Hawaiʻi's LNG bridge to green ammonia would cost far more than staying fossil

The argument for bringing liquefied natural gas to Oʻahu is straightforward enough. LNG could replace oil for a period, potentially lower generation costs and give Hawaiʻi more time to build out renewable electricity. The difficulty is that Hawaiʻi law requires electric utilities to reach 100% renewable electricity generation by 2045, so LNG cannot be the fuel at the end of the bridge.

That makes the far end of the bridge part of today’s decision. The Hawaiʻi State Energy Office’s fuel study identifies imported green ammonia and hydrogen among the technologies that could eventually replace fossil gas, alongside local biodiesel. None of those pathways has been committed to, and no green-ammonia supply contract or conversion project has been approved. But if LNG infrastructure is justified partly on the assumption that it can later transition to a renewable imported fuel, then the economics of that transition deserve to be examined before the LNG investment is made.

I modeled that transition in Hawaiʻi’s LNG Bridge Has an Expensive Far Shore, including the LNG and green-ammonia generation costs, household solar-and-battery economics and the local-energy pathway I previously developed for Hawaiʻi.

The numbers make the concern difficult to treat as a secondary detail. In the source-transparent electricity-cost model behind the analysis, a new LNG plant operating at high utilization produces electricity at roughly 21 cents per kilowatt-hour on the modeled generation boundary. The green-ammonia case is about 95 cents per kilowatt-hour on that same boundary.

That is not a forecast of Hawaiʻi retail electricity prices, and it is not a bid from an ammonia supplier. It is a modeled comparison of the energy-conversion chain. Renewable electricity is first used abroad to produce hydrogen, which is not becoming or going to become nearly as cheap as projections from years ago—not mine—thought it would. The hydrogen is converted into ammonia for transport, shipped to Hawaiʻi, delivered through new receiving infrastructure, converted back into hydrogen in the modeled case and finally used to generate electricity. Each step consumes energy and adds equipment, operating costs and losses.

The resulting question is not whether green ammonia can technically be made or transported. It can. The question is why Hawaiʻi would want to turn renewable electricity into molecules overseas, ship those molecules across the Pacific and turn them back into electricity if a large share of the same energy service can be supplied directly with local solar, batteries and flexible demand.

Households provide a useful way to see the difference. For a modeled detached Oʻahu home using 700 kilowatt-hours per month, a 6-kilowatt rooftop solar system, 10-kilowatt-hour battery and daytime water-heating control cover about three quarters of annual electricity demand. Under the September 2026 rates and assumptions used in the analysis, the modeled system has a simple cash payback of about 8.4 years after the assumed state tax credit. Roof condition, financing, actual consumption and tax-credit eligibility can all change that result materially.

The more revealing exercise is a stress test. If the full additional cost of the modeled ammonia generation case were passed through electricity sales, the same household’s simple solar-and-battery payback falls to about 4.4 years. That is not a prediction that Oʻahu bills will reach the modeled level. It shows how households able to produce and shift their own electricity become increasingly insulated from expensive imported-fuel pathways as those pathways become more costly.

There is a system-level complication as well. Both the LNG and ammonia generation-cost cases assume high plant utilization. The more households and businesses install rooftop solar, batteries and flexible loads, the fewer kilowatt-hours a centralized thermal plant sells. Its capital and fixed operating costs then have to be recovered across a smaller volume of generation, putting upward pressure on the cost of each remaining kilowatt-hour.

That creates an awkward feedback for the bridge strategy. Distributed solar, storage and demand flexibility are not merely competitors to the eventual ammonia exit; they can also weaken the economics of the LNG bridge itself by reducing the utilization of the infrastructure built to support it.

There is another pathway available. In my earlier work on Hawaiʻi’s energy transition, I laid out a sequence built around rooftop and parking-canopy solar, batteries, managed EV charging, daytime water heating, efficient cooling, suitable wind, grid upgrades and a relatively small locally sourced biomethane reserve for difficult periods. Commercial roofs and parking areas can produce electricity near loads, while flexible cooling, charging and water heating can consume more of it when the sun is available. That’s available in the TFIE Strategy Briefing report The Clean Energy Future Hawaiʻi Can Actually Build. 

That does not make the transition trivial. Hawaiʻi still has to strengthen its grid, manage land constraints, build storage, electrify suitable end uses and deal separately with the harder fuels used in aviation, shipping and other sectors. But those are problems of building a local electricity system rather than repeatedly converting electricity into imported fuel and back again.

The State Energy Office acknowledges the importance of local renewables, but its alternative-fuels study did not examine that buildout in comparable detail. Before Hawaiʻi commits to an LNG bridge, the comparison should include not just LNG versus oil today, but the complete cost of the proposed bridge, the plausible cost of getting off it and the local alternative that may shrink demand for both.

For households able to install solar and batteries, the modeled economics are already material at current prices. For renters and households without the capital or suitable roofs, the answer should be shared solar, storage and access to the same savings rather than leaving them more exposed to imported-fuel costs.

The central decision is larger than whether LNG can temporarily beat oil. It is whether Hawaiʻi should build new fuel infrastructure whose eventual renewable exit could be far more expensive than the local electrical pathway available in parallel.

The full TFIE Strategy Briefing analysis includes the cost model, household scenario and the alternative Hawaiʻi transition pathway used to test the LNG-to-ammonia proposition.