Electrifying Oʻahu: Shrinking the Island’s Energy System Before Decarbonizing It

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Energy discussions about Hawaiʻi often begin with the largest numbers in the system. Aviation fuel, maritime bunkering, and military logistics move large quantities of petroleum through Oʻahu’s ports and fuel infrastructure. Those flows dominate many statistical summaries of the state’s energy system, and they create the impression that the transition away from fossil fuels must be equally large. But much of that energy does not power the island’s civilian economy. Jet fuel loaded onto aircraft leaving Honolulu powers flights to the mainland and overseas. Fuel bunkered onto cargo ships supports trade across the Pacific. Military fuel supports operations that extend far beyond the islands. When the goal is to understand what local policy and investment can actually change, those flows must be separated from the energy used by residents and businesses on Oʻahu.

The analysis therefore begins with a cleaned boundary. Removing overseas aviation fuel, foreign maritime bunkering, and military fuel use shrinks the system to the portion that supports the island economy itself. After those removals the remaining primary energy entering the system is on the order of thirty nine thousand gigawatt hours per year. That energy arrives mostly as petroleum variants used to generate electricity, provide heat and power transportation, along with smaller contributions from solar, wind, waste to energy, biomass, and environmental heat drawn through heat pumps. This boundary does not ignore aviation or shipping. It simply places them outside the local civilian energy system so that the island economy can be analyzed independently.

A Sankey diagram provides a clear way to visualize the resulting flows. In this diagram each flow is measured in gigawatt hours and represented as a band whose width corresponds to the magnitude of the energy. Primary energy enters the system through imports of petroleum products, renewable electricity generation, waste to energy combustion, and environmental heat captured by heat pumps. Electricity generation converts petroleum fuel into electricity, which then flows through the grid to residential, commercial, industrial, and transportation sectors. At the end of the diagram, energy divides into useful services and rejected energy, reflecting the thermodynamic losses inherent in both energy conversion and end use technologies.

The baseline Sankey for domestic Oʻahu demand shows about thirty nine thousand gigawatt hours of primary energy entering the system each year. Of that total, roughly six thousand gigawatt hours become useful energy services across the island’s economy. The remaining thirty three thousand gigawatt hours appear as rejected energy, primarily in the form of heat released during electricity generation or inefficiencies in motors, heating systems, and other equipment. This imbalance illustrates the central problem of fossil based energy systems. Combustion processes waste large fractions of the energy contained in fuels, leaving a large rejected energy wedge in the diagram.

Electrification is the first step toward changing that picture. Electric technologies are fundamentally more efficient than combustion based ones. Electric motors convert most of the electricity they receive into mechanical motion. Heat pumps transfer heat instead of generating it from combustion, allowing them to deliver multiple units of thermal energy for each unit of electricity consumed. Modern electronics and lighting systems require far less energy than earlier technologies. When these technologies replace combustion based systems, the useful services remain the same but the primary energy required to deliver them declines.

Ground transportation is a large transformation. A gasoline vehicle converts about 20% of the fuel energy in its tank into motion. The remaining 80% becomes waste heat through exhaust and engine losses. A battery electric vehicle converts roughly 70% of the electricity it receives into motion. In the Sankey diagram, replacing gasoline and diesel vehicles with electric ones removes large petroleum flows from the transportation sector. The useful transportation services remain constant, but the energy required to provide them falls sharply. If a fleet originally consumed 10,000GWh of gasoline and diesel energy, electrification could reduce the energy required to deliver the same mobility services to roughly 3,000GWh of electricity.

Interisland aviation is another sector that can shift to electricity. Flights between the Hawaiian Islands are relatively short. The longest routine commercial interisland route between Kona and Lihue is about 490km. China has already certified a four passenger general aviation aircraft. Emerging hybrid electric aircraft designed for regional routes have ranges which will be 1,000km with passenger capacities approaching 100 seats, per my own analysis as someone who has sat on the advisory boards of two electric airplane startups, hybrid electric aviation startups I’ve had conversations with and major global discount airline strategists I’ve spoken about this with. These aircraft rely on electric propulsion systems that are more efficient than conventional turbine engines, with hybridization required for divert and reserve energy, not most flight energy. In the Sankey diagram, the avgas and jet fuel previously allocated to interisland aviation disappears and is replaced with a modest flow of electricity that delivers the same passenger transport services.

Local maritime transport can follow a similar path. Interisland barges, ferries, harbor craft, and smaller vessels typically burn marine diesel today. New battery electric ferries and coastal cargo vessels demonstrate that maritime electrification is already practical for short routes. A large battery electric passenger ferry with capacity for more than two thousand passengers is in sea testing for service in South America. Electric container vessels carrying around 700 TEU have entered service on China’s Yangtze River and coastal shipping routes. These examples show that battery electric propulsion can deliver high efficiency for marine transport. In the Sankey model, marine diesel for island passages consumption is replaced by a smaller electricity flow that provides the same propulsion services.

Buildings represent the next major opportunity. Fossil fuels in Oʻahu buildings are not used for space heating, which is minimal in a tropical climate. Instead they are used for cooking, water heating, and certain commercial processes. Electrification replaces these with induction cooking equipment, electric resistance heating, and heat pump water heaters. Heat pumps are particularly important because they draw energy from the surrounding air or water. In the Sankey diagram this appears as environmental heat entering the system alongside electricity. A heat pump water heater might deliver three units of thermal energy for every unit of electricity consumed, so the environmental heat contribution can be twice the electricity input.

Industrial energy use follows a similar pattern. Many industrial processes rely on motors that can be driven by electric power instead of diesel engines. Process heat applications can be replaced by heat pumps under 200° Celsius, electric boilers, resistance heating, induction furnaces and several other electric heat solutions. These technologies eliminate combustion and increase the fraction of input energy that becomes useful work. In the Sankey diagram, petroleum and gas flows into industry shrink while electricity and environmental heat increase.

After these electrification steps the structure of the energy system changes noticeably. Petroleum flows shrink dramatically while electricity flows expand. Environmental heat becomes a visible contributor to the energy system because heat pumps capture thermal energy from the environment. The rejected energy wedges in transportation and buildings shrink because electric technologies waste less energy than combustion engines or burners. However, a large rejected energy wedge remains in electricity generation itself because oil fired power plants convert only about one third of fuel energy into electricity.

This stage of the transition is deliberately incomplete. The island still burns petroleum to generate electricity. Electrification reduces the total energy required to run the economy, but the electricity itself still comes from fossil fuels. In the revised Sankey diagram most petroleum imports now flow directly into electricity generation rather than transportation or buildings. The power plants reject large amounts of heat as part of the conversion process. The system is smaller and more efficient than before, but it is not yet decarbonized.

Even in this intermediate stage the benefits are clear. The total primary energy entering the island system falls because electrified technologies need less energy to deliver the same services. Electricity demand rises because transportation and heating loads shift onto the grid, but the total energy demand still declines. If the original system required thirty nine thousand gigawatt hours of primary energy, the electrified system might operate with roughly twenty thousand. This reduction matters because it determines how much renewable generation must be built in the next phase. In this intermediate, incomplete phase, I’ve chosen to eliminate local refining of fossil fuels and petroleum products because it’s going away in the end state regardless, and represented all very low sulfur fuel oil (VLSFO) for electricity generation as imported. This is not to say that there will be a scenario where this occurs, but merely to point out that the refinery on O’ahu has no future.

The remaining fossil energy node is now concentrated in electricity generation. Nearly all petroleum entering the system flows into oil fired power plants. This concentration simplifies the decarbonization problem. Instead of replacing fossil fuels in dozens of different end uses, the transition can focus on replacing the electricity supply itself. Wind, solar, and storage can displace oil fired generation once the demand side has already been electrified.

Sharp eyes will notice that the total energy services has declined between the two Sankeys. I chose to keep that variance in the charts, not wishing to obfuscate the challenges of this analysis. When I extracted the non-domestic aviation and shipping fuel energy, I made conservative assumptions. When I electrified ground, sea and air transportation I made conservative assumptions. When I electrified all heat I made conservative assumptions. When I’d finished that process, a large amount of final energy provided by fossil fuels remained, roughly an order of magnitude more than seemed reasonable. As such, I kept a tenth of the remainder and allocated it across a reasonable electrification pathway. The future is not crisp and clean, but the direction of travel is clear regardless.

The next phase of the transition will examine how renewable energy can replace the oil fired electricity generation shown in the current Sankey diagram. Because electrification has already reduced total energy demand, the renewable capacity required to supply the island is smaller than it would have been under the original fossil based system. Wind and solar generation can provide the bulk of the energy, while batteries and other storage technologies maintain grid stability.

Viewed as a sequence, the transformation becomes clearer. First the system boundary is cleaned to remove aviation, maritime, and military fuel flows that do not power the local economy. Next, end uses across transportation, buildings, and industry are electrified, shrinking the energy system and reducing rejected energy. Finally, the electricity supply itself can be decarbonized by replacing oil fired generation with renewable energy. The Sankey diagram makes each step visible, showing how the flows change as the transition progresses.