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The starting point for evaluating biomethane in Hawaiʻi is the fully electrified Oʻahu energy system that emerged from the earlier Sankey analysis. That work removed overseas aviation fuel, long-distance maritime bunkering, and military energy use from the island energy balance. It also electrified transportation, buildings, and industry while replacing combustion heating systems with electric technologies such as heat pumps and resistance heating. Once combustion losses disappear, the scale of the island’s energy system becomes much smaller than the petroleum system that preceded it. Electricity demand required to deliver the same useful services falls to roughly 6,000GWh per year for the civilian economy on Oʻahu. That number provides the reference point for evaluating every remaining supply and demand option. The problem is no longer how to replace tens of thousands of gigawatt hours of fossil fuels. The problem is how to operate a reliable renewable electricity system that supplies about six terawatt hours annually.
From previous analysis, solar energy and batteries carry most of the load in that scenario. Solar potential on the island exceeds annual demand even under conservative assumptions, and batteries shift generation from midday to evening. Wind provides additional diversity and produces electricity during hours when solar output declines. District seawater cooling reduces peak electricity demand in the urban core. Even with these components in place, the electricity system still needs a small layer of firm capacity. Cloudy weather, unusual wind conditions, or simultaneous equipment outages can create short periods when stored energy and renewable generation are insufficient. These events are rare, but the grid must still be designed to handle them. The goal is not continuous backup generation. The goal is a modest strategic reserve that can supply electricity for hours or days when needed.
Biomethane fits naturally into that role. Biomethane is methane produced from biological waste streams through anaerobic digestion or landfill gas capture. Organic material such as sewage sludge, food waste, and decomposing landfill waste generates methane as microbes break down the material in oxygen-free environments. That methane can be cleaned and upgraded to pipeline quality fuel and burned in conventional gas engines or turbines. The fuel behaves similarly to fossil natural gas in power generation equipment, but the carbon originates from recent biological sources rather than fossil deposits. Biomethane therefore avoids adding new fossil carbon to the atmosphere while still providing firm combustion-based electricity when necessary…