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Ellis’s early calculations suggest there may be something like 10 trillion tons of natural, or “geologic” hydrogen buried underground worldwide. Many reserves will be too deep or remote to tap easily — around hydrothermal vents in the deep ocean, for instance. But if Ellis is right, then just a small fraction could meet the world’s needs for centuries. And it could in places be tapped for less than $1,000 per ton, says Emily Yedinak of the U.S. Department of Energy’s (DOE) Advanced Research Projects Agency-Energy making it substantially cheaper than manufactured hydrogen.
As well as being cheap and carbon-free, natural hydrogen is also potentially a renewable resource. Ellis estimates that the Earth may generate hundreds of millions of tons of new natural hydrogen annually. But he warns against getting carried away. “I am cautiously optimistic,” he says, “but we need some more data to be convinced.”
Others simply don’t believe it. Stuart Haszeldine, a geologist at the University of Edinburgh, says, “Hydrogen is very leaky. It leaks almost as fast as it is produced, and certainly over geological time, it’s not accumulated to any great extent.”
Zgonnik is enthusiastic, however. He believes these leaking flows can be tapped as well as trapped reserves. “We should tap these flows, or they will continue to leak to the surface and be lost,” he says. The generation process might even be augmented or kick-started, he suggests, by injecting water into iron-rich rocks where there is none.
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