Is Seawater the Next Big Fuel Source?
The Navy showed us it's possible, but is our most abundant natural resource a practical energy solution?
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In April, the Navy announced a breakthrough in transforming seawater, the earth's most abundant natural resource, to fuel. Researchers used it to fly a model jet powered with an internal combustion engine like its full-sized counterparts. What are the implications of such a technology in a world scrambling for clean, efficient energy?
According to U.S. Navy research chemist Dr. Heather Wilhauer, the new process takes roughly 23,000 gallons of seawater to produce one gallon of liquid hydrocarbon fuel. You might suspect that solves two problems at once: dependence on fossil fuels and rising sea levels. The trouble with the latter is that the excess water simply goes right back into the ocean. The first question is more complicated.
To create the fuel, Wilhauer's team extracted carbon dioxide and hydrogen bound in the water and recombined those gases in a catalyst reactor to produce the liquid fuel. The process can be applied to different metals to engender methanol, liquid natural gas, gasoline, diesel, or jet fuel. “Because it's a synthetic process, you can tailor it to whatever fuel you need,” Wilhauer notes.
If that sounds like the jackpot, it could be—in a perfect world. Like water that's pumped uphill using electricity and later released to generate electricity, the CO2 and hydrogen extracted from the sea end up back in the water where they started. “You have to put more energy in to get the fuel than you get out of the fuel when you use it,” says Brentan Alexander, founder of the Stanford Energy Club and Senior Mechanical Engineer at Wrightspeed. “So it's still net-energy negative. When you start applying that towards generating fuel on a larger scale in the United States, you're going to run into a really hard wall to make that cost-effective, because natural gas is cheap.”
But for the Navy, which moves 1.2 billion gallons of fuel annually, it makes perfect sense. “Our aircraft carriers are nuclear powered, but we still have to get fuel out to there to fly the airplanes,” says Rear Admiral Kevin Slates, who works on the Navy's environmental and energy programs. Barges must frequently haul resupply fuel across oceans to aircraft carriers, and other ships protect those barges, all of which require their own fuel. “This would allow us to produce fuel at the point of consumption and basically untether that ship,” says Rear Admiral Slates. It also eliminates risk of potential fuel spills during transport. “The delivered cost of fuel to our fleet at sea is obviously more expensive than what we're paying at a pump. Then [seawater fuel] becomes cost-competitive much quicker than for, say, commercial automobiles.”
The same may be true for powering remote islands like Hawaii, which have unlimited access to seawater and whose fuels also need to be hauled in from afar. If seawater processing plants existed on Hawaii shores, it, too, could be untethered. The fuel could even power cars in this scenario if the price is right. And because no chemicals are added in the conversion process, there's effectively no waste, only water released back into the ocean at its initial pH. But this, too, is likely a far-away reality.
“It all hinges on whether it can scale up to produce the quantities that we need,” says Rear Admiral Slates, which could take ten to 15 years. “It's clearly a game-changing, innovative technology that we're really interested in.”