s identity and economy. Community opposition has been significant in some areas, particularly along the North Shore where wind farms are visible from popular beaches and towns.

Because of these constraints, planning studies often estimate relatively modest onshore wind expansion potential. The Hawaiʻi Natural Energy Institute and other analyses that draw on National Renewable Energy Laboratory resource assessments suggest that Oʻahu might support around 160MW of onshore wind under conservative land use assumptions. Given that about 120MW already exists, this implies that perhaps another 40MW could be developed without expanding into more contentious sites. Even a more permissive interpretation might bring total onshore wind capacity to roughly 200 or 250MW if existing sites were repowered with larger turbines and a few additional projects were approved.

Using a representative capacity factor of 35% for future installations, 200MW of onshore wind would produce about 613GWh per year. At 250MW the annual output would rise to about 767GWh. Compared with the electrified Oʻahu demand of roughly 6,000GWh, that contribution would represent about 10% to 12% of annual electricity supply. Onshore wind therefore appears capable of making a meaningful contribution to the island’s renewable energy mix, but won’t dominate the system.

Offshore wind enters the conversation because the wind resource over the surrounding ocean is strong and consistent. Offshore turbines benefit from higher wind speeds and fewer obstacles, which often leads to capacity factors above 40%. In many regions of the world offshore wind has become the largest source of new renewable electricity because large areas of shallow continental shelf allow hundreds of turbines to be installed on fixed foundations. In principle the waters around Hawaiʻi offer a large wind resource that could support similar developments.

The challenge is the shape of the seabed. Around Oʻahu the ocean floor drops rapidly from the shoreline to deep water. Depths greater than 100 meters occur within a short distance of shore, and depths of several thousand meters lie farther offshore. Conventional offshore wind turbines rely on fixed foundations anchored to the seabed. These foundations become impractical and extremely expensive once water depths exceed about 60 meters. This means that most of the offshore wind resource around Oʻahu cannot be accessed with traditional offshore wind technology.

Floating offshore wind provides a potential solution. Instead of mounting turbines on fixed foundations, floating wind platforms support the turbine on a buoyant structure anchored with mooring lines. Several designs are currently in use, including spar buoy platforms, semi submersible platforms, and tension leg systems. These platforms allow turbines to operate in waters hundreds or even thousands of meters deep. Floating wind farms such as Hywind Scotland, WindFloat Atlantic off Portugal, and Hywind Tampen in Norway demonstrate that the technology works at commercial scale.

Floating wind turbines can use the same large machines as conventional offshore wind farms. Turbines rated at 12 to 15MW are now common in offshore projects, and designs approaching 20MW are under development. A floating wind farm with 500MW of installed capacity could therefore consist of around 30 to 40 turbines. If those turbines operate at a capacity factor of 45%, the project would produce roughly 2,000GWh per year. A 1GW floating wind fleet would generate about 4,000GWh annually, enough to supply roughly half of Oʻahu’s electrified electricity demand.

Despite these promising numbers, floating offshore wind faces significant economic and logistical challenges in Hawaiʻi. Offshore wind maintenance relies on specialized vessels, cranes, and trained technicians. In regions such as the North Sea, these resources are shared across dozens of wind farms and hundreds of turbines. The cost of service vessels, spare parts, and offshore crews is distributed across a large fleet. Hawaiʻi does not have that scale. A single floating wind farm near Oʻahu would require many of the same resources but would spread the cost across far fewer turbines.

Geographic isolation adds to the challenge. The global supply chain for offshore wind components is concentrated in Europe and parts of East Asia. Transporting large turbine blades, nacelles, and floating platform components to Hawaiʻi would require long shipping distances and specialized port facilities. Maintenance logistics would face similar challenges. Spare parts inventories and heavy lift vessels would need to be available locally or shipped across the Pacific when needed.

Floating wind does have one operational advantage. Some platform designs allow turbines to be towed back to port for major maintenance rather than serviced offshore with heavy lift vessels. This can simplify repairs and reduce the need for extremely large offshore cranes. However, even this approach requires ports capable of handling large floating structures and specialized crews trained in offshore wind technology.

When these logistical and economic factors are considered, the role of offshore wind in Hawaiʻi becomes clearer. Floating wind could supply significant amounts of energy and complement solar generation by producing electricity at different times of day. But the cost structure of a small isolated project is likely to be higher than in regions with dense offshore wind development. Any floating wind deployment in Hawaiʻi would probably need to be large enough to justify the supporting infrastructure, or it would require strong policy support.

Given these realities, expanding onshore wind capacity appears more likely than building floating offshore wind in the near term. Onshore projects benefit from existing infrastructure, shorter construction timelines, and lower capital costs. Repowering existing wind farms with modern turbines could increase output without expanding the physical footprint significantly. Even modest increases in onshore wind capacity could provide several hundred gigawatt hours of additional renewable electricity each year.

The fully electrified Oʻahu energy system requires about 6,000GWh of electricity annually. Solar resources alone appear capable of exceeding that requirement. Wind therefore serves a complementary role rather than the primary one. Onshore wind offers modest but practical contributions that help diversify generation and improve resilience. Offshore wind offers larger theoretical potential but faces economic and logistical hurdles that may limit its near term deployment.

The numbers tell the story clearly. A few hundred megawatts of onshore wind, including repowering, could provide around 600 to 800GWh per year. Floating offshore wind could provide more if built at scale, but the costs and operational complexity make that unlikely. Solar, batteries, and demand management will likely form the backbone of Oʻahu’s renewable energy system, while onshore wind contributes a smaller share that improves reliability and reduces reliance on storage. That doesn’t end the journey however. Oceanic water cooling and biomass energy still have to be explored. Arguments that LNG is required run into the pleasant reality of a lot of free available energy to be harvested.